Wednesday, 13 March 2013


   Let us study about standard  2 Mbps frame format G.704  / G.732.

   Each 2 Mbps frame contains 256 bits ( 32 timeslots) at a repetition rate of 8 kb/s. The first timeslot i.e.TS 0 is reserved for framing, error-checking and alarm signals. Remaining 31 channels can be used for data traffic. Individual timeslots / channels can be used for 64 kbps PCM. Sometimes TS16 is reserved for signalling.  For example - ISDN primary rate D channel signalling (Q.931).

     The start of 32 timeslot frame is signified by the frame alignment word 0011011 in TS0 of alternate frames. In the other frame, bit 2 is set to one and bit 3 contains the A-bit for sending alarm to the far end. If three frame alignment words in four are received in error, then the receiving terminal declares loss of frame alignment and initiates a resync process.

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