59
D14049.05
February 2009
Grey Headline
(continued)
TANDBERG
VIDEO COMMUNICATIONS SERVER
ADMINISTRATOR GUIDE
Introduction
Getting started
Overview and
status
System
configuration
VCS
configuration
Zones and
neighbors
Call
processing
Bandwidth
control
Firewall
traversal
Appendices
Applications
Maintenance
SIP
About SIP on the VCS
The VCS supports the SIP protocol. It can act as a:
SIP registrar
•
SIP proxy
•
SIP Presence Serve
•
r
.
The VCS will 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.
In order to support SIP,
SIP mode must be enabled
and at least one of the SIP transport protocols
(i.e. UDP, TCP or TLS) must be active.
Using the VCS as a SIP registrar
In order 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 enable the VCS to act as a SIP Registrar,
you must
configure it with the SIP domai
n
(s) 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, then the VCS will not act as a SIP Registrar.
Proxying registration requests
If the VCS has no 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 will not proxy any registration requests. The request will be rejected with a “
403
Forbidden
” message.
Proxy to known only
•
: the VCS will proxy the registration request but only to its neighbor, traversal
client and traversal server zones.
Proxy to any
•
: the VCS will proxy the registration requests in accordance with its Call Policy and
transforms. See
Call processing
for more information.
The
SIP registration proxy mode
setting also impacts the VCS’s behavior when acting as a
SIP proxy server
.
Using the VCS as a SIP proxy server
When
SIP mode
has been enabled the VCS may act as a SIP Proxy server. The role of a proxy server
is to forward requests (such as REGISTER and INVITE) from endpoints or other proxy servers. These
requests are forwarded on to other proxy servers or to the destination endpoint.
Whether or not the VCS acts as a SIP proxy server, and its exact behavior when proxying requests,
is determined by the
SIP Registration Proxy Mode
setting. In addition, this also depends on the
presence of Route Set information in the request header and whether or not the proxy server from
which the request was received is a neighbor of the VCS.
A Route Set can specify the path that must be taken when requests are being 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 which signals that the VCS must be included
on any call to that endpoint. The information is usually required in situations where firewalls exist
and the media must follow a specified path in order to successfully traverse the firewall. For more
information about the path header field, see
RFC 3327 [10]
.
When the VCS proxies a request that contains existing Route Set information, it will forward it
directly to the URI specified in the path. Any call policy configured on the VCS will therefore be
bypassed. This may present a security risk if the information in the Route Set cannot be trusted.
For this reason, you can configure the VCS with three different behaviors when proxying requests, as
follows:
If the
•
SIP Registration Proxy Mode
setting is
Off
, the VCS will not proxy any requests that have
an existing Route Set. Requests that do not have an existing Route Set will still be proxied in
accordance with existing call policy (e.g. zone searches and transforms). This setting provides
the highest level of security.
If the setting is
•
Proxy to known only
, the VCS will proxy requests with an existing Route Set only
if the request was received from a neighbor zone (including traversal client and traversal server
zones). Requests that do not have an existing Route Set will be proxied in accordance with
existing Call Policy.
If the setting is
•
Proxy to any
, the VCS will proxy all requests. Those with existing Route Sets will
be proxied to the specified URI; those without will be proxied in accordance with existing call
policy.
The
SIP registration proxy mode
setting only applies to dialog-forming requests, e.g. INVITE
and SUBSCRIBE. Responses, such as NOTIFY, are always proxied regardless of this setting.
SIP overview
