Artem Naluzhny wrote:
> On 4/14/06, Paul Kyzivat <[EMAIL PROTECTED]> wrote:
>
>
>>[your call flow was mangled almost to the point of complete
>>incomprehensibilty by the time it reached my mail reader (Thunderbird).
>>I *think* I figured it out.]
>
>
> Gmail ;) OK, once again:
>
> Caller side SIP server Callee side
> | | |
> @-> INVITE ------------------>| |
> | m=audio 16428 RTP/AVP 4 0 2 8 100 101 |
> | | |
> | @-> INVITE ------------------>|
> | | m=audio 16428 RTP/AVP 4 0 2 8 100 101
> | | |
> | |<- 200 OK -------------------@
> | | m=audio 16460 RTP/AVP 4 100 101
> | | |
> |<- 200 OK -------------------@ |
> | m=audio 16460 RTP/AVP 4 100 101 |
> | | |
> | | |
> @-> re-INVITE --------------->| |
> | c=IN IP4 0.0.0.0 | |
Much better! (I did figure it out right.)
>>You need to say more about the players here. Is the SIP server an agent
>>for the callee? Is it a B2BUA? Or a "proxy"?
>
>
> b2bua
>
>
>
>>If it is a B2BUA, you have options, though they may start to get
>>complicated. It can answer the invite from the caller itself. Then it
>>can reinvite the callee, offering at least one of the codecs that had
>>been previously agreed and offering one that it does support as well,
>>listing the supported one first as preferred. If the one it supports is
>>accepted all is well. If not, it won't be able to do MOH, and may want
>>to reinvite again specifying a=inactive, or c=0.
>
>
> I know but the original callee replied in '200 OK' on the original
> INVITE with only best codec not with all supported codecs. My SIP
> server can not keep my own MOH in all possible codecs. Actually the
> only solution I have at the moment is to send MOH in one of G711
> codecs in the case (if we belive that all user agents support G711).
>
> Any options to learn the supported codec list?
At least some of your options are:
- When you reinvite to do MoH, just offer those codecs in which you are
capable of doing MoH, plus at least one of the codecs from the earlier
answer. With luck one of your supported codecs will be chosen. If your
codecs are refused and only the prior codecs are accepted, then you just
can't do MoH.
- as venkatesh proposed, send a reinvite with no offer. Let the callee
specify whatever codecs it wants. It SHOULD return all that it supports,
not just those that were already in use. If so, and if one of them is
one you can do MoH with then you are set. If you can't do MoH with any
of those offered then you are out of luck.
In either case you need to be prepared for the case when you just can't
do MoH.
Paul
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