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SS7 – NSL/HSL links & timeslots

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  • #50013

    I wonder can anyone can help me with some basic ss7 definitions/questions I have.
    My understanding is that a normal speed E1 trunk connection can carry 32 timeslots (all in), information transmitted in each time slot is termed a channel or link.
    Can i assume that this is correct, that there is a one-to-one equivalence between timeslots and links?

    Also, if High speed Links utilize the full bandwidth on a E1 connection, and than each HSL would be a full E1 instead of a 64Kbit/s channel, then we no longer have the concept of timeslots within a HSL? As a single link takes up the full bandwidth, or are they (timeslots) still relevant in different HSL cases.

    Thanks for any help received


    E1 is a standard that uses 32 TS onto a 2Mb/s link.

    If you want to use a 2Mb/s link without this “32 timeslots” structure it is possible, but then it is not an E1 anymore. It’s just a copper cable. And you’ll have to define a new LAYER-1 protocol in order to carry data.


    Hi pix

    Its not so much the technology, but the nomenclature that maybe i’m not getting. I understand the TDM nature of a standard NSL link, and i’m think that links are differentiated between each other within the E1 trunk by timeslots (carried in the SLS). The above is something would like confirmed, if not can a link be said to also exist over multiple timeslots/channels?

    But when you come to High-speed links, these allow full bandwidth utilization of a 2.048Mbps E1 for a single SS7 link, therefore if one (HS)link uses the whole bandwidth, and each link equates to one timeslot, then have the TDM periods have changed, or is the HSL existing across all timeslots?


    ok, i get it.
    one transfer can use several links (= timeslots) to perform the exchange of data.
    the transfer is defined at the LAYER 3, and the “LAYER 3” transfer occupies several “LAYER 1” timeslots. Therefore it can happen than one transfer uses the full E1 : 31 links.

    (beware : all E1 have max 31 TS useable for transfer. 1 TS is always reserved for “framing”. And if there is one SS7, then you have only 30 TS useable for data).

    Wallis Dudhnath

    Sorry for the late response.

    With a UK operator I used to look at SS7 and PCM – Pulse Code Modulation – for E1.0 (2.048Mbits/s) systems. This was well before SDH. A Mux (Multiplexer) approach was
    used to “step up” circuits to a higher bandwidth. This was the PDH “mux mountain”.

    A time slot is a recurring interval of time. It is a property of a digital system.

    For a E1.0 (2.048) PCM system that bandwidth is derived as follows:-

    -Number of Time slots: 32 TS, or Timeslots
    -Sampling rate: 8000Hz
    -Encoding: 8bits

    Bandwidth is: 32 (TS) * 8000Hz * 8bits
    Bandwith is: 2.048Mbits/s

    Two time slots cannot be used. By convention, Time Slot 16 is “reserved” for Signalling. Time slot 0 is reserved for synchronisation and frame alignment. Therefore, this means that with a E1.0 TDM (Time Division) PCM system 30 Time Slots are used to convey Voice (speech) as a digital
    information stream.

    VBR/ Wallis Dudhnath

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