A T1 transfers data symmetrically (at the same upload and download speed) between two points at 1.544 Mbps, and is ideal for customers who need a high-speed connection to the Internet or wide-bandwidth link in their virtual or real private network.

A T1 line actually consists of 24 individual channels, each supporting 64 Kbps. Each channel can be configured to carry voice or data traffic. Most telephone companies allow the customers to buy just a few of these individual channels, a package known as fractional T1 access (see Fractional T1). Typically, fractional T1 lines are sold in increments of 56 Kbps (the extra 8 Kbps per channel is used for data management), with a full T1 capable of accommodating 200-plus users and a variety of network services.

If your business or organization has eight or more phone lines and spends more than $750 per month for telecommunications, you should consider converting to a T1 line.

Budget-conscious companies and other high-bandwidth users sometimes gravitate towards SDSL because it’s viewed as a “cheaper” solution. But SDSL has one major drawback. Because of the technical limitations of the DSL protocol, only those customers fewer than 10,000 feet from their Central Office can receive 1.5 Mbps SDSL.

On the other hand, T1s are engineered to extend tens of miles, so almost all customers of a serviced Central Office can purchase T1 service. In addition, the local exchange carrier will remove bridge taps, load coils, and splices from the wiring when provisioning a T1. They won’t do this for a DSL circuit.

Integrated T1 (also called channelized T1) is a digital carrier modulation method in which a T1 line is divided into 24 channels, each having a maximum data speed of 64 Kbps, and each capable of supporting a unique application that can run concurrently with, but independently of, other applications on different channels.

Integrated T1 has become popular with businesses because of its flexibility. It allows an enterprise to run several services, such as local telephone, long-distance telephone, Internet, and Voice over IP (VoIP) over a single circuit simultaneously. Integrated T1 should not be confused with fractional T1. A fractional T1 line is leased to the customer at a fraction of the data-carrying capacity of a conventional T1 line and at a correspondingly lower cost.

Integrated T1 offers other important benefits besides performance. For example, users pay substantially less than they would if they purchased comparable “unbundled” voice and data services a la carte. Because everything comes in one package, customers don’t waste time dealing with multiple vendors. Nor do they have to wade through a stack of separate bills at the end of the month. Instead, they receive a single, easy-to-understand invoice.

Fractional T1 is a T1 digital phone line that is leased to at a fraction of its data-carrying capacity and at a correspondingly lower cost. A T1 line contains 24 channels, each with a data transfer capacity of 64 Kbps. The customer can lease a number of the 24 channels. The transmission method and speed of transfer remain the same. Overhead bits and framing are still used, but the unrented channels simply contain no data.

Fractional T1 lines are typically a less expensive option for companies that do not require a full T1 connection. They also afford businesses scalability – allowing them to start with a low-density solution and migrate to higher-density solutions as their transmission needs grow.

T3 lines (which offer 672 64 Kbps channels) are also offered as a fractional service.

A T3, or DS3, connection is a point-to-point dedicated line that provides 672 64 Kbps voice or data channels – the equivalent of 28 T1 lines. A T3 is used to transmit digital signals at 44.736 megabytes per second and has enough bandwidth to transmit full-motion real-time video and very large databases over a busy network.

T3 lines are used mainly by Internet Service Providers (ISPs), large companies or universities connecting to the Internet backbone or constructing their own network highway. It also is a viable solution for companies looking to resell bandwidth to their customers.

T3 users who want to add capacity often have to buy it in the next available increment, which can be extremely costly (between $3,000 and $20,000 per month or more depending on the distance). A less-expensive alternative is a “burstable” T3 that provides bandwidth on demand, without a high fixed monthly payment. Low-cost burstable lines are available through collocation, or “colo,” facilities that offer shared bandwidth-on-demand services via a large OC3 or OC12 pipe.