Supplementary Services Features for FXS Ports on Cisco IOS Voice Gateways Configuration Guide, Cisco IOS Release 15M&T

RFC 2833 DTMF Digit Relay Support on SCCP Controlled Endpoints

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. This feature is not supported in Cisco Unified CME or Cisco Unified SRST.

The RFC 2833 DTMF Digit Relay feature is enabled by default on the Cisco IOS gateway and on the Cisco Unified Communications Manager, where it can be disabled. No configuration is required on the SCCP analog gateway or on Cisco Unified Communications Manager to enable this feature.

SCCP Gateway Controlled Fax Relay

Before Cisco IOS Release 12.4(6)XE, SCCP gateways supported fax passthrough only. In Cisco IOS Release 12.4(6)XE and later releases, 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 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 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.

For configuration information, see the “Configuring SCCP Gateway Fax Relay Features” section.

SCCP Gateway Controlled Modem Relay

There are two ways to transport modem traffic over VoIP networks: modem pass-through and modem relay.

Modem pass-through transports modem signals through a packet network using PCM encoded packets; traffic is susceptible to packet loss, jitter, and latency in the IP network.

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.

Before Cisco IOS Release 12.4(6)XE, only modem pass-through only and Cisco Unified Communications Manager-controlled modem relay were supported for SCCP gateways. In Cisco IOS Release 12.4(6)XE and later releases, the SCCP Gateway Controlled Modem Relay feature adds support for SCCP gateway-controlled modem relay.

Cisco uses a proprietary protocol, NSE, to signal events that are exchanged between gateways, using Real-time Transport Protocol (RTP) packets. SCCP gateway-controlled modem-relay bypasses NSE parameter negotiation between gateways and uses the NSE mechanism to indicate the gateway control mode to the other gateway. NSE signaling capability must be configured on both the originating and terminating gateways to enable modem-relay calls for SCCP analog endpoints.

For configuration information, see the “Configuring SCCP Gateway Controlled Modem Relay” section.

Note In addition to a proprietary, NSE-based modem-relay implementation, Cisco offers V.150.1 modem-relay implementation. The VMWI for SCCP FXS Ports in Cisco IOS feature supports only NSE modem relay. For information about feature mode, see the “Configuring Feature Mode” section.

Configuring SCCP Gateway Fax Relay Features

To configure SCCP gateway fax relay features, perform the following steps.

SUMMARY STEPS

1. enable

2. configure terminal

3. voice service voip

4. fax protocol t38 nse force

5. fax protocol cisco

6. fax-relay sg3-to-g3

7. end

DETAILED STEPS

Examples

The following output from the show voice dsp command displays fax codec settings:

The following output from the show voice call summary command display fax codec settings:

Troubleshooting Tips

The following commands can help troubleshoot SCCP fax relay features:

• debug voip application stcapp all
• debug voip vtsp all

Configuring SCCP Gateway Controlled Modem Relay

This task configures SCCP gateway controlled modem relay.

Prerequisites

SCCP gateway controlled modem relay must be configured on both the originating and terminating gateways.

SUMMARY STEPS

1. enable

2. configure terminal

3. voice service voip

4. modem relay nse codec [g711u | g711a] gw-controlled

5. end

DETAILED STEPS

Verifying and Troubleshooting DTMF Relay, Fax Relay, and Modem Relay for SCCP FXS Ports in Cisco IOS Feature Configuration

To verify the configuration of VMWI for SCCP FXS Ports in Cisco IOS features, use the show-running config command. A sample output is located in the “Configuration Examples for DTMF Relay, Fax Relay, and Modem Relay for SCCP FXS Ports in Cisco IOS” section.

Use the following commands to verify and troubleshoot the configuration of the dial tone generation after remote onhook feature:

• show dial-peer voice number—Displays whether the dial tone after remote onhook feature is enabled.
• show stcapp device voice-port port—Displays whether the dial tone after remote onhook feature is enabled.
• debug voip application stcapp all—Displays detailed debugging for SCCP and STC application ports.
• debug voip application stcapp port port-number—Displays detailed debugging for the specified SCCP and STC application port.

Use the following commands to verify and troubleshoot the configuration of the ground start FXS ports feature:

• show stcapp device summary—Displays a summary of endpoints associated with the STC application, their states, types and call control device.
• show voice port slot/subunit/port—Displays whether ground-start signaling is enabled and displays port states.
• debug vpm signal—Displays supervisory disconnect event messages.

Use the following commands to verify and troubleshoot the RFC 2833 DTMF digit relay feature.

• debug voip application stcapp port port-number—Displays RFC 2833 send and receive payload messages.
• debug voip hpi—Displays digital signal processor (DSP) programming.
• debug voip rtp session named-event—Verifies the gateway sending inband DTMF signaling.

Use the following commands to verify and troubleshoot SCCP gateway controlled modem relay:

• show voice call summary—Displays modem relay voice port settings.
• show voice dsp—Displays modem relay DSP channel status.
• debug voip application stcapp all—Displays STC application modem relay information.
• debug voip dsm all—Displays modem relay DSP stream manager (DSM) messages.
• debug voip dsmp all—Displays modem relay distributed stream media processor (DSMP) messages.
• debug voip hpi all—Displays gateway DSP modem relay termination codes and messages indicating probable causes for disconnection.

Use the following commands to verify and troubleshoot SCCP gateway controlled fax relay:

• show voice call summary—Displays fax relay voice port settings.
• show voice dsp—Displays fax relay DSP channel status.
• debug voip application stcapp all— Displays STC application fax relay information.
• debug voip dsm all—Displays fax relay DSM messages.
• debug voip dsmp all—Displays fax relay DSMP messages.
• debug voip hpi all—Displays gateway DSP fax relay information on RTP packet events.
• debug voip vtsp all—Displays gateway voice telephony service provider (VTSP) debugging information for fax calls.

Note For more information on these commands, see the Cisco IOS Voice Command Reference, Cisco IOS Debug Command Reference, Release 12.4T, and Cisco IOS Configuration Fundamentals Command Reference, Release 12.4.

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