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Introduction
One of the functions of the VCS is to route calls to their appropriate destination,
based on the address or alias received from a locally registered endpoint or
external zone.
There are a number of steps involved in determining the destination of a call, and
some of these steps can involve transforming the alias or redirecting the call to
other aliases. It is important to understand the process before setting up your
dial plan so you can avoid circular references, where an alias is transformed from
its original format to a different format, and then back to the original alias.
The VCS is able to detect circular references. If it does identify one it will
terminate that branch of the search and return a "policy loop detected"
error message.
VCS search process
The process followed by the VCS when attempting to locate a destination endpoint
is shown in the diagram opposite.
1.
The user enters into their endpoint the alias or address of the destination
endpoint. This alias or address can be in a number of
2.
The destination address is sent from the caller's endpoint to its local VCS (i.e.
the VCS to which it is registered).
3.
The VCS applies any
pre-search transforms
4.
The VCS applies any
Call Policy
to the (transformed) alias. If this results in a
new alias, the process starts again, with the new alias checked against the
pre-search transforms.
5.
The VCS applies any
User Policy
(if FindMe is enabled) to the alias. If the
alias is a FindMe name that resolves to one or more new aliases, the process
will start again; all the resulting aliases will be checked against pre-search
transforms and Call Policy.
6.
The VCS then
searches, in order of priority, all its zone
those configured on the Local Zone (which includes any cluster peers). At each
priority, zones are searched first in the native protocol and then, if the VCS
interworking configuration allows, the alternative protocol. If the alias matches
an ENUM zone, this may return a URI. If so, the process starts again; the URI is
checked against any pre-search transforms, Call Policy and User Policy.
7.
If the alias is found within the Local Zone or by one of the external zones, the
VCS will attempt to place the call to that zone.
8.
If the alias is not found, the VCS will respond with a message to say that the
call has failed.
Overview and
Introduction
Getting started
status
D14049.05
February 2009
Call processing diagram
different address
types.
to the alias.
matches, including
System
VCS
Zones and
configuration
configuration
Call
Bandwidth
neighbors
processing
control
92
TANDBERG
VIDEO COMMUNICATIONS SERVER
Firewall
Applications
Maintenance
traversal
ADMINISTRATOR GUIDE
Appendices
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