Vcs As A Sip Registrar - Cisco TelePresence Video Communication Server Administrator's Manual

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
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UDP is 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. 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 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
requests for any endpoints attempting to register with an alias that includes 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
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the 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
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the 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.
If an endpoint is registered to the VCS, the VCS will be able to forward inbound calls to that
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endpoint.
If the VCS is not configured with any SIP domains, the VCS will act as a SIP server. It may proxy
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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 [41].
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.
Cisco VCS Administrator Guide (X6.1)
SIP domains for which it will be authoritative. It will then handle registration
Protocols
registration control settings.
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