[SIPForum-discussion] Reg: SDP offer

[Tomasz Zieleniewski]

Hi,

Yes this RFC compliant.
Usage of zero port has the following reason.
Generally any new media streams are created by new additional
media descriptions in the SDP.
New stream are added below the existing ones.
But in the case when one side want's to utilize and allready
existing stream it sets its port to zero.
Then any new media descriptions which replace the previous ones
must appear below any existing media sections.

Kind regards
Tomasz Zieleniewski

2009/4/8 prem ranjan <prem.behera at gmail.com>:
> Hi,
> I have the following scenario:
> A calls B
> A sends INVITE with the following SDP:
>
> v=0
> o=780 409699 409699 IN IP4 192.168.0.20
> s=-
> c=IN IP4 151.98.90.197
> t=0 0
> m=audio 41270 RTP/AVP 8 18 4 96
> a=rtpmap:96 telephone-event/8000
> a=ptime:20
> a=SilenceSupp:off
> a=fmtp:96 0-15
> a=nortpproxy:yes
>
>
> B answers the following SDP in 180 Ringing:
>
> v=0
> o=- 38000001 1239174750 IN IP4 151.98.90.196
> s=SDP Data
> c=IN IP4 151.98.90.196
> t=0 0
> m=audio 18990 RTP/AVP 8 96
> a=rtpmap:96 TELEPHONE-EVENT/8000
> a=ptime:20
> a=sqn:0
> a=cdsc:1 image udptl t38
> a=cpar: a=T38FaxVersion:0
> a=cpar: a=T38MaxBitRate:14400
> a=cpar: a=T38FaxRateManagement:transferredTCF
> a=cpar: a=T38FaxMaxBuffer:280
> a=cpar: a=T38FaxMaxDatagram:260
> a=cpar: a=T38FaxUdpEC:t38UDPRedundancy
>
> After this Call is successful.
> Now B wants to send a FAX. For this it creates a Re-Invite with the
> following SDP:
>
> v=0
> o=- 38000001 1239174761 IN IP4 151.98.90.196
> s=SDP Data
> c=IN IP4 151.98.90.196
> t=0 0
> m=audio 0 RTP/AVP 8
> a=ptime:10
> m=image 33815 udptl t38
> a=T38FaxVersion:0
> a=T38MaxBitRate:14400
> a=T38FaxRateManagement:transferredTCF
> a=T38FaxMaxBuffer:1800
> a=T38FaxMaxDatagram:260
> a=T38FaxUdpEC:t38UDPRedundancy
>
> Now my question is, can we have the value "Zero" in the audio port. Is this
> RFC compliant???
>
> Kind Regards,
> Prem Ranjan Behra
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