What is a T1 Router?
How a T1 router works and how
to get on free with your T1 service.
By: John Shepler
You may already have a broadband router
or an IP network router, but what is a T1 Router?
A T1 router is simply a router with the
necessary interface circuitry to connect directly to a T1 line.
Often, it is set up as an Internet access router to provide dedicated
Internet service to an organization's computer networks. Other
T1 routers are used to connect local area networks to each other
through T1 private lines.
Why the special interfacing? A T1 line
can carry your network traffic, but it is not inherently an IP
or Ethernet format service. T1 service was originally designed
to carry multiple telephone lines that had been digitized. It
still serves that purpose to provide a cost advantage in connecting
a dozen or more telephone lines to a PBX system. As such, T1
uses a proprietary protocol based on synchronous time division
multiplexing rather than the packet switching protocol that is
the current standard for nearly all local area networks.
You don't have to worry about the messy
business of timing, framing and line coding. A T1 router takes
care of the necessary conversions transparently. The T1 line
from the "smart jack" provided by the telephone company
installers plugs into one port of the T1 router. Your network
plugs into another. Once it is setup to meet the requirements
of both the T1 line and your LAN, you have a gateway for network
traffic to the Internet or another business location.
So normal routers don't work with T1 lines?
Yes and no. You can connect a regular IP based router to a T1
line using a couple of specialized interface boxes called CSUs
and DSUs. The CSU or Channel Service Unit is the device that
connects directly to the T1 line at the telco demarcation point.
It handles the electrical interface between the bipolar T1 signals
and the digital signals used by networking equipment. It also
provides a "loopback" function so that correct operation
of the T1 line can be checked remotely by the T1 line carrier.
The DSU or Data Service Unit works something like a modem to
convert the packet network signals to and from the TDM format
used on the T1 line. Usually the CSU and DSU are combined into
one piece of equipment called a CSU/DSU.
What makes a T1 router is the CSU/DSU circuitry
that is built into the router chassis or available as a plug-in
module. With router and CSU/DSU in one box, you have the convenience
of a single device to handle the WAN or wide area network connection
to a T1 line. You can also get T3 routers if you need more bandwidth.
A T3 router can handle the higher speed network traffic of a
45 Mbps T3 line and has the CSU/DSU interface particular to T3
You could go out and buy your own T1 router
or perhaps a plug in module for your current network router.
But it may make more sense to let your T1 carrier provide the
T1 router as well as the line service. Many T1 providers will
give you the router at no charge or a small increase in the monthly
T1 lease charge. You save the cost of hundreds or even thousands
of dollars of capital investment in router hardware. Plus the
T1 carrier can now manage the T1 line through the router interface
and right up to your network connection. That makes troubleshooting
much easier than if you have multiple pieces of equipment from
multiple vendors.Don't buy a T1 router until you see if
you can get one free with your T1 line service.
How About Ethernet?
Carrier Ethernet directly competes with T1 and is available with both copper and fiber optic delivery. Bandwidths range from 2 or 3 Mbps on the low end up to 10 Gbps and beyond. Pricing per Mbps is more attractive than T1 lines. Managed service options also include edge routers as part of the service package.
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