ADSL-BC

SIP Proxy Redundancy
An average SIP proxy server can handle tens of thousands of subscribers. A backup server allows an active server to be temporarily switched out for maintenance. Cisco phones support the use of backup SIP proxy servers to minimize or eliminate service disruption.

A static list of proxy servers is not always adequate. If your user agents are served by different domains, for example, you would not want to configure a static list of proxy servers for each domain into every Cisco IP phone.

A simple way to support proxy redundancy is to configure a SIP proxy server in the Cisco IP phone configuration profile. The DNS SRV records instruct the phones to contact a SIP proxy server in a domain named in SIP messages. The phone consults the DNS server. If configured, 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 forth. The Cisco IP phone tries to contact the hosts in the order of their priority.

If the Cisco IP phone currently uses a lower-priority proxy server, the phone periodically probes the higher-priority proxy and switches to the higher-priority proxy when available.

Configuring Survivable Remote Site Telephony (SRST) Support
The proxy and outbound proxy fields in the Ext tab can be configured with an extension that includes a statically-configured DNS SRV record or DNS A record. This allows for failover and fallback functionality with a secondary proxy server. The format for the parameter value is:

FQDN format: hostname[:port][:SRV=host-list OR :A=ip-list]
host-list: srv[|srv[|srv…]]
srv: hostname[:port][:p=priority][:w=weight][:A=ip-list]
ip-list: ip-addr[,ip-addr[,ip-addr…]]

The default priority is 0 and default weight is 1. The default port is 0, and the application substitutes the proper port value (for example, port 5060 for SIP).

Dual Registration
The phone always registers to both primary (or primary outbound) and alternate (or alternate outbound) proxies. After registration, the phone sends out Invite and Non-Invite SIP messages via primary proxy first. If there is no response for the new INVITE from the primary proxy, after timeout, the phone should attempt with the alternate proxy.

Dual registration is supported per line basis. Three new parameters are added which can be configured via Web GUI and remote provisioning:

Alternate Proxy—Default is empty
Alternate Outbound Proxy—Default is empty
Dual Registration—Default is NO (turned off)
Upon configuring the parameters, reboot the phone for the feature to take effect.


Note The administrator should specify a value for primary proxy (or primary outbound proxy) and alternate proxy (or alternate outbound proxy) for the feature to function properly.

Limitations for Dual Registration and DNS SRV Redundancy
Beginning from this release (7.5.6) the limitations for Dual Registration and DNS SRV redundancy are as follows:

When Dual Registration is enabled, DNS SRV Proxy Fallback/Recovery must be disabled.
Do not use Dual Registration in conjunction with other Fallback/Recovery mechanisms. For example: Broadsoft mechanism.
When Dual Registration is enabled, the parameter Auto Register when Failover must be disabled.
There is no recovery mechanism for feature request. However, the administrator can adjust the re-registration time for a prompt update of the registration state for primary and alternate proxy.
Alternate Proxy and Dual Registration
When the parameter, Dual Register is set to no alternate proxy is ignored.

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