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A T1 Line is a Telecom term for a 1.544Mhz facility that carries a variety of services from a carrier to a customer's location. A T1 Line is also known as a "Hi-Cap" for a High Capacity circuit, and more formally as a DS1, for "Digital Service level 1", a T1 is its most common name. A T1 is carried by 4 copper wires (or via fiber and converted back to copper at the customer site) and can support a wide range of services to include voice, data, and video. Through multiplexing, a T1 can carry a combination of all of these services into a single circuit, reducing monthly access costs as opposed to buying individual DS0 (analog or digital) circuits. How and Where T1 Lines are Used. T1s are considered high capacity circuits, typically used by Telephone companies and medium to large business users that require more than a handful of individual lines, trunks, or DS0-level data circuits. Economies of scale come into play by combining circuits together into a single access facility. (The cost break-even point is typically 7-11 DS0s cost the same as a T1). In terms of capacity, a T1 is equal to 24 DS0s of capacity. (24 DS0s x 64kb plus 8kb overhead). Once the T1 is leased, adding DS0 capacity requires very little lead-time, and no additional monthly cost for the access facility. Access is the most common use for T1 Lines, however, for larger businesses, point-to-point T1 services may link two locations in a private network arrangement, either across town, or across the country. T1s can carry voice or data, as it is a digital transport service that is limited only in terms of its overall capacity. Common Names / Muxing Levels:
Typical Applications. DS0s are typically used as voice-level or dial-up data channels. DS1s are typically used as either private point-to-point circuits between facilities, or more typically, access from a business to either their local or long distance provider. DS3s are typically used where more than one DS1 is needed for capacity. While a T1 might be deployed for capacity reasons, not all DS0 timing slots must be activated, so if a company needs 256KB of capacity, a typical installation might have a T1 established for "access" and only 4 DS0s "activated" on the T1 facility.
ESF/B8ZS T1s also have the benefit of ESF monitoring, which allows the carrier to setup ESFMUs (monitoring units) to watch the performance of the T1 itself without disrupting the services carried by the T1. ESFMUs track performance using the 8kb ESF channel for statistics. ESF/B8ZS is required for Fractional T1s since the access T1 is not channelized, and contiguous bandwidth is required to allow a single circuit greater than DS0 speed. Termination Options. T1 Lines will typically terminate at the customer premises into a variety of options, including a channel bank, DTI Card (Direct Termination Interface to a PBX), D/I Mux, or TDM Mux. (Note: if these devices don't provide CSU-functionality, the T1 will terminate first into a CSU for testing and line build-out equalization, then into the device) The CPE termination equipment (Customer Premises Equipment) will be dependant upon the services carried by the T1 Line. |
T1 Line
