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
|
1.
|
Open the Gateway General Settings page (Setup menu > Signaling & Media tab > Gateway folder > Gateway General Settings), and then from the 'Fax Signaling Method' drop-down list (IsFaxUsed), select No Fax. |
|
2.
|
On the Fax/Modem/CID Settings page, do the following: |
|
●
|
Configure the 'Fax Transport Mode' parameter to Bypass [FaxTransportMode = 2]. |
|
●
|
Configure the 'V.21 Modem Transport Type' parameter to Enable Bypass [V21ModemTransportType = 2]. |
|
●
|
Configure the 'V.22 Modem Transport Type' parameter to Enable Bypass [V22ModemTransportType = 2]. |
|
●
|
Configure the 'V.23 Modem Transport Type' parameter to Enable Bypass [V23ModemTransportType = 2]. |
|
●
|
Configure the 'V.32 Modem Transport Type' parameter to Enable Bypass [V32ModemTransportType = 2]. |
|
●
|
Configure the 'V.34 Modem Transport Type' parameter to Enable Bypass [V34ModemTransportType = 2]. |
|
3.
|
Configure the [BellModemTransportType] parameter to [2] (Bypass). |
|
4.
|
Configure the [NSEMode] parameter to [1] (enables NSE). |
|
5.
|
parameter the [NSEPayloadType] parameter to [100]. |