Re: [sipx-users] ITSP call goes through but no audio
> I'm testing a SIP trunk to Covista Communications. I'm able
> to receive and send calls but there's two catches:
>
> 1. Placing a call from internal to my cell phone, I do not
> hear ring tones but the cell phone will ring and caller ID is
> shown properly. If I answer the cell I do not hear any audio
> in either direction however according to captures and the
> phones the call is connected.
>
> 2. Inbound calls (cell phone to internal) I hear a ring tone
> and also see correct caller ID but there's still no audio
> after answering. Again, all appears normal on captures and the phones.
>
> RTP captures are showing a difference in codecs. G.711 on
> outbound, example:
>
> 22.588943 172.16.1.200 -> 172.16.1.2 RTP PT=ITU-T G.711
> PCMU, SSRC=0x94955FF, Seq=27757, Time=688410696
>
> and G.729 inbound, example:
>
> 6.758089 172.16.1.200 -> 172.16.1.2 RTP PT=ITU-T G.729,
> SSRC=0x3CA4274A, Seq=25643, Time=1257971077
>
> Could this be the problem?
This could very well be the problem if the SIP phone you use does not
support asymmetric codecs nor does the lock-down procedure described in
Section 10.2 of RFC3264. To prove it, reconfigure your phone's
audio/rtp preferences to only use G.729. This will eliminate the
possibility of codec asymmetry - if the call now works, you have your
answer.
bob
