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Collaboration, Voice & AV · Intermediate

Internet Low Bitrate Codec (iLBC)

A royalty-free narrowband speech codec designed for robustness to packet loss, at 13.33 or 15.2 kbps.

Definition

iLBC (RFC 3951) encodes each frame independently so that a lost packet does not affect the decoding of later packets, giving graceful degradation on lossy networks. It operates with 30 ms frames at 13.33 kbps or 20 ms frames at 15.2 kbps. Cisco supports iLBC on IP phones, gateways and CUCM regions as an alternative to G.729 on lossy links.

Example

A CUCM region pair for remote teleworkers is configured to allow iLBC because of lossy home internet connections.

Exam tip

iLBC is chosen for loss resilience; G.729 is chosen for lowest bandwidth.

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