Polycom SOUNDPOINT SIP 2.2.0 - Manual (Page 84)

Administrator’s Guide SoundPoint IP / SoundStation IP
4 - 36
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
Warning 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
Internet
PSTN
Hosted VoIP Service
Provider
VoIP SMB Customer
Premise
DNS Server
Call Server 1A
Call Server 1B
SIP Capable Router
Server2
Note It is possible to configure the phone for more than two servers per registration, but
you need to exercise caution when doing this to ensure that the phone and network
load generated by registration refresh of multiple registrations do not become
excessive. This would be of particularly concern if a phone had multiple
registrations with multiple servers per registration and it is expected that some of
these servers will be unavailable.