Cisco TelePresence Video Communication Server Administrator's Manual page 148

Calling process
The process below is followed when an ENUM (E.164) number is dialed from an endpoint registered
with your VCS:
1. The user dials the E.164 number from their endpoint.
2. The VCS initiates a search for the E.164 number as dialed. It follows the usual
3. After applying any pre-search transforms, the VCS checks its
configured with a Mode of either:
Any alias, or
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Alias pattern match with a pattern that matches the E.164 number
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4. The target zones associated with any matching search rules are queried in rule priority order.
If a target zone is a neighbor zone, the neighbor is queried for the E.164 number. If the neighbor
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supports ENUM dialing, it may route the call itself.
If a target zone is an ENUM zone, the VCS attempts to locate the endpoint through ENUM. As
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and when each ENUM zone configured on the VCS is queried, the E.164 number is
transformed into an ENUM domain as follows:
i. The digits are reversed and separated by a dot.
ii. The DNS suffix configured for that ENUM zone is appended.
5. DNS is then queried for the resulting ENUM domain.
6. If the DNS server finds at that ENUM domain a NAPTR record that matches the transformed
E.164 number (that is, after it has been reversed and separated by a dot), it returns the associated
URI to the VCS.
7. 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 (applying any pre-search transforms, then searching
local and external zones in priority order).From this point, as it is now searching for a SIP/H.323
URI, the process for
In this example, we want 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: +44123456789.
We know that the NAPTR record for example.com uses the DNS domain of e164.arpa.
1. We create an ENUM zone on our local VCS with a DNS suffix of e164.arpa.
2. We configure a search rule with a Pattern match mode of Any alias, and set the Target to the
ENUM zone. This means that ENUM will always be queried regardless of the format of the alias
being searched for.
3. We dial 44123456789 from our endpoint.
4. The VCS initiates a search for a registration of 44123456789 and the search rule of Any alias
means the ENUM zone is queried. (Note that other higher priority searches could potentially match
the number first.)
5. Because the zone being queried is an ENUM zone, the VCS is automatically triggered to transform
the number into an ENUM domain as follows:
a. The digits are reversed and separated by a dot: 9.8.7.6.5.4.3.2.1.4.4.
b. The DNS suffix configured for this ENUM zone, e164.arpa, is appended. This results in a
transformed domain of 9.8.7.6.5.4.3.2.1.4.4.e164.arpa.
6. DNS is then queried for that ENUM domain.
7. 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.
8. 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.
Cisco VCS Administrator Guide (X6.1)
URI dialing is followed.
Dial plan and call processing
call routing
search rules to see if any of them are
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process.