Active discussions
WikiProject Computing / Networking (Rated C-class, Low-importance)
This article is within the scope of WikiProject Computing, a collaborative effort to improve the coverage of computers, computing, and information technology on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
C-Class article C  This article has been rated as C-Class on the project's quality scale.
 Low  This article has been rated as Low-importance on the project's importance scale.
Taskforce icon
This article is supported by Networking task force (marked as Mid-importance).
WikiProject Telecommunications (Rated C-class, Mid-importance)
This article is within the scope of WikiProject Telecommunications, a collaborative effort to improve the coverage of Telecommunications on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
C-Class article C  This article has been rated as C-Class on the project's quality scale.
 Mid  This article has been rated as Mid-importance on the project's importance scale.

E1 frame structureEdit

Part of this section is incorrect. Nothing in the E1 framing structure requires TS16 to be used for signalling. The section relating to TS16 "cas" signalling should be removed. E1 framing is TS0 for synchronisation and TS1-31 are free for voice. TS16 being used by signalling is an implementation choice not intrinsic to an E1 structure. In international circuits TS1 is most often used for SS7 signalling and TS16 is used for voice, for example.

The sections relating to NFAS and FAS are similarly not intrinsic to an E1, again they are implementation choices when utilising an E1 as an access carrier (specifically ISDN - and vastly more commonly in the US not Europe or rest of the world where E1 are the standard TDM carrier). (talk) 13:41, 24 September 2015 (UTC)

Historical Note on E1 and T1Edit

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)

Unfinished BusinessEdit

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)

E1 & PCMEdit

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. 15:08, 26 March 2007 (UTC)

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

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. 14:54, 27 March 2007 (UTC)

I have linked the references to G.703 and G.704 directly to the early part of the article, which should resolve the above point. Mobilesense (talk) 09:34, 26 May 2010 (UTC)

Salam to All —Preceding unsigned comment added by (talk) 11:50, 4 December 2007 (UTC)

E1 Carrying capacityEdit

I would like to know that tha capacity of E1 which is 2 MBPS is forward + Reverse or 2MB each side. also pls let me know what is the working mechanism for the same. —Preceding unsigned comment added by (talk) 07:38, 19 August 2010 (UTC)

E2: E3: E4Edit

It is unclear what ″ ITU-T Rec. G.751 (see Figure 20)″ is referring to. Please include a reference for this source.Theking2 (talk) 08:23, 6 February 2014 (UTC)


The figure with the different types of bits has some strange features, or indeed errors.

  • below, the colour light green is not included as representing frame alignment bits; however, these six bits are the multiframe alignment word and are therefor in fact alignment bits
  • the six bits in the colour light green are 000000, but the corresponding text states that the multiframe alignment word is 001011 and therefor 000000 seems incorrect
  • the bits a14 -- d14 are missing and the bits a16 -- d16 are mentioned twice

Bob.v.R (talk) 23:32, 8 April 2015 (UTC)

The author of this figure does not respond to my comments, unfortunately. Bob.v.R (talk) 16:42, 3 July 2015 (UTC)
Return to "E-carrier" page.