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 circuits.
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 through T1 Rex.
