[SIPForum-discussion] Reg: SDP offer

[Abhishek Kumar]

Hi Prem,
According to RFC 4583 for SDP.
in m line port value can be 0 but , it a specific meaning.

Fields in the 'm' Line

   This section describes how to generate an 'm' line for a BFCP stream.

   According to the SDP specification [11], the 'm' line format is the
   following:

      m=<media> <port> <transport> <fmt> ...

   The media field MUST have a value of "application".

   The port field is set following the rules in [7].  Depending on the
   value of the 'setup' attribute (discussed in Section 7), the port
   field contains the port to which the remote endpoint will initiate
   its TCP connection or is irrelevant (i.e., the endpoint will initiate
   the connection towards the remote endpoint) and should be set to a
   value of 9, which is the discard port.  Since BFCP only runs on top
   of TCP, the port is always a TCP port.  A port field value of zero
   has the standard SDP meaning (i.e., rejection of the media stream).

regards,
-Abhishek


On Wed, Apr 8, 2009 at 4:34 PM, prem ranjan <prem.behera at gmail.com> wrote:

> 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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