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===About the E1/T1 carrier systems===
The E-carrier system is the standardization of digital communications, where a single wire can be used to carry more than one simultaneous voice conversations.

It was first designed in America. There it has the name T-carrier, but the CEPT (European Conference of Postal and Telecommunications Administrations) revised and improved it becoming today the standard for the majority of countries, minus USA, Canada and Japan.
The whole idea is to group more circuits to form a high bandwidth network. For now, only the E1 (30 circuits) and E3 (512 circuits) are used. E1 is transmited as 32 time slots and E3 as 512 timeslots. This way, private end-to-end E1 circuits can be provided to the users in different countries that want to share a single high speed link.

Here are some technical data about E1. The 2048Mbit/s speed is achieved using E1 carriers. This is possible by splitting this number into 32 time slots. Each time slot sends and receives a 8-bit sample 8000 times per second. This leads to 8*8000*32=2048Mbit/s. There are two timeslots that are specialized on other things than data transport. These are TS0 (time slot 0), used for framing purposes and TS16, used for singalling and control.

The T-carrier is the American version of the E-carrier. These two types are incompatible. The DS0 (the basic unit) is a channel of 64kbit/s, normally used for voice circuit. The transfer rate is 1544Mbit/s, obtained like this: the highest frequency for human voice is 4000Hz. When converting analog to digital, there is a need to at least double that frequency for the sample rate. Each T1 frame contains 1 byte for each one of the 24 channels and a control bit. S, the result is ( (8*24+1)*2*4000=1544000bit/s.


'''See also'''
* [[About VoIP]]
* [[About PSTN]]
* [[Signaling module]]