bit stuffing in plesiochronous digital hierarchy

[sarahr202]

Hi everybody.

http://www.technologyuk.net/telecommunications/communication_technologies/plesiochronous_digital_hierarchy.shtml

Please consider the following extract from the above link.

The multiplexer takes one bit from each incoming date stream in turn for onward transmission (a process known as

bit interleaving The multiplexer initially assumes that each tributary data stream is  running at the maximum allowed bit rate, and looks for the next bit from  a particular data stream at the appropriate time. Every so often  (unless all incoming data streams are indeed running at exactly their  maximum allowed speed, which is highly unlikely), the multiplexer will  look for an incoming bit that has not yet arrived. If this occurs, a stuffing(or justification) bit is added to the multiplexed data stream in place of an actual data bit to maintain the outgoing bit rate.

My question is why do we want to maintain outgoing bit rate of a multiplexer with the help of " stuffing bit" ?

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Thanks and have a great weekend.

[Giuseppe Larosa · Accepted solution]

Hello Sarah,

PDH has been made obsolete by SDH many years ago ( fiffteen -  twenty years ago)

Please consider to read about SDH to avoid to waste your time.

http://mars.tekkom.dk/mediawiki/images/d/d0/Introduction-to-SDH.pdf

About your question: 

In simple words because PDH is missing a clock reference it has to provide one embedded with data so the need to keep an almost constant bit rate.

Hope to help

Giuseppe