We hope our T1 FAQ (frequently asked questions) is
helpful to you. One step we have taken is to add a glossary of
some of the technical terms used in answering the questions.
Any of the technical terms in that are underlined and hyperlinked may be clicked on to pull the
definition at the bottom of the page. Clicking on return after
each definition will bring you back to the original spot.
Next time some one asks you what a T1 is just send
them here for a basic overview. If you have a question you
would like added to this FAQ or any questions or needs what so ever
just contact us we will be glad
to help.
What
isT1 service?
Simple answer
- T-1 is a type of telephone service
capable of transporting the equivalent of 24 conventional telephone
lines, using only two pairs of wires.
Technical Answer
- The T-1 was
originated byAT&T
in 1962 as a method to be able to send additional data along a
common 2 pair of copper wire. The technology was originally to be
used for "long-haul" voice communication, but in recent
times has been used for data transmission. The T-1's digital
signaling technology has grown into a variety of new themes, and
applications. The European E-1, the T-3, Frame
Relay, ISDN and many other technologies can
trace their roots to the reliable T-1.
What
Is a T-1 Circuit?
Simple Answer- T-1 is a high-speed data circuit with
four wires, two of which are used for transmitting and the other two
for receiving. The T-1 is capable of transmitting and receiving data
at a rate of about 1.5 million bits-per-second (BPS). Thus, the
T-1's data transmission rate is more than 50 times faster than a PC
modem operating at 28,800 BPS.
Technical Answer- T-1 circuits provide a bandwidth of 1.536 "usable"
Mbps on 24 channels of 64 kbps each. This allows for the 8 kbps
framing overhead. The aggregation of these channels can be
subdivided as a "fractional" T-1 of 64 kbps each. As the
cost of T-1 lines has reduced, the move seems to be to use the
entire bandwidth rather than parceling the channels/lines out for
different applications, or to different locations.
Why
is a T1 used for voice communications?
Answer -The
main advantage of T-1 is cost savings over equivalent service on
regular analog lines.In
general the cost of most 24 channel T1s is about the same as 12
standard telephone lines.This
enables a business requiring 24 phone lines to do so for the cost of
12.Another
advantage is that T-1 is a digital transmission and therefore less
prone than regular phone lines to loss and interference.
Why
is a T1 used for data communications?
Answer -
Speed
is the primary reason for data over T1.If a company transmits large files regularly outside their
office an T1 can be a great asset as well as if they receive large
amounts of Data. With
the expansion of the internet and the requirement to send data at
higher speeds, T-1 technology has been essential for dedicated T-1
lines.
Can a T1 Be Used for both
Voice and Data Communications?
Answer
- With a piece of equipment
called a multiplexer (which is similar to a
channel bank), the T-1 can be distributed into data circuits and
voice channels. For example, a T-1 could be used to carry 12
telephone lines plus two data circuits at 386K baud.This would be an example of an integrated T1 circuit.
What's
a CSU?
Answer -
The
Channel Service Unit (CSU) receives and transmits signals from and
to the WAN (wide area network) line and provides a barrier for
electrical interference from either side of the unit. The CSU can
also echo loop-back signals from the phone company for testing
purposes.Often a
CSU and DSU are combined into a single piece of equipment called a
CSU/DSU.
What
is a DSU?
Answer
- The Data Service Unit (DSU) manages line control, and
converts input and output between RS-232C,
RS-449, or V.xx frames from the LAN (Local Area
Network) and the time-division multiplexed (TDM)
DSX frames on the T-1 line. The DSU manages timing errors and signal
regeneration. The DSU provides a modem-like interface between the
computer as Data Terminal Equipment (DTE) and the
CSU. Often a CSU and DSU are combined into a single piece of
equipment called a CSU/DSU.
Definitions
Frame
Relay - Frame relay is a
telecommunication service designed for cost-efficient data
transmission for intermittent traffic between local area networks
(LANs) and between end-points in a wide area network (WAN). Frame
relay puts data in a variable-size unit called a frame and leaves
any necessary error correction (retransmission of data) up to the
end-points, which speeds up overall data transmission
ISDN- Integrated Services Digital Network is a set of standards
for digital transmission over ordinary telephone copper wire as well
as over other media. Home and business users who install an ISDN
adapter (in place of a modem) can see highly-graphic Web pages
arriving very quickly (up to 128 Kbps). ISDN requires adapters at
both ends of the transmission so your access provider also needs an
ISDN adapter.
Multiplexer
- a device that sends multiple signals
on a carrier channel at the same time in the form of a single,
complex signal to another device that recovers the separate signals
at the receiving end.
V.xx -The identifier used by two modems
when the “handshake” with each other to determine the fast rate
of speed they can use to speak to one another.In other words if you have a 56K modem and dial into a 28K
modem the two modems “talk” and determine a connection speed of
28,800 kbs.Often
expressed as follows V.35, V.40 or V.90.V.90 is a typical 56K connection.
TDM -
TDM (time-division multiplexing) is a scheme in which numerous
signals are combined for transmission on a single
communications line or channel. Each signal is broken up into many
segments, each having very short duration. The circuit that combines
signals at the source (transmitting) end of a communications link is
known as a multiplexer. When received on the other end of the line another
multiplexer then breaks the signals back down based on the timing of
which they are inserted into the combined signal.Hence the term time division.
