About Sip; Vcs As A Sip Registrar - Cisco TelePresence Administrator's Manual

About SIP

The VCS supports the SIP protocol. It acts as a SIP registrar, SIP proxy and as a SIP Presence Server.
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.
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At least one of the SIP transport protocols (UDP, TCP or TLS) must be active. Note that the use of UDP is
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not recommended for video as SIP message sizes are frequently larger than a single UDP packet.

VCS as a SIP registrar

For a SIP endpoint to be contactable via its alias, it must register its Address of Record (AOR) and its
location with a SIP registrar. The SIP registrar maintains a record of the endpoint's details against the
endpoint's AOR. The AOR is the alias through which the endpoint can be contacted; it is a SIP URI and
always takes the form username@domain.
When a call is received for that AOR, the SIP registrar refers to the record in order to find the endpoint to
which it corresponds. (Note that the same AOR can be used by more than one SIP endpoint at the same
time, although to ensure that all endpoints are found they must all register with the same VCS or VCS
cluster.)
A SIP registrar only accepts registrations for domains for which it is authoritative. The VCS can act as a SIP
registrar for up to 200 domains. To make the VCS act as a SIP registrar, you must configure it with the
domains for which it will be authoritative. It will then handle registration requests for any endpoints attempting
to register against that domain.
Whether or not the VCS accepts a registration request depends on its
SIP endpoint registration
There are two ways a SIP endpoint can locate a registrar with which to register: manually or automatically.
The option is configured on the endpoint itself under the SIP Server Discovery option (consult your endpoint
user guide for how to access this setting; it may also be referred to as Proxy Discovery).
If the Server Discovery mode is set to automatic, the endpoint will send a REGISTER message to the
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SIP server that is authoritative for the domain with which the endpoint is attempting to register. For
example, if an endpoint is attempting to register with a URI of john.smith@example.com, the request
will be sent to the registrar authoritative for the domain example.com. The endpoint can discover the
appropriate server through a variety of methods including DHCP, DNS or provisioning, depending upon
how the video communications network has been implemented.
If the Server Discovery mode is set to manual, the user must specify the IP address or FQDN of the
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registrar (VCS or VCS cluster) with which they want to register, and the endpoint will attempt to register
with that registrar only.
The VCS is a SIP server and a SIP registrar.
Cisco VCS Administrator Guide (X7.1)
registration control settings.
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Protocols
SIP