AudioCodes Mediant 800 - V.150.1 Modem Relay

CHAPTER15 Media
Mediant 800 Gateway & E-SBC | User's Manual
a=T38FaxMaxBuffer:1024
a=T38FaxMaxDatagram:122
a=T38FaxRateManagement:transferredTCF
a=T38FaxUdpEC:t38UDPRedundancy
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."
● This section is applicable only to the Gateway application.
● The V.150.1 Modem Relay feature is available only if the device is installed with a
License Key that includes this feature. For installing a License Key, see License
Key.
● 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 the sales representative of your purchased device.
● 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
Coder Groups table.
● The V.150.1 SPRT Tx payload type is according to the remote side offered SDP.
➢ To configure V.150.1 Modem relay:
1. In the Coder Groups table (see Configuring Coder Groups), configure the coder to V.150.
2. On the Fax/Modem/CID Settings page, configure the V.150.1 parameters appearing under the
'V.150.1 Modem Relay Settings' group:
a. Set the 'SSE Payload Type Rx' parameter to the V.150.1 SSE payload type that the
device uses when it offers the SDP.
b. Set the 'SSE Redundancy Depth' parameter to the number of sent SSE redundant
packets. The parameter is important in case of network impairments.
c. For additional V.150.1 related parameters, see Fax and Modem Parameters.
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