[SIPForum-discussion] Reg: SDP offer

[jayesh.kadam at wipro.com]

Prem,

 

The SDP is fine.  It provides m=image line indicating support of T.38
for transmitting fax.  Zero in audio line indicates non-support of audio
codec for transmitting SDP.  Ideally, if B wanted to use T.38 for fax,
the Re-invite should only have 'image' media line, but having m=audio
line with zero port is not an issue and is RFC compliant.

 

Regards,

Jayesh

________________________________

From: discussion-bounces at sipforum.org
[mailto:discussion-bounces at sipforum.org] On Behalf Of prem ranjan
Sent: Wednesday, April 08, 2009 4:35 PM
To: discussion at sipforum.org
Subject: [SIPForum-discussion] Reg: SDP offer

 

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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