Cisco Cisco IOS Software Release 12.4(2)XB6

© 2006 Cisco Systems, Inc. All rights reserved.

The RFC 2833 DTMF Digit Relay feature on the SCCP analog gateway sends RFC 2833 digits through 
Real-time Transport Protocol (RTP) packets and out-of-band (OOB) digits to Cisco Unified 
Communications Manager.

SCCP Gateway Controlled Fax Relay adds support for the following fax relay features for SCCP analog 
endpoints: 

T.38 named signaling events (NSE) forced fax relay—Provides an ITU-T standards-based method 
for fax relay. Data is packetized and encapsulated according to the T.38 standard fax protocol. The 
SCCP gateway uses NSEs to indicate T.38 fax relay switchover. Configuring the gateway to 
unconditionally use T.38 NSE forced fax relay enables interoperation with a Cisco IOS voice 
gateway that does not support interworking and negotiation of T.38 fax relay and NSE attributes at 
the time of call setup. 

Cisco fax relay—Proprietary fax relay implementation that uses RTP to transport fax data. Fax relay 
is the default mode for passing faxes through a VoIP network, and Cisco fax relay is the default fax 
relay type on Cisco IOS voice gateways. 

Super Group 3 (SG3) to G3 fax relay—Allows the fax stream between two SG3 fax machines to 
negotiate down to G3 speeds (less than 14.4 kbps) allowing SG3 fax machine interoperation over 
T.38 fax relay with G3 fax machines. 

With Modem Relay, the modem signals are demodulated at one gateway, converted into digital form, and 
carried in Simple Packet Relay Transport (SPRT) packets to the other gateway. There the modem signal 
is re-created and remodulated, then passed to the receiving modem. Modem relay lessens bandwidth 
requirements and significantly reduces the effect that dropped packets, jitter, and latency have on the 
modem session. 

Configuration information is included in the 

 module in the

at the following URL: