Routing And Proxy Support - Cisco 7960G Administrator's Manual

Chapter 1 Product Overview
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Routing and Proxy Support

The Cisco SIP IP phone supports the following routing and proxy features:
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Local (180 Ringing) or remote (183 Session Progress) call progress tone.
Call redirection information support using the Diversion header.
Proxy routing
The route attribute in the dial-plan template file can be used to indicate to which proxy—default,
emergency, fully qualified domain name (FQDN)—the call should be initially routed. For example,
to configure an emergency proxy, specify the value of the route attribute as "emergency."
Backup SIP proxy
When the primary proxy does not respond to the INVITE message sent by the phone after the
configured number of retries, the phone sends the INVITE to the backup proxy. This is independent
from the proxy defined in the route attribute in the dial-plan template used.
The Cisco SIP IP phone attempts to register with the backup proxy. All interactions with the backup
proxy, such as authentication challenges, are treated the same as the interactions with the primary
proxy. The backup proxy is used only with new INVITE messages that fail to communicate with the
primary proxy. Once the backup proxy is used, it is active for the duration of the call.
The location of the backup SIP proxy can be defined as an IP address in the default configuration
file.
Emergency SIP proxy
An optional emergency SIP proxy can be configured with the route attribute of the template tag in
the dial-plan template file. When an emergency SIP proxy is configured and a call is initiated, the
phone generates an INVITE message to the address specified in the proxy_emergency parameter.
The emergency proxy is used for the entire call.
The location of the emergency proxy can be defined as an IP address in the default configuration file.
Support of the DNS SRV query
The Domain Name Server (DNS) SRV query is used to locate servers for a given service. SIP on
Cisco IP phones uses a DNS SRV query to determine the IP address of the SIP proxy or redirect
server. The query string generated is in compliance with RFC 2782 and prepends the protocol label
with an underscore (_), as in "_protocol._transport." The addition of the underscore reduces the risk
of the same name being used for unrelated purposes.
In compliance with RFC 2782 and the draft-ietf-sip-srv-01 specification, the system can remember
multiple IP addresses and use them properly. In the draft-ietf-sip-srv-01 specification, it is assumed
that all proxies returned for the SRV record are equivalent such that the phone can register with any
of the proxies and initiate a call using any other proxy.
Network Address Translation (NAT) and outbound proxy
Enable or disable NAT with the nat_enable parameter. You can configure the address of the NAT or
firewall server using the nat_address parameter.
You can configure the IP address and port number of the outbound proxy server. When outbound
proxy is enabled, all SIP requests are sent to the outbound proxy server instead of to the
proxyN_address. All responses continue to reconcile the normal Using processing rules. The media
stream is not routed through the outbound proxy.
Cisco SIP IP Phone Administrator Guide, Release 6.x and 7.x
Routing and Proxy Support
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