<< T1 >>
What is T1?
A T1or Trunk Level 1 is a term for a digital carrier
facility used to transmit a DS-1 formatted digital signals
at 1.544 megabits per second. This is made up of 24
digital channels. This requires a digital connection
device (CSU/DSU {customer switching unit/digital switching
unit}) to connect to four wires to carry the information.
Most small Internet providers have a T1 (or a fractional
T1) line as their connection to the Internet. A Full
T1 should accommodate from one to over 200+ users and
other services from an Internet provider. Unlike the
modem that is in most computers a T1 line requires a
CSU/DSU and the connection. The modem that is in your
computer is analog. The newer 56K modems are a transition
from analog to user affordable digital technology. The
newer ISDN modems are digital to allow for the higher
speeds.
How it works:
The T1
is like a large water main that serves a city, a large
amount of water or traffic flows through it. Unlike
the water hose in your front yard (your modem) the T1
is the major carrier of the Internet traffic. The T1
connects the backbone provider to the ISP provider via
the telco (telecommunications provider) The signal comes
into the CSU/DSU and then goes to the router. From there
it goes into the master name server and may be routed
to other servers. One of these severs may be a modem
or terminal server that allows you to connect to the
Internet. You log in and are verified as a user on the
local network and then are allowed to proceed to the
larger network (Internet).
What may affect You?
Things
that may affect you are how busy the site is on the
other side of the Internet. If I work from a Unix prompt
and move files from one site to another using the FTP
protocol. I would expect them to move as fast as my
network connection (1.54megabits/sec) would allow, a
1 megabyte file will travel at about 120K/sec or take
8.3 seconds. If you are accessing the same file from
a 28.8 modem then it would be expected that (because
you have a 28.8 connection) that it would take 347 seconds
or 5.8 minutes. This is optimum situation, however because
of traffic at the other site it may take longer due
to the number of people accessing the site and the files.
The kind of connection that particular site has (ie
T1). The number of users that are actually accessing
the site affects what I would expect to see for a file
transfer. If I'm the only one accessing a web site then
I would expect the files to travel very quickly. If
there are many users all accessing the files then I
would expect things to slow down because of the traffic.
The more traffic the slower the files travel.
What is a CSU/DSU?
A CSU/DSU
[Channel Service Unit / Data Service Unit] is a piece
of equipment that connects a leased line from the telephone
company to the customer's equipment (such as a router).
It performs line encoding and conditioning functions
and often has a loopback function for testing. Although
CSU/DSU's look similar to modems, they are not modems,
and they don't modulate or demodulate between analog
and digital. All they really do is interface between
a 56K, T1, or T3 line and serial interface (typically
a V.35 connector) that connects to the router. Many
newer routers have 56K or T1 CSU/DSUs built into them.
CSU/DSU's for 56K, T1, and T3 lines are NOT the same
and are not interchangable as a general rule. In the
case of a T1 CSU/DSU, it passes the data in 64K chunks
(time slots) on the 24 different channels (64K x 24
= 1.54MB).
What is a Full T1?
When a
carrier gives you the option of purchasing a full T1,
you can get the full 1.544Mbps circuit unchannelized
direct into the Internet (or Frame Network, or Point-to-Point);
also known as a clear channel T1. A Fractional T1 is
a channelized T1 with only some of the channels turned
on. Fractionals are normally priced in terms of Kbps.
For example you can get 384kbps, 512kbps or 768kbps
from most carriers. However, given the cost of provisioning,
you may be better off paying a couple hundred dollars
extra for the full line.
Are Frame Relay, VPN, Dedicated Internet and T1 the
same?
Frame Relay,
VPN and Dedicated Internet Access all use T1 connections
to make the respective service possible, but they are
not the same. By itself, Trunk Level 1 service is nearly
useless. It takes a standard or protocol like Frame
Relay or VPN to provide data transport over a Wide Area
Network. The four most common uses of a T1 line include:
- From
one point to another, the is often referred to a Private
Line;
- From
one point into a secure carrier network as with Frame
Relay;
- From
one point into the public Internet;
- From
one point into a carrier's voice network.
What is a difference
between DSL and a T1?
The primary
difference between DSL and a T1is in the level of over
subscription that occurs before the service reaches
the end user. When you purchase a full T1 of Internet
access, what you are generally getting is access to
1.544 Mbps of transmission on the carrier's network,
regardless of what other customers are transmitting
and receiving. To better illustrate this, let's assume
that a carrier has capacity for 150 Mbps at any given
time. This means that the at the most, they would sell
is 100 T1s; Tier One carrier networks are seldom oversubscribed.
For every megabyte of capacity, they can sell one megabyte
access to a customer. DSL works differently then T1
lines - and costs less - because of over subscription.
When you use a DSL connection your service runs through
a piece of equipment called a DSLAM, as opposed to running
directly into the Internet. The DSLAM acts as a point
of aggregation between the DSL subscribers and the direct
connection to the Internet (normally a T1 or DS-3).
Typical DSL over subscription rates run from 4:1 to
25:1. Or in other words, for every one megabyte of demand
coming into the DSLAM, a fraction of that is available.
The benefit to this design is that a DSL provider can
provide a 2 Mbps connection for a fraction of the T1
price. The disadvantage is that when the DSLAM gets
busy, your connection speed will slow considerably.
The price
of an Internet T1 is generally made up of two components:
the local loop price and the port price. The local loop
is what connects your location to the carrier's POP
(Point of Presence). Local T1 loops are priced according
to the distance from your location to the carrier's
POP and are priced differently by all carriers. If you
are looking for T1 prices it is best that you receive
quotes from multiple carriers to insure that you get
the best deal available. As a rule you can expect an
Internet T1, including local loop, to cost between $400
and $1,300 a month, depending on the installation location
and the desired speed of the service.
A
large company needs something more than a T1 line. The
following table shows some of the common line designations:
DS0 - 64 kilobits per second
ISDN - Two DS0 lines plus signaling (16 kilobits per
second), or 128 kilobits per second
T1 - 1.544 megabits per second (24 DS0 lines)
T3 - 43.232 megabits per second (28 T1s)
OC3 - 155 megabits per second (84 T1s)
OC12 - 622 megabits per second (4 OC3s)
OC48 - 2.5 gigabits per seconds (4 OC12s)
OC192 - 9.6 gigabits per second (4 OC48s
Benefits
• Reliable - T1 lines are dedicated for your use
only. Unlike DSL, the T1 line is not shared by other
people. The line is reserved exclusively for you - giving
you the peace of mind that your connection will work,
and stay working.
• Fast - T1 lines are reserved for your use only
- giving you all the bandwidth the line can handle -
1.54 megabits per second
• Guaranteed - the speed, quality and uptime of
a T1 line is guaranteed - your business will always
be connected.
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