Hi,
I am trying to establish a fax session between two gateways using Sofia sip
calls. I have already established the audio call using Sofia SIP INVITE.
Following that, I am trying to establish fax call, with another INVITE message.
Following is the code I am using to send INVITE message for fax. Note that
before this INVITE a audio call is already established between two gateways.
g_chLocalSdpMedia[0] = '\0';
sprintf(g_chLocalSdpMedia,"m=image %d udptl t38\r\n",g_LocalRtpPort);
strcat(g_chLocalSdpMedia, "a=T38MaxBitrate:14400\r\n");
strcat(g_chLocalSdpMedia,"a=T38FaxRateManagement:transferredTCF\r\n");
nua_invite(op_active->handle,
/* other tags as needed ... */
SOATAG_USER_SDP_STR(g_chLocalSdpMedia),
SOATAG_RTP_SORT(SOA_RTP_SORT_LOCAL),
SOATAG_RTP_SELECT(SOA_RTP_SELECT_SINGLE),
TAG_END());
With this I am expecting to see:-
" m= image 9000 udptl t38
a= T38MaxBitrate:14400
a=T38FaxRateManagement:transferredTCF"
But when I see in the network capture file, I am seeing this request
incorporates a request for media audio with port 0 like
"m= audio 0 RTP/AVP 19
m= image 9000 udptl t38
a= T38MaxBitrate:14400
a=T38FaxRateManagement:transferredTCF"
Why Sofia sip stack is adding the "m=audio 0 RTP/AVP 19" preceding the actual
t38 media message. I have captured another log where two D-link gateways
communicate for T.38 Fax, and there I do not see such a request preceding T38
INVITE message. I am suspecting it is causing interfacing problems for my
gateway to establish fax sessiob with D-link gateway.
Could anybody please tell me how should I avoid this audio media line being
prepended to the fax image media line request in INVITE SDP message.
With Best Regards,
Kaustubh Patwardhan
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