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iLBC Support for SIP and H.323

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iLBC Support for SIP and H.323

Table Of Contents

iLBC Support for SIP and H.323

Prerequisites

Restrictions

Information About iLBC Support for SIP and H.323

How to Configure an iLBC Codec


iLBC Support for SIP and H.323

The internet Low Bitrate Codec (iLBC) is a standard, high-complexity speech codec suitable for robust voice communication over IP. The iLBC has built-in error correction functionality that helps the codec perform in networks with high-packet loss. This codec is supported on both Session Initiation Protocol (SIP) and H.323.

Prerequisites

Cisco Unified Border Element

Cisco IOS Release 12.2(11)T or a later release must be installed and running on your Cisco Unified Border Element.

Cisco Unified Border Element (Enterprise)

Cisco IOS XE Release 2.5 or a later release must be installed and running on your Cisco ASR 1000 Series Router.

Restrictions

The iLBC Support for SIP and H.323 feature is supported on the following:

IP-to-IP gateways with no transcoding and conferencing

All c5510 DSP-based platforms

Information About iLBC Support for SIP and H.323

The internet Low Bit Rate Codec (iLBC) is designed for narrow band speech and results in a payload bit rate of 13.33 kbits per second for 30-millisecond (ms) frames and 15.20 kbits per second for 20 ms frames.

When the codec operates at block lengths of 20 ms, it produces 304 bits per block, which is packetized as defined in RFC 3952. Similarly, for block lengths of 30 ms it produces 400 bits per block, which is packetized as defined in RFC 3952.

The iLBC has built-in error correction functionality to provide better performance in networks with higher packet loss.

How to Configure an iLBC Codec

This section includes the following tasks:

Configuring an iLBC Codec on a Dial Peer

Configuring an iLBC Codec in the Voice Class

Configuring an iLBC Codec on a Dial Peer

The iLBC is intended for packet-based communication. Perform the following steps to configure the iLBC codec on a dial peer.

SUMMARY STEPS

1. enable

2. configure terminal

3. dial-peer voice tag voip

4. rtp payload-type cisco-codec-ilbc [number]

5. codec ilbc [mode frame_size [bytes payload_size]]

6. exit

DETAILED STEPS
 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

dial-peer voice tag voip

Example:

Router(config)# dial-peer voice 10 voip

Enters dial-peer configuration mode for the VoIP dial peer designated by tag.

Step 4 

rtp payload-type cisco-codec-ilbc [number]

Example:

Router(config-dial-peer)# rtp payload-type cisco-codec-ilbc 100

Identifies the payload type of a Real-Time Transport Protocol (RTP) packet. Keyword and argument are as follows:

cisco-codec-ilbc [number]—Payload type is for internet Low Bit Rate Codec (iLBC). Range: 96 to 127. Default: 116.

Note Do not use the following numbers because they have preassigned values: 96, 97, 100, 117, 121 to 123, and 125 to 127.
If you use these values, the command will fail. You must first reassign the value in use to a different unassigned number, for example:

rtp payload-type nse 105
rtp payload-type cisco-codec-ilbc 100

Step 5 

codec ilbc [mode frame_size [bytes payload_size]]

Example:

Router(config-dial-peer)# codec ilbc mode 30 bytes 200

Specifies the voice coder rate of speech for a dial peer. Keywords and arguments are as follows:

mode frame_size—The iLBC operating frame mode that will be encapsulated in each packet. Valid entries are 20 (20ms frames for 15.2kbps bit rate) or 30 (30ms frames for 13.33 kbps bit rate). Default is 20.

bytes payload_size—Number of bytes in an RTP packet. For mode 20, valid values are 38 (default), 76, 114, 152, 190, and 228. For mode 30, valid values are 50(default), 100, 150, and 200.

Step 6 

exit

Example:

Router(config-dial-peer)# exit

Exits the current mode.

Configuring an iLBC Codec in the Voice Class

When using multiple codecs, you must create a voice class in which you define a selection order for codecs; then, you can apply the voice class to VoIP dial peers. The voice class codec global configuration command allows you to define the voice class that contains the codec selection order. Then, use the voice-class codec dial-peer configuration command to apply the class to individual dial peers.

To configure an iLBC in the voice class for multiple-codec selection order, perform the following steps.

You can configure more than one voice class codec list for your network. Configure the codec lists and apply them to one or more dial peers based on which codecs (and the order) you want supported for the dial peers. Define a selection order if you want more than one codec supported for a given dial peer.

SUMMARY STEPS

1. enable

2. configure terminal

3. voice-class codec tag

4. codec preference value ilbc [mode frame_size] [bytes payload_size]

5. exit

6. dial-peer voice tag voip

7. voice- class codec tag

8. exit

DETAILED STEPS
 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enters privileged EXEC mode. Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

voice class codec tag

Example:

Router(config)# voice class codec 99

Enters voice-class configuration mode and assigns an identification tag number for a codec voice class. The argument is as follows:

tag—Unique identifier on the router. Range is 1 to 10000.

Step 4 

codec preference value ilbc [mode frame_size] [bytes payload_size]

Example:

Router(config-voice-class)# codec preference 1 ilbc 30 200

Specifies a list of preferred codecs to use on a dial peer. Keywords and arguments are as follows:

value—Order of preference, with 1 being the most preferred and 14 being the least preferred.

mode frame_size—The iLBC operating frame mode that will be encapsulated in each packet. Valid entries are 20 (20ms frames for 15.2kbps bit rate) or 30 (30ms frames for 13.33 kbps bit rate). Default is 20.

bytes payload_size—Number of bytes in an RTP packet. For mode 20, valid values are 38 (default), 76, 114, 152, 190, and 228. For mode 30, valid values are 50(default), 100, 150, and 200.

Step 5 

exit

Example:

Router(config-voice-class)# exit

Exits the current mode.

Step 6 

dial-peer voice tag voip

Example:

Router(config)# dial-peer voice 16 voip

Enters dial-peer configuration mode for the specified VoIP dial peer.

Step 7 

voice-class codec tag

Example:

Router(config-dial-peer)# voice-class codec 99

Assigns a previously configured codec selection preference list (the codec voice class that you defined in step 3) to the specified VoIP dial peer.

Note The voice-class codec command in dial-peer configuration mode contains a hyphen. The voice class command in global configuration mode does not contain a hyphen.

Step 8 

exit

Example:

Router(config-dial-peer)# exit

Exits the current mode.

Verifying iLBC Support for SIP and H.323

You can use the following commands to check iLBC status:

show voice call summary

show voice call status

show voice dsmp stream

show call active voice

show call history voice

show voice dsp and its extensions

show dial-peer voice

show voice dsp channel operational-status