T1 Data

A T1 is considered to be a Data T1 when it carries only digital data services. (Voice-grade dialup data does not qualify) Since a Data T1 data line carries only T1 data services, it will typically be terminated by a Mux on the customer end and either a DXC 1/0 or DXC 1/1 on the carrier end, depending upon whether the Data T1 carries a single circuit or multiple data services. The combined services do not have to be individual DS0 circuits. The only stipulation is that the total bandwidth can be combined by the appropriate multiplexing equipment on either end to combine and/or map the circuits towards their appropriate destination.

Typical Examples (each example depicts a full T1):

• 10 x 64k data circuits and 14 x 56kb data circuits
• 256kb data (ISP bandwidth) and 20 56kb data circuits
• 512kb data (ISP bandwidth), 2 x 56kb Frame relay access circuits, and 18 56kb data circuits

Framing and Line Coding. Since Data T1s carry only data, it is strongly suggested that the T1 access facility be provisioned using ESF/B8ZS framing and line coding. The first part, ESF, refers to Extended Super-Framing , which allows for a single 8kb channel for control of the entire T1 and is a requirement for services greater than 56kb in speed. B8ZS refers to Binary Eight, Zero Suppression. This line coding option allows for extended streams of zeros without losing timing 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.

Theory Lesson. In its basic form, any DS-Level circuit can be broken down into multiple "channels" where each represents a time slot. Divide a 1.544 MHz DS1 by 24 (less 8kb for framing and line coding) and the result is 24 x 64 KB circuits. These DS0s can be voice or data, provided that the service can be combined into a 64 KB data stream. The concept of multiplexing is combining several slower speed circuits (or services) into a single higher speed circuit (for more details see our multiplexing page ). This practice is very commonplace in the Telecommunications infrastructure. DS0s are combined into DS1s, DS1s are combined into DS3s. DS-level circuits are carried by copper pairs. Once you exceed the 45 MB speed reached by DS3s, a conversion to optical circuits takes place.

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