Linksys WIP310 SPA500 Series and WIP310 IP Phone Administration Guide - Page 93
SIP Proxy Redundancy, RFC3311 Support, Configuring Survivable Remote Site Telephony SRST Support
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Configuring SIP, SPCP, and NAT Session Initiation Protocol and Cisco IP Phones 4 SIP Proxy Redundancy An average SIP proxy server may handle tens of thousands of subscribers. A backup server allows an active server to be temporarily switched out for maintenance. Cisco phones support the use of backup SIP proxy servers to minimize or eliminate service disruption. A static list of proxy servers is not always adequate. If your user agents are served by different domains, for example, you would not want to configure a static list of proxy servers for each domain into every Cisco IP phone. A simple way to support proxy redundancy is to configure a SIP proxy server in the Cisco IP phone configuration profile. The DNS SRV records instruct the phones to contact a SIP proxy server in a domain named in SIP messages. The phone consults the DNS server. If configured, 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 Cisco IP phone tries to contact the hosts in the order of their priority. If the Cisco IP phone currently uses a lower-priority proxy server, the phone periodically probes the higher-priority proxy and switches to the higher-priority proxy when available. Configuring Survivable Remote Site Telephony (SRST) Support The proxy and outbound proxy fields in the Ext tab can be configured with an extension that includes a statically-configured DNS SRV record or DNS A record. This allows for failover and fallback functionality with a secondary proxy server. The format for the parameter value is as follows: FQDN format: hostname[:port][:SRV=host-list OR :A=ip-list] host-list: srv[|srv[|srv...]] srv: hostname[:port][:p=priority][:weight][:A=ip-list] ip-list: ip-addr[,ip-addr[,ip-addr...]] The default priority is 0 and default weight is 1. The default port is 0, and the application substitutes the proper port value (for example, port 5060 for SIP). RFC3311 Support The Cisco SPA 525G supports RFC3311, the SIP UPDATE Method. Cisco SPA 500 Series and WIP310 IP Phone Administration Guide 82