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D 14049.01
07.2007
88
TANDBERG VIDEO COMMUNICATION SERVER
ADMINISTRATOR GUIDE
Text goes here
Introduction
Getting
Started
System
Overview
System
Configuration
H.323 & SIP
Configuration
Registration
Control
Zones and
Neighbors
Call
Processing
Firewall
Traversal
Bandwidth
Control
Maintenance
Appendices
TANDBERG
ADMINISTRATOR GUIDE
TANDBERG VIDEO COMMUNICATION SERVER
ADMINISTRATOR GUIDE
Call
Processing
Prerequisites
In order for a local endpoint to be able to dial a remote endpoint
using ENUM via your VCS, the following three conditions must
be met:
There must be a NAPTR record available in DNS that maps
the remote endpoint’s E.164 number to its URI. It is the
responsibility of the administrator of the remote enterprise
to provide this record, and they will only make it available if
they wish the endpoints in their enterprise to be contactable
via ENUM dialing.
You must configure an ENUM zone on your local VCS. This
ENUM zone must have a DNS Suffix that is the same as the
domain where the NAPTR record for the remote endpoint is
held.
You must configure your local VCS with the address of at
least one DNS server that it can query for the NAPTR record
(and if necessary any resulting URI).
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ENUM Dialing
Process
Below is the process that is followed when an ENUM (E.164)
number is dialed from an endpoint registered with your VCS:
The user dials the E.164 number from their endpoint.
The VCS initiates a search for the E.164 number as dialed.
It follows the usual alias search process, first applying any
local zone transforms, then searching local and Alternate
registrations and FindMe names for the E.164 number.
If the E.164 number is not found locally, the VCS will check
all its zones to see if any of them are configured with either:
an AlwaysMatch, or
a PatternMatch with pattern that matches the E.164
number.
These zones will then be queried in priority order.
If one or more of the zones that contain a match is a
neighbor zone, the neighbor will be queried for the E.164
number. If the neighbor supports ENUM dialing, it may route
the call itself.
If one or more of the zones that contain a match is an
ENUM zone, this will trigger the VCS to attempt to locate
the endpoint through ENUM. As and when each ENUM
zone configured on the VCS is queried, the E.164 number is
transformed into an ENUM domain as follows:
the digits are reversed and separated by a dot
the DNS Suffix configured for that ENUM zone is
appended.
DNS is then queried for the resulting ENUM domain.
If the DNS server finds at that ENUM domain a NAPTR
record that matches the transformed E.164 number (i.e.,
after it has been reversed and separated by a dot), it returns
the associated URI to the VCS.
The VCS then initiates a new search for that URI
(maintaining the existing hop count). The VCS starts at the
beginning of the search process (i.e. applying any local zone
transforms, then searching locally, then searching zones).
From this point, as it is now searching for a SIP/H.323 URI,
the process for URI Dialing is followed.
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ENUM Dialing for Outgoing Calls
Example
In this example, we wish to call Fred at Example Corp. Fred’s
endpoint is actually registered with the URI fred@example.com,
but to make it easier to contact him his system administrator
has configured a DNS NAPTR record mapping this alias to his
E.164 number: +44 118 123 456.
We know that the NAPTR record for example.com uses the DNS
domain of e164.arpa.
We create an ENUM zone on our local VCS with a DNS suffix
of e164.arpa.
We configure this zone with a pattern match mode of
AlwaysMatch, so that ENUM will always be queried
regardless of the format of the alias being searched for.
We dial 44 118 123 456 from our endpoint.
The VCS initiates a search for a registration of
44 118 123 456. Because the ENUM zone we have
configured has a match mode of AlwaysMatch, it is queried
at the same time as any other zones with a matching
priority.
Because the zone being queried is an ENUM zone, the VCS
is automatically triggered to transform the number into an
ENUM domain as follows:
the digits are reversed and separated by a dot:
6.5.4.3.2.1.8.1.1.4.4
the DNS Suffix configured for this ENUM zone,
e164.arpa, is appended.
This results in a transformed domain of
6.5.4.3.2.1.8.1.1.4.4.e164.arpa.
DNS is then queried for that ENUM domain.
The DNS server finds the domain and returns the
information in the associated NAPTR record. This tells the
VCS that the E.164 number we have dialed is mapped to the
SIP URI of fred@example.com.
The VCS then starts another search, this time for
fred@example.com. From this point the process for
URI Dialing is followed, and results in the call being
forwarded to Fred’s endpoint.
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