Vcs As A Sip Proxy Server; Proxying Registration Requests - Cisco TelePresence Administrator's Manual

If an endpoint is registered to the VCS, the VCS will be able to forward inbound calls to that endpoint.
n
If the VCS is not configured with any SIP domains, the VCS will act as a SIP server. It may proxy
n
registration requests to another registrar, depending upon the SIP registration proxy mode setting.
SIP registration resiliency
The VCS supports multiple client-initiated connections (also referred to as "SIP Outbound") as outlined in
RFC 5626.
This allows SIP endpoints that support RFC 5626 to be simultaneously registered to multiple VCS cluster
peers. This provides extra resiliency: if the endpoint loses its connection to one cluster peer it will still be able
to receive calls via one of its other registration connections.

VCS as a SIP proxy server

The VCS acts as a SIP proxy server when SIP mode is enabled. The role of a proxy server is to forward
requests (such as REGISTER and INVITE) from endpoints or other proxy servers on to further proxy servers
or to the destination endpoint.
The VCS's behavior as a SIP proxy server is determined by:
the SIP registration proxy mode setting
n
the presence of Route Set information in the request header
n
whether the proxy server from which the request was received is a neighbor of the VCS
n
A Route Set specifies the path to take when requests are proxied between an endpoint and its registrar. For
example, when a REGISTER request is proxied by a VCS, the VCS adds a path header component to the
request. This signals that calls to that endpoint should be routed through the VCS. This is usually required in
situations where firewalls exist and the signaling must follow a specified path to successfully traverse the
firewall. For more information about path headers, see
When the VCS proxies a request that contains Route Set information, it forwards it directly to the URI
specified in the path. Any call processing rules configured on the VCS are bypassed. This may present a
security risk if the information in the Route Set cannot be trusted. For this reason, you can configure how the
VCS proxies requests that contain Route Sets by setting the SIP registration proxy mode as follows:
Off: requests containing Route Sets are rejected. This setting provides the highest level of security.
n
Proxy to known only: requests containing Route Sets are proxied only if the request was received from a
n
known zone.
Proxy to any: requests containing Route Sets are always proxied.
n
In all cases, requests that do not have Route Sets are proxied as normal in accordance with existing call
processing rules. This setting only applies to dialog-forming requests, such as INVITE and SUBSCRIBE.
Other requests, such as NOTIFY, are always proxied regardless of this setting.

Proxying registration requests

If the VCS receives a registration request for a domain for which it is not acting as a Registrar (the VCS does
not have that SIP domain configured), then the VCS may proxy the registration request onwards. This
depends on the SIP registration proxy mode setting, as follows:
Cisco VCS Administrator Guide (X7.1)
RFC 3327.
Protocols
Page 80 of 479