3Com VCX V7122, Руководство пользователя

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V7122 Gateway User Guide
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When fax/modem transmission ends, the reverse is carried out, and bypass coder is
switched to regular voice coder.
Supporting V.34 Faxes
V.34 fax machine support is available only in bypass mode (fax relay is not supported) when
the channel is configured in one of the configurations described below:
FaxTransportMode = 2 (Bypass)
V34ModemTransportType = 2 (Modem bypass)
In this configuration, both T.30 and V.34 faxes work in Bypass mode
Or
FaxTransportMode = 1 (Relay)
V34ModemTransportType = 2 (Modem bypass)
In this configuration, T.30 faxes use Relay mode (T.38) while V.34 fax uses Bypass mode.
In order to use V.34 fax in Relay mode (T.38), you must configure:
FaxTransportMode = 1 (Relay)
V34ModemTransportType = 0 (Transparent)
V32ModemTransportType = 0
V23ModemTransportType = 0
V22ModemTransportType = 0
This configuration forces the V.34 fax machine to work in T.30 mode.
Supporting V.152 Implementation
The gateway supports the ITU-T recommendation V.152 (Procedures for Supporting Voice-
Band Data over IP Networks). Voice-band data (VBD) is the transport of modem, facsimile,
and text telephony signals over a voice channel of a packet network with a codec appropriate
for such signals.
For V.152 capability, the gateway supports T.38 as well as VBD codecs (that is, G.711 A-law
and G.711
μ -law). The selection of capabilities is performed using the coders table.
When in VBD mode for V.152 implementation, support is negotiated between the gateway
and the remote endpoint at the establishment of the call. During this time, initial exchange of
call capabilities is exchanged in the outgoing SDP. These capabilities include whether VBD
is supported and associated RTP payload types ('gpmd' SDP attribute), supported codecs,
and packetization periods for all codec payload types ('ptime' SDP attribute). After this initial
negotiation, no Re-INVITE messages are necessary as both endpoints are synchronized in
terms of the other side's capabilities. If negotiation fails (that is, no match was achieved for
any of the transport capabilities), fallback to existing logic occurs (according to the parameter
IsFaxUsed).
Below is an example of media descriptions of an SDP indicating support for V.152.
v=0
o=- 0 0 IN IPV4 <IPAdressA>
s=-
t=0 0
p=+1