How POS is sent via STM lines?

Discussion in 'Cisco' started by Yehavi Bourvine, Mar 28, 2006.

  1. Hello,

    I have a question about packing IP packets inside STM-1 transmision lines
    using POS:

    The POS standard says (roughly) to take the IP packet, encapsulate it into
    PPP and then put this into the VC4 payload. The VC4 payload is 2,340 bytes, so
    what is done when there are small packets to send? Are they simply
    concatanated one after the other in one payload?
    if there is nothing to send (or not enough packets to fill the payload) how
    is it padded? with HDLC flags?

    Thanks! __Yehavi:
    Yehavi Bourvine, Mar 28, 2006
    #1
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  2. Yehavi Bourvine

    Guest

    Yehavi Bourvine 58-4279 wrote:
    > I have a question about packing IP packets inside STM-1 transmision lines
    > using POS:
    >
    > The POS standard says (roughly) to take the IP packet, encapsulate it into
    > PPP and then put this into the VC4 payload. The VC4 payload is 2,340 bytes, so
    > what is done when there are small packets to send? Are they simply
    > concatanated one after the other in one payload?
    > if there is nothing to send (or not enough packets to fill the payload) how
    > is it padded? with HDLC flags?


    To map PPP into SDH you need octet-stuffed HDLC encapsulation
    (HDLC flag, address/control and FCS). The HDLC frames are send back
    to back and inter-frame gap is filled with HDLC flags. The result is
    then
    scrambled before inserting into the VC-n payload.

    Check ITU-T G.707 or RFC 2615.

    Regards,
    Bert
    , Apr 1, 2006
    #2
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