The VCS can provide interworking between SIP and H.323,
translating between the two protocols to enable endpoints that
only support one of these protocols to call each other.
To support SIP,

SIP mode must be enabled

and at least one of

the SIP transport protocols (UDP, TCP or TLS) must be active.

Using the Cisco VCS as a SIP registrar

For a SIP endpoint to be contactable via its registered alias, it
must register its location with a SIP registrar. The VCS can act as
a SIP registrar for up to 20 domains.
SIP aliases always take the form username@domain. To make
the VCS act as a SIP registrar, you must

configure it with the

SIP domains

for which it will be authoritative. It will then accept

registration requests for any endpoints attempting to register with
an alias that includes that domain.
If no domains are configured, the VCS will not act as a SIP
registrar but it may proxy the request to another registrar
depending upon the SIP registration proxy mode setting.

Using the Cisco VCS as a SIP Presence Server

The VCS supports the SIP-based SIMPLE protocol. It can act as a:

•

Presence Server

•

Presence User Agent

for any of the

SIP domains

for which it is authoritative.

For full information on how to use the VCS as a SIP Presence
server, see the

Presence

section.

Using the Cisco VCS as a SIP proxy server

The VCS can act 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

•

the presence of Route Set information in the request header

•

whether the proxy server from which the request was received
is a neighbor of the VCS

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 signalling
must follow a specified path to successfully traverse the firewall.
For more information about path headers, see

RFC 3327 [10]

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.

•

Proxy to known only: requests containing Route Sets are
proxied only if the request was received from a known zone.

•

Proxy to any: requests containing Route Sets are always
proxied.

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 has no SIP domains configured, or it receives a
registration request for a domain for which it is not acting as a
Registrar, then the VCS may proxy the registration request. This
depends on the SIP registration proxy mode setting, as follows:

•

Off: the VCS does not proxy any registration requests. They are
rejected with a “

403 Forbidden” message.

•

Proxy to known only: the VCS proxies the request in
accordance with existing call processing rules, but only to
known neighbor, traversal client and traversal server zones.

•

Proxy to any: this is the same as Proxy to known only but for
all zone types i.e. it also includes ENUM and DNS zones.

Accepting proxied registration requests

If the VCS receives a proxied registration request, in addition to
the VCS's standard

registration controls

, you can also control

whether the VCS accepts the registration depending upon the
zone through which the request was received. You do this through
the Accept proxied registrations setting when

configuring a zone

Proxied registrations are classified as belonging to the
zone they were last proxied from. This is different from
non-proxied registration requests which are assigned to a
subzone within the VCS.

SIP endpoint registration

A SIP endpoint registers with the VCS (or another SIP registrar) to
identify its current location and thus enable it to receive calls.
To register your SIP endpoint with a SIP registrar, enter the IP
address or FQDN of the SIP registrar into your SIP endpoint.
To use the VCS as the SIP registrar for a particular endpoint,
the VCS must be configured with the SIP domain used by the
endpoint (VCS configuration > Protocols > SIP > Domains).

Movi v2.0 (or later) clients

As for any other SIP endpoint, the VCS acts as a SIP registrar
and SIP proxy for Movi™ v2.0 (or later) clients - no other special
support or configuration is required on the VCS.

SIP overview