What is E1 and T1 in telecommunication ?

I was preparing for an interview for Huawei Telecommunication Company of Nepal for the Post Telecom Equipment Engineer on last week.I don’t have any books and notebook which I used to have in my college day.I had very much less time for preparing Interview. From the seniors, I came across that frequently asked question lies around E1 and T1. Thus I google for the values for E1 and T1. I found a beautiful website which gave me a detail information on these.huawei_logo_nepal

Below data may help you in your future so I thought to keep here in my blog.

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 – 24 Number 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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