Polycom Version 2.0.3B manual

Technical Bulletin 5844

SIP Server Fallback Enhancements on SoundPoint® IP Phones

This technical bulletin provides detailed information on how the SIP application has been enhanced to support SIP server fallback.

This information applies to SoundPoint IP phones running SIP application version 2.1 or later.

Introduction

Server redundancy is often required in VoIP deployments to ensure continuity of phone service for events where the call server needs to be taken offline for maintenance, the server fails, or the connection from the phone to the server fails.

Two types of redundancy are possible:

•Fail-over: In this mode, the full phone system functionality is preserved by having a second equivalent capability call server take over from the one that has gone down/off-line. This mode of operation should be done using DNS mechanisms or “IP Address Moving” from the primary to the back-up server.

•Fallback: In this mode, a second less featured call server (router or gateway device) with SIP capability takes over call control to provide basic calling capability, but without some of the richer features offered by the primary call server (for example, shared lines, presence, and Message Waiting Indicator). Polycom phones support configuration of multiple servers per SIP registration for this purpose.

In some cases, a combination of the two may be deployed.

In SIP 2.1, the fallback behavior has been enhanced and this behavior is described in this document.

Note	Your SIP server provider should be consulted for recommended methods of
	configuring phones and servers for fail-over configuration.

Warning The server redundancy behavior in SIP2.1 has changed from that implemented in prior releases. Prior to SIP 2.1, the reg.x.server.y parameters (see section

4.6.2.1of the SIP 2.0 Administrator's Guide) could be used for fail-over configuration. The older behavior is no longer supported. Customers that are using the reg.x.server.y. configuration parameters where y>=2 should take care to ensure that their current deployments are not adversely affected. For example the phone will only support advanced SIP features such as shared lines, missed calls, presence with the primary server (y=1).

<January, 2007> 3725-17472-001/A