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No way audio (silence) issue is noticed on transcoded SIP-SIP calls on CUBE when supplementary services like Hold/Resume or Call Transfer is invoked. Issue is observed with both SCCP based transcoding and LTI (Local Transcoding Interface) based transcoding. When using SCCP Based Transcoding, "show sccp connection" output looks as below during no-way audio issue (Mode - Inactive, rport - Empty, ripaddr - Empty, conn_id_tx - Empty) CUBE-2#show sccp connections sess_id conn_id stype mode codec sport rport ripaddr conn_id_tx 65545 36 xcode inactive g729 16414 0 :: 65545 40 xcode inactive g711a 16412 0 :: When using LTI based transcoding, "show dspfarm dsp active" shows no entry of the call during no-way audio CUBE-2#show dspfarm dsp active SLOT DSP VERSION STATUS CHNL USE TYPE RSC_ID BRIDGE_ID PKTS_TXED PKTS_RXED Total number of DSPFARM DSP channel(s) 0
IOS Release 15.3(3)M Issue happens only under following condition. 1. When "midcall-signaling passthru media-change" is configured on CUBE 2. There is change in codec in one of the call leg after invoking supplementary services like Hold/Resume or Transfer
1. Disable "midcall-signaling passthru media-change" Voice service voip Sip no midcall-signaling passthru media-change 2. Use same codec through-out the call (Avoid change in codec behavior by controlling supported codec list)
Considering following call flow, where ITSP -> SIP (G711alaw and G711ulaw) -> CUBE -> SIP (G729) -> CUCM -> IP Phone 1. Call was made from PSTN to IP Phone-1 2. CUBE allocates local transcoder due to codec mismatch Media Path : ITSP -> G711alaw -> CUBE -> Transcoder -> G729r8 -> IP Phone 3. IP Phone Places call on hold and call gets connected with MoH Server Media Path : ITSP -> G711alaw -> CUBE -> Transcoder -> G729r8 -> MoH Server 4. When IP Phone retrieves the call, a. CUCM Sends "Re-Invite" without SDP (Delayed offer Re-invite) to CUBE b. CUBE Respond back with "SIP 200 OK" with SDP and completes the media negotiation (No change in codec) c. CUBE then sends "Re-Invite" to ITSP for media negotiation with all supported codecs(Both G711alaw and G711ulaw) d. ITSP Respond to "Re-Invite" with "SIP 200 OK" SDP where "G711ulaw codec" gets negotiated, whereas previously negotiated codec was "G711alaw" e. At this point CUBE closes existing transcoder channel and fails to reopen DSP channel causing no-way audio issue.
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