ATM http://webopedia.internet.com/TERM/A/ATM.html
Cable Modem http://webopedia.internet.com/TERM/c/cable_modem.html
DNS http://freesoft.org/CIE/Course/Section2/index.htm
DLS/ADLS http://www.everythingdsl.com/
TCP/IP http://www.psc.edu/networking/perf_tune.html
ETHERNET http://www.ots.utexas.edu/ethernet/
APPLETALK http://members.yourlink.net/aaron/atalkconf.html
DNS
The DNS directory service consists of DNS data, DNS servers, and Internet protocols for fetching data from the
servers. The billions of resource records in the DNS directory are split into millions of files called zones. Zones
are kept on authoritative servers distributed all over the Internet, which answer queries according to the DNS
network protocols. In contrast, caching servers simply query the authoritative servers and cache any replies.
Most servers are authoritative for some zones and perform a caching function for all other DNS information.
Most DNS servers are authoritative for just a few zones, but larger servers are authoritative for tens of thousands
of zones.
When you look for the latest networking news, remembering to point your browser at www.lantimes.com is a lot
easier than remembering the site's numeric IP address. But if you examined the packets that pass between your
browser and the LAN Times site, you'd see that it's 204.151.55.175 in the packet header that guides your requests
through the Internet labyrinth. Domain Naming Service (DNS), an Internet protocol and distributed database,
provides the mapping between these disparate addresses. Having a basic understanding of how DNS works is key
to successfully administering an Internet-connected network.
First we need to take a quick look at the structure of Internet host names. The last portion of a host name, such
as .com, is the top-level domain to which the host belongs. In addition to the .com domain, there are six other top-
level domains assigned by InterNIC, the coordinating body for Internet name services.
If your site is outside the United States, the organization that assigns domain names has its own standards. In most
cases, top-level domains for non-U.S. hosts look something like .co.uk or .ac.uk, which indicate a company or academic
institution in the United Kingdom.
At the top of the DNS database tree are root name servers, which contain pointers to master name servers for each
of the top-level domains. For example, to find out the numeric address of www.lantimes.com, a DNS server would
ask the root name server for the address of the master name server for the .com domain. In turn, the master name
servers for each of the top-level domains contain a record and name-server address of each domain name. So in
trying to find out the numeric address of www.lantimes.com, the DNS server asks the .com server for the name of the
server that handles the lantimes.com domain.
The individual name servers for each domain name, such as lantimes.com, contain detailed address information for
the hosts in that domain. So in our example, the DNS server then asks the lantimes.com server for the name of the
server that handles the lantimes.com domain. Finally, this most specific name server supplies the DNS server with
the IP address of the machine called www.lantimes.com.
Providing DNS to your users is an important part of linking them to the Internet. There are two basic ways to configure
DNS. One option is to use your ISP's (Internet service provider's) DNS server. Many ISPs will let you do this. Another
option is to set up a DNS server on your own network.
If your network-support staff is small and your needs are simple, having your ISP provide DNS services is the best option.
There are three steps to this process. First, have your ISP inform the InterNIC that it is providing both primary and
secondary DNS services for your organization. Second, your ISP will give you the numeric IP addresses of the primary
and secondary DNS servers, which you'll need to configure your users' TCP/IP stacks. You can do this by entering the
information manually either at the desktop or at your Dynamic Host Configuration Protocol (DHCP) server. Finally, you
need to tell your ISP about the DNS records that you wish to publish to allow outside users to interact with your network.
In addition, if you want to receive E-mail from the Internet, you will need to have a Mail Exchange (MX) record for your
domain in your ISP's DNS database. MX refers to a machine that accepts E-mail con-nections for your domain.
An MX record has three parts: your domain name, the name of the machine that will accept mail for the domain, and
a preference value. The preference value lets you build some fault tolerance into your mail setup. Your domain can
have multiple MX records, such as the following:
Acme.com mail.acme.com 0 ; Acme.com mail2.acme.com 10 ; and Acme.com mail.isp.net 100.
In this case, mail delivery will be attempted to mail.acme.com first because it has the lowest preference value. If
delivery fails, mail2.acme.com will be tried next. If mail2 is also down, mail will be sent to a relay host called
mail.isp.net, which in this case is at Acme's ISP. If you plan to use your ISP's DNS server, you'll also need to have
the ISP set up some A records, which associate IP addresses with computer names. Each of the computers mentioned
in your MX records needs an A record to associate them with an IP address.
You may also want to set up A records for each of your workstations if your users need to use ftp (File Transfer Protocol)
to download software from the Internet. This is because some ftp sites perform a lookup to get the DNS name of the
machine from whi ch they receive download requests. If the machine has no name, the sites deny the request.
You'll also need A records for any public servers you maintain. For example, if you have a World Wide Web server,
you'll need to have the ISP set up an A record linking the name www.acme.com to the IP address of your Web server.
If your ISP does not provide name services or if you need to have a DNS server at your site to support internal networking
applications, the first thing you need to know is that you must have at least two name servers--a primary and a secondary.
This is because the InterNIC will not grant you a domain name unless there are at least two DNS servers on the
Internet with information about that domain. Another reason for a second server is that you really need the fault
tolerance a second name server can provide. If your one and only DNS server goes down, users will be cut off from
the Internet.
Some sites take a middle-of-the-road approach and use an onsite DNS server as well as their ISP's. Because maintenance
of the domain names is done at the primary name server, choosing which one is primary and which is secondary is quite
important. If you choose to administer the primary name server yourself, keep in mind that you'll have to maintain the
DNS records. If you choose to have a secondary name server onsite, your ISP will do all of the work, and your secondary
name server will simply download the data about your domain from the primary server periodically.
Why should you bother with having a DNS server on your LAN in the first place? There are a few reasons.
First, if you are running IP network-based applications inside your network that require users to connect to internal
machines by name, it is not a great idea to advertise the names and addresses of these machines. DNS can give hackers
a map of your network, so setting up an internal DNS server that does not publish information to the world is a good idea.
Second, a DNS server inside your network le ts you be the master of your own domain. You can make changes, additions,
and deletions on your own schedule. Finally, name resolution will be faster for your users because your DNS server is
probably not as heavily loaded as your ISP's server. Now that you've got the basics of how DNS works, you stand a much
greater chance of successfully administering your Internet-connected network.
TCP
The Transmission Control Protocol (TCP)
In the Internet, Inter-Process Communications is implemented using the TCP "transport-layer" protocol. TCP
provides an "end-to-end" (or point-to-point) IPC service which is:
reliable
all data is delivered correctly, without errors, even though the underlying delivery service may be unreliable
connection-oriented
the protocol provides procedures for establishing and concluding interprocess connections.
byte stream
ie, no visible packetisation so far as the application processes are concerned
full duplex
data can flow in either direction over an established connection, without restriction.
TCP is widely regarded as the best transport protocol ever developed, and has no serious competitors.
TCP OperationIn order to provide reliable, connection oriented service, TCP breaks the incoming application byte streaminto segments. The maximum size of a segment is called the MSS. A segment consists of a header, and some data.The last data byte in each segment is identified with a 32-bit byte count field in the segment header.When a segment is received correct and intact, a special acknowledgement segment is returned to thesending TCP containing the byte count of the last byte correctly received.The network service can fail to deliver a segment. If the sending TCP waits for too long for an acknowledgment,it times out and resends the segment, on the assumption that the datagram has been lost.The network can potentially deliver duplicated segments, and can deliver segments out of order.TCP buffers or discards out of order or duplicated segments appropriately, using the byte count for identification.Format of a TCP SegmentA segment consists of a 20-byte header and (optionally) some data, thus: Port numbers define the process fromwhich this segment was sent, and the destination processSequence Numbers identify last byte of data sent and received.TCP Port NumbersTCP provides an interprocess delivery system, so it needs to identify processes in the two "end systems" which itconnects. To do this, it defines an abstract address called a port number. Two processes can communicate byagreeing on the port numbers they will use for communications. Port numbers are the addresses of the TCPprotocol---each segment contains port numbers for each of the sending and receiving processes.In order to set up a TCP connection, a process notifies the TCP software that it is waiting for connections "at" acertain port number. By definition, such a process is called a server. A client process which needs to connect tothe server asks its local TCP software to allocate an unused port number and establish the connection. Once theconnection is established, the two processes can communicate.In order to manage TCP connections, a group of port numbers (0 to 1023) have been defined to be used byprocesses providing well known services. Most Unix systems provide server processes corresponding to all thewell-known services.TCP Servers and ClientsNote that the port number is used to name processes. Because the client establishes communication, it doesnot need a well-known port number, and so an unused one (> 1023) is randomly allocated by the TCP software,eg:Optional Topic: TCP ConnectionsThe connection phase in TCP uses a 3-way handshake of control segments:The 3-way handshake is necessary because TCP is layered on the unreliable datagram service provided by IP,so that these control segments can be lost, duplicated or delivered out of order.This could lead to trouble if original or retransmitted segments arrive while the connection is being established -the handshake used overcomes this problem.A TCP connection is closed using another (modified) 3-way handshake sequence involving the use of FIN controlsegments. An interesting consequence of the full-duplex nature of TCP, and the concept of graceful close is that aTCP connection can be half-open if one side closes the connection and the other does not.
What is DSL Center?
DSL Center is the source of information on DSL or "digital subscriber lines," the latest technology which can
bring the Internet into your home or office over existing wiring at speeds hitherto reserved for people who
could afford T1 connectivity.What is DSL?
This technology uses existing the copper pair wiring that exists in almost every home and office. Special
hardware attached to both the user and switch ends of line allows data transmission over the wires at far
greater speed than the standard phone wiring.What does DSL mean for me?
At home or at the office, DSL gives you great data transmission speed for a reasonable price. In addition,
it is a constant connection so you have access to the Internet and e-mail 24/7. There is no need to dial in
to your ISP each time you want to get on-line.If DSL is so great, why isn’t everyone doing it?
Because connection speeds can vary, many people prefer the fixed speed of an ISDN or a T1. In addition,
DSL is not available in many areas because of distance from a Central Office or because the local telephone
companies have not yet introduce this product. But with DSL technology developing this rapidly, we expect
that many telephone companies will be introducing it and that efforts will be made to improve the transmission
over greater distances.
DSL Glossary – expanding the acronyms into plain English to help you understand the reality behind the lingo.
DSL Up-to-the-Minute Information – submit your own updates and tips and read the latest about this rapidly
expanding technology.DSL (Digital Subscriber Line) is a technology for bringing high-bandwidth information to
homes and small businesses over ordinary copper telephone lines. xDSL refers to different
variations of DSL, such as ADSL, HDSL, and RADSL. Assuming your home or small business
is close enough to a telephone company central office that offers DSL service, you may be able
to receive data at rates up to 6.1 megabits (millions of bits) per second (of a theoretical 8.448
megabits per second), enabling continuous transmission of motion video, audio, and even
3-D effects. More typically, individual connections will provide from 1.544 Mbps to 512 Kbps
downstream and about 128 Kbps upstream. A DSL line can carry both data and voice signals
and the data part of the line is continuously connected. DSL installations began in 1998 and
will continue at a greatly increased pace through the next decade in a number of communities
in the U.S. and elsewhere. Compaq, Intel, and Microsoft working with telephone companies
have developed a standard and easier-to-install form of ADSL called G.Lite that is accelerating
deployment. DSL is expected to replace ISDN in many areas and to compete with the cable
modem in bringing multimedia and 3-D to homes and small businesses. Dataquest, a market
research firm, forecasts 5.8 million lines installed by the end of 1999.
How It Works
Traditional phone service (sometimes called "Plain Old Telephone Service" or POTS) connects
your home or small business to a telephone company office over copper wires that are wound
around each other and called twisted pair. Traditional phone service was created to let you
exchange voice information with other phone users and the type of signal used for this kind
of transmission is called an analog signal. An input device such as a phone set takes an
acoustic signal (which is a natural analog signal) and converts it into an electrical equivalent
in terms of volume (signal amplitude) and pitch (frequency of wave change). Since the telephone
company's signalling is already set up for this analog wave transmission, it's easier for it to use
that as the way to get information back and forth between your telephone and the telephone
company. That's why your computer has to have a modem - so that it can demodulate the
analog signal and turn its values into the string of 0 and 1 values that is called digital
information.Because analog transmission only uses a small portion of the available amount of information
that could be transmitted over copper wires, the maximum amount of data that you can receive
using ordinary modems is about 56 Kbps (thousands of bits per second). (With ISDN, which one
might think of as a limited precursor to DSL, you can receive up to 128 Kbps.) The ability of your
computer to receive information is constrained by the fact that the telephone company filters
information that arrives as digital data, puts it into analog form for your telephone line, and
requires your modem to change it back into digital. In other words, the analog transmission
between your home or business and the phone company is a bandwidth bottleneck.
Digital Subscriber Line is a technology that assumes digital data does not require change into
analog form and back. Digital data is transmitted to your computer directly as digital data and
this allows the phone company to use a much wider bandwidth for transmitting it to you.
Meanwhile, if you choose, the signal can be separated so that some of the bandwidth is used
to transmit an analog signal so that you can use your telephone and computer on the same
line and at the same time.
Splitter-based vs. Splitterless DSL
Most DSL technologies require that a signal splitter be installed at a home or business, requiring
the expense of a phone company visit and installation. However, it is possible to manage the
splitting remotely from the central office. This is known as splitterless DSL, "DSL Lite," G.Lite,
or Universal ADSL and has recently been made a standard.Modulation Technologies
Several modulation technologies are used by various kinds of DSL, although these are being
standardized by the International Telecommunication Union (ITU). Different DSL modem makers
are using either Discrete Multitone Technology (DMT) or Carrierless Amplitude Modulation (CAP).
A third technology, known as Multiple Virtual Line (MVL), is another possibility.Factors Affecting the Experienced Data Rate
DSL modems follow the data rate multiples established by North American and European
standards. In general, the maximum range for DSL without repeaters is 5.5 km (18,000 feet).
As distance decreases toward the telephone company office, the data rate increases. Another
factor is the gauge of the copper wire. The heavier 24 gauge wire carries the same data rate
farther than 26 gauge wire. If you live beyond the 5.5 kilometer range, you may still be able to
have DSL if your phone company has extended the local loop with optical fiber cable.The Digital Subscriber Line Access Multiplexer (DSLAM)
To interconnect multiple DSL users to a high-speed backbone network, the telephone company
uses a Digital Subscriber Line Access Multiplexer (DSLAM). Typically, the DSLAM connects to
an asynchronous transfer mode (ATM) network that can aggregate data transmission at gigabit
data rates. At the other end of each transmission, a DSLAM demultiplexes the signals and
forwards them to appropriate individual DSL connections.Who's Offering It When
Here is a sample of current and planned offerings in the U.S. DSL is also being offered in the
UK and elsewhere.According to Flashcom, it is now the largest and fastest growing provider of DSL service in the
United States. Service is now available in all major US cities. Pricing starts at $49.95 monthly
and includes Internet access. In most locations, installation and customer premise equipment
is free with a two-year agreement.Beginning in April 2000, FreeDSL will offer free hardware and setup and no monthly charge in
a number of markets. For the service, users must agree to provide personal information for
demographic use and to have a small navigational bar containing advertising always visible
while connected. To get the free DSL modem, you need to refer 10 people to the FreeDSL site.
There may be other requirements.In the Midwest United States, Primary Network is offering DSL service to St. Louis, Missouri-
area residents and businesses. Primary Network will become the largest Midwest provider of
DSL service, with 20 central office sites operational by September. Called DSL Accelerator,
Primary plans to offer this service in the Kansas City and Springfield, Missouri areas by
November 1, 1999. Download maximums will be between 384 Kbps and 1.54 Mbps.
Upload maximums will be between 128 Kbps and 384 Kbps. Prices start at $49.95 monthly
and include Internet Access. For more information, please visit http://www.primary.net/dsl/.Bluestar Communications is currently offering DSL in Nashville and Memphis, Tennessee, and
in Louisville and Lexington, Kentucky, and plans to offer service in 25 other cities by early 2000.
SBC Communications plans to bring ADSL to over 8 million homes in California, Missouri, and
Texas by the beginning of 2000. In California, over 255 telephone company central offices will
provide service to 5 million homes and 900,000 businesses. In Missouri and Texas, SBC's
Southwestern Bell company will upgrade 271 central offices for 3.2 million homes and 440,000
businesses. Customers will need a $198 "ADSL modem" and will pay a basic $39 a month on
yearly basis for unlimited service, or $49 with access to the Internet. Business or high-demand
users can pay more and get faster download and upload speeds. For the basic rate, users are
guaranteed 384 Kbps downstream and 128 Kbps upstream. Power users can get up to 6 Mbps
downstream and 384 Kbps upstream.Bell Atlantic has announced plans for a wide deployment of ASDL in the Northeastern U.S. to
both home and corporate customers. The service is currently offered in the Boston,
Philadelphia, Pittsburgh, Washington DC, and Northern New Jersey metropolitan areas.
The New York City metropolitan area launched in mid-July, 1999. Additional markets will
be announced in the future. Bell Atlantic offers what it calls Personal Infospeed DSL at speeds
of 640 Kbps downstream and 90 Kbps upstream for $39.95 a month, or $59.95 a month including
Internet access. Professional Infospeed offers speeds of 1.6 Mbps downstream and 90 Kbps
upstream at $59.95 per month, or $109.95 per month with Internet access. Power Infospeed
provides up to 7.1 Mbps downstream and 680 Kbps upstream for $109.95 per month, or
$189.95 per month with Internet access. Network equipment providers are Alcatel, Globespan,
and Westell. Among PC manufacturers that will support Infospeed technology are Apple
Computer, Compaq, and Dell Computer.BellSouth is offering a splitter-based ADSL service in 30 markets through Network Service
Provider (NSP) channels. BellSouth provides access to all DSL-qualified loops through a
single asynchronous transfer mode (ATM) port in each of 13 LATAs in eight Southeastern
states. Access One, BellSouth's service partner, has committed to deploy a minimum of
10,000 DSL lines to its customers over the next two years.US West plans to offer DSL service in 40 cities in the western part of the U.S. Currently,
DSL is offered in Portland, Oregon, and Seattle, Washington. US West uses CAP modulation
but says they are equipped to support DMT if that becomes a standard.GTE Corporation has offered ADSL to 1,000 living units in Marina del Rey, California since
November, 1997. Downstream data rates are up to 1.5 Mbps and upstream up to 384 Kbps.
Residences are charged $99 a month.NETinc, a Canadian company, is deploying ADSL in Hamilton, Ontario, using Paradyne
technology. Dowstream data rates will be up to 7 Mbps and upstream up to 1 Mbps.
Service to residences will be about $50 a month, to corporations $200 a month.Optimum Communications furnishes both ADSL and HDSL in the Florida West Coast/
Tampa area. Downstream data rates are up to 3.2 Mbps and upstream up to 1.2 Mbps.
Monthly rates are about $99 a month.The ADSL Forum offers a much more complete List of ADSL Trials and Deployments.
Hardware Offerings
Rockwell's Consumer DSL chipset is used in telecommunications equipment made by Nortel.
Nortel sells the equipment to carriers and to Internet service providers and Rockwell sells the
modems through the usual retail channels. The equipment offers a 1 Mbps data rate.3Com and Texas Instruments offer a hybrid modem supporting both dial-up 56 Kbps and rate
adaptive ADSL (RADSL).Types of DSL
ADSL
The variation called ADSL (Asymmetric Digital Subscriber Line) is the form of DSL that will
become most familiar to home and small business users. ADSL is called "asymmetric"
because most of its two-way or duplex bandwidth is devoted to the downstream direction,
sending data to the user. Only a small portion of bandwidth is available for upstream or
user-interaction messages. However, most Internet and especially graphics- or multi-media
intensive Web data need lots of downstream bandwidth, but user requests and responses are
small and require little upstream bandwidth. Using ADSL, up to 6.1 megabits per second of data
can be sent downstream and up to 640 Kbps upstream. The high downstream bandwidth
means that your telephone line will be able to bring motion video, audio, and 3-D images to your
computer or hooked-in TV set. In addition, a small portion of the downstream bandwidth
can be devoted to voice rather data, and you can hold phone conversations without
requiring a separate line.Unlike a similar service over your cable TV line, using ADSL, you won't be competing for
bandwidth with neighbors in your area. In many cases, your existing telephone lines will
work with ADSL. In some areas, they may need upgrading.
CDSL
CDSL (Consumer DSL) is a trademarked version of DSL that is somewhat slower than ADSL
(1 Mbps downstream, probably less upstream) but has the advantage that a "splitter" does
not need to be installed at the user's end. Rockwell, which owns the technology and makes a
chipset for it, believes that phone companies should be able to deliver it in the $40-45 a month
price range. CDSL uses its own carrier technology rather than DMT or CAP ADSL technology.FreeDSL
A service offering and not a technology, FreeDSL is a company offering free ADSL hardware
and setup with no monthly charge for service. For the service, users must agree to provide
personal information for demographic use and to have a small navigational bar containing
advertising always visible while connected. To get the free DSL modem, you need to refer
10 people to the FreeDSL site. There may be other requirements. FreeDSL reportedly plans
to offer optional premium services at a future time.G.Lite or DSL Lite
G.Lite (also known as DSL Lite, splitterless ADSL, and Universal ADSL) is essentially a slower
ADSL that doesn't require splitting of the line at the user end but manages to split it for the
user remotely at the telephone company. This saves the cost of what the phone companies
call "the truck roll." G.Lite, officially ITU-T standard G-992.2, provides a data rate from 1.544
Mbps to 6 Mpbs downstream and from 128 Kbps to 384 Kbps upstream. G.Lite is expected to
become the most widely installed form of DSL.HDSL
The earliest variation of DSL to be widely used has been HDSL (High bit-rate DSL) which is
used for wideband digital transmission within a corporate site and between the telephone
company and a customer. The main characteristic of HDSL is that it is symmetrical: an equal
amount of bandwidth is available in both directions. For this reason, the maximum data rate
is lower than for ADSL. HDSL can carry as much on a single wire of twisted-pair as can be
carried on a T1 line in North America or an E1 line in Europe (2,320 Kbps).IDSL
IDSL (ISDN DSL) is somewhat of a misnomer since it's really closer to ISDN data rates and
service at 128 Kbps than to the much higher rates of ADSL.RADSL
RADSL (Rate-Adaptive DSL) is an ADSL technology from Westell in which software is able to
determine the rate at which signals can be transmitted on a given customer phone line and
adjust the delivery rate accordingly. Westell's FlexCap2 system uses RADSL to deliver from
640 Kbps to 2.2 Mbps downstream and from 272 Kbps to 1.088 Mbps upstream over an
existing line.SDSL
SDSL (Symmetric DSL) is similar to HDSL with a single twisted-pair line, carrying 1.544 Mbps (
U.S. and Canada) or 2.048 Mbps (Europe) each direction on a duplex line. It's symmetric
because the data rate is the same in both directions.UDSL
UDSL (Unidirectional DSL) is a proposal from a European company. It's a unidirectional
version of HDSL.VDSL
VDSL (Very high data rate DSL) is a developing technology that promises much higher data
rates over relatively short distances (between 51 and 55 Mbps over lines up to 1,000 feet or
300 meters in length). It's envisioned that VDSL may emerge somewhat after ADSL is widely
deployed and co-exist with it. The transmission technology (CAP, DMT, or other) and its
effectiveness in some environments is not yet determined. A number of standards organizations
are working on it.x2/DSL
x2/DSL is a modem from 3Com that supports 56 Kbps modem communication but is
upgradeable through new software installation to ADSL when it becomes available in the
user's area. 3Com calls it "the last modem you will ever need."A DSL Summary Table
DSL Type Description Data Rate
Downstream;
Upstream Distance Limit Application
IDSL ISDN Digital Subscriber Line 128 Kbps 18,000 feet on 24 gauge wire Similar to the ISDN
BRI service but data only (no voice on the same line)CDSL Consumer DSL
from Rockwell 1 Mbps downstream; less upstream 18,000 feet on 24 gauge wire Splitterless
home and small business service; similar to DSL LiteDSL Lite (same as G.Lite) "Splitterless" DSL without the "truck roll" From 1.544 Mbps to 6
Mbps downstream, depending on the subscribed service 18,000 feet on 24 gauge wire The
standard ADSL; sacrifices speed for not having to install a splitter at the user's home or
businessG.Lite (same as DSL Lite) "Splitterless" DSL without the "truck roll" From 1.544 Mbps to 6
Mbps , depending on the subscribed service 18,000 feet on 24 gauge wire The standard
ADSL; sacrifices speed for not having to install a splitter at the user's home or businessHDSL High bit-rate Digital Subscriber Line 1.544 Mbps duplex on two twisted-pair lines;
2.048 Mbps duplex on three twisted-pair lines 12,000 feet on 24 gauge wire T1/E1 service
between server and phone company or within a company;WAN, LAN, server access
SDSL Symmetric DSL 1.544 Mbps duplex (U.S. and Canada); 2.048 Mbps (Europe) on a
single duplex line downstream and upstream 12,000 feet on 24 gauge wire Same as for
HDSL but requiring only one line of twisted-pairADSL Asymmetric Digital Subscriber Line 1.544 to 6.1 Mbps downstream;
16 to 640 Kbps upstream 1.544 Mbps at 18,000 feet;
2.048 Mbps at 16,000 feet;
6.312 Mpbs at 12,000 feet;
8.448 Mbps at 9,000 feet Used for Internet and Web access, motion video, video on demand,
remote LAN accessRADSL Rate-Adaptive DSL from Westell Adapted to the line, 640 Kbps to 2.2 Mbps downstream;
272 Kbps to 1.088 Mbps upstream Not provided Similar to ADSLUDSL Unidirectional DSL proposed by a company in Europe Not known Not known Similar
to HDSLVDSL Very high Digital Subscriber Line 12.9 to 52.8 Mbps downstream;
1.5 to 2.3 Mbps upstream;
1.6 Mbps to 2.3 Mbps downstream 4,500 feet at 12.96 Mbps;
3,000 feet at 25.82 Mbps; 1,000 feet at 51.84 Mbps ATM networks;
Fiber to the Neighborhood