Broadband First-Mile
Technologies
Tom Schmidt
Schmidt Consulting
Revised August 21,
2016
Tom@tschmidt.com
http://www.tschmidt.com
Abstract
Today, most
residents in developed countries have access to multi-megabit Internet access
that costs little more than dialup and a phone line did a couple of decades
ago. The proliferation of smart phones is driving demand for fast Internet
access not just at home but everywhere. The day of the Star Trek communicator
is at hand.
Over its
relatively short lifetime the Internet has been transformed from an interesting
technology used to share expensive mainframes to an essential component of
everyday life most of us take for granted.
February
2011 marked an important milestone in Internet history, IANA issued the last
IPv4 address blocks to the regional registrars. IPv4 address space is limited
to 4 billion hosts. Various methods have been implemented to extend its
lifetime but the address space is now exhausted. IPv6, the next generation
Internet protocol, has been around for years but because it is not backward
compatible the adoption rate has been painfully slow.
This paper
provides an overview of the various technologies used to deliver Internet
access and the role played by the Internet Service Provider (ISP).
Table of Contents
1
ISP Overview... 1
1.1
Essential Core Functions. 2
1.1.1
Customer Connection - Physical 2
1.1.2
Customer Connection – Logical 3
1.1.3
Authentication. 3
1.1.4
Address Allocation. 3
1.1.5
IPv6 Support 4
1.1.6
Packet Routing. 4
1.1.7
Transit Network. 4
1.1.8
Multicast (IGMP) 5
1.1.9
Quality of Service (QoS) 5
1.1.10 Service
Level Agreement (SLA) 6
1.1.11 Acceptable
Use Policy (AUP) 6
1.1.12 Communication
Assistance for Law Enforcement Act (CALEA) 6
1.1.13 Technical
Support 6
1.1.14 Billing. 7
1.2
Common But Non-essential Services. 7
1.2.1
Domain Name System (DNS) 7
1.2.2
E-Mail 8
1.2.3
Usenet 8
1.2.4
Web Hosting. 8
1.2.5
Cloud File Storage. 8
1.2.6
Virtual Private Networking (VPN) 8
1.2.7
Voice over IP (VoIP) 9
1.2.8
IP Radio. 11
1.2.9
IP Television (IPTV) 11
1.3
Content Delivery Network (CDN) 12
1.4
Connection Sharing.. 13
1.5
Blocked Ports. 14
1.6
Traffic Shaping.. 14
1.7
Usage Caps. 14
1.8
Digital Rights Management (DRM) 15
1.9
Deep Packet Inspection (DPI) 15
1.10
Latency vs Speed.. 15
1.11
Asymmetric Speed.. 15
1.12
Measuring Speed.. 16
1.13
Speed Optimization.. 17
1.14
Load Balancing vs Bonding.. 17
1.15
Servers and Dynamic IP Allocation.. 17
1.16
When “Unlimited” Doesn’t Mean “Unlimited”. 17
1.17
When “Always On” Doesn’t Mean “Always On”. 18
1.18
Security and Privacy.. 18
1.19
Network Neutrality.. 19
1.20
Finding an ISP. 19
2
Plain Old Telephone Service (Dialup) 20
2.1
Dial Up Networking (DUN) 20
2.2
Session Duration.. 20
2.3
Multilink.. 21
2.4
Impairments. 21
2.4.1
Slower Than Expected Speed. 21
2.4.2
Call Waiting. 21
2.4.3
Shared Phone Line. 21
2.5
Installation.. 21
2.6
Life in the Slow Lane.. 21
3
T-1 and E-1 Digital Carrier.. 22
3.1
Converting Voice to Digital Bits. 22
3.2
Channelized vs. Unchannelized.. 22
3.3
Provisioning.. 22
3.4
CSU and DSU.. 23
3.5
Smartjack.. 23
3.6
Installation.. 23
3.7
Beyond T-1. 24
4
Integrated Service Digital Network (ISDN) 25
4.1
Dial Up Networking.. 25
4.2
Installation.. 25
4.3
IDSL.. 25
5
Digital Subscriber Line (xDSL) 26
5.1
VDSL vs ADSL.. 27
5.2
Splitter vs Inline Filter.. 28
5.3
Interleave vs Fastpath.. 28
5.4
Bonding.. 29
5.5
Dry Loop. 29
5.6
Impairments. 29
5.6.1
Network Interface Device (NID) 29
5.6.2
Distance. 30
5.6.3
Bridged Taps. 31
5.6.4
Load Coils. 31
5.6.5
Loop Carrier. 32
5.6.6
Noise and Crosstalk. 32
5.6.7
Backhaul Congestion. 32
5.7
Safety.. 32
5.8
Installation.. 32
6
Fiber to the Curb (FTTC) 33
6.1
VDSL2 Vectoring.. 34
6.2
Bonding.. 34
6.3
Impairments. 34
6.3.1
Video Compression Artifacts. 34
6.4
Installation.. 34
7
Data Over Cable Service Interface Specification (DOCSIS) 35
7.1
Impairments. 36
7.1.1
Shared Medium.. 36
7.1.2
Limited Upload. 36
7.1.3
Noise Ingress & Signal Leakage. 37
7.1.4
Whitespace Broadband. 37
7.1.5
Signal Level 37
7.2
Safety.. 37
7.3
Installation.. 37
8
Broadband Over Power Line (BPL) 38
9
Fiber to the Premise (FTTP) 39
9.1
Point-to-Point Ethernet.. 39
9.2
Passive Optical Network (PON) 39
9.2.1
PONs PONs and more PONs.
40
9.2.2
A-PON B-PON.. 40
9.2.3
G-PON.. 42
9.2.4
10G-PON.. 43
9.2.5
E-PON.. 43
9.2.6
10G-EPON.. 43
9.3
MoCA.. 43
9.4
Controversy.. 44
9.4.1
ONT Installation. 44
9.4.2
Power Outage. 44
9.4.3
Copper Decommissioning. 44
9.4.4
Competitors. 44
9.4.5
Municipal Broadband. 44
9.5
Installation.. 44
10
Fixed Wireless. 45
10.1
WiMAX.. 45
10.1.1 Installation. 45
10.2
Wi-Fi Hot Spot.. 46
10.3
White Spaces Broadband.. 46
10.4
Optical Point-to-Point.. 46
11
Satellite.. 47
11.1
Geosynchronous. 47
11.2
Low Earth Orbit (LEO) 48
11.3
Medium Earth Orbit (MEO) 48
11.4
Installation.. 48
12
Cellular.. 49
12.1
Cellular Data Evolution.. 50
12.1.1 1st
Generation Cellular Digital Packet Radio (CDPD) 51
12.1.2 2nd
Generation General Packet Radio Service (GPRS) 51
12.1.3 3rd
Generation CDMA2000 - Evolution Data Optimized (EvDO) 51
12.1.4 3rd
Generation GSM – Enhanced Data Rates for GSM (EDGE) 51
12.1.5 3rd
Generation UMTS - High Speed Downlink Packet Access (HSDPA) 51
12.1.6 3rd
Generation UMTS – Evolved High Speed Packet Access (HSPA+) 51
12.1.7 Pre4th
Generation 3GPP Long Term Evolution (LTE) 51
12.1.8 4th
Generation 3GPP LTE Advanced. 51
12.1.9 5th
Generation - 2020 time frame. 51
12.2
Locked Phones. 53
12.3
Caps. 53
12.4
Roaming.. 53
12.5
Wi-Fi Centric.. 53
12.6
Tethering.. 53
12.7
Installation.. 53
Closing Thoughts. 54
1
ISP Overview
Internet popularity is driving demand for ever-faster
service, and exerting downward pressure on price. Connection between end user
and ISP is often called the last-mile.
This implies there is a magical entity out there called “The Internet” and
customers are passive consumers of Internet goodness. I prefer the term
first-mile. It better denotes Internet value being the result each person’s
connection as both contributor and consumer. Today most citizens in
industrialized countries have access to some form of high-speed access.
Broadband is increasing seen as a utility without which citizens are unable to
fully participate in society.
Broadband is a much abused and inexact term. The United
States Federal Communication Commission (FCC)
is constantly redefining minimum broadband speed. It had been 200 kbps. Basic
broadband increased requirement to 768 - 1500 kbps toward customer
(downstream). In July 2010 the National
Broadband Plan increased minimum speed to 4Mbps toward customer and 1 Mbps
up. In Feb 2015 the FCC raised the definition of broadband to: 25Mbps
down 3Mbps up.
Most of us utilize an
Internet Service Provider (ISP).
The ISP owns leases or otherwise has access to a connection to each customer.
The picture below provides a high level overview of how ISPs connect customers
to the
Internet.
Figure 1 ISP Functional Block Diagram
Connecting to an ISP would not have much value if the only
people you can communicate with are other customers. To provide worldwide
connectivity ISPs connect to other ISPs at peering points. This allows traffic
be delivered anywhere in the world.
ISPs exert a great deal of control over how customers use
the Internet. Much is made of Internet robustness and redundancy. That is true
of the Internet in general but for most of us the ISP acts as the on-ramp
gatekeeper, limiting how it can be used. In most locations broadband
competition is nonexistent or extremely limited. ISP business policy has
significant impact on how customers use the Internet and how new Internet
services are deployed.
There are several essential functions that must be provided
by the ISP, as they are the only entity capable of doing so. There are many
services, often associated with ISPs, which can be provided by anyone. The
distinction between essential and non-essential functions is important when
discussing Network
Neutrality. As broadband access becomes more pervasive ISPs and policy
makers need to balance business considerations with public interest.
Essential Core Functions
·
Customer Connection
·
Customer Authentication
·
IP Address Allocation
·
Packet Routing
·
Peering
·
Multicast (IGMP)
·
Quality of Service (QoS)
·
Service Level Agreement (SLA)
·
Acceptable Use Policy (AUP)
·
CAELA
·
Customer Support
·
Billing
Non-Essential Services
·
Name Resolution (DNS)
·
E-mail
·
Usenet
·
Web Hosting
·
Cloud File Storage
·
Virtual Private Network (VPN)
·
Voice over IP (VoIP)
·
Fixed Mobile Convergence (FMC)
·
IP Radio
·
IP Television (IPTV)
ISPs deliver a suite of services. When evaluating an ISP it
is important to keep in mind which features are core functions, only the ISP
can provide, and which are value add that can be provided by a third-party.
1.1.1
Customer Connection - Physical
First and foremost the ISP needs to provide a method for
customer to access the ISP network.
Some ISPs own the First-Mile access network; Cable and fiber
to the premise (FTTP) are examples of this type of ISP. The ISP owns and
manages the outside plant customer connection. DSL ISPs typically rent physical
access to legacy copper phone line from Incumbent Local Exchange Carriers
(ILEC) and collocate their equipment in the phone
company central office.
Dialup ISPs use the Public Switched Telephone Network PSTN to connect customers. The ISP
creates regional points of presence (POP) near the customer so customer is able
to call a local ISP telephone number, avoiding per minute charges. The
ISP in turn digitally terminates phone lines to support V.90/92 dialup speeds.
Wireless ISPs do not provide a physical connection at all.
Rather they obtain a FCC license to use the public airwaves to connect to
customers. This applies to both fixed and mobile wireless. Once the customer
connects to a nearby ISP radio Internet backhaul is performed much the same as
other ISPs.
Customer interface requirements differ greatly depending on
type of service and whether or not the ISP provides the network access device.
For example Cable, DSL, and FTTP ISPs typically provide the customer with a
standard’s based modem with either Ethernet or USB customer interface. In the US T-1 is a tariffed
telecommunication service. The FCC defined customer interface as two pair
copper circuit typically implemented via a smart-jack. Dialup ISPs
require customer obtain a V.90/92 or ISDN modem. Fixed wireless ISPs typically
supply and install customer antenna and radio. Cellular providers often provide
a subsidized smart phone when customer signs up for service. However this trend
is in decline with customers often able to purchase an unlocked phone on the
open market.
1.1.2
Customer Connection – Logical
ISP provides either a routed or bridged customer
connection. Residential accounts are typically bridged; customer connects
to ISP as if they were part of the ISP LAN. VLAN techniques prevent users from
seeing each other’s traffic. Business class accounts are typically routed
rather than bridged. ISP’s edge router communicates with customer’s edge
router. Routed connections are more flexible, but also more complex, then
bridged.
1.1.3
Authentication
The ISP needs a mechanism to insure only authorized
customers connect to its network. For some types of service the link between
customer and ISP is hardwired so any traffic appearing on the link is assumed
to originate from customer. T1 and FTTP are typical hardwired connections.
Shared media such as Cable and wireless need a way to identify customer. DOCSIS modems include a digital signature to
prevent unauthorized access. ADSL
ISPs typically use Point-to-Point Protocol over Ethernet (PPPoE) to authenticate customers.
Telco’s like PPPoE because it facilitates support for third-party ISPs. Dial up
ISPs typically utilize Point-to-Point Protocol (PPP) to
authenticate customers using same RADIUS servers as PPPoE.
1.1.4
Address Allocation
Each Internet host requires a unique address. ISPs typically
provide residential customers with a single public IPv4 address. Large
customers may obtain their addresses directly from Internet Corporation for
Assigned Names and Numbers (ICANN)
or from wholesale ISPs. IPv4
defines a 32-bit address space yielding about 4-billion possible
addresses. That was a large number back when the Internet was limited to
a few educational and government institutions but has become a serious
limitation today. As a result IPv4 addresses are in very short supply.
Next generation Internet protocol IPv6
increases address space to 128-bits, a truly humongous number. With IPv6 even
residential customers are issued a large block of addresses.
IP addresses serve multiple functions. They denote a
specific Internet host; each host needs an IP address. IP addresses also
facilitate routing because they are allocated in blocks. If IP addresses were
issued randomly each router would need to potentially look through billions of
addresses to determine how to handle each packet. By aggregating addresses into
large blocks routers only need look at a few high order address bits to
determine how to forward packets.
Business accounts are typically configured statically.
Static allocation is preferred for commercial accounts. With a static address
customer settings are configured manually, based on information provided
off-line by the ISP. This eliminates possibility of address change interfering
with remote access.
Most residential accounts obtain IP address dynamically.
This is convenient because it eliminates need for non-technical customers to
manually configure IP address, subnet mask, gateway address and DNS server
address. Dynamically assigned address may change at any time making it
difficult to operate servers.
Due to the severe shortage of IPv4 addresses some ISPs are
forced to issue customer private addresses and translate the private address to
one of the public addresses assigned to the ISP. This is the same technique
used by residential customer to share a single IP address with multiple computers.
While this is fairly transparent to customer it prevents them from running any
type of server and potentially causes problems if any of the customers engage
in bad behavior. From the Internet’s perspective they all originate from the
same IP address.
1.1.5
IPv6 Support
February 2011 witnessed a major milestone on the journey to
mass deployment of IPv6, IANA made the final allocation of IPv4
addresses. This event has been long anticipated but having finally occurred
ought to spur more rapid deployment of IPv6, the successor to IPv4. IPv6
represents a significant improvement over IPv4 but adoption has been painfully
slow. The reason is IPv6 is not backward compatible with IPv4. This is because
IPv4 has a 32 bit address space supporting approximately 4 billion hosts (4.3 x
109) IPv6 uses 128 bits for a mind boggling 340 Undecillion hosts
(3.4 x1038). The massive address space allows large blocks of
address to be allocated, thus easing routing and management.
Since IPv6 is not backward compatible ISPs offer a number of
ways to support the transition.
1) Dual-Stack
is probably the easiest to understand. The ISP provides customer with
both IPv4 and IPv6 addresses. Customer equipment uses the appropriate version
to communicate with the remote host, preferentially using IPv6. The down
side of this implementation is the need to provide the customer with a public
routable IPv4 address and the customer network gear has to support both IPv4
and IPv6. The lack of IPv4 addresses is why it is imperative the Internet adopt
IPv6.
2) Dual-Stack
lite The ISP provides only IPv6 addresses to customers, all traffic between
customer and the ISP network is IPv6. When a customer accesses an IPv4 Internet
host the customer’s router encapsulates the IPv4 address and transports it over
the IPv6 connection to the ISP. The ISP uses carrier grade NAT (CGN) much like
the way a typical home network shares a single IP address today. Customer’s
router disencapsulates IPv4 packets and distributes
IPv4 and IPv6 packets within the LAN. Just to keep life interesting the term
CGN has been depreciated and it is now called large scale NAT (LSN) to more
accurately reflect what the technique does.
3) Tunneling
(6in4) is a way for IPv6 packets to be transported over an IPv4only network to
another IPv6 network. This is probably not of interest for most readers of this
paper but is very useful for companies with many locations that have adopted
IPv6 internally.
A significant force driving IPv6 adoption is the cellular
phone network, especially outside the US where the IPv4 shortage is more
acute. The proliferation of smart phones means the network needs to hand
out an IP address per person rather than per residence greatly increasing the
number of addresses needed.
1.1.6
Packet Routing
The term Internet is a contraction of Inter network. Internet
is literally a network of networks. Routers are used to forward
packets between networks. Devices know whether or not a host they are trying to
reach is local. To access a remote host packets are forwarded to a router,
called a gateway, attached to the local area network LAN. The router uses
its knowledge of connection topology to make intelligent forwarding decisions.
This process is repeated multiple times until packet finally reaches its
ultimate destination. Routers learn connection topology by exchanging routing
information. In the case of most residential customers this forwarding
decision is trivial as there is only one connection to the Internet.
1.1.7
Transit Network
Signing up with an ISP would not be very useful if customer
was limited to only communicating with other customers of the same ISP. The
early Internet consisted of a few nodes interconnected by point-to-point links
rented from the old Bell
System. As the Internet grew it became apparent there was a need for a
high-speed data network to interconnect high usage nodes. Transit
providers span continents and oceans providing the backbone. Transit providers
exchange traffic with each other and accept traffic from ISPs. Large companies,
ISPs and governments often connect directly to one another, called Peering, eliminating the need
to use a transit provider for some traffic. Smaller ISPs purchase bandwidth
from third party wholesale suppliers. The end result is regardless how one connects
it is almost always possible to communicate with anyone else on the Internet.
This drawing is very simplified; typically all but the
smallest ISP will have multiple connections to various transit providers and
often peering connections to other ISPs. Routing protocols chose the best route
to deliver each packet. One of the network neutrality concerns is that ISPs
will choose less congested routes for partners resulting in slower performance
if a customer is accessing a non-preferred site.
Figure 2 Peering
1.1.8
Multicast (IGMP)
Internet is a powerful communication medium. A user is able
to connect to another host anywhere in the world virtually instantly. As
powerful as this type of communication is it is not well suited for broadcast,
delivery of one program to many subscribers simultaneously. Traditional
broadcast business model grew out of the technical limitation of radio. Station
owner built a transmitter and anyone within range was able to receive the
broadcast.
The one-to-one connection model used by the Internet makes
it difficult to cost effectively broadcast programs since each listener
requires a unique network session. Internet Group Management Protocol (IGMP)
creates the infrastructure to deliver a single stream to multiple users. At
each branch a decision is made whether or not to forward the stream. If an
active listener is downstream packets are forwarded, if not they are dropped.
This conserves channel capacity by suppressing streams no one is listening to.
IGMP dramatically reduces server load since only a single copy is transmitted.
Internet broadcasting is still in its infancy and IGMP is not commonly
implemented by ISPs. For multicast to function each router between sender and
receiver needs to support IGMP.
1.1.9
Quality of Service (QoS)
Internet is an egalitarian best effort network. This
works amazing well for transferring large chunks of data from point A to point
B. The network continues to operate in the presence of all sorts of
impairments and failures. However: best effort does not work well with latency
critical applications such as telephony and streaming media when dealing with
network congestion. For example a Voice over IP (VoIP) phone call requires round
trip latency under 150ms. Excessive delay makes carrying on a conversation
difficult and when extreme virtually impossible. On the other hand if a print
job is delayed a little no one is likely to notice as long as it completes
successfully.
When a switch or router encounters congestion it buffers
incoming packets until it is able to forward them. Normally this occurs on a
first in first out (FIFO) basis. Quality of Service (QoS
) metric allows latency
sensitive packets to receive priority queuing. This simple strategy works well
if latency critical traffic is a small percent of total. QoS
marks packets with a (Diffserv)
priority level. When congestion occurs higher value packets are delivered
first. Lower value packets are delayed or discarded during periods of extreme
congestion. QoS service allows more graceful
degradation by moving high priority packets to the head of the queue.
As discussed in a later section traffic shaping and
preferential packet treatment is controversial. Network Neutrality proponents
are concerned ISPs will strike business deals with partners to preferential
deliver their data at the expense of competitors. It is important to
remember Quality of Service mechanisms do not provide additional channel
capacity. They simply redefine winners and losers. When channel capacity does
not meet “offered load” (an old telecom term) some policy must be in place to
deal with congestion. The PSTN
managed congestion by withholding dial tone or returning an “all trunks busy”
message when call could not be completed. The Internet handles congestion
by delaying packets or in extreme cases dropping them. QoS
controls which packets get delayed. Many argue deploying additional capacity is
more cost effective then implementing a complex differential service mechanism.
To be maximally effective QoS
requires end-to-end deployment. Technical and business problems facing QoS is much the same as IGMP. There is little value until
“everyone” deploys it and little incentive to be an early adopter. ISP and all
intermediate nodes need to monitor packet privilege level and treat them
accordingly. Controls at each level need to monitor statistics to prevent
“tragedy of the
commons.” If too many packets ask for priority handling they all suffer.
Most residential broadband service is asymmetric; download
is much faster than upload. There is benefit in shaping upload traffic so
higher priority traffic is treated preferentially at the edge of the customer’s
network. Customer’s edge router examines outbound packets and prioritizes them.
Many residential routers already do this to a limited extent giving TCP/IP ACKs
preferential treatment. Similar treatment may be applied to VoIP or critical
gaming packets.
1.1.10
Service
Level Agreement (SLA)
One of the main differences between residential and business
accounts is the Service Level Agreement (SLA). SLA
defines things like: minimum speed, maximum latency, service reliability and
mean time to repair. The SLA imposes performance guarantees ISP must meet
and penalties if they do not. This is one of the reasons business class service
is so expensive. Residential accounts are typically best effort. If connection
fails or experiences congestion ISP is under no obligation to correct problem
on an expedited basis.
1.1.11
Acceptable
Use Policy (AUP)
Acceptable use policy (AUP) defines
customer responsibility, how service may be used and penalty for misuse. For
example, residential customers are typically prohibited from reselling access
or running servers and ISP often block certain types of traffic. In an attempt
to reduce cost some residential ISPs impose usage caps to limit monthly
download and upload. Most ISP’s reserve the right to revise
the AUP at any time making for a pretty one-sided contract.
1.1.12
Communication
Assistance for Law Enforcement Act (CALEA)
CALEA
passed in 1994 and has been greatly expanded over the years. It requires the
ISP to install special equipment to facilitate wiretapping of customer’s
digital traffic by law enforcement. Originally it was limited to voice
traffic but has been expanded to include all ISPs. There is a lot of pressure
on ISPs to retain customer web browsing history and to make it available to law
enforcement and antiterrorism agencies. This has been especially prevalent in
Europe but is also happening in the US.
1.1.13
Technical
Support
Regardless of how good service is on occasion will be
necessary to contact technical support to resolve problems. Tech support
responsiveness dramatically affects overall customer satisfaction.
Most residential broadband providers offer only limited help
in troubleshooting problems. Finger pointing can be frustrating when a customer
is trying to resolve a complex interaction and ISP does not consider it their
responsibility. Specialized web sites such as DSLReports can
be an effective alternative. DSL Reports is a good example of an Internet
community; members post questions and assist each other in dealing with network
issues.
ISPs would not stay in business long if they could not
charge for service. During the Dotcom era some dialup ISPs offered advertising
supported free access, those companies are long gone.
Most ISPs offer flat rate billing based on speed tier.
Monthly cost is based on connection speed not how much the service is used.
Some ISPs set monthly bandwidth consumption quotas, exceeding monthly cap
results in an extra charge or a reduction in speed. Caps are controversial
because measurement tends to be inaccurate and they have little to do with the
cost of providing service. Caps are pretty common for Cable and wireless
providers, often imposing a significant surcharge. Usage based billing is very
common for Cellular service. Andrew Odlyzko has written extensively about customer pricing
preferences – what people are willing to pay for and how they prefer paying for
it.
There is no comparable notion of telephone long distance in
the Internet world. It does not cost any more to access a web site cross the street
as around the world. Back in the early days of the telephone it was very
difficult and expensive to transport calls over long distances. The advent of
fiber optic technology has reduced transmission cost so it represents only a
small fraction of the cost to deliver Internet access. The distance independent
paradigm of the Internet is beginning to affect how traditional telephone calls
are billed. By way of example the bundled wireline phone service provided by my
ADSL CLEC does not impose per minute charges for domestic or Canadian phone
calls. The monthly bill covers unlimited Internet and domestic phone usage.
1.2
Common But Non-essential Services
This section examines services often provided by ISPs but
that can be provided by third parties or in some cases even the customer. This
distinction is important in the Network Neutrality debate. If an ISP decides to
offer a non-standard or value-add service and customer or third party is able
to supply a similar service the impact is dramatically different than if the
ISP implements a proprietary core service.
1.2.1
Domain Name System (DNS)
I struggled with whether to put DNS in the essential or
non-essential session.
The Domain Name System (DNS) translates
Uniform Resource Locator (URL)
to IP address. Without DNS web sites would have to be accessed by IP
address. DNS is unique in that it is the only fully distributed database
in existence. DNS name space is evaluated right to left. Naming convention
begins with an implied “.” at the extreme right of the top level domain (TLD),
the root domain. Next in the hierarchy are the TLDs (com, gov, edu, uk, ru), then registered
domain name (tschmidt is my registered domain within
the .com top level domain), then one or more sub domains. As each level is
traversed it provides information about then next lower level until ultimately
the IP address of the particular host server is determined.
If DNS is unable to resolve a domain name it returns an
error message. Some ISPs have attempted to monetize incorrect URL entry by
returning advertising supported web page if the URL cannot be resolved.
DNS redirection is controversial. Some customers may find redirection useful,
other not.
There are lots of public
DNS servers available if you do not like the one provided by your ISP. They
can also be handy for troubleshooting if your ISP is experiencing DNS
problems. For many years I used the popular TreeWalk
program to run my own DNS resolver. The web site has expired so I can no longer
recommend using it. Gibson Research has a handy DNS benchmarking tool to test
performance of multiple resolvers.
So why did I say I struggled with this topic, since it is
obvious you do not have to use your ISP’s DNS server? The issue is content
distribution networks (CDN). CDNs cache content physically close to the end
user, sometimes even at the ISP data center. Using a DNS resolver other than
the one provided by your ISP can actually degrade performance. This is because
the DNS server will be unaware of any private arrangements between the ISP and
CDN and the physical location of the public DNS server is likely significantly
different then the ISP DNS. The result is the public DNS server will return the
IP address of a non-optimum CDN caching edge server degrading performance.
Just about all ISPs provide email. It is wise to consider
ISP e-mail account a throwaway. If you change ISP or the ISP is sold your email
address changes making it difficult for folks to stay in touch. For a more
permanent address use one of the free e-mail services such as Yahoo or Gmail or better yet register your own
domain.
One useful way to use ISP email is for home automation
devices. We have several that send notification emails, either at a fixed time
of day or due to certain events. Sending these emails from your ISP account to
another email account is a great way to verify both are operating properly.
Usenet Newsgroups are a valuable source of up to date
information. Usenet is text based and predates the web. Most ISPs used to
include Usenet access.
Due to declining interest in Usenet and legal attacks related to pornography
many ISPs are eliminating Usenet support. Usenet access is available from a
number of specialized companies. Usenet
Compare has a nice comparison list of newsgroup providers.
1.2.4
Web Hosting
Many ISPs provide web site hosting for residential
customers. This allows customers to have an Internet presence without having to
register a domain name or run their own server. ISP runs a virtual server
enabling many web sites to run on a single computer. ISP web hosting is a boon
to residential customers by providing a painless way to create a web presence.
As with email use of the ISP web server binds customer’s web site to the
ISP. There are many hosting alternatives that decouple personal web sites
from the specific ISP.
1.2.5
Cloud File Storage
The cloud is the new
buzzword for outsourcing services over the Internet. Many ISPs offer some form
of network storage either as part of the plan or as an extra cost add on.
Storing your information on the Internet means you can access it from anywhere
without the need to run your own server and if your house burns down or
computer crashes your data is safe. On the other hand the fate of your
data is in the hands of others.
1.2.6
Virtual Private Networking (VPN)
Virtual Private Network (VPN) uses the public Internet to
create private communication paths. Depending on how it is implemented it may
be a feature that only the ISP is able to deliver or something the customer or
third-party is able to engineer. Once the province of large companies VPNs are
attractive for any customer that needs to securely access their network remotely.
Large companies make extensive use of MPLS to implement a geographically
dispersed corporate LAN. To users, regardless of location, resources appear to
be on the LAN. Service provider configures edge routers such that data
presented to it is delivered to the correct physical location. ISP isolates
each company’s traffic so in is invisible to other companies.
Figure 4 MPLS VLAN
More MPLS/VPN details in this Network World
article.
It is also possible for customers to create their own VPN
using IPsec. In this case
customer, rather than service provider, creates a secure end-to-end path
through the public Internet. IPsec is used extensively to support satellite
offices and telecommuters.
SSL/TSL is
another mechanism used to provide end-to-end privacy. SSL was originally
developed by Netscape to protect web based financial transactions. Because it
is built into all browsers many companies are using it, rather than IPsec, to
provide remote employee access.
1.2.7
Voice over IP (VoIP)
Public switched telephone network (PSTN) represents a hundred years
of engineering. Recently packet based telephony has become a serious contender.
Rather than traditional circuit switching Voice over IP (VoIP) uses packet-based
communication to deliver two-way real time voice. Voice communication is very
demanding. Voice data rate is low by Internet standards only 8-64 kbps in each
direction. However latency is critical. If packets are delayed more than a few
hundred milliseconds voice quality is seriously degraded.
Figure 5 Voice over IP
As with any new technology many players have entered the
market. Most will fail but a few will succeed. If your
ISP offers VoIP check the service thoroughly. The asymmetric nature of most
residential service, upload being much lower than download, makes it easy to
saturate the connection. Quality of Service (QoS) may
be required to mark VoIP packets, as high priority so they get preferential
treatment.
1.2.7.1 Number Portability
In the US the FCC mandates telephone number
portability. In most cases you will be able to transfer your existing
wire-line phone number to new VoIP phone service or to another wire-line
carrier. I recently switched our wire-line phone and DSL Internet from the
incumbent phone company to a competitive exchange carrier. Number portability
allowed us to maintain the same land line phone number we have had for many
years. We also took advantage of number portability when we switched cellular
providers.
1.2.7.2 E911
Voice over IP represents many challenges for E911ememgency
service. Unlike wire-line POTS where telephone location never changes, a VoIP
call can originate anywhere. Cellular networks have struggled for years to
implement E911 service using triangulation or GPS to locate subscribers.
1.2.7.3 Fixed Mobile Convergence (FMC)
There is tremendous interest in multimode cellular phones
able to utilize both traditional cellular network and opportunistically, Wi-Fi
networks. Fixed
Mobile Convergence (FMC) represents a win-win situation for both customer
and wireless provider. For providers it utilizes the vast potential of the
Internet and private LANs to remove traffic from expensive cellular radio
networks. For customer it represents potentially lower cost and improved
performance. For business it represents a way to eliminate traditional
PBX wired telephone infrastructure without paying extravagant per minute
charges. Depending on national legal restrictions it may offer arbitrage
advantage for multinational corporations to treat voice like email, bypassing
local phone companies and eliminating per minute charges.
Figure 6 Fixed Mobile Convergence
An alternative to Wi-Fi is femtocells being offered by
several Cellular phone companies. Femtocells are low power cellular base
stations that utilize customer’s broadband connection to deliver coverage to a
single home. As with Wi-Fi Cellular providers
like it because it moves traffic off cell stations.
At this point it is unclear what if any role the ISP will
play. FMC looks like any other real time traffic to the ISP. Our cell phone provider
Republic Wireless has been
aggressive developing this technology. It works extremely well for us in
terrain challenged NH where we have poor cell phone coverage at home.
1.2.7.4 Roaming
A difficult problem is seamless roaming between networks. To
a limited extent this is already being done by Wi-Fi as a user moves between
Access Points. However for this to work all APs must be under the same
administrative control. In an ideal world a device associates with a network
and as it moves it automatically reconnects to the best network at the new
location seamlessly without any interruption in service. As an example a
imagine a user beginning a Wi-Fi session at home, gets in their car and moves out
of range and is handed off to the Cellular network. They stop for breakfast and
are back with range of a different Wi-Fi network, and lastly they arrive at
work and now join the corporate LAN. The IEEE 802.21 media
independent handover services working group tackled this difficult
problem.
ISPs do not appear much interested in becoming content
aggregators for radio the way they are for TV. But other than much lower
bandwidth requirement Internet radio is not much different than Internet TV. Radio-Locator is a convenient way to
find Internet radio stations.
1.2.9
IP Television (IPTV)
Over-the-air (OTA), Cable and DBS TV all
use basically the same transmission scheme. RF spectrum is divided into
channels. US TV channels are 6 MHz wide, in Europe 8 MHZ. Channels were
initially specified to carry a single analog standard definition TV program.
Migration to digital transmission allows each channel to carry multiple high
definition (HDTV) and/or standard definition programs (SDTV).
IPTV
represents a fundamentally different way to deliver TV leveraging packet-based
technology. IPTV opens the door to demand based programming. The traditional broadcast
model is one-to-many, an artifact of radio transmission. Once a transmitter is
set up anyone within range is able to receive the program. Video on
demand (VoD
) is like going to the
library, rather than changing channels. One simply selects the program of
interest and it is delivered virtually instantly anywhere anytime to any device
the end user chooses.
Using MPEG-2 compression SDTV requires about 2
Mbps and HDTV 15 Mbps. MPEG-4 yields significantly lower data
rates for equal image and sound quality. These rates are the result of
spectral (within the picture) and temporal (over time) data compression. Raw
data is much too high to be delivered economically.
Video on
demand represents many challenges compared to traditional broadcast. Each user
is able to start/stop the program at any time requiring a discrete program feed
to each user rather than a single feed to all users as with broadcast.
Figure 7 IP
TV
Historical
residential ISP assumed customer traffic model of primarily bursty
download traffic such as loading web pages or accessing email. Streaming
TV and to a lesser extent streaming radio lock up significant bandwidth for
extended periods of time. This is much more demanding than browsing.
IPTV
dramatizes the disruptive nature of the Internet. Since the end of WWII Cable companies have wired areas to
deliver broadcast TV over coax and more recently fiber. Cable network is
intimately bound to TV delivery. As residential broadband speed increases the
door opens for new providers to bundle content and deliver it without the need
to either build or own the means of local delivery. ISPs are worried about
being relegated to commodity bandwidth providers.
Basic to the
design of the Internet is the notion of direct end-to-end communication.
When Computer A wants to exchange data with Computer B routers between the two
move packets the most efficient way they can on a packet by packet basis. The
popularity of streaming video services like YouTube and Netflix stresses the
network as millions of users access the same content from diverse
locations.
Figure 8
Content Delivery Network
Video is very
bandwidth intensive. Video on demand requires a one-to-one connection between
user and server as opposed to the one-to-many model of traditional broadcast.
Being demand based each user may be viewing a different program or different
time within the same program. To address the growing interest in video on
demand (VoD) specialized service providers, called
Content Delivery Network (CDN), have become popular. The CDN
replicate programs on many caching servers and locates them near the ultimate
end user. Often they have special peering arrangements with large ISPs or are
located within the ISP’s data center itself. CDNs reduce the amount of
traffic flowing over Internet transit network because they are able to source
the file near where it is being viewed. When a customer requests a particular
program the ISP’s DNS servers return the address of the local caching server to
most efficiently stream the program to the customer.
Historically
when a customer contracted with an ISP they were given a block of IP addresses
large enough to meet their needs. IPv4 address shortage forced ISPs to rethink
how they allocate scarce addresses. Most residential broadband ISPs restrict
customer to a single IPv4 address. This creates a quandary; how to cost
effectively connect multiple hosts to the Internet? The most common workaround
is Network Address Translation (NAT) coupled with use of private IP
addresses. RFC 1918 reserves three blocks of IP
addresses guaranteed not used on the Internet. Because these addresses are not
used on the public Internet they can be reused multiple times.
Combining
NAT, more properly Network Address Port Translation since both address and port
number are modified, and private addresses allow a virtually unlimited number
of computers to share an Internet connection even though the ISP only provides
a single address. NAT provides translation between private addresses on LAN and
single public address issued by ISP on WAN.
NAT only
affects non-local communication. When a request cannot be serviced locally it
is passed to the NAT router, called a gateway. The router modifies packets by
replacing private address with public address issued by ISP and if needed
modifies port number to support multiple sessions and calculates a new
checksum. The router sends the modified packet to remote host
as-if-it-originated-from-the-router. When router receives the reply the
modifications are reversed and the packet forwarded to the originating host.
Router tracks individual sessions so multiple computers are able to share a
single address. From the Internet’s perspective local hosts are invisible. The
router looks like a single computer with the address of the public IP issued by
the ISP.
IPv6, with
its vast address range, does not require NAT. Each device will have its own
public IP address. This changes the nature of residential routers. NAT, though
not technically a firewall, blocks all incoming connection requests from remote
hosts. Unless specifically programmed with port forwarding rules it does not
know which device on the LAN to forward the request. This default behavior is
lost with IPv6. Residential routers that support IPv6 should block incoming
connection requests unless specifically programmed otherwise.
Internet is
designed as a transparent end-to-end bit delivery network. This means any host
is able to communicate with any other host. TCP/IP and UDP/IP use ports so a host can manage
multiple simultaneous sessions. Ports are 16-bit unsigned values yielding
up to 65,535 ports for each connection type. When a service is defined a port
number is selected for initial contact. This is called the well-known port. For example the
well-known port for HTTP Web access is 80. When a remote user
attempts to connect it sends the request to TCP port 80. Once the initial
connection is established both computers agree to a use a different combination
of ports for ongoing communication. An analogy is to think of well-known port
as a doorbell. If ISP blocks access to well-known port remote users are
unable to connect.
It is common
practice for residential ISPs to block incoming port 80 to prevent customers
from running web servers, port 25 to send email to prevent spam, and ports 137,
138, 139, and 445 to prevent remote access to Windows LAN based SMB file sharing. In an effort to
reduce file trading some ISPs throttle or block ports used for peer-to-peer
(P2P) file trading applications. Impact of blocked ports varies.
To get around
blocked port it is easy to reconfigure server to use a non-standard port. If
access is limited to a small group of friends it is easy enough to simply
inform everyone which port to use. If goal is wider public access use of
nonstandard ports is a problem. Without knowing the port number remote users are
unable to connect. URL forwarding is a technique to work
around this restriction.
Internet is
as an egalitarian best effort network. This means as packets arrive they are
processed on a first come first serve basis. With enough channel capacity
incoming packets never have to wait.
Residential
ISPs made assumptions about typical customer usage when they set monthly
charges and designed infrastructure. Business model assumed bursty
data flow predominantly web browsing, email, and occasional file download.
Proliferation of Peer-to-Peer (P2P) file trading and streaming video
services, such as YouTube and IPTV upset these
assumptions. ISPs are struggling to carry more traffic than originally
planned.
Some ISPs are
responding with traffic quotas. When customer exceeds quota either speed is
reduced or additional charge incurred. There have been numerous stories of
unwitting customers being billed for thousands of dollars in overage charges on
their cell phone data account. One the other hand some ISPs detect undesirable
traffic and throttle speed rather than blocking it entirely.
ISPs often
justify usage based pricing as a way to control congestion; however congestion
is a temporal phenomenon having little to do with aggregate usage.
Congestion only occurs when instantaneous demand exceeds capacity. As has been
well documented usage Caps are really being used to generate additional revenue
or to protect legacy business models.
The other
common complaint is the measuring technique is not very accurate.
The
proliferation of digital media devices and networking is making the traditional
media world nervous because digital technology allows rapid lossless copying.
From a technology standpoint the digital rights management (DRM) mechanisms used to prevent this have
been a spectacular failure and in some cases have actually caused damage to
end-user devices.
If you or
someone on your network is found to be violating copyright law the owner will
notify the ISP and the ISP will in turn notify you of the
violation.
A recent concern
is Apples removal of the analog headphone jack from their smart phones. This is
widely seen as a way to extend DRM end to end. While the industry loves DRM it
often prevents users from accessing content they have legally obtained.
Some ISPs use
a technique called Deep Packet Inspection (DPI) to determine how customer is using
the Internet and block or throttle use they deem harmful. DPI can also be used
to obtain additional information about customer’s Internet usage. This data is
of interest to targeted marketing vendors. The use of DPI falls into a grey
area of what is and is not acceptable ISP behavior. In addition many
governments want to know about what their citizens are doing and press ISPs to
track customer usage.
In the quest
for ever-faster speed it is important not to lose sight of the interplay
between speed and latency. As an example a truck carrying DVDs exhibits
very high speed (bits per second) once it arrives but also high latency because
it takes hours or days for the data to arrive. Round trip latency is defined as
time it takes a packet to go from source to destination and back again. Factors
affecting latency are: connection speed, modem overhead, distance, propagation
speed, and network congestion.
Modems
operate on “chunks” of data increasing latency because entire block must be
processed before being passed to next stage. Data cannot be used until the last
bit in the bock is received. DSL modems often use a technique called interleave
to reduce sensitivity to transient noise. This is effective in maximizing
robustness by reducing effect of errors but adds latency because it operates
over a larger data block. Low speed connections such as dialup often use
smaller packet size to minimize this effect.
Light travels
186,000 miles per second in vacuum. Optical fiber is somewhat slower about 70%
of light in vacuum. A packet traveling the 3,000 from New York to LA takes
about 25 ms in each direction. To this one must
add delay at each router between source and destination. Normally this delay is
negligible but if network becomes congested router must temporally store
incoming packets until outgoing path is free. In extreme cases router will
discard packets. When packets are lost upper level protocol either requests
retransmission (TCP/IP) or in the case of streaming data (UDP/IP) fakes missing
data.
Impact of
latency is heavily dependent on data type. Interactive use such as gaming and
Voice over IP (VoIP) telephony place stringent demands on
latency but do not require much bandwidth. File transfer on the other hand is
relatively insensitive to latency but places great importance on speed.
Typical
first-hop latency: T1 or FTTP 1ms, Cable/DSL 5-30ms, Dialup 100 ms, Geosynchronous Satellite 500ms. For a more
in-depth explanation see “It’s the Latency Stupid.”
Most
residential broadband service is asymmetric: download is much faster than
upload. This is done for technical and business reasons. Asymmetric speed
allows ISP to position residential service differently than business and charge
higher fee for business class service.
Low upload
speed makes it difficult to run a server or use Voice over IP since upload pipe
is easily saturated.
End user LAN
is rarely the determinate of Internet speed as wired and wireless LAN
performance normally greatly exceeds Internet access speed. Speed is typically
limited by first-mile WAN connection. It can be a challenge teasing out various
components of end-to-end performance to see if ISP is working as advertised.
IP
transmission splits data into 1500 byte chunks called packets (1-byte =
8-bits). Some of the 1500 bytes are used for network control so are not
available for user data. TCP/IPv4 uses 40 (TCP/IPv6 60 bytes) of the 1500 bytes
for control. NOTE: this analysis assumes use of maximum size packets. Since
overhead is fixed using smaller packet incurs higher overhead percentage.
With 40-bytes reserved for control out of every 1500-bytes sent only 1460 are
available for data. This represents 2.6% overhead.
Some ISPs,
typically phone companies, use a protocol called Peer to Peer Protocol over
Ethernet (PPPoE) to transport DSL data. This is an
adaptation of PPP used by dialup ISPs. Telco’s like PPPoE because it
facilitates support of third party ISPs as mandated by the FCC. PPPoE
appends 8-bytes to each packet increasing overhead to 48-bytes reducing payload
to 1452. Where PPPoE is used overhead is increased to 3.2%.
DSL
connections typically use Asynchronous Transfer Mode (ATM) (AAL5) to carry DSL traffic. ATM was
designed for low latency voice telephony. When used for data it adds
significant overhead. ATM transports data in 53-byte Cells of which only 48 are
payload the other 5 are control. Each 1500-byte packet is split into multiple
ATM cells. A 1500-byte packet requires 32 cells (32 x 48 = 1,536 bytes). The
extra 36-bytes are padded, further reducing ATM efficiency. 32 ATM cells
require modem transmit 1,696 bytes of which only 1452 carry payload. Where
ATM/PPPoE is used overhead is increased to 14.4%.
TCP/IP
overhead 2.6% efficiency 97.4%
TCP/IP/PPPoE
overhead 3.2% efficiency 96.8%
TCP/IP/PPPoE
over ATM overhead 14.4%, efficiency 85.6%
NOTE: This is best-case
speed. Errors, transmission delays, etc. will reduce speed from this value. The
higher the speed the greater the impact of even modest impairments on thru put.
It is easy to
determine best-case file transfer rate if modem data rate is known. Broadband
marketing rate may not the same as modem transfer rate. Some Telco’s set
transfer rate higher than marketed speed to compensate for overhead. That way
speed test result will be close to marketed speed. Most broadband modems
have status page allowing user to observe true transfer rate. This is the rate
modem connects to ISP not speed computer connects to modem or router which is
typically 10 Mbps, 100 Mbps or 1 Gbps.
Sync rate of
my FirstLight ADSL service is 7002 kbps down and 996
kbps up. FirstLight uses DHCP so there is no PPPoE
overhead but does use ATM. Best case speed for my connection is 6,036
kbps down and 859 kbps up. Actual speed test results reported by DSL Reports and Speedtest.net
are shown below.
Figure 9 Speed
Test Result
TCP requires
receiver periodically send an Acknowledge to let sender know everything is
OK. If the transmitter has not received acknowledgement after it sends a
number of packets it stops transmitting and waits. This is called the receive
window. For high speed connection or where latency is high default
receive window (RWIN) should be increased to prevent
pauses in transmission. Most modern Operating Systems do a good job optimizing
RWIN so little is gained by changing it.
If router
supports QoS having it give ACKs priority will
improve file transfer rate if upload becomes congested.
The other
important tweak is packet size, called the maximum transmission unit (MTU). Maximum packet size is typically
limited to1500 bytes. Normally this setting is fine for broadband access,
dialup uses a much lower MTU typically 576. PPPoE encapsulation adds 8
bytes to each packet. This reduces maximum packet size to 1492 bytes. If sender
attempts to transmit a larger packet it will either be rejected or fragmented
into two parts, with attendant performance degradation.
If one link
is not able to deliver adequate speed the obvious solution is to add links.
There are two ways to manage multiple links load balancing and bonding.
With load
balancing a router with multiple WAN ports is used to share the load. As connection
requests come into the router from the LAN it determines which link to use
based on link capacity and loading. A given session is constrained by the speed
of whichever link it is assigned. Aggregate performance is increased because
the router parcels out requests to all the links. A typically web page consists
of dozens of separate HTTP sessions to different servers. Load balancing will
help in that case. If you are downloading a video load balancing will have no
effect.
Bonding is
transparent to IP it looks like a single faster pipe. Bonding requires
cooperation between the ISP and customer where load balancing can be performed
unilaterally by the customer. In the case of DSL bonding is typically
performed by the ATM layer that splits data among multiple ATM streams. DOCSIS3
modems do something similar allowing the ISP to allocated more than one channel
for Internet delivery.
While bonding
is able to dramatically improve speed based on the number of connection it has
little if any effect on latency. The reason is the modem processing that must
occur at each end is the same and even though it is invisible to IP bits need
to travel over multiple paths and be reassembled before they are handed off to
IP.
Most
residential accounts are configured automatically each time customer
connects. Dynamically assigned IP address makes it difficult to run a
server because address may change at any time preventing remote users from
connecting until they learn new address. Dynamic DNS service provides a workaround
to run servers on dynamic accounts. A daemon runs on either the router or
server to detect address changes. When a change occurs it notifies DNS service
which in turn automatically updates A records for the site. Even with automatic
DNS update there will still a period of time after the address changes where
server is not accessible and active sessions are aborted. Dynamic DNS services
are really only suitable for casual personal servers, not business use.
There has
been much press about residential and cellular providers marketing unlimited
service and then imposing usage caps or throttling heavy users. Some ISPs have
gone so far as to call heavy users bandwidth hogs. The controversy is not about
an ISP’s right to set terms of use but rather misleading marketing. It is about
calling a service unlimited then throttling or disconnecting customer if they
use it too much.
Broadband
service is marketed as “always on.” Exactly what this means is subject to
interpretation. The most “on” service is a bridged or routed connection
configured with a static IP address. Once service is configured connection is
permanent and always available until the next time the ISP needs to reallocate
IP addresses or power fails.
Dynamic Host
Configuration Protocol (DHCP) assigns client an IPv4 address for a
limited period called a lease. Before lease expires client attempts to renew.
As long as ISP continues to renew the lease the user is never disconnected.
From customer’s perspective service is always on, lease renewal is transparent.
Some ISPs bind IP address to hardware MAC address. The same IP address is
assigned as long as customer does not change equipment. IPv6 uses a somewhat different
mechanism DHCP-PD or Router Advertisement but the end result is the same,
customer equipment is automatically configured by the ISP.
Point-to-Point-Protocol
over Ethernet (PPPoE) or ATM (PPPoA) works
like traditional PPP dialup. This type of service is common
for ADSL. It leverages ISP investment in RADIUS authentication and billing
equipment. Customer provides username/password to authenticate, once
authenticated ISP issues an IP address. If connection becomes idle the user is
disconnected. Most residential routers include a keep-alive mechanism so
connection is never disconnected. From the user’s perspective the connection is
always on as long as the ISP is able to maintain an active RADIUS log in
session.
Some ISPs
limit maximum connect time. After a certain number of hours connection is
dropped and must be reestablished. This sort of behavior is common for dialup
ISPs and Wi-Fi Hotspots. When connection is dropped customer must log in again
to regain Internet access.
Internet is a
rough and tumble world often likened to the Wild West. The power of worldwide
connectivity means anyone on the planet with an Internet connection is in a
position to attack another connected computer. ISPs often block certain ports
to reduce danger to unsophisticated users. Port blocking is a double edge sword
as it may interfere with customer’s legitimate use of the Internet. Some ISP's
go further acting as a firewall protecting customer from hostile attack and
examining email for dangerous content or attachments. Some users consider
this a great feature in the battle against spam and viruses. Others see it as
an unwelcome intrusion in what should be individual control of network
access.
The ISP is
privy to all traffic that flows through its system. This raises two concerns,
nosey ISPs and subpoenas. ISP can easily monitor how customers use the
Internet, what sites they go to, what email they send and receive and in some
cases even snoop usernames and passwords if they are sent in the clear. Privacy
concerns have been exacerbated recently with expanded government snooping due
to war on terrorism. US government asked ISPs to provide information about
customer Internet usage without a court order and in most cases ISPs complied.
Internationally governments are mandating ISPs retain customer traffic
information for years. The EU has pretty stringent privacy policy but at the
same time wants ISPs to maintain long term customer usage records to facilitate
law enforcement.
ISP’s privacy
policy determines how customer information is used and protected. It is
reasonable to expect ISP to collect and use information for diagnostic purposes
and to improve service. However, some ISPs sell or otherwise make use of
customer’s browsing data, for example as a way to create targeted ads.
Popularity of
wireless networks raises additional security concerns. In a wired network
an attacker must physical connect to the network. With
wireless an attacker is able to eavesdrop from some distance away. This
is especially worrisome with Wi-Fi hot spots since they are in public places
and the integrity of owner is often unknown. When using public Hot Spots one
should be careful accessing any resource over a wireless network where passwords
are exchanged in the clear. Specifically email as POP/SMTP credentials are sent
in the clear. If at all possible use SSL authentication to access email
accounts. At home use Wireless Protected Access WPA2 with a strong password to protect
privacy. WPA2 provides robust over the air encryption.
IPv6
addressing presents another possible security issue. One of the addressing
schemes uses the 48-bit MAC address for the low order bits of the
128-bit IPv4 address. This means hard coded machine MAC address that is
normally not visible outside the LAN in IPv4 becomes part of the pubic IP
address and remains the same even when connected to a different ISP. A
solution to this problem is to have the computer use a random number rather
than the MAC address.
As Internet
access becomes pervasive there is growing tension between ISP business
practices and public policy. ISPs are concerned about being relegated to
commodity bandwidth provider. As such they are frantically trying to create
business relationships with select third parties to offer bundled services.
Network Neutrality proponents are
concerned ISPs will created walled gardens and be in position to favor some
companies and disadvantage others. Opponents of Network Neutrality argue ISPs
ought to be able to do anything they want with their own network.
The reason I
went into so much detail earlier about required and optional ISP services was
to identify those services that only an ISP is able to deliver. Network
Neutrality ought to insure network transparency is maintained, innovation
encouraged and ISP allowed to offer value add services while being prevented
from acting as gatekeeper. Internet’s rapid rise in popularity is the result of
its open architecture. Entrepreneurs need to be able to create new business
models and interact with customers without requiring permission or cooperation
of the network owner.
It can be
difficult finding information about local ISPs. First step is contacting your
town’s Cable franchise and incumbent telephone company.
Many states
are participating in the national broadband mapping program to
determine broadband availability. The NH the program is called cleverly
enough: NH broadband mapping and planning program.
NHBPM is working to deliver more accurate and detailed data on a town by town
basis and has a speed test to record actual customer speed. The ease of use and
data quality varies a lot by state.
If all else
fails the state public utility commission may have complied information about
ISPs. Internet access is an unregulated business but of significant interest to
most PUCs.
Dialup has
come a long way from Bell 103 acoustic modem operating at 300 bps to current
crop of V.90/92 modems capable of over 50,000 bps. Dialup Internet access is
available anywhere there is telephone service. It will even work on cellular at
very low speed in a pinch. Almost all Dialup ISPs support ITU-T V.90/92 standard. V.90 modems
deliver up to 56 kbps (download) over the PSTN. In the US FCC power limitation
reduces maximum speed to 53 kbps. V.90 transmission from subscriber to ISP
(upload) uses V.34 mode limiting maximum upload speed to 33.6 kbps. If modem
cannot connect in V.90 mode it automatically falls back to V.34 mode in both
directions with a maximum speed of 33.6 kbps.
V.92 is a
minor enhancement to V.90. Upload speed is increased slightly to 48 kbps and
implements faster auto negotiation to reduce call setup time. V.44 improves
compression of reference test data to 6:1 vs 4:1 with V.90. Compression
increases apparent speed because it reduces the number of bits transmitted over
slow telephone network. Modem on Hold (MOH) allows modem to park a data session
allowing user to answer a short incoming call. This works in conjunction with
Phone Company Call Waiting feature and requires support
from the ISP.
V.90/92
requires ISP modem connect to phone company digital trunk. Only a single
digital to analog conversion can exist between ISP and user. Phone lines are
analog between customer and central office or remote terminal. At that point
they are digitized at 64 kbps. This means POTS modem technology has reached its
theoretical maximum speed. To obtain higher speed requires use of different
technology.
At connect
time modem probes phone line to determine noise and attenuation characteristics
in order to set initial connect speed. Speed is constantly adjusted in response
to varying line conditions. To obtain maximum speed V.90 and V. 92 modems
require phone circuit that exceeds minimum FCC requirements.
Dialup
networking (DUN) is used to establish an Internet
connection. The most common method used to traverse the telephone network is
via Point-to-Point Protocol (PPP). PPP allows Internet Protocol (IP)
packets to traverse the serial point-to-point telephone link between user and
ISP. DUN automatically dials ISP phone number, waits for modem to connect and
establishes PPP session. The ISP performs user authentication and assigns an IP
address. DUN monitors the connection and notifies user when it
disconnects. In Windows, Internet Explorer can automatically activate DUN when
attempting to connect to a web site.
Dialup ISP
business model assumes customer stay connected for relatively short periods of
time. To enforce this most ISP’s automatically disconnect customer when limit
is reached. Session will also be dropped due to extended inactivity.
In the quest for higher speed some dialup ISPs support Multilink.
Multilink binds two dialup links into a single faster connection. If customer
typically connects at say 44 kbps multilink doubles speed to 88 kbps. Multilink
requires two modems; two phone lines, and an ISP that supports it. Where
available it is a useful technique to obtain better performance from dialup.
Software at
each end of the link splits data between each connection effectively doubling
speed. Unfortunately because data is still traveling over low speed dialup
multilink does not improve latency.
Multilink is
also used with ISDN to bind the two bearer channels together yielding a128 kbps
connection.
Modem data
connection is more demanding than voice. There are many reasons for slow dialup
even though phone sounds normal. Dialup modem impairments are discussed at
length in a separate paper.
Call waiting
generates an alert tone to inform the user someone else it attempting to call.
The call waiting process interferes with an existing data call. Call waiting
can be temporally disabled at the beginning of a call. The sequence varies by
locale, in our area it is *70. Unfortunately sending the disable sequence to a
line not equipped with call waiting is interpreted as part of the dialed
number, resulting in an incorrect connection. This is a problem if the modem
uses multiple lines and not all are equipped with Call Waiting.
If dialup
modem shares a phone line with telephone or fax machine there is possibility of
mutual interference. If modem is in use picking up a phone will cause modem to
disconnect. Conversely if phone is in use modem may attempt to connect
interfering with call. One can use a privacy device that monitors phone line
voltage to prevent this. When phone is idle open circuit voltage is high around
48 volts, when a phone/modem is in use voltage drops to less than 10 volts. Privacy
adapters measure line voltage to prevent phone use if a call is already in
place. There are a couple of inconvenient side effects to this approach.
Privacy device prevents calls being transferred from one phone to another and
it confuses line use indicators built into many phones. I designed a Modem Access Adapter to prevent
interference when modem and phone share the same line.
Other than
requiring a V.90/92 modem there is no installation. PCs, especially laptops,
used to include a built in dialup modem. With the advent of Ethernet and Wi-Fi
that is typically no longer the case and will need to purchase a dialup modem
and connect it to the phone line. Once that is done create a DUN profile and
log into the ISP.
Dialup has
the advantage of being accessible anywhere there is a landline phone. It can
even be shared by multiple users on a home LAN. For several years in the late
90’s I shared a dialup connection on our home LAN, first using a connection
sharing program and later a router. The problem with dialup is its
incredibly low speed compared to other forms of Internet access. A couple of
decades ago, before web sites became so graphics intensive and software
programs become chatty and need multi megabyte patches, dialup worked well.
Today it is excruciating slow.
The US Bell
System developed T-1 digital carrier during the early 60’s
to reduce interoffice transmission cost. Prior to T-1 analog frequency division
multiplexing (FDM) was used to carry voice traffic
between telephone switching centers. FDM carrier used a 4-wire circuit to carry
24 voice channels, one pair in each direction. T-1 was designed to also carry
24 voice channels, facilitating transition from FDM to TDM. E-1 digital carrier, used in Europe, is
similar transporting 30 voice channels. Each voice channel is digitized
resulting in a 64 kbps data rate. 24 channels require 1.536 Mbps plus an 8 kbps
control channel resulting in data rate of 1.544 Mbps (E1 is 2.048 Mbps). T-1
has a DS-1 channel speed of 1.544 Mbps and is carried over a 4-wire copper
facility. Popular usage has corrupted this distinction. T-1 is now commonly
used to mean any 1.544 Mbps service.
In the early
1980’s T-1 was tariffed and made available to customers. T-1 continues to
be popular in commercial service carrying both voice and data. T-1 pricing has
dropped dramatically over the years as technology improves and the result of
competitive pressure from alternative broadband services.
Voice grade
phone service occupies the frequency band of 300-3000 Hz. Low frequencies are
suppressed to minimize interference from 50/60 Hz power lines. Increasing upper
frequency beyond 3000 Hz does little to improve intelligibility, at the expense
of greater bandwidth. Digital sampling must be performed at least twice the
highest frequency of interest to recover the original analog signal. Engineers
chose a sample rate of 8,000 times a second. It was found sampling to 12-bits,
resulting in 4096 possible values, produced excellent voice quality. This
required 96 kbps per channel resulting in a composite data rate that exceeded
what 1960s technology could deliver. To reduce data rate engineers decided to
use only 8-bits or 256 values per sample, resulting in a 64 kbps data stream.
To minimize quality degradation, conversion is performed logarithmically. When
sound level is low samples are close together. During loud passages samples are
farther apart. This masks quantizing noise generated by the conversion process.
Two slightly different methods are used, µ-law in US and A-law in Europe. The resulting digital
signal is called Pulse Code Modulation (PCM). 24 phone calls in US (T-1) or 30
Europe (E-1) are interleaved using Time Division Multiplexing (TDM) combined with an 8 kbps signaling
channel the composite data stream is 1.544 Mbps (US) or 2.048 Mbps Europe.
PCM coding
scheme developed for T-1 is what makes V.90 and V.92 dialup modems possible and
also the reason dialup is limited to 56 kbps. Logarithmic sampling minimizes
effect of audible noise but only allows 7 of the 8 bits be used for data. 8,000
samples per second times 7-bits per sample results in maximum data rate of
56,000 bits per second. Dialup modems have reached their theoretical limit.
When used for
Internet access voice channelization is neither required nor desired. T-1 data
circuits are unchannelized exposing total channel
capacity to the IP layer. IP, rather than T-1, performs multiplexing. Some
circuits are provisioned to allow flexible control of channelization. This
allows an Integrated Access Device (IAD) to dynamically allocate bandwidth
between voice and data.
The original
implementation of T-1 required regenerators spaced every 6,000 feet.
Regenerators recreate bipolar signals, allowing T-1 to deliver very low error
rates compared to analog carrier. Regenerators can be powered from the T-1
line, called a span, eliminating need for local power. T-1 bipolar signaling is
relatively noisy. This requires care during circuit provisioning to prevent
interference between T-1 and other services, including other T-1s and DSL in
the same cable.
Early T1
required a 4-wire circuit, 1-pair in each direction. Newer T1 deployments using
HDSL2 only need a single pair. Digital signal processing techniques similar to
that used with DSL reduce outside plant cable requirement and increases
distance between regenerators.
4-wire T-1
circuit can be up to 50 miles, with regenerator every mile. Very long T-1
circuits are rare nowadays as fiber is more cost effective.
Channel
Service Unit (CSU) is connected directly to the 4-wire
facility. The CSU regenerates T-1 bipolar signals before handing them off to
Data Service Unit (DSU). The CSU provides keep alive and
Loopback testing enabling Telco to monitor line quality.
T-1 uses
bipolar plus and minus 3-volt pulses, between pulses line voltage returns to
zero. The Digital Service Unit (DSU) converts bipolar signals to a
synchronous interface such as V.35 using both RS232 single ended and RS422 differential signaling to connect to
customer equipment.
In the US CSU
and DSU are built into customer premise equipment (CPE), such as a T-1 router.
In the rest of the world CSU is owned by service provider, CPE includes only
the DSU.
When T-1 was developed the interface between CSU and DSU, called DSX-1,
was designated the demarcation point between Telco and customer. DSX-1 is still
the demarcation point in rest of the world. During US deregulation the FCC
defined the 4-wire facility as the demarcation point. This caused problems for
service providers as now management and quality assurance functions were no
longer under their control but provided by customer premise equipment (CPE).
The solution
was the Smartjack. It
presents a 4-wire (2-pair) interface to customer and implements service
provider Loopback test function. This allows Telco to perform testing and
maintenance functions while complying with FCC regulations.
Smartjacks can be also used to deliver T-1 service to customers
by converting other transmission schemes to traditional 2-pair T-1.
The service
provider will typically install the Smartjack within
a few hundred feet of where drop cable enters the building. Customer needs to
purchase a router and install it. The cable between CPE and Smartjack
is a regular Category rated patch cable.
Modern wired
telephone network is almost entirely digital except
for the 2-wire analog POTS customer loop. With digital technology multiple
voice channels can easily be carried over a single circuit. The digital carrier
hierarchy is based on voice channels. The lowest level, called Digital Service
0 (DS-0), is a single PCM digitized voice circuit of 64 kbps. Next is DS-1 (24
voice circuits over T-1 carrier) operating at 1.544 Mbps, then DS-2 (T-2)
operating at 6.312 Mbps equivalent to 4 T-1 circuits. Then DS-3 (T-3) at 44.736 Mbps equivalent to 28 T-1 circuits.
Higher speed
is optical using Synchronous Optical Network (SONET) and ITU Synchronous Digital
Hierarchy (SDH). Optical Carrier 1 (OC-1) and Synchronous
Transport Signal Level 1 (STS-1) operate at 51.84 Mbps, next is STS-3 (OC-3)
155.52 Mbps, then STS-12 (OC-12) operating at 622.08 Mbps and so forth.
Beginning with STS3 hierarchy increases by a factor of four at each step. 10G
bps STS-192 (OC-192) is an interesting convergence point. It is the first time
Ethernet and SONET/STS operate at the same speed opening the door for Ethernet
being carried directly over SONET.
PON – Passive Optical Network
E-PON – Ethernet PON 1/1G
10G-EPON – 10Gig Ethernet PON 10/10G
or 10/1G
B-PON – Broadband PON (First
generation ATM based) 622 dn/155Mbps up
G-PON – Second generation PON 2.4 G dn/1.2 G up
10G-PON –
10/5G
Tremendous success of
T1/E1 prompted the Telephone industry to look for a way to deliver high-speed
digital service directly to customer. Integrated Service Digital Network
(ISDN) was supposed to be the next big
thing poised to revolutionize the telephone industry. Alas things have not
played out that way. Deployment missteps and high cost have slowed
deployment. ISDN is viable where other forms of high-speed access are not
unavailable but its window of opportunity has long since passed.
Basic rate
ISDN provides two 64 kbps bearer channels (B channels), and a 16 kbps data
control channel (D channel) over a single voice grade copper loop. Primary Rate
ISDN is basically a T-1 connection. ISDN is a circuit switched
technology with very fast call setup time. Being digital the full 64 kbps is
available. By current standards ISDN broadband is extremely slow.
ISDN requires
a Terminal Adapter (TA). TA connects to ISDN line, provides
two POTS analog phone lines, and a serial data connection.
ISDN, like T1/E1, allows use of regenerators to extend distance between
customer and central office.
ISDN is a
circuit switched technology. To access the Internet a phone call is made to the
ISP, just as with dialup. Once connected access speed is 64
kbps due to the end-to-end digital nature of the connection. If the ISP
offers multilink the second channel can be bonded to create a 128 kbps link.
Extra channel can be automatically torn down and set up as needed to free up
capacity for voice call.
Cost
Tip – ISDN is a switched service. Make
sure ISP has access numbers, Points of Presence (POP); close enough so calls
are flat rate. Failure to do so will result in a rude surprise when the phone
bill arrives. Telco’s offer different types of ISDN service for Internet access
unmetered is ideal.
The provider
will bring up and terminate the ISDN line at the premise NID, just like a
typical POTS line. Customer is responsible for inside wiring and terminal
equipment. There is very little new ISDN equipment being produced, so the
customer will likely have to purchase it used. Once voice access is working
need to connect RS232 serial cable to computer. PCs used to include one or two
RS232 serial ports. Serial ports are considered legacy and are often eliminated
from new product. If that is the case there are many USB to serial adapters on
the market. Once connected will need to configure DUN with account
credentials and log into the ISP.
ISDN digital
subscriber line (IDSL), uses ISDN signaling to deliver 144
kbps data only service at greater distance than typical DSL. IDSL does not make
any use of the circuit switched telephone network, just the loop between the
Central Office and customer, much like ADSL.
Digital
Subscriber Line (DSL) technology utilizes telephone copper
wiring between subscriber and phone company central office (CO) or Remote
Terminal (RT) to deliver high-speed data. This allows local exchange carrier
(LEC) to generate additional revenue by leveraging its massive investment in
copper outside plant cabling. Several types of DSL have been developed hence
the xDSL moniker. The most common types are
Asymmetric DSL (ADSL) G992.1, ADSL2 (G.992.3), ADSL2+ (G.9925)
and Symmetric DSL (SDSL). Telco’s like DSL not only as another revenue source
but because it gets long duration data calls off the Public Switched Telephone
Network (PSTN). This minimizes need for expensive
upgrades to circuit switched phone network.
ADSL was initially developed for video on
demand and has been repurposed for Internet access with higher download speed,
toward the subscriber, than upload. It uses frequencies above those used with
Plain Old Telephone Service (POTS) allowing it to coexist with voice
service. This minimizes cost by allowing a single copper pair to be used for
both voice and data. Typical ADSL speed is 768 – 7,000 kbps downstream
(toward customer) and 128 - 800 kbps upstream (toward Internet). ADSL2
increases that to 12 down and 1 Mbps up. ADSL2+ doubles maximum download rate
over short loops.
The Digital Subscriber Line Access Multiplexer (DSLAM) at the Telephone Central Office or
Remote Terminal is connected to the customer’s phone line. The voice portion is
passed through a low pass filter and delivered to POTS phone switch. DSLAM
recovers customer data and uses Asynchronous Transfer Mode (ATM) to link
customer to ISP. Telco’s use ATM because it facilitates support of third party
ISPs. At the customer location a similar filter is used to separate DSL from
POTS. This can be a single whole house POTS/DSL splitter or filter connected
ahead of each non-DSL device.
Early
business class DSL used proprietary Symmetric DSL (SDSL). It has largely been replaced with
ITU standard based DSL
Maximum DSL
speed is a function of line length, wire gauge and line quality. ADSL service
is limited to about 18,000 feet, with closer customers able to obtain higher
speed. A variant of ADSL2 called Reach Extended adds a couple thousand feed at
low speed. Remote DSLAMs, called Remote Terminals (RT),
shorten loop distance by moving the DSLAM closer to the customer. This
increases number of potential customers within range and shorter loop increases
maximum speed.
FCC
regulations require Incumbent Local Exchange Carrier (ILEC) allow third party
data local exchange carriers (CLEC) access to copper access network.
Copper subscriber loop is tariffed as an unbundled network element (UNE). DLECs rent collocation space within
the central office and install their own DSLAMs and backhaul facilities.
Even ILECs need to set up a separate entity to deliver DSL because unlike phone
service data is not a regulated service.
DSL can also
be configured as a wholesale service. ISP enters into an agreement with a DLEC.
The DLEC in turn rents copper circuit from the ILEC, installs DSLAM within the
central office and transports customer traffic to the ISP’s point of
presence. This is why Telco’s like using ATM to deliver DSL It allows
them to offer wholesale DSL service. As such they evolved a complex
interconnect scheme consisting of 1) physical copper loop, 2) Asynchronous
Transfer Mode (ATM) virtual circuits to transport customer packets over the
First-Mile network to the respective ISP 3) typical ISP functions. DSL may
involve three different companies, ILEC supplying copper service, DLEC first
mile transport, and ISP doing the rest.
Wholesale DSL
service has not worked out well; most of the players have left the market.
Colocation is still viable for copper. The FCC has not deemed fiber an
unbundled network element so DLECs are often not able to rent dark fiber, only
copper. MegaPath,
formally Covad, is probably the best known DLEC. In
NH FirstLight Fiber in NY acquired the CLEC G4
Communication and continues to offer DSL and voice service.
VDSL2 is a
high speed variant of ADSL using the same Discrete MultiTone
(DMT) modulation scheme to transmit data in
the 100 Mbps range over short loops. It accomplishes this by using many more
tones resulting in a much higher upper frequency. VDSL2 is the preferred method
to deliver fiber to the curb (FTTC) and is often used to convert fiber for
distribution in multitenant buildings.
ADSL and
Voice telephone share a single copper circuit. At each end filters prevent DSL
from interfering with voice phone service. To reduce cost ADSL service
providers include inline filters as part of a customer self-install kit.
Customer is instructed to installed filter at each non-DSL device. Having
customer self-install filters eliminates expense of a truck roll.
An alternative
to per device filtering is a whole house POTS/DSL splitter. Splitter provides low
pass filter isolating voice from high frequency DSL tones. Splitter has two
outputs; “Data” connected directly to DSL modem and “Voice” connected to inside
phone wiring. Some splitters contain a half-ringer test circuit after the
low pass POTS filter. This allows removal of half-ringer in NID, minimizing DSL
signal loading. Splitters do a better job isolating DSL from voice then
inline filters. Where speed is high or signal is marginal a splitter will
improve margin.
Figure 16
Inline Filter and Whole House POTS/DSL Splitter
DSL lines are
susceptible to noise bursts from many sources such as: lightning, ignition
noise, radio transmissions and power line faults. DSL spec writers were aware
of this and included forward error correction (FEC). FEC adds redundant check bits to
data stream. If noise corrupts data these extra bits are used to recover the
data. As long as only a few bits are damaged receiver is able to correct errors
avoiding need for retransmission.
If noise
burst is long it corrupts too many bits for receiver to undo damage. In that
case bad packet is passed to higher layer protocol. TCP/IP TCP requests
retransmission. Needless to say that takes a "long" time. UDP/IP,
used with VoIP and streaming data does not have a retransmission scheme. There
is not enough time to retransmit data before it is needed by application.
Streaming applications have provisions to fake missing data. How bad missing
data affects quality depends on the application and how extensive the damaged.
When
interleave is turned on bits from several frames are interleaved in time. If
noise burst is long relative to bit time it corrupts many bits. When receiver deinterleaves data corrupt bits are now spread across
multiple frames - increasing chance FEC is able to correct them. This
eliminates need for retransmission or application having to fake missing data.
As speed
increases number of bits affected by a given noise burst increases. Let’s say a
noise burst corrupts a single bit at 768 kbps. At 1500 two bits and at 3000 the
same pulse affects four. In addition as transmission speed increases signal to
noise margin decreases making transmission more susceptible to noise
corruption.
Downside of
Interleave is slightly higher latency because multiple frames are processed as
a single entity. The penalty for Interleave goes down as speed goes up since a
given frame takes less time to transmit at higher speed. Unless you are an avid
gamer interested in absolute lowest possible ping time Interleave is
transparent. Other network effects swamp out the slight increase (10-20 ms) in first hop ping. Telco’s did not implement Interleave
to annoy gamers; they did it to improve overall customer satisfaction.
The ADSL2
specification allows multiple phone lines to be bonded together to obtain
higher speed. This is accomplished through an ATM inverse multiplexing
protocol. In some instances this may be a cost effective strategy to
increase speed.
The most
common type of ADSL shares the same physical circuit as telephone. The cost of
the line is charged to the telephone DSL in effect rides for free. It is
possible to get DSL as a standalone called dry loop. In that case the ISP will
pass along an addition charge to cover the cost of renting the circuit. In some
cases this is not much less than actually having phone service.
Cost Tip
– rather than go dry loop see how much it costs to get some sort of lifeline
POTS service. You may need to ask as this may not be a published rate. Cost may
not be much more than dry loop, and you have the benefit of landline to call
911 if needed and having dial tone make it somewhat easier to troubleshoot DSL
and minimizes the risk a careless craftsperson will reassign the loop to
someone else assuming it is idea.
DSL uses
100-year old copper telephone network to carry high-speed data. This is an
impressive engineering accomplishment. Unfortunately not all phone lines are
suitable for DSL. Assuming the local central office (CO) or remote terminal
(RT) is equipped for DSL it may not be available for a number of reasons. This
section discusses common problems and where applicable workarounds.
In the bad
old days before US telecom divestiture (1880’s to early 1980’s) Phone Company
supplied service, owned customer premise equipment (CPE) and leased it to
customer. Customer was prohibited from connecting anything to the telephone
network. With divestiture Phone Company regulated responsibility was limited to
delivering service to premise. Inside wiring and CPE became the customer’s
responsibility.
This created
a dilemma for the Phone Company, how to determine if a problem was their
responsibility or that of the customer? Enter the Network Interface Device (NID). NID is the demarcation point,
between Phone Company and customer. It incorporates lightning protection and a
method to easily disconnect customer premise equipment (CPE) from the telephone
network. Early NIDs used modular jack connected to old style carbon block
lightning protector. Over time NIDs evolved into an integrated package and gas
tube surge protection replaced carbon block. Gas tube protection is preferred
because module is hermetically sealed, provides more consistent over voltage
protection and has lower shunt capacitance then carbon block. Carbon protectors
have to tendency to increase circuit noise over time. This may cause problems
if DSL signal is weak.
Phone Company
uses automatic test equipment called mechanized loop test (MLT) to periodically test copper phone
lines. They wanted a device; built into the NID, which allowed MLT to determine
where the network ended and where customer responsibility began. There have
been two different approaches to this: MTU and Half-Ringer.
MTU was
developed during the early days of deregulation. It is a pretty clever device;
it consists of a series pass voltage controlled switch on each leg of the Plain
Old Telephone Service (POTS) circuit. During normal phone usage switch conducts
and POTS equipment operate normally. Testing, done at a lower voltage, does not
trigger the series element thus isolating CPE side from the telephone
network. MTU being a series pass device has four leads, two connect to
Telco side the other two to CPE.
Unfortunately
MTU’s are incompatible with DSL. DSL modem does not draw current from phone
line so MTU never turns on. The MTU isolates DSL modem from the telephone
network. If your line has an MTU it must be removed. For reasons too involved
to go into here MTU’s caused other problems and have not been used for years.
If your phone line had an MTU it was most likely removed years ago, but it is
possible some were missed. Automated testing should flag the existence of an
MTU, but not always.
Half-Ringer
is a simple circuit that emulates old style electromechanical Western Electric ringer providing a test
signature for automatic test equipment. It consists of a capacitor, resistor,
and back-to-back Zener diodes. ADSL is designed to operate in the presence of a
half ringer so in most cases it will have no effect on ADSL. It does represent
a small load so if signal is marginal removing it may help. SDSL is not able to
operate in the presence of a Half-Ringer and it must be
removed.
Excerpt from Broadband Forum Technical Report 013.
It has been
standard practice in many areas of the United States to install, at the Network
Interface Device (NID), a network termination device called a half ringer. It
is an example of an AC termination device since it is detected using AC
techniques.
A normal POTS
mechanical ringer is made up of an inductor and capacitor in series bridged
between Tip and Ring. The half ringer is a capacitor in series with a Zener
diode and resistor. This, in the U.S., is a 0.47 micro Farad capacitor
without the addition of the inductive part of the circuit, hence the name
‘half’ ringer.
ADSL service
is limited to about 18,000 feet. Some ILECs are installing Remote Terminals
(RT) to reduce cable distance allowing them to serve more customers at higher
speed. ADSL2 and Reach Extended ADSL2 have slightly extended maximum distance.
Obtaining accurate pre order distance estimate can be a difficult. The
effective wire distance between DSLAM and customer is often substantially
longer than driving distance making map based estimates questionable.
A back of the
envelop method to calculated wire distance is to multiple downstream
attenuation by 250 to obtain distance in feet. The graph below shows
typical downstream speed vs length. The portion at 80-90 dB is extra distance
obtained by virtue of ADSL2 Reach Extended option. By way of example I am a DSL
customer, my attenuation is 46dB and modem syncs at 7Mbps +/-400kbps with 6-10
dB margin.
Figure 17 DSL
Distance vs Speed
When
telephone feeder cable is installed it is not known how many customer circuits
will be needed at each location. The solution is to run a large feeder
cable past many customers. As service is installed the technician selects an
unused cable pair and splices it to the drop cable. The circuit feeding the
drop may continue for hundreds or thousands of feet beyond the customer,
resulting in a bridged tap. Bridged taps are of no consequence for telephone
service but can degrade DSL. The presence of a bridged tap causes DSL signal to
split at the tap going down both paths. When it reaches the end it is reflected
back into the line, creating interference. DSL is designed to tolerate some
amount of bridged tap, but if circuit is marginal it may cause problems or push
customer over distance limit. SDSL providers typically pay Telco to remove
bridged taps. This is expensive and is not ordinarily done for low cost
residential ADSL.
Resistance and
impedance attenuate signals. This effect is more pronounced at high frequencies
and long circuits. Load coils are used on long loops to
cancel these harmful effects resulting in better voice characteristics. Load
coils are typically installed on loops over 18,000 feet. H88 load coils, the
most common type, are spaced every 6,000 feet beginning 3,000 feet from the
central office.
Unfortunately
load coils are incompatible with DSL. They flatten response over the voice
frequency range but severely attenuate high frequencies used by DSL. If Load
coils are present they must be removed.
Digital Loop
Carrier (DLC), Digital Added Main Line (DAML) et
al are techniques to allow multiple telephone
customers to share a single copper circuit. Phone companies use loop carrier
when there are no available circuits and in rural areas where cost of active
electronics is less than running a dedicated circuit to customer. Unfortunately
most forms of DLC are incompatible with DSL.
Telco feeder
cable carries many different services: POTS, ISDN, DSL and T-1. Phone circuits
often closely parallel power lines picking up power line noise. Imperfections
cause unintentional coupling from one circuit to another. This raises the noise
floor. If noise becomes excessive speed is impacted.
Residential
DSL is not typically warranted for speed, it is a best effort service. If noise
is present during phone call customer is more likely to get problem resolved
than if it only affects DSL or dialup.
Much
advertising ink has been spilt stating DSL is not shared. While that is
certainly true all Internet connections are shared at some point, the issue is
where and will it affect service. With DSL the chokepoint is backhaul from the
DSLAM, especially in the case of remote terminals. If backhaul becomes
congested all user of that DSLAM will suffer.
Copper phone
circuit is able to carry not only telephone and Internet but dangerous
voltages. This may occur due to nearby lighting strikes or accidental
connection between power line and phone. One of the functions of the NID is to
protect people and equipment from hazardous voltages. Older installation use
carbon block protector while newer use hermetically sealed gas tube. Both have
the same function, when exposed to excessive voltage they short the phone line
to ground.
Assuming you
already have a landline most residential ADSL is self-install, the ISP sends
out an ADSL router and several inline filters. Filters need to be connected to
each non-DSL device and the modem located in a convenient place. Connect
modem to PC with an Ethernet cable and plug modem into phone jack. Most ISPs
use PPPoE that requires customer enters a username and password. In many cases
the router has a walled–garden mode until it is configured that walks the
customer through the required steps.
If router
includes Wi-Fi that will also need to be configured as well as any devices that
use it. For best security use WPA2 to protect privacy.
If this is
dry loop or there is no phone at the location the ISP will need to work with
the local exchange carrier to install a drop. It is the customer’s
responsibility to perform inside wiring.
VDSL2 is optimized for very high-speed
service over short telephone loops. Think of VDSL as ADSL on steroids. It uses
the same DMT modulation as ADSL but many more tones extending the upper
frequency range to 10s of MHz. The sweet spot for
VDSL2 is 50 Mbps @3,000ft. To deploy VDSL carriers are building fiber to the
curb (FTTC) networks. Video ready access device
(VRAD) cabinets are deployed in the field
near customer and linked to telephone central office via fiber. This allows the
carrier to deliver triple play converged services: data, voice, and TV while
leveraging existing copper infrastructure.
Figure 19 Fiber to the Curb
VSDL2 is fast enough to deliver limited television service while at the
same time providing high-speed Internet. Standard definition TV (SDTV) requires
2-3 Mbps per program while high definition (HDTV) is about 15 Mbps using MPEG2
compression. MPEG4 is more effective reducing rate by about half to 1.5/8 Mbps
respectively.
To shorten
distance between DSLAM and customer the Telco has to deploy active electronics
deep in the field near the customer. Data between the VRAD and Central Office
is carried over fiber.
VRADs are
controversial because they are rather large and targets for graffiti. In many
urban areas there is significant customer resistance. VRADs are typically
located near existing cross connect boxes to gain access to customer copper
circuit. VRADs require both AC and backup power.
ATT&T has
been the most aggressive US Company rolling out VRADs and VDSL2 with mixed
results. They are finding speed is often less than satisfactory and there is a
huge problem because customer speed is so dependent on distance and line
quality.
Because VDSL2
uses such high frequency crosstalk is a problem. Copper customer loop uses
twisted pair but the twist is fairly loose unlike the tight twist of Category 5
or 6 cables. The loose twist means circuit is less able to reject high
frequency noise. Phone cable often consists of hundreds of pairs. Noise from
one circuit is coupled into the others degrading performance. If VDSL2
crosstalk can be eliminated much higher and more consistent speed can be
delivered over the same length circuit.
Vectoring is a crosstalk reduction
strategy that monitors multiple circuits and computes noise effects for each
line and then modifies transmission to reduce the effect. When Vectoring
is applied to all pairs in the cable 100Mbps at 1500 feet and 50Mbs at 3000
feet become practical.
For vectoring
to be successful all VDSL circuits must be under the same management – this
poses a problem where VDSL is used by both the incumbent and completive
carriers. Due to the much lower frequencies used by ADSL and ADSL2+ crosstalk
from those signals does not have much effect on VDSL2.
Bonding is
another way to increase end user speed but is relatively expensive as it
requires two customer loops, and two interfaces at both the DSLAM and customer
modem. A bonded connection looks like a single higher speed link to Internet
traffic.
An
interesting take on bonding is rather than treating a 2-pair circuit as two
separate channels treat it is three channels referenced to a common
ground. Making this work requires substantially signal processing.
At this point this is at the research stage and is not being implemented by
carriers.
Impairments
are the same as for ADSL, but due to the much higher frequencies involved
everything is much more critical.
In order to
make the most of limited customer first mile network video tends to be more
heavily compressed then OTA, Cable or Satellite TV.
Installation
is much the same as ADSL. If service includes TV the provider will supply
set-top-boxes.
Cable TV (CATV) industry started in the 1950’s as
Community Access TV in areas where roof top antennas did not provide adequate
reception. Early pioneers found they could locate a large antenna on a
local mountaintop and distribute broadcast TV over coaxial cable. By the 1990’s
the industry was looking for new revenue streams and ways to fend off inroads
being made by Direct Broadcast Satellite (DBS).
Historically
Cable TV has been a one-way medium. TV signals originated at the CATV Head End
(HE) and were delivered to subscribers over
coaxial cable. To accommodate Internet service the Industry needed to upgrade
unidirectional one way “broadcast” cable distribution with a bidirectional
system. This involved replacing distribution amplifies with bidirectional amps.
Previous upgrades had modified the coaxial network with Hybrid Fiber Coax (HFC). Fiber is deployed deep into the CATV
network. Redundant fiber loops interconnect the Head End to hubs. The hubs in
turn connect to local nodes that convert fiber to coax. Coax is only used for
relatively short distance connecting individual subscribers to HFC network.
Cable Labs, an industry consortium,
developed DOCSIS to deliver two-way Internet service
over the HFC CATV network. DOCSIS 1 delivers per segment bandwidth of up to 42
Mbps toward customer and 10 Mbps upload. DOCSIS 2 increased upload to about 30
Mbps. DOCSIS 3 increased downstream to 150 Mbps and upstream to 100 Mbps by
bonding multiple channels. DOCSIS 3.1 increased speed to 10Gbps down and 1 Gbps up. Note this is the total data rate for a particular
node that may consist of a 100 or so customer.
Cable is a
shared network; to prevent eavesdropping and attachment of unauthorized modems
DOCSIS encrypts traffic in both directions.
Some early
Cable Internet deployments were unidirectional. Cable network was used for
downstream transmission and dialup for upstream. This allowed CATV operators to
quickly offer high-speed Internet service prior to upgrading cable facility to
carry bi-directional data.
CATV is
typically thought of as a residential service. CATV industry is actively
courting commercial customers. High speed and low cost makes Cable based
Internet access an attractive alternative to expensive T-1 service.
The CATV
network, much like the phone network, has been pressed into service to deliver
high speed Internet connectivity. There are a number of issues that interfere
with obtaining maximum possible speed.
Cable is a
shared medium. Each user competes with others on the same segment. While all
Internet access is shared at some point Cable is shared in the first-mile. As
more customers subscribe Cable provider, called Multi System Operator (MSO) must reduce number of subscribers per
segment to deliver acceptable service. MSOs are aggressively driving
fiber deeper in their outside plant to reduce the number of customers serviced
by a node allowing them to offer higher speed.
This is why
Cable industry has been so aggressive going after “bandwidth-hogs,” customers
that either upload or download a lot. It is not uncommon to have
daily/monthly cap on residential cable accounts. If cap is exceeded speed is
throttled or service discontinued.
DOCSIS uses a
time slot mechanism, called Time Division Multiplexing Access (TDMA), to facilitate equitable upload over
the shared cable segment. The Cable industry assumes customers will primarily
use download capacity. Customers are taking advantage of Internet peer-to-peer
capabilities to create and host their own data, use Voice over IP (VoIP) telephone service, and peer-to-peer
file sharing. This creates a strain on limited Cable upload capability.
There are a
number of techniques to increase upload performance. Synchronous Code Division
Multiple Access (S-CDMA) works better in the lower
frequency upstream channels unsuitable for Advanced Time Division Multiple
Access (A-TDMA). Another technique, channel
bonding, combines multiple upstream channels to increase performance. The
latest DOCSIS specification goes a long way to alleviating the upload problem.
Cable systems
operate up to about 900 MHz Much of this range is not authorized for over the
air TV and is used by other wireless services. This places stringent demands on
the cable operator to prevent RF leaking out of the network interfering with
other radio user or leaking in interfering with subscribers. Ingress leakage is
an especially difficult problem for the low frequencies (below Channel 2) 54
MHz used for DOCSIS upload.
Whitespace
broadband uses locally unused TV channels to deliver radio based broadband. The
concern is that having a nearby transmitter, even though it is low power, will
inject enough noise into the CATV network to degrade performance.
Cable Company
endeavors to maintain adequate signal levels to support both DOCSIS Internet
access and TV. Common practice is to install a two way splitter where cable
enters the residence. One drop is connected directly to the DOCSIS modem, the
other to TV. If multiple TVs are used a bidirectional amplifier may be needed
to make up for signal loss through the splitter. DOCSIS modem should always be
connected to the two-way splitter rather than behind an amplifier.
Coax cable,
being an electrical conductor, may carry stray currents into the building. NEC
requires the shield to be bonded to building ground system to minimize
potential shock hazard. Excessive noise or AC hum can degrade both TV and
Internet access.
If Cable has
never been installed the MSO will need to install coaxial drop, ground coaxial
cable shield where it enters the building and install a splitter. DOCSIS modem
goes to one output of the splitter the other is used to connect one or more
TVs. Depending on signal levels and number of TVs the installer may need to
install a distribution amplifier.
If premises
is already wired for cable all the installer will typically need to do is
install a splitter near where the cable enters the building and run a new drop
to the modem location.
Because Cable
is a shared medium the MSO binds a particular modem to the account. If you need
to change the modem will most likely have to contact the cable company to
update their information.
Assuming they
provide a DOCSIS modem as opposes to a modem/router combo will need to purchase
your own residential router if you want to use more than one device.
In the quest for high speed Internet what about electric utilities? One
would think they are well positioned to take advantage of this growing demand.
At a seminar I attended many years ago the speaker commented that electric
companies are ideally positioned to be broadband providers because they have: 1)
Rights of way, 2) Guys with trucks, and 3) know how to send out a bill every
month. In short they appear to be well positioned to roll out high speed
Internet access. Alas except for a few isolated cases with municipal power
utilities that have rolled out fiber optic networks this has not happened.
Broadband
over Power Lines (BPL) in the context of this paper refers
to delivering high speed Internet access over the long distance electrical
transmission grid. It is distinct from the HomePlug Alliance specification using electrical
wiring to create an Ethernet LAN.
The same
technique that shoehorns megabit DSL onto phone lines can be used to send bits
over power lines. Electric utilities have experience with this technology. They
use a much slower version to transport telemetry SCADA data from remote substations. If
successful it represents a low cost way to deliver broadband without the need
to string expensive fiber optic cables.
The reality
is the power transmission network has turned out not to be well suited to high
speed Internet access so interest has waned. Where this technology may have a
future is in narrowband communication in support of the Smart Grid. Smart meters need a way to
communicate with the mothership and some flavor of BPL will likely be used.
The holy
grail of broadband is fiber optic service all the way to the customer, called Fiber-to-the-Premise (FTTP). A fiber
network costs $1000 to $2500 per home passed. To put that into perspective it
is about twice the cost of copper phone line and three times that of
Cable. Service providers are faced with the difficult business decision
of choosing to invest in technology to extend life of existing copper network
or take the plunge and install fiber. Deploying fiber puts the company in a
very strong long term competitive position but demands tremendous up front
capital investment. Triple-play: voice, data and video takes
advantage of fiber’s tremendous bandwidth to deliver multiple services over a
single network.
Fiber is
ideal for Greenfield locations. Installing fiber in a new location is cheaper
than the combined cost of deploying traditional Copper POTS phone lines and HFC
Cable network and results on much lower maintenance cost.
High cost of
deploying FTTP is an impediment to adoption. Companies are working hard to
reduce both labor and component cost. As more systems are installed cost is
falling rapidly. These efforts range from use of fiber optic ribbon cable and preterminated cable assemblies to installing fiber in sewer
mains or abandoned water and gas pipes. Advances in fiber optic cable
manufacture reduce the effect of tight bends on optical loss. Bend insensitive
cable is ideal for multitenant buildings.
FTTP is able
to emulate analog plain old telephone service (POTS) by reserving channel capacity and
digitally encoding voice. From a subscribers perspective service is identical
to legacy POTS. This is not Voice over IP; this is being done at the physical
layer. It is also possible to implement phone service as Voice over IP (VoIP).
TV program
can be delivered by emulating the methods used by Cable providers. A third
“color” lambda is used to transmit programs from
head end to customer. At the ONT the optical signal is converted to RF and
delivered over existing coaxial cable to set-top-boxes like those used for
Cable.
Optical
networks are well suited for IPTV Video on Demand (VoD). VoD
requires tremendous network capacity, especially HDTV. Each HDTV program requires
about 15 Mbps; SDTV 2 Mbps. FTTP has enough capacity to easily deliver
individual HDTV programs to a family of four with enough capacity left over for
Internet access.
With Switched
Ethernet a customer is directly connected to a port on an Ethernet edge switch,
typically located in a remote enclosure relatively close to customer. The
advantage of this approach is costly electro/optical interfaces only need
operate at link rate, typically 100 Mbps or 1 Gig rather than the aggregate PON
rate. Customer premise equipment is cheaper since it only has to convert a
point-to-point optical interface to Ethernet.
Switched
Ethernet simplifies provisioning. Once a customer is connected, increasing or
decreasing access speed can be performed by reconfiguring the edge switch.
Whereas with PON customer provisioning may require sending a craftsperson out
to physically modify split ratios. Privacy is very good, as only traffic
destined for the customer is visible at customer’s drop. Down side is
requirement for remote equipment huts to house Ethernet switches and need for
backup power during emergencies.
Passive
Optical Network (PON) uses a single optical fiber to
deliver services to 32 or more customers. Traffic toward customer is
broadcast to all endpoints. Upstream traffic utilizes a time
division-multiplexing (TDM) scheme to insure access
fairness. Traffic in each direction is carried by a different color,
called Lambdas. Wavelength Division Multiplexing (WDM) is the optical equivalent of
Frequency Division Multiplexing (FDM) used at lower frequencies. WDM allows
a single fiber to carry multiple channels in each direction without interfering
with one another. Convergence points contain passive optical splitters to
connect multiple customers to a single trunk fiber. PONs advantage is it does
not require active electronics in the field and a single fiber is able to serve
many customers.
In addition
to Internet access PON is able to deliver TV by emulating the legacy CATV
hybrid fiber coax (HFC) network. This is accomplished by using a third Lambda
to carry CATV information. At customer location an optical/electro converter
translates PON optical signal to traditional CATV coax electrical interface, much the
same as a CATV node. This preserves backward compatibility with legacy CATV
network.
Figure 24 PON
Outside Plant
Both ITU and
IEEE Ethernet in the first mile have developed PON specifications. Download
speed ranges from a low of 622 Mbps for the first generation ITU standard to
10Gps in both ITU and IEEE versions.
ATM PON uses ATM to provide data and voice
virtual circuits over single fiber. APON specification delivers aggregate
bandwidth 622 Mbps down and 155 Mbps up. Maximum fiber distance is 20 km (65 kft).Broadband PON (B-PON) uses a third optical wavelength to
emulate legacy CATV network for triple play service. ATM is used for transport
reducing effective IP payload by about 10% due to ATM overhead. One also needs
to factor in AAL2 POTS voice channels at 64 kbps each. Assuming a 1:32
split ratio B-PON delivers about 18 Mbps down and 4.5 up to each customer.
1550 nm is
used to emulate CATV Hybrid Fiber Coax (HFC) network. In the US TV channels
are 6 MHz wide. Each channel can be used to for a single analog SDTV channel or
up to 42 Mbps of data. This enabled a single channel to carry multiple SDTV or HDTV programs.
1490 nm is
used to transmit data toward the customer. Each ONT “sees” all packets on the
cable. However only those destined to the customer are forwarded to customer’s
Ethernet connection.
1310 nm is
used to transmit data from customer to ONL. Upstream traffic is based on
a time division-multiplexing scheme to insure fairness. Unused slots are
reclaimed and are available to other customers.
The system
being deployed by Verizon FIOS includes 4 emulated POTS
channels. This is not Voice over IP. POTS channels are carried over ATM, making
them invisible to Internet traffic. Voice quality is identical to regular POTS,
typically better due to short length of copper circuit.
Figure 25 B-PON Triple Play
Verizon
residential PON installation consists of an Optical Network Terminal (ONT)
typically mounted on exterior wall and a battery backed power supply inside the
home.
A single
fiber connects ONT to the PON network. Verizon is making heavy use of preterminated fiber to reduce installation cost. Fiber and
UPS wiring connect to left hand Telco side of the ONT. The right hand customer
side has four analog POTS interfaces, an F connector for TV and a RJ45 Ethernet
connector for data.
During power
failure Internet and TV portions are shut down after a few minutes to conserve
battery life. The uninterruptible power supply (UPS) keeps voice service active for about
12 hours when idle and about 4 –5 “talk” hours.
GPON ITU-T G984.1 and G.984.2 increases
speed to 2.5 Gbps down and 1.25 Gbps
up. GPON does away with ATM eliminating so-called ATM cell tax. Higher speed of
GPON makes it better suited to IP based Video on demand (VoIP) then first
generation BPON and has replaced BPON for new installs. Three lambdas are used
as with B-PON, data down, data up, and CATV emulation.
Figure 28
G-PON
Third generation ITU standard delivering 10G down, 2.5 up.
IEEE Ethernet
in the First Mile working group developed an Ethernet version of PON that does
away with ATM and delivers Gigabit (1.25 Gbps) speed.
E-PON is faster than B-PON (622/155 Mbps) but not as fast as new ITU GPON
(2.4/1.2 Gbps).
Second
generation Ethernet PON increases speed to 10/1Gbps with an option for
symmetrical 10/10 Gbps. The down side of
symmetric 10G-EPON is the need for expensive optical transmitters in customer
ONT.
FTTP cable TV
emulation is unidirectional – toward customer. This creates a problem for smart
set-top-boxes that need to communicate with the head-end. Initially
set-top-box required both coax and Ethernet connection. While that is
conceptually easy it is labor intensive to install new cable as most home do
not have Ethernet drop near TV.
Multimedia
over Coax Alliance (MoCA) technology utilizes RG6
coaxial TV wiring for data. This eliminates need to run Category rated twisted
pair cable to each set-top-box. MoCA can also
be used to transport IP based video on demand (VoD). MoCA uses frequencies above those needed by Cable TV to
create a LAN. In an analogous fashion as to what DSL does with voice telephony.
Once MoCA is installed the same coax used to deliver
conventional TV broadcast programs also provides Internet access.
FTTP
represents a complete rethinking of how wired communication service is
delivered. Building a FTTP network is a major construction project involving
installation of fiber cabling, termination facilities and customer premise
equipment.
There have
been numerous horror stories about damage to other utilities and homeowner
property during installation of FTTP. There have also been problems where
CPE was installed in violation of National Electrical Code (NEC) requirements.
Legacy analog
POTS phone network is powered by telephone switching office. During power
outages batteries and diesel generators maintain system power indefinitely. It
is not feasible to deliver power over an optical network. Customer’s terminal
equipment is battery backed so during power outage it continues to operate.
Backup time is a function of battery size. Larger the battery the longer
service stays operational during a power failure. Batteries are relatively
short lived components and need to be replaced every few years at customer’s
expense. Even at modest power consumption rate it takes a large battery to
provide multiday power.
Fiber outside
plant (OSP) is much more reliable than copper
dramatically reducing maintenance costs. Phone Companies have made no secret
long-term goal is to discontinue use of copper outside plant.
In the US FCC
regulations require Incumbent Local Exchange Carriers (ILEC) to share certain copper unbundled
network elements (UNE) with third party service providers.
That regulation does not apply to fiber.
Once a
locality is wired with FTTP it makes little economic sense for additional
competitors to enter the market. First-mile is the most expensive and least
profitable portion of the global telecommunication network. This natural
monopoly, of the Internet on-ramp, creates vexing government policy questions.
How does one balance the need for universal access with the massive capital
outlays needed to deploy fiber?
Some municipalities frustrated by the slow roll
out of high-speed service are installing their own fiber and renting it to
third party service providers or delivering data, video and phone service
(triple play) themselves. This is a hotly debated topic. Should
municipalities build their own fiber network or is this is best left to private
enterprise?
Assuming this
is a new install provider will have to install a new fiber optic drop either
aerial or underground. If it is underground direct burial cable is plowed into
the lawn. The main part of the ONT is typically mounted on the outside of the
building. The ONT needs to be grounded to the building ground system. Power
Supply and battery are located inside near an unswitched
outlet. If POTS phones are to remain active they are disconnected from
the old copper NID and reconnected to the ONT. An Ethernet cable delivers
Internet access and a router, typically supplied by the ISP, is used to share
the connection. If TV service is purchased coaxial cable drops are run to each
location for the set top box and in most cases MoCA
is used to connect the set top box to the service provider for billing and
video on demand.
Often time
the old copper circuit will be decommissioned.
In areas
not served by wired high-speed Internet Wireless ISPs (WISP) are rushing
to fill the void. WISPs use radios that operate in both licensed and
spectrum. Point-to-Point service may also be implemented using free range
optical links that do not have to be licensed but must meet safety standards as
pertains to eye damage due to the use of high power lasers.
The first
question that comes to mind is what is the difference between Cellular and
WISP? Cellular began life as a voice centric mobile service and added
data as an enhancement. Today the bulk of mobile cellular traffic is data due
to the popularity of smart phones. Cellular service is optimized for use
while is in motion; WISPs are optimized for fixed location.
WISPs use
Point-to-Point and Point-to-Multipoint distribution. In some cases customer’s
equipment functions as a router creating a mesh network expanding service footprint.
In a PtP network a dedicated link is created between
two locations. In a PtMP network a central hub
services multiple customers.
Wireless ISPs
use a central radio to cover a large territory eliminating need to run cable
all the way to the customer’s location. Radio technology is ideal for
rural areas where low population density makes installing copper or fiber
uneconomic. As picture shows signal may take a direct path or if obstructions
exist ISP may deploy repeaters. Repeater acts as a router forwarding packets
and extending coverage area. Directional antennas can be used to create
multiple sectors increasing total bandwidth.
World Interoperability for Microwave Access (WiMAX) is a trade association promoting
this evolving standard and hopes make it as successful in the metropolitan area
network (MAN) space as Wi-Fi has become for local area networks (LAN). Distance
is about 10 miles in Non Line of Sight (NLOS) and 30 miles over line of sight
(LOS). Maximum data rate is about 30 Mbps. As with other wireless technologies
speed and distance are inversely related, the greater the distance the lower
the speed.
WiMAX is based on IEEE 802.16 specification for wireless
metropolitan area networks (WMAN). 802.16 specify operation between 2 - 66MHz.
It is up to the WISP to choose the most appropriate frequency band and obtain
any required licenses. There was early interest in using WiMAX as a cellular
data standard but LTE has won that battle. WiMAX is being primarily deployed
for fixed wireless.
The WISP
normally supplies the radio equipment and installs it at the customer’s
location. Customer is then able to use a residential router to share the
connection.
The tremendous popularity of IEEE 802.11 Wi-Fi Wireless LANs created the phenomena of Wi-Fi hot
spots. All sorts of entities from libraries to hotels to airports have
installed public Wi-Fi Access creating Wi-Fi hot spots. Customer connecting
to the hotspot typically has to go through some type of portal experience. The
portal requires the user agree to certain terms and conditions. Once connected
user is able to access the Internet. In some cases the service is free in
others pay to play.
Wi-Fi was
designed as a short-range wireless LAN. Attempts to provide citywide coverage
using Wi-Fi Access Points has not been successful. The limited range of Wi-Fi
makes it unsuitable as a metropolitan area network (MAN).
White Space refers to unused TV channels.
FCC is investigating allowing unoccupied TV channels to be used for low power
Internet access. This effort is controversial. Nearby white space transmitter
may cause unacceptable levels of interference with consumer AV gear. This will
affect both Cable TV subscribers and over the air viewers. In addition it will
be very difficult for a white space radio to determine if a particular channel
is in use or vacant.
Point-to-Point
links are often optical. Optical interfaces are
inexpensive compared to RF and very fast. The downside is birds, fog and snow
obstruct transmission path.
Satellites
act as a very tall antenna vastly expanding coverage area. Geosynchronous
satellites occupy an extremely high orbit so they appear to be stationary. Low
and Medium orbit satellites are much lower and require a large number to cover
the globe. The success delivering TV programs using geosynchronous satellites
prompted interest in using satellites to deliver Internet.
Science Fiction
author Arthur C Clark is generally credited with proposing the notion of geosynchronous satellites in his 1945
paper Extra-Terrestrial Relays. On Earth this distance
is 22,236 miles above mean sea level, now called the Clark orbit. Clark’s idea
has been a boon to Radio and TV broadcasting.
Orbital time
is a function of distance. The further a satellite is from earth the longer the
orbit duration. Clark realized that at a certain distance orbital time would
equal 24 hours. If the satellite is in equatorial orbit a 24-hour orbit means
the satellite appears to stay positioned over the same spot permanently.
The great
height of geosynchronous satellite creates continent sized signal footprint for
each satellite. Since satellite appears fixed in space expensive antenna
tracking mechanisms are not required.
When small
aperture Direct Broadcast Satellite (DBS) TV became popular it was natural to
adopt this technology to high-speed Internet access. One-way
implementation uses satellite link for high-speed download and dialup modem for
upload. Two-way service uses satellite link in both directions.
Speed is a matter of
transmit power and antenna size. As satellites have become more sophisticated
transmit power has been increased resulting in greater down load speed.
Unfortunately
the great height of geosynchronous orbit adds significant latency making this
type of service more appropriate for large file transfer than interactive
browsing. One-way latency Ground — Sat -- Ground is about ¼ second (250 ms). If the satellite is used in both directions latency is
about 500 Ms. When dialup is used for upload total latency is reduced to about
350 ms. that is still too long for effective browsing
or telephone service.
Satellite
capacity is shared by many uses. Service providers implant Fair Access Policy (FAP) to allocate capacity equally to all
customers.
To reduce
latency satellite must be nearer to Earth. There have been several attempts to
use Low Earth Orbit (LEO) satellites to provide Internet
communication service but they have not been commercially successful. Covering
the globe requires a constellation of hundreds of expensive satellites. The two
most famous attempts were Iridium and Teledesic.
Recently Elon Musk of SpaceX fame has become a
proponent of LEO Internet. Perhaps he will succeed where others have
failed.
MEO satellites occupy the distance between
LEO and geosynchronous orbit. O3b Networks is building an equatorial
constellation orbiting about 5,000 miles above sea level. When complete
the constellation will provide coverage 45 degrees north and south of the
equator.
The ISP
normally supplies the radio equipment and installs it at the customer’s
location. Customer is then able to use a residential router to share the
connection. Antenna needs an unobscured view of the satellite. Since
Geosynchronous satellites are in equatorial orbit antenna elevation gets
depressed the further north you are.
Unlike other wireless networks the cellular network is designed to be
used while in motion. Cellular phone service is hugely popular. What started
out as an expensive lunchbox sized 2-way radio a
couple of decades ago is now smaller than a pack of cigarettes and is
considered an essential part of everyday life by much of the population.
Some customers, especially younger ones, eschew landline phone altogether in
favor of a cell phone. 90% of American adults have a cell phone and more than
60% of these are smart phones with Internet access. Worldwide there are almost
7 billion cellular subscriptions about half of which have Internet access.
Some folks have gone so far as to rely solely on their smart phone for
Internet access or tether their phone to create a home network rather than pay
for wired Internet.
The
attraction of wireless connectivity is not limited to voice. Almost from the
beginning the cellular network was pressed into data service, typically with
less than stellar results. Today Smart Phone usage is driving rapid
conversion of the network from one optimized for voice to one optimized for
data. The bulk of cellular traffic is now generated by Internet access and
streaming content rather than voice. The advent of high speed LTE is
causing mobile carriers to rethink their business model. Verizon in particular
is pitching LTE as an alternative to DSL in the areas they sold off their
wireline business.
The chart below from the ITU shows pretty
dramatic increase in worldwide cellular Internet usage.
Figure 36
Global Mobile Internet Use
It is common
to talk about the cellular network generationally 1st – 5th
even though there is no hard and fast definition. 1st generation was
the original analog circuit switched network in the 1980’s. 2nd
generation was digital but still used circuit switching circa 1990’s. Early
2000’s saw the migration to 3rd generation digital spread spectrum
optimized for Internet access at 200kbps data rate – the FCC definition of broadband
at the time. Currently service providers are migrating to 4th
generation delivering 100 Mbps speed. Quite an accomplishment for a device you
can hold in your hand while traveling at speed or in the skyscraper canyons of
a modem city. Things move fast in the cellular world, no sooner has 4th
generated been deployed then the marketing machine has been cranked up talking
about 5th generation. It is
still very early in the development cycle deployment is not expected until at
least the 2020 timeframe. Hallmarks of 5G are: 1 Gbps,
reduced latency, increased use if very high frequencies and micro cell sites.
United States
is unique compared to the rest of the world where national cellular standards
exist. The FCC chose not to mandate a particular standard. As a result we have
a confusing patchwork of competing standards but that also allows companies to
rapidly bring innovative services to market. Early cellular protocol was
analog: Advanced Mobile Phone System (AMPS). The modern cellular network is
digital. In the US some carriers use Global System for Mobile Communication (GSM) as does most of the rest of the world
while others have adopted Code Division Multiple Access (CDMA2000). With the increased
emphasis on mobile Internet that is changing and LTE has become a worldwide
standard.
The
tremendous popularity of mobile Internet is driving adoption of more spectrally
efficient transmission standards to increase speed and the need for more RF
bandwidth to increase channel capacity. In the aftermath of the US transition
from analog to digital TV in 2009 channels 52-69 were auctioned off. Much
of this spectrum will be used to expand the cellular data network. The
FCC is auctioning off additional TV channels and has recently made additional
microwave bands available for cellular.
Data rate is
a complex interaction affected by: channel size, power, interference and
modulation. Due to the nature of radio communication throughout is often
significantly slower than peak data rate. None the less modem cellular network
provides meaningful high speed access pretty reliability.
Figure 37Evolving
Cellular Data Standards
CDPD is the granddaddy of wireless data
service. It used the analog advance mobile phone systems (AMPS) to deliver an
anemic 9.6 or 14.4 kbps. Due to the heavy compression used on the cellular
network dialup speed is significantly lower than landline PSTN US carriers
stopped supporting CDPD in 2005.
GPRS data rate is in the 100kbps range.
Modern
Cellular network is digital capable of much faster data transport then early analog
system. EvDO
rev A delivers download speed in the 3.1 Mbps range.
Rev B increases speed to 4.9 Mbps per channel
EDGE is an enhancement to GPRS delivering
300 kbps.
HSDPA is an all-digital packet technology.
Data rate is around 14 Mbps.
HSPA+ is an evolution of HSPA that
dramatically increases speed while maintaining the same radio interface. HSPA+
delivers up to 168Mbps toward the user and 22 Mbps up. In the US AT&T and
T-Mobile have adopted HSPA+
LTE is part of the Third Generation
partnership project for GSM networks (3GPP). Focus is migrating cellular data to
packet based, rather than circuit switched network and delivering substantially
higher speed then today’s cellular network. LTE delivers Multi-megabit speed
with very low latency. Data rate is in the 100-300Mbps down 50-75Mbps up.
Long Term Evolution Advanced is the next
generation version of LTE that meets all the requirements set
forth in 3GPP for 4th generation radio. 1Gps aggregate data rate down,
500 Mbps up with improved spectral efficiency.
Mobile
generations come every decade or so. 5th generation is still very
much in the early research stage focused on how the network is used and people
interact along with significantly faster speed. Micro sites will deliver
improved speed in dense urban areas.
LTEworld
Figure 38 US LTE Deployment
Phones are typically bound to a
particular carrier’s network and cannot be easily moved to a competitor.
Most Cellular data plans have
relatively low monthly data usage limit with significant overage charges. The
high speed now available to cellular subscribers makes it easy to blow through
monthly cap streaming video.
Connectivity costs vary dramatically
between home area and when you are out of range of you
normal carrier and voice or data is transported by another carrier.
An interesting wrinkle on cellular
are companies like Republic Wireless a mobile virtual network
operator (MVNO). The smart phone preferentially uses Wi-Fi.
Whenever the phone is connected to a Wi-Fi network voice, text and data are
transported over Wi-Fi. The cellular network is only used when Wi-Fi is not
available.
Tethering is
an interesting way to use your cell phone to connect one or more additional
devices. Depending on the phone the LAN connection may be USB, Bluetooth or
Wi-Fi. If the phone includes router capability you can connect multiple
devices, if not will need an external router.
Being mobile
there is no installation. Increasingly providers are moving away from
subsidizing phones as part of a multiyear contract. In general FCC number
portability can be used to transfer your existing wired or wireless phone
number to the new carrier.
Where
cellular service is sold as residential broadband the radio and antenna is
mounted exterior to the house as with traditional WISP and a router is used to
share the connection.
The Internet represents a fundamentally new method of
human communication as important as the written word and the printing press.
Never before has it been so easy and inexpensive to
communicate with anyone on the planet.
Never before have ordinary
citizens owned the printing presses.
Never before have citizens been able to band together
so effectively to express their support or displeasure at government or
business.
Never before has it been so easy to create original
audio, visual, and written works.
Never before have creators and patrons
been so closely linked.
The coming decades will profoundly change human
civilization.
