Cisco 8831 Administration Manual page 35

Chapter 3 Configure SIP and NAT
Parameter
Alternate Proxy
Alternate Outbound Proxy
Register
Make Call Without Reg
Register Expires
Use DNS SRV
Description
This feature provides fast fallback when there is network partition at he
Internet or when the primary proxy (or primary outbound proxy) is not
responsive or available. The feature works well in a Verizon
deployment environment as the alternate proxy is the Integrated Service
Router (ISR) with analog outbound phone connection.
Enter the proxy server addresses and port numbers in these fields. After
the phone is registered to the primary proxy and the alternate proxy (or
primary outbound proxy and alternate outbound proxy), the phone
always sends out INVITE and Non-INVITE SIP messages (except
registration) via the primary proxy. The phone always registers to both
the primary and alternate proxies. If there is no response from the
primary proxy after timeout (per the SIP RFC spec) for a new INVITE,
the phone attempts to connect with the alternate proxy. The phone
always tries the primary proxy first, and immediately tries the alternate
proxy if the primary is unreachable.
Active transactions (calls) never fall back between the primary and
alternate proxies. If there is fallback for a new INVITE, the
subscribe/notify transaction will fall back accordingly so that the
phone's state can be maintained properly. You must also set Dual
Registration in the Proxy and Registration section to Yes.
Enables periodic registration with the proxy. This parameter is ignored
if a proxy is not specified. To enable this feature, select Yes. Defaults
to Yes.
Enables making outbound calls without successful (dynamic)
registration by the phone. If set to no, the dial tone plays only when
registration is successful. To enable this feature, select Yes. Defaults to
No.
Defines how often the phone renews registration with the proxy. If the
proxy responds to a REGISTER with a lower expires value, the phone
renews registration based on that lower value instead of the configured
value.
If registration fails with an "Expires too brief" error response, the
phone retries with the value specified in the Min-Expires header of the
error.
The range is from 32 to 2000000. Defaults to 3600 seconds.
Enables DNS SRV lookup for the proxy and outbound proxy. To enable
this feature, select Yes. Otherwise, select No. Defaults to No.
Cisco Unified IP Conference Phone 8831 for Third-Party Call Control Administration Guide
Configure SIP
3-9