Talk:E-carrier

In 1972, some 10 years following the commercial success of T1 in the US, Europe decided to develop its own digital transmission technology. As expected, CEPT wanted to design a different transmission format, named E for Europe. (To have their own standard was a European fetish then, as for example their TV formats, size of letter paper, shape of electric plugs, and at one time different rail gauge for each country.) With the hindsight learned from the T1 system, E1 is indeed a much superior design.

The differences are as follows.

1. 32 8-bit time slots per frame, all numbers powers of 2, compared to the 193-bit frame of T1, which requires hiccups in counting.
2. 30 voice channels for E1 vs. 24 for T1. Since telephone equipment are grouped in 12, the number 30 results in acceptable "misalignment" of office wiring plan. Conversion between E1 and T1 results in idle channels except for 5 T1 to 4 E1 conversion.
3. One 8-bit timeslot reserved for OA&M for E1. The single bit for T1 proved inadequate.
4. One 8-bit timeslot reserved for signaling, available for CAS , SS7 , or ISDN . The T1 format resorted to robbed bit signaling for CAS, and reassign a voice timeslot for SS7 and ISDN, resulting in a 23 channel system. Horrors!
5. Clear 64 Kbit/s data capacity for E1. T1 has to cope with robbed bit.

In fairness, T1 fully met the goals of voice transmission at the time. It was a victim of its own success, namely it spawned the digital transmission revolution, for which the T1 format was then found wanting. LoopTel 02:51, 1 December 2006 (UTC) [reply ]

For all the careful planning and design of the E1 format, one item remained unfinished, namely the remote terminal command syntax. A basic tool for troubleshooting a failed line is to do loopbacks a section at a time. If one person from one end of a line segment can send a command to a remote end to effect a loopback, then this obviates the need to send a second person to the remote end, saving a "truck roll".

For T1, this command structure was dictated by AT&T , then in control of all T1 systems. For E1, CEPT had set aside certain bits in TS0 for this purpose, called SA bits. However, the committee could not agree on the exact format of the commands. As a result, each manufacturer determined its own proprietary command codes. An E1 terminal of one brand could not communicate with a terminal of another brand in the troubleshooting procedure. This of course leads to brand loyalty, which is exactly what the manufacturers desired.LoopTel 02:22, 2 December 2006 (UTC) [reply ]

Where is the direct reference to PCM? E1 circuits are synonymous with PCM, G.703 and HDB3 encoding in Europe. There needs to be refrerence to this in the article text not left as an indirect reference to G.703 at the end. 217.36.0.13 15:08, 26 March 2007 (UTC) [reply ]

PCM, G.703, and HDB3 are all separate things and not synonymous. — RevRagnarok ^{Talk Contrib} 16:39, 26 March 2007 (UTC) [reply ]

Agreed, however in Europe the vast majority of engineers will understand an E1 circuit to be a 2048kb/s channelised circuit which is PCM adheres to G.703 and encoded using HDB3, as this was the original use and definition of an E1 in the PDH hierachy. So whilst PCM, G.703 & HDB3 are not synonymous with eachother (which isn't what I stated anyway) an E1 circuit is effectively synonymous with all of them individually. 217.36.0.13 14:54, 27 March 2007 (UTC) [reply ]