Linksys SPA 900 SERIES manual Feature Descriptions, SIP Proxy Redundancy

Chapter 1 Introducing Linksys IP Phones

Feature Descriptions

Table 1-2 Speech Quality Metrics

G.729	Medium	4
G.723.1	High	3.8

Note Linksys IP phones support all the above voice coding algorithms.

Feature Descriptions

Linksys IP phones are full featured, fully programmable IP phones that can be custom provisioned within a wide range of configuration parameters. This chapter contains a high-level overview of features to provide a basic understanding of the feature breadth and capabilities of Linksys IP phones.

•SIP Proxy Redundancy, page 1-5

•Supported Codecs, page 1-6

•Other Features, page 1-7

SIP Proxy Redundancy

In typical commercial IP Telephony deployments, all calls are established through a SIP proxy server. An average SIP proxy server may handle tens of thousands of subscribers. It is important that a backup server be available so that an active server can be temporarily switched out for maintenance. Linksys IP phones support the use of backup SIP proxy servers so that service disruption should be nearly eliminated.

A simple way to support proxy redundancy is to configure a SIP proxy server in the Linksys IP phone configuration profile.

a.In Linksys SPA Configuration menu web GUI, enter your service provider name in the Proxy field. The system

b.In the DNS SRV Auto Prefix filed, enter Yes.

c.In the User DNS SRV field, enter Yes.

d.The phone tries to register and the server sends a list of IP addresses in order of priority. (automatically)

where the list is arranged in order of priority. The Linksys IP phone attempts to contact the highest priority proxy server whenever possible.

The dynamic nature of SIP message routing makes the use of a static list of proxy servers inadequate in some scenarios. In deployments where user agents are served by different domains, for instance, it would not be feasible to configure one static list of proxy servers per covered domain into every Linksys IP phone. One solution to this situation is through the use of DNS SRV records. Linksys IP phones can be instructed to contact a SIP proxy server in a domain named in SIP messages. The Linksys IP phone 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 Linksys IP phone tries to contact the list of hosts in the order of their stated priority.

	Linksys IP Phone Administrator Guide
Firmware Version 5.1		1-5