Version 6.2
443
February 2011
SIP User's Manual
8. IP Telephony Capabilities
8.3.7
Fax and Modem Capabilities
This section describes the device's fax and modem capabilities, and includes the following
main subsections:
Fax and modem operating modes (see ''Fax/Modem Operating Modes'' on page
)
Fax and modem transport modes (see ''Fax/Modem Transport Modes'' on page
)
V.34 fax support (see V.34 Fax Support on page
V.152 support (see ''V.152 Support'' on page
8.3.7.1 Fax/Modem Operating Modes
The device supports two modes of operation:
Fax/modem negotiation that is not performed during the establishment of the call.
Voice-band data (VBD) mode for V.152 implementation (see ''V.152 Support'' on page
): fax/modem capabilities are negotiated between the device and the remote
endpoint at the establishment of the call. During a call, when a fax/modem signal is
detected, transition from voice to VBD (or T.38) is automatically performed and no
additional SIP signaling is required. If negotiation fails (i.e., no match is achieved for
any of the transport capabilities), fallback to existing logic occurs (according to the
parameter IsFaxUsed).
8.3.7.2 Fax/Modem Transport Modes
The device supports the following transport modes for fax per modem type
(V.22/V.23/Bell/V.32/V.34):
T.38 fax relay (see ''T.38 Fax Relay Mode'' on page
G.711 Transport: switching to G.711 when fax/modem is detected (see ''G.711 Fax /
Modem Transport Mode'' on page
)
Fax fallback to G.711 if T.38 is not supported (see ''Fax Fallback'' on page
Fax and modem bypass: a proprietary method that uses a high bit rate coder (see
''Fax/Modem Bypass Mode'' on page
NSE Cisco’s Pass-through bypass mode for fax and modem (see ''Fax / Modem NSE
Mode'' on page
Transparent with events: passing the fax / modem signal in the current voice coder
with adaptations (see ''Fax / Modem Transparent with Events Mode'' on page
Transparent: passing the fax / modem signal in the current voice coder (see ''Fax /
Modem Transparent Mode'' on page
RFC 2833 ANS Report upon Fax/Modem Detection (see ''RFC 2833 ANS Report
upon Fax/Modem Detection'' on page
)
‘Adaptations’ refer to automatic reconfiguration of certain DSP features for handling
fax/modem streams differently than voice.
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