T1 Lines | At 1.5Mbps and about $200/month, why have they remained relevant?


T1 Lines | At 1.5Mbps and about $200/month, why have they remained relevant?


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T1 lines (or E1 lines in EMEA) and their variants such as T2,T3…T5 have been around for a long time – from as far back as the 1960s. Despite relentless pressure from emerging higher bandwidth, and low cost/bit technologies T1 lines remain relevant for certain applications and in certain market segments. In this article T1 lines and the reasons for their survival are briefly reviewed.

About T1 Lines

A T1 line can be defined as a physical transmission medium capable of transmitting 1.544Mbps (1.536Mbps + 8 bits for channel control). The European equivalent, E1 is capable of 2.048Mbps. When initially developed by Bell Labs a T1 line consisted of a twisted copper pair but today T1 signals can be transmitted over optical fiber and other media, even wireless.

Since T1 lines were originally designed for voice transmission, their capacity was defined in terms of the number of voice channels. In the old Plesiochronous Digital Hierarchy (PDH) and later SONET/SDH, a voice channel was referred to as DS0 (Digital Signal Zero) equivalent to 64Kbps. Thus, a T1 line is capable of carrying 1.536Mbps/64Kbps or 1536Kbps/64Kbps = 24 voice channels. The corresponding E1 circuit carries 2.048Mbps or 32DS0.

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