What is E1 / T1 ?

The PDH (plesiochronous Digital Hierarchy) has 2 primary communication systems as its foundation.

These are,
T1 system based on 1544kbit/s that is recommended by ANSI &
E1 system based on 2048kbit/s that is recommended by ITU-T.

Common Characteristics :- 

1. Both are having Same Sampling Frequency i.e. 8kHz.
2. In both (E1 & T1) Number of samples/telephone signal = 8000/sec.
3. In both (E1 & T1) Length of PCM Frame = 1/8000s = 125µs.
4. In both (E1 & T1) Number of Bits in each code word = 8.
5. In both (E1 & T1) Telephone Channel Bit Rate = 8000/s x 8 Bit = 64 kbit/s.

Differing Characteristics :-

1. In E1 Encoding/Decoding is followed by A-Law while in T1 Encoding/Decoding is followed by µ-Law.
2. In E1 - 13 Number of Segments in Characteristics while in T1 - 15 Number of Segments in Characteristics.
3. In E1 - 32 Number of Timeslots / PCM Frame while in T1 - 24Number of Timeslots / PCM Frame.
4. In E1 - 8 x 32 = 256 number of bits / PCM Frame while in T1 - 8 x 24 + 1* = 193 number of bits / PCM Frame. (* Signifies an additional bit).
5. In E1 - (125µs x  8)/256 = approx 3.9µs is the length of an 8-bit Timeslot while in T1 - (125µs x  8)/193 = approx 5.2µs is the length of an 8-bit Timeslot.
6. In E1 - 8000/s x 256 bits = 2048kbit/s is the Bit Rate of Time-Division Multiplexed Signal while in T1 - 8000/s x 193 bits = 1544kbit/s is the Bit Rate of Time-Division Multiplexed Signal.

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