Cisco SPA112 Administration Guide - Page 36

Configuring Voice Getting Started with Voice Services 4 Supported Codecs The ATA voice ports support the following codecs: Codec Description G.711 (A-law and mu-law) Very low complexity codecs that support uncompressed 64 kbps digitized voice transmissions at one through ten 5 ms voice frames per packet. These codecs provide the highest narrow-band voice quality and uses the most bandwidth of any of the available codecs. G.726-32 Low complexity codec that supports compressed 32 kbps digitized voice transmission at one through ten 10 ms voice frames per packet. This codec provides high voice quality. G.729a ITU G.729 voice coding algorithm used to compress digitized speech. G.729a is a reduced complexity version of G.729 requiring about half the processing power of G.729. The G.729 and G.729a bit streams are compatible and interoperable, but not identical. The administrator can select the preferred codecs to be used for each line. See Audio Configuration, page 104. In addition, negotiation of the optimal voice codec sometimes depends on the ability of a device to match a codec name with the codec used by the far-end device. You can individually name the various codecs so that the ATA can successfully negotiate the codec with the far-end equipment. For more information, see Audio Configuration, page 104. SIP Proxy Redundancy In typical commercial IP Telephony deployments, all calls are established through a SIP proxy server. A typical SIP proxy server can handle thousands of subscribers. It is important that a backup server be available so that an active server can be temporarily switched out for maintenance. The ATA supports the use of backup SIP proxy servers (through DNS SRV) so that service disruption is minimized. Cisco SPA100 Series Phone Adapters Administration Guide 36