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Cisco Bug: CSCuo63703 - Delayed cut through of audio on DX650 phones with RTP Sequence Number

Last Modified

Mar 30, 2016

Products (1)

Known Affected Releases


Description (partial)

Delayed cut through of audio on DX650 phones after ringing phase, for (out-of-spec) RTP streams that exhibit hard resets of RTP sequence number and timestamp without change of SSRC (source identifier).

Cisco Ip phones DX650 running firmware sipdx650.10-0-2-32 show delayed audio cut through, if the RTP stream is manipulated such that RTP SEQ or TS values for a single SSRC are overwritten/reset by an external processor.  This is strictly according to spec.  

This defect relates to relaxing the behaviour of DX650 to be more accepting of an RTP stream which exhibits these out-of-spec SEQ/TS resets. 

Example: start of call, transmitter or translator device starts RTP SEQ=0, TS=0.  After 5 seconds of ringing, the SEQ has increased to say, 5000.  Call is answered, and transmitter or RTP translator device restarts SEQ=0,TS=0, without changing the SSRC.  DX phone now goes silent (sees this as a bunch of delayed, duplicate packets arriving), until SEQ of stream gets to 5001, hence, silence for 5s at start of call, after pickup.
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