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Abis: Structure of timeslots on E1

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  • #57707 Reply
    Tom Fox

    I am looking for information on the allocation of E1 timeslots for Abis.

    I understand that TS0 is reserved for signalling. I understand that per TRX that two timeslots are reserved for voice/data and that each of these timeslots are composed of 16 kbit/s sub-channel. I understand that the remaining timeslots are allocated for signalling associated for the call(s) and for signalling associated with each cell (BCCH/RACH/FACH/PCH).

    What is not clear to me is if these signalling timeslots are at 16 kbit/s or at 64 kbit/s?

    Also, what is the relationship between the voice timeslots and the call signalling timeslots? Is it vendor specific? And what are typical relationships.

    Thanks in advance,


    #57708 Reply

    Hi Tom Fox,

    Let’s call the “RSL” the logical channel for 1 TRX.
    Let’s call the “TCH nibble” the 16kb/s sub-channel on the Abis.

    One TRX requires 8 TCH nibbles = 8 * 16 = 2 Abis timeslots. (because 1 Abis TS = 4 nibbles = 64kb/s)

    Your question regarding the RSL:
    1 TRX can require more or less signalling, depending if there are a lot of SDCCH traffic, or half rate traffic.
    In normal conditions, 4 RSL are sharing 1 Abis timeslot (64kb/s). The sharing is not static : it is dynamic. Each RSL could sometimes use the full 64kb/s, if the 3 others are idle… (it’s an example)

    If RSL is highly loaded, you could decide to share only 2 RSL on the same TS.

    So typical RSL usage is 16kb/s in average. Could be up to 32kb/s in special case.


    #57709 Reply
    Muhammad Atif

    Hi Pix
    Thanks for your help.I want to know can you please tel me which standard deals with it which you have mentioned above .

    #57710 Reply


    I have no idea. It’s certainly in the serie 44 or 45 of the 3GPP, look for BTS-BSC protocols (layer 3).

    The Exorpixt.

    #57711 Reply

    The explanation given is very good. My question is;

    What is the loading for SDCCH traffic on RSL and that of TCHF/H? Is it quantifiable?

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Reply To: Reply #57711 in Abis: Structure of timeslots on E1
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