Cisco AS5350XM

Voice Enhancement Features for Cisco IOS Release 12.4(24)T
Information About Voice Enhancement Features for Cisco IOS Release 12.4(24)T
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Cisco AS5350XM and Cisco AS5400XM Universal Gateways Software Configuration Guide
Figure 1 Modem Pass-through Call Flow through a Protocol
The following steps describe the progress of a call based on the initial recognition of a 2100-Hz tone
(±
15 Hz) (as shown in Figure 1):
1. Switch the active codec in use on the call to G.711 (if a codec other than G.711 was previously in
use).
2. Disable the high pass filter.
3. Disable voice activity detection (VAD) and comfort noise generation (CNG).
4. Switch from any adaptive or dynamic jitter buffer in use to a fixed-length jitter buffer. (A depth of
200
ms is recommended when switching to a fixed-length jitter buffer.)
To enable the modem pass-through feature, use the modem passthrough command in voice service
configuration mode:
modem passthrough {nse | protocol codec {g711alaw | g711ulaw [redundancy]}}
• Select the nse keyword to use NSEs
• Select the protocol keyword to use SIP/H.323 protocol to signal modem pass-through
• Select the codec g711alaw keyword to indicate G.711 a-law (64,000 bps) for E1
• Select the codec g711ulaw keyword to indicate G.711 mu-law (64,000 bps) for T1
• Select the codec g711 ulaw redundancy keywords to use packet redundancy for modem traffic (in
compliance with RFC 2198)
Ingress
Gateway
Egress
Gateway
Modem
PBX
Access Server/
Modems
PBX
IP Cloud
Modem call
Starts out as a voice call
2100 Hz modem tone detected
Upspeed codec to G.711
Disable VAD;
Config playout buffer
Modem
tone
Upspeed codec to G.711
Disable VAD;
Config playout buffer
Send a SIP re-invite
If the negotiation succeeds
NTE for phase
reversal
Modem training
Modem pass-through call established
Phase Reversal Detected
Disable ECAN
Disable ECAN
Modem tone
with phase
reversal
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