Hi,
I just ran some tests with various brands of phones and none send ptime in
their SDP, which makes this harder to understand. Here is one from a polycom.
Are you saying that even though 3 media formats are listed, they are
represented as one media stream? Is there an example of one that includes
multiple media streams you can point me to. I guess I am now thoroughly
confused. When my SIP gateway sends g729a10 and g729a20 to a snom, the call
fails because only ptime 10 is listed and the phone is only configured to
receive g729a20. But, as I mentioned, my SIP GW wants to talk 10 or 20.
However, if I make a call to the SIP GW, it connects at 729a20. Does this make
any sense at all?
Session Description Protocol
Session Description Protocol Version (v): 0
Owner/Creator, Session Id (o): - 1172011391 1172011391 IN IP4
10.153.90.9
Owner Username: -
Session ID: 1172011391
Session Version: 1172011391
Owner Network Type: IN
Owner Address Type: IP4
Owner Address: 10.153.90.9
Session Name (s): Polycom IP Phone
Connection Information (c): IN IP4 10.153.90.9
Time Description, active time (t): 0 0
Session Start Time: 0
Session Stop Time: 0
Session Attribute (a): sendrecv
Media Description, name and address (m): audio 2224 RTP/AVP 0 8 18
Media Type: audio
Media Port: 2224
Media Proto: RTP/AVP
Media Format: ITU-T G.711 PCMU
Media Format: ITU-T G.711 PCMA
Media Format: ITU-T G.729
Media Attribute (a): rtpmap:0 PCMU/8000
Media Attribute Fieldname: rtpmap
Media Format: 0
MIME Type: PCMU
Media Attribute (a): rtpmap:8 PCMA/8000
Media Attribute Fieldname: rtpmap
Media Format: 8
MIME Type: PCMA
Media Attribute (a): rtpmap:18 G729/8000
Media Attribute Fieldname: rtpmap
Media Format: 18
MIME Type: G729
>
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of
> [EMAIL PROTECTED]
> Sent: Wednesday, February 21, 2007 2:09 PM
> To: [email protected]
> Subject: Re: [Sip-implementors] SDP and ptime in RFC4566 is faulty
>
> From: "Vick, Steven"
>
> There in lies the problem. The Aspect endpoint is sending two media
> streams.
>
> There are two media streams being offered, but the Ptime is only
> represented for the first one on the list. This happens regardless of
> how many media streams (or whether they're the same codec type) are
> in
> the SDP. This is why I see the ptime in the rfc as needing some
> enhancements.
>
> No, it's only offering one media stream, because there is only one "m"
> line in the SDP:
>
> Session Description Protocol
> Session Description Protocol Version (v): 0
> Owner/Creator, Session Id (o): - 1171987362 1171987362 IN
> IP4 10.153.96.5
> Session Name (s): Aspect Communications SDP Session
> Connection Information (c): IN IP4 10.153.96.5
> Time Description, active time (t): 0 0
> Media Description, name and address (m): audio 10034 RTP/AVP
> 18 18 101
> Media Title (i): telephone-event 8000
> Connection Information (c): IN IP4 10.153.96.5
> Media Attribute (a): sendrecv
> Media Attribute (a): ptime:10
> Media Attribute (a): rtpmap:18 G729/8000
> Media Attribute (a): fmtp:18 annexb=no
> Media Attribute (a): rtpmap:18 G729/8000
> Media Attribute (a): fmtp:18 annexb=no
> Media Attribute (a): rtpmap:101 telephone-event/8000
>
> All the "a" lines offer altnerative encodings to be used within the one
> media stream. As you note, SDP has the limitation that only one ptime
> attribute can be given for a single media stream. If you want to be
> able to use more than one ptime, you have to offer one media stream for
> each ptime.
>
> Dale
>
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