T1 defined

A digital transmission link with a capacity of 1.544 Mbps. T1 uses two pairs of normal twisted wires, the same as found in most residences. T1 normally handles 24 voice conversations, each one digitized at 64 Kbps. T1 is a standard for digital transmission in the United States. T1 lines are used to connect networks across remote distances. Bridges and routers are used to connect LANs over T1 networks. A T1 line is typically used by small and medium-sized companies with heavy network traffic. It is large enough to send and receive very large text files, graphics, sounds, and databases instantaneously, and is the fastest speed commonly used to connect networks to the Internet. Sometimes referred to as a leased line, a T1 is basically too large and too expensive for individual home use.

Why T1?

A T1 provides 1.544 fully synchronous data from the Internet to the end user. Cable & ADSL are asynchronous, which means your inbound speed can reach speeds of 1.544 Mbps, but your outbound speed is much slower, usually 128 Kbps (1/12 the speed). What this means is that outbound traffic such as e-mail, web hosting, and file transfers only work as fast as your slowest link. For example, if you had two offices connected via VPN over a cable connection of 1.544/128, the fastest traffic could ever move between the two locations is 128 Kbps.

Other carriers may try to sell you on SDSL as opposed to cable or ADSL. What this means is that the traffic is synchronous and you have a full 1.544 Mbps in both directions. However, with SDSL, you are still bound to the same basic limitations as cable and ADSL which includes shared media, distance limitations, and over subscription.

• Shared Media: Every customer in your subscription area shares the pipe to the Internet via a DSLAM. During peak hours, when other customers are using the DSL, your connection speed drops.
• Distance Limitations: The limit for DSL service is 18,000 feet, though for speed and quality of service reasons many DSL providers place a lower limit on the distances for the service. At the extremes of the distance limits, DSL customers may see speeds far below the promised maximums, while customers nearer the central office have faster connections.
• Over Subscription: When you purchase a full T1 of Internet access, what you get is access to 1.544 Mbps of transmission on the carrier's network, regardless of what other customers are transmitting and receiving. DSL works differently - and costs less - because of over subscription. 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.