Modem Relay - AudioCodes Mediant 500 E-SBC User Manual

User's Manual
Notes:
•
The T.38 negotiation should be completed at call start according to V.152
procedure (as shown in the INVITE example below).
•
T.38 mid-call Re-INVITEs are supported.
•
If the remote party supports only T.38 Version 0, the device "downgrades" the
T.38 Version 3 to T.38 Version 0.
For example, the device sends or receives the following INVITE message, negotiating both
audio and image media:
INVITE sip:2001@10.8.211.250;user=phone SIP/2.0
Via: SIP/2.0/UDP 10.8.6.55;branch=z9hG4bKac1938966220
Max-Forwards: 70
From: <sip:318@10.8.6.55>;tag=1c1938956155
To: <sip:2001@10.8.211.250;user=phone>
Call-ID: 193895529241200022331@10.8.6.55
CSeq: 1 INVITE
Contact: <sip:318@10.8.6.55:5060>
Supported: em,100rel,timer,replaces,path,resource-priority,sdp-
anat
Allow:
REGISTER,OPTIONS,INVITE,ACK,CANCEL,BYE,NOTIFY,PRACK,REFER,INFO,SUB
SCRIBE,UPDATE
Remote-Party-ID:
<sip:318@10.8.211.250>;party=calling;privacy=off;screen=no;screen-
ind=0;npi=1;ton=0
Remote-Party-ID: <sip:2001@10.8.211.250>;party=called;npi=1;ton=0
User-Agent: Audiocodes-Sip-Gateway-/v.6.00A.013.007
Content-Type: application/sdp
Content-Length: 433
v=0
o=AudiocodesGW 1938931006 1938930708 IN IP4 10.8.6.55
s=Phone-Call
c=IN IP4 10.8.6.55
t=0 0
m=audio 6010 RTP/AVP 18 97
a=rtpmap:18 G729/8000
a=fmtp:18 annexb=no
a=rtpmap:97 telephone-event/8000
a=fmtp:97 0-15
a=ptime:20
a=sendrecv
m=image 6012 udptl t38
a=T38FaxVersion:3
a=T38MaxBitRate:33600
a=T38FaxMaxBuffer:1024
a=T38FaxMaxDatagram:122
a=T38FaxRateManagement:transferredTCF
a=T38FaxUdpEC:t38UDPRedundancy
14.2.4 V.150.1 Modem Relay
The device can be configured to transfer modem calls using a subset of the ITU-T V.150.1
Modem Relay protocol. The device also supports V.150.1 modem relay coder negotiation
in the initial SIP INVITE and 200 OK, using the SDP body according to the USA
Department of Defense (DoD) UCR-2008, Change 2 specification. This eliminates the need
for sending a re-INVITE to negotiate V.150.1. The device sends an INVITE's SDP offer in a
Version 6.8 169
14. Media
Mediant 500 E-SBC