Cisco SRP521W-K9-G1 Administration Guide - Page 89

Configuring Voice Configuring Voice Services 6 G.726-32 G.729a 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. 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 171. 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 SRP can successfully negotiate the codec with the far-end equipment. For more information, see Audio Configuration, page 171. 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 SRP supports the use of backup SIP proxy servers (through DNS SRV) so that service disruption is minimized. An easy way to support proxy redundancy is to configure your DNS server with a list of SIP proxy addresses. The SRP can be instructed to contact a SIP proxy server in a domain named in the SIP message. The SRP consults the DNS server to get a list of hosts in the given domain that provides SIP services. If an entry exists, the DNS server returns an SRV record that contains a list of SIP proxy servers for the domain, with their host names, priority, listening ports, and so on. The SRP tries to contact the list of hosts in the order of their stated priority. If the SRP is currently using a lower priority proxy server, it periodically probes the higher priority proxy to see whether it is back on line, and switches back to the higher priority proxy when possible. SIP Proxy Redundancy is configured in the Line pages (1-4) in the Services Ready Platform Configuration Utility. See Line Pages (1-2), page 156. Cisco SRP500 Series Services Ready Platforms Administration Guide (SRP520 Models) 89