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  • SIP Codec List

    Have an issue with Codecs being sent in SDP on a SIP trunk. Site codec for inter and intra both contain only G729 and G711. However, in SIP calls the SDP invite we see a whole lot more-- BV32/16000, BV16/8000, G729, PCMU/8000, PCMA/8000. Opened a ticket with TAC and the tech tried telling me that "Not necessarily, it might send any codecs for negotiation." . I asked what is the point of having a codec list if it just sends "any" codec for negotiation? He responds with "To set the priority if multiple codecs are there.",, this again makes no sense as it is not even doing this. I have pulled pcaps of other systems and what is in the list is what is being sent out. This tech even went to confirm what he said with his team lead and said they agreed.
    Am I missing something here??

  • #2
    The codec list is just what you want to only negotiate at. If a call is sent with G729 or G711u and on the PBX you have only configured to allow G711u, it should negotiate the call at that codec. If you only have those 2 and some reason the call was sent with a codec not on the list, the call should drop as the 2 sites couldn't negotiate a compatible codec to complete the call. This is why in the last you put your priority codecs at the top and leave the rest at the bottom of the list in the event an usual codec request gets sent/negotiated.

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    • #3
      You mean outgoing calls?
      Where are you taking the trace, on the SIParator/SBC? I'm just wondering if Mitel is sending those on an outbound call, or the SBC is adding them.
      I believe I have only seen Mitel send what is in the Codec lists, so I also find that a bit strange.
      Nonetheless, the codecs that you need are in there as well, so it shouldn't be a problem.

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      • #4
        The Codec List used on SIP trunks is the Codec List on that site's Inter-site Codec setting. If you are using an Ingate with SIP trunks you can allow only certain Codecs to be sent and received in SDP

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