Polycom SIP 3.0.2 User Manual

 Configuring Your System

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timeout defined in RFC 3261. If it is not the last server in the list, the 
maximum number of retries using the configurable retry timeout is used. 

For more information, refer to 

 on page 

 and 

.

Phone Configuration
The phones at the customer site are configured as follows:

• Server 1 (the primary server) will be configured with the address of the 

service provider call server. The IP address of the server(s) to be used will 

be provided by the DNS server. For example:

reg.1.server.1.address="voipserver.serviceprovider.com"

• Server 2 (the fallback server) will be configured to the address of the 

router/gateway that provides the fallback telephony support and is 

on-site. For example:

reg.1.server.2.address=172.23.0.1

If DNS is used to resolve the address for Servers, the DNS server is unavailable, 

and the TTL for the DNS records has expired, the phone will attempt to contact the 

DNS server to resolve the address of all servers in its list before initiating a call. 

These attempts will timeout, but the timeout mechanism can cause long delays (for 

example, two minutes) before the phone call proceeds “using the working server”. 

To mitigate this issue, long TTLs should be used. It is strongly recommended that 

an on-site DNS server is deployed as part of the redundancy solution.

 

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PSTN Gateway

Hosted VoIP Service 

Provider

DNS Server

Call Server 1A

Call Server 1B

SIP Capable Router

Server2