Modem Relay - AudioCodes Mediant 3000 User Manual

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
15.2.4 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
format to negotiate V.150 modem relay using the same port as RTP, as shown in the
example below:
a=cdsc:1 audio udpsprt 114\r\n
a=cpar:a=sprtmap:114 v150mr/8000\r\n
a=cpar:a=fmtp:114
mr=1;mg=0;CDSCselect=1;mrmods=1,3;jmdelay=no;versn=1.1\r\n\
You can configure the payload type for the outgoing SDP offer, using the
NoAudioPayloadType parameter. You can set the parameter to "NoAudio", whereby RTP is
not sent and the device adds an audio media only for the Modem Relay purpose. This is
also in accordance to DOD UCR 2008 specification: "The AS-SIP signaling appliance
MUST advertise the "NoAudio" payload type to interoperate with a "Modem Relay-
Preferred" endpoint that immediately transitions to the Modem Relay state without first
transmitting voice information in the Audio state."
Notes:
•
The V.150.1 Modem Relay feature is available only if the device is installed with a
Software License Key that includes this feature. For installing a Software License
Key, see ''Software License Key'' on page 697.
•
V.150.1 modem relay feature support is a subset of the full V.150.1 protocol and is
designed according to the US DoD requirement document. It therefore, cannot be
used for general purposes.
•
V.150.1 modem relay is applicable only to the Gateway application.
•
The V.150.1 feature has been tested with certain IP phones. For more details,
please contact your AudioCodes sales representative.
•
The V.150.1 SSE Tx payload type is according to the offered SDP of the remote
side.
•
The V.150.1 SPRT Rx payload type is according to the 'Payload Type' field in the
Coders table.
•
The V.150.1 SPRT Tx payload type is according to the remote side offered SDP.
User's Manual 208
Mediant 3000
Document #: LTRT-89730