User's Manual 202 Document #: LTRT-89730
Mediant 3000
Note: When the device is configured for modem bypass and T.38 fax, V.21 low-
speed modems are not supported and fail as a result.
Tip: When the remote (non-AudioCodes) gateway uses the G.711 coder for voice
and doesn’t change the coder payload type for fax or modem transmission, it is
recommended to use the Bypass mode with the following configuration:
• EnableFaxModemInbandNetworkDetection = 1.
• 'Fax/Modem Bypass Coder Type' = same coder used for voice.
• 'Fax/Modem Bypass Packing Factor'(FaxModemBypassM) = same interval as
voice.
• ModemBypassPayloadType = 8 if voice coder is A-Law or 0 if voice coder is Mu-
Law.
15.2.2.5 Fax / 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 parameters defining payload type for AudioCodes proprietary Bypass mode -- 'Fax
Bypass Payload Type' (RTP/RTCP Settings page) and ModemBypassPayloadType (ini file)
-- are not used with NSE Bypass.
When configured for NSE mode, the device includes in its SDP the following line:
a=rtpmap:100 X-NSE/8000
Where 100 is the NSE payload type.
The Cisco gateway must include the following definition:
modem passthrough nse payload-type 100 codec g711alaw
 To configure NSE mode:
1. In the SIP General Parameters page (Configuration tab > VoIP menu > SIP
Definitions > General Parameters), set the 'Fax Signaling Method' parameter to No
Fax (IsFaxUsed = 0).
2. In the Fax/Modem/CID Settings page, do the following:
a. Set the 'Fax Transport Mode' parameter to Bypass (FaxTransportMode = 2).
b. Set the 'V.21 Modem Transport Type' parameter to Enable Bypass
(V21ModemTransportType = 2).
c. Set the 'V.22 Modem Transport Type' parameter to Enable Bypass
(V22ModemTransportType = 2).
d. Set the 'V.23 Modem Transport Type' parameter to Enable Bypass
(V23ModemTransportType = 2).
e. Set the 'V.32 Modem Transport Type' parameter to Enable Bypass
(V32ModemTransportType = 2).
f. Set the 'V.34 Modem Transport Type' parameter to Enable Bypass
(V34ModemTransportType = 2).
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