Fax and Modem NSE Mode

In this mode, fax and modem signals are transferred using Cisco-compatible Pass-through bypass mode. Upon detection of fax or modem answering tone signal, the terminating device sends three to six special NSE RTP packets (configured by the [NSEpayloadType] parameter; usually to 100). These packets signal the remote device to switch to G.711 coder, according to the 'Fax/Modem Bypass Packing Factor' parameter. After a few NSE packets are exchanged between the devices, both devices start using G.711 packets with standard payload type (8 for G.711 A-Law and 0 for G.711 Mu-Law). In this mode, no re-INVITE messages are sent. The voice channel is optimized for fax/modem transmission (same as for usual bypass mode).

The following parameters that configure the payload type for the AudioCodes proprietary Bypass mode are not used with NSE Bypass: 'Fax Bypass Payload Type' and [ModemBypassPayloadType].

When configured for NSE mode, the device includes the following line in the SDP, where 100 is the NSE payload type:

a=rtpmap:100 X-NSE/8000

The Cisco gateway must include the following definition:

modem passthrough nse payload-type 100 codec g711alaw

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To configure NSE mode:

On the Fax/Modem/CID Settings page, do the following:

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Configure the 'Fax Transport Mode' parameter to Bypass [FaxTransportMode = 2].

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Configure the 'V.21 Modem Transport Type' parameter to Enable Bypass [V21ModemTransportType = 2].

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Configure the 'V.22 Modem Transport Type' parameter to Enable Bypass [V22ModemTransportType = 2].

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Configure the 'V.23 Modem Transport Type' parameter to Enable Bypass [V23ModemTransportType = 2].

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Configure the 'V.32 Modem Transport Type' parameter to Enable Bypass [V32ModemTransportType = 2].

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Configure the 'V.34 Modem Transport Type' parameter to Enable Bypass [V34ModemTransportType = 2].

Configure the [BellModemTransportType] parameter to [2] (Bypass).

Configure the [NSEMode] parameter to [1] (enables NSE).

parameter the [NSEPayloadType] parameter to [100].