AudioCodes MediaPack 114 Bedienungsanleitung PDF herunterladen (Seite 319)

Version 5.6 319 November 2008

SIP User's Manual 7. IP Telephony Capabilities

7.3 Fax and Modem Capabilities

7.3.1 Fax/Modem Operating Modes

The device supports two modes of operations:

 Fax / modem negotiation that isn’t performed during the establishment of the call.

 VBD mode for V.152 implementation (refer to ''Supporting V.152 Implementation'' on

page 325): fa

x / 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).

7.3.2 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 (refer to ''Fax Relay Mode'' on page 319)

 Fax and mod

em bypass: a proprietary method that uses a high bit rate coder (refer to

''Fax/Modem Bypass Mode'' on page 320)

 NSE Cisco’

s Pass-through bypass mode for fax and modem (refer to ''Fax / Modem

NSE Mode'' on page 322)

 Tran

sparent: passing the fax / modem signal in the current voice coder (refer to ''Fax /

Modem Transparent Mode'' on page 322)

 Tran

sparent with events: passing the fax / modem signal in the current voice coder

with adaptations (refer to ''Fax / Modem Transparent with Events Mode'' on page 323)

 G.711 Tran

sport: switching to G.711 when fax/modem is detected (refer to ''G.711 Fax

/ Modem Transport Mode'' on page 323)

 Fax fallback to G.711 if T.38 is not su

pported (refer to ''Fax Fallback'' on page 324)

‘Adaptation

s’ refer to automatic reconfiguration of certain DSP features for handling

fax/modem streams differently than voice.

7.3.2.1 T.38 Fax Relay Mode

In Fax Relay mode, fax signals are transferred using the T.38 protocol. T.38 is an ITU

standard for sending fax across IP networks in real-time mode. The device currently

supports only the T.38 UDP syntax.

T.38 can be configured in the following ways:

 Switching to T.38 mode using SIP Re-INVITE messages (refer to ''Switching to T.38

Mode using SIP Re-INVITE'' on page 320)

 Automatically

switching to T.38 mode without using SIP Re-INVITE messages (refer to

''Automatically Switching to T.38 Mode without SIP Re-INVITE'' on page 320)

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