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TANDBERG VIDEO COMMUNICATION SERVER
ADMINISTRATOR GUIDE
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Introduction Getting
Started
System
Overview
System
Configuration
H.323 & SIP
Configuration
Registration
Control
Zones and
Neighbors
Call
Processing
Firewall
Traversal
Bandwidth
Control Maintenance Appe ndices
TANDBERG
ADMINISTRATOR GUIDE
TANDBERG VIDEO COMMUNICATION SERVER
ADMINISTRATOR GUIDE
Call
Processing
About URI Dialing
A URI address typically take s the form name@example.com,
where name is the alias and example.com i s the domain.
URI dialing makes use of DNS to enable en dpoints registered
with different systems to loc ate and call each other. With URI
dialing, it is possible to find an end point by using DNS to locate
the domain in the URI address and t hen query that domain for
the alias.
Without URI dialing, you would ne ed to neighbor all the systems
to each other in order for one syste m to be able to locate an
endpoint registered to anothe r system. This does not scale
well as the number of systems grows. It is a lso inconvenient
for making one-off c alls to endpoints registered wi th previously
unknown systems.
Endpoints must register with th e VCS using a URI address in
order to be reachable using URI di aling.
Enabling URI Dialing via the VCS
URI dialing is enabled separatel y for outgoing and incoming
calls.
Outgoing Calls
To enable endpoints registered to you r VCS to place calls
directly using URI dialing, you mus t:
configure at least one DNS zone, an d
configure at least one DNS Ser ver.
This is described in the sectio n Configuring URI dialing for
outgoing calls.
Incoming Calls
To enable endpoints registered to you r VCS to receive calls
directly using URI dialing, you mus t:
ensure all endpoints are register ed with a URI address
configure appropriate DNS r ecords, depending on the
protocols and transport t ypes you wish to use.
This is described in the sectio n Configuring URI dialing for
Incoming calls.
Firewall Traversal Calls
To configure your system so that you can pl ace and receive
calls using URI dialing through a f irewall, see the section URI
Dialing and firewall traversa l.
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URI Dialing Overview
URI Dialing
If a DNS zone and/or a DNS server have not bee n
configured on the local VCS, ca lls made using URI
dialing could still be placed if th e local VCS is
neighbored with another VCS t hat has been appropriately
configured. Any URI dialed calls w ill go via the neighbor. This
configuration is useful if you wa nt all URI dialing to be made via
one particular system, e.g. a VC S Border Controller.
URI Resolution Process via DNS
When a system is attempting to loc ate a destination URI
address using the DNS system, the g eneral process is as
follows:
The system will send a query (via i ts DNS server) for a
SRV record for the domain in the UR L. If available, this
SRV record will return informat ion about the authoritat ive
gatekeeper (H.323) or proxy (SIP) for that d omain (e.g. its
FQDN and listening port).
The system will then send out anoth er query for an A/AAA A
record for the FQDN returne d in the SRV record. If available,
this will return the actual IP addr ess of the gatekeeper/
proxy. Once its IP address has be en discovered, the system
will query that gatekeeper/proxy for t he URI.
If a relevant SRV record cannot be l ocated, the system will
fall back to looking for an A or AA AA record for the domai n in
the URL. If such a record is found, t he call will be routed to
that IP address.
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