What Can I Expect from T1 Line Bandwidth?

More than three million businesses across the United States are connected to the internet and the telephone network with T1 lines. This makes T1 one of the most widely used broadband technologies in the country. Faster transmission rates are available but the implementation of these technologies has not approached the market share of T1 services. T1 line bandwidth is based on a standard developed by AT&T in the late 1950s. AT&T gathered data by pushing data rates increasing faster through their Chicago long lines until error rates rose too high. They then backed off the speed to a level with a safe margin.

In Europe, the E1 standard has higher effective throughput thanks to different framing schemes and other differences. The two standards are not compatible. T1 standards have not evolved beyond the 1960s because any improvements will obsolete the existing infrastructure. T1 line bandwidth is 1.544 Mbps. Because a portion of the full bandwidth is used for framing, the actual top bandwidth is 1.536 Mbps.

Some of the services deliverable across T1 lines includes voice, point-to-point data, voice-over-broadband (VOIP), VPN and internet backbone connectivity. Each T1 line can deliver up to 24 full duplex phone channels or up to 192,000 bits per second if configured as unchannelized.

DSL can match T1 line bandwidth for residential service but availability is limited to a certain distance from phone company switching centers. The transfer rate changes over distance too. DSL service is considered "best effort" and service disruptions can last several hours or even days. A service guarantee is rarely included with DSL service.

A residential internet connection that is unavailable may be an inconvenience. When a business depends on internet or telephone service for income any outage quickly becomes intolerable. T1 lines are much more reliable than DSL or Dial-up. Typical T1 leases include service level agreements that can cost the service provider when the line becomes unavailable. Disruptions of service are measured in minutes and restoring service quickly is important to the provider's bottom line as well as the customer's.

Leasing a full T1 line is often too expensive for smaller businesses and the full bandwidth may not be needed. Fractional T1 lines are less expensive than full T1 service, depending on the location. Some providers market fractional T1 as "point-to-point" service. The cost reduction of fractional T1 is not proportional to the reduction of bandwidth. The local phone system charges the T1 provider the same for fractional and full T1 local loops. The bandwidth charges are around ten percent for the total cost so reducing bandwidth 50% may reduce the T1 service rates by less than 20%. Some businesses relying heavily on internet accessibility but not requiring the full bandwidth find the reliability of fractional T1 worth the expense. Fractional T1 is easily and quickly upgraded to full T1.

Metered T1 service is charged by the bandwidth used and is a good choice for businesses that require full T1 line bandwidth only a few times a month. Burstable T1 lines are capable of full bandwidth when required but scale back to much lower levels when not in use. These are cost effective for businesses that only require T1 bandwidth a few times a month and especially when combined with voice services.

T1 line reliability is often 99.99% or better and guaranteed by the carrier. DSL cannot come close to this level of reliability. For more bandwidth, T1 lines can be bonded together in up to 3 pairs for bandwidth up to 9Mbps or more. Some larger carriers offer fractional T3 lines with bandwidth several times that of a full T1, but at significant cost savings over full T3 lines.