T1 lines were originally developed by the telephone companies for their own use. The idea was to consolidate 24 separate analog phone lines into a single digital trunk. The key features were serial digital transmission over no more than two twisted pair, regeneration to extend transmission distance indefinitely, nailed-up private line connections between two locations, a multiplexing scheme to keep the 24 simultaneous conversations separate and distinct, and a line speed of 1.5 Mbps.
This legacy service is still widely available and is called T1 telephone or T1 CAS for Channel Associated Signaling. It is used to connect business PBX telephone systems to telephone service providers for outside lines. Most businesses can get easily get by with 24 outside lines, so only a single T1 line is needed. There is a newer version of this service called ISDN PRI or T1 PRI for Primary Rate Interface. The underlying T1 line works the same. What’s different is that one channel is reserved for switching, dialing and data such as ANI or Caller ID. That leaves 23 outside telephone lines on one T1 PRI, still right for most small and medium businesses. Larger companies and telephone intensive businesses such as call centers can order multiple T1 PRI lines to gain more outside phone lines.
The designated T1 line speed of 1.5 Mbps, chosen to support existing telephone infrastructure, made it very attractive as a way to connect businesses to the Internet and for connecting company networks across long distances. Companies became more and more computerized with terminals and later PCs on every desktop. Internal networks eventually standardized on Ethernet as a network protocol and speeds increased to 10 Mbps, 100 Mbps and 1,000 Mbps. In the early days, even larger companies used dial-up modems for file transfers. Dedicated lines ran at 64 Kbps and 128 Kbps. That was fine when data files were small, few and far between. It wouldn’t work anymore when data moved from paper to disk files.
The trick to using a telephone-inteneded technology as a digital private line is to treat the entire line bandwidth as a single entity and ignore the 8 bit increments that define individual telephone channels. This is a clear channel pipe arrangement. You’ll need a router to connect to your network and a T1 interface card for the router. Plug this into the T1 “smart jack” installed by the service provider at each end of the line and you’ve got a 1.5 Mbps data connection.
A valuable characteristic of point to point T1 data lines is that they are permanently connected or “nailed up.” The actual wires, one or two twisted pair of telco wiring, are assigned to your T1 line and nothing else. No one else can gain access like they might on the Internet. This is what makes the dedicated line both dedicated to your use and private. The line goes from point A to point B and nowhere else.
What if you want to connect to another location? You can either cancel the T1 line you have now and get a new one going to that other location, or add another T1 line so you can connect to both the current and new location. You can add as many T1 lines as you like, but they all only go between two locations. What some companies do is create their own private network by running point to point dedicated T1 lines from each branch office back to headquarters. Then they set up a star network with HQ managing all traffic between the branches and headquarters and from one branch to another.
What if you like the idea of dedicated point to point service but really need more than 1.5 Mbps? That can be achieved by bonding T1 lines to double, triple or gain up to 12 Mbps of line speed. You can also use T3 lines (DS3 bandwidth) instead of T1 for 45 Mbps of bandwidth or SONET fiber optic lines starting at 155 Mbps. An alternative is Carrier Ethernet E-Line which gives you point to point Ethernet connections from 2 Mbps on up to 10 Gbps.
Can your business make good use of point to point dedicated T1 lines or higher bandwidth services? If so, get prices and availability on the line services right for your company.
Note: Picture of twisted pair cable courtesy of Wikimedia Commons.