The E carrier telecommunications system and the associated E 1, etc lines has been created by the European Conference of Postal and Telecommunications Administrations (CEPT) as a digital telecommunications carrier scheme for carrying multiple links.
The E-carrier system enables the transmission of several (multiplexed) voice/data channels simultaneously on the same transmission facility or line. Of the various levels of the E-carrier system, the E1 and E3 levels are the only ones that are used.
E carrier beginnings
The life of the E carrier standards started back in the early 1960s when Bell Laboratories, where the transistor was invented some years earlier, developed a voice multiplexing system to enable better use to be made of the lines that were required, and to provide improved performance of the analogue techniques that were used.
The step of the process converted the signal into a digital format having a 64 kbps data stream. The next stage is to assemble twenty four of the data streams into a framed data stream with an overall data rate of 1.544 Mbps. This structured signal was called DS1, but it is almost universally referred to as T1.
In Europe, the basic scheme was taken by what was then the CCIT and developed to fit the European requirements better. This resulted in the development of the scheme known as E carrier - the E standing for Europe or European.
The E1 designation can be seen to refer to not only the system itself but also raw data rate.
E carrier system basics
More specifically E1 has an overall bandwidth of 2048 kbps and provides 32 channels each supporting a data rate of 64 kbps. The lines are mainly used to connect between the PABX (Private Automatic Branch eXchange), and the CO (Central Office) or main exchange.
The E1 standard defines the physical characteristics of a transmission path, and as such it corresponds to the physical layer (layer 1) in the OSI model. Technologies such as ATM and others which form layer 2 are able to pass over E1 lines, making E1 one of the fundamental technologies used within telecommunications.
A similar standard to E1, known as T1 has similar characteristics, but it is widely used in North America. Often equipment used for these technologies, e.g. test equipment may be used for both, and the abbreviation E1/T1 may be seen.
E carrier line formats and data rates
Within the E carrier system there is a hierarchy of different levels of the system. The overall E carrier system is designed so that the base level or E0 signal rate is designed so that each higher level can multiplex a set of lower level signals.
The framed E1 line is able to carry 30 E0 data channels. In addition to this there is a further signalling channel required for the operation of the system.
High level E carrier links carry 4 signals from the level below.
It will be seen that the data rates achieved are not the exact multiples of the lower level links that might be expected. It is found that each level has a capacity greater than would be expected from simply multiplying the lower level signal rate. For example the E2 data rate is 8.448 Mbit/s and not 8.192 Mbit/s which equates to the E1 rate multiplied by 4.
The reason for this is that less overhead and signalling data is required when the higher rate E carrier links are used.
|E carrier link designation||Data Rate|
E1 and also T1 are well established for telecommunications use. However with new technologies such as ADSL, DSL, and the other IP based systems that are now being widely deployed, these will spell the end of E1 and T1. Nevertheless they have given good service over many years, and they will remain in use as a result of this wide deployment for some years to come.
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