Cisco Cisco Expressway Maintenance Manual
Calling process
The process below is followed when searching for an ENUM (E.164) number:
1.
2.
to see if any of them are
configured with a Mode of either:
—
Any alias, or
—
Alias pattern match with a pattern that matches the E.164 number
3.
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 supports
ENUM dialing, it may route the call itself.
ENUM dialing, it may route the call itself.
—
If a target zone is an ENUM zone, the Expressway attempts to locate the endpoint through ENUM. As and
when each ENUM zone configured on the Expressway is queried, the E.164 number is transformed into an
ENUM domain as follows:
when each ENUM zone configured on the Expressway is queried, the E.164 number is transformed into an
ENUM domain as follows:
1.
The digits are reversed and separated by a dot.
2.
The DNS suffix configured for that ENUM zone is appended.
4.
DNS is then queried for the resulting ENUM domain.
5.
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 Expressway.
is, after it has been reversed and separated by a dot), it returns the associated URI to the Expressway.
6.
The Expressway then initiates a new search for that URI (maintaining the existing hop count). The Expressway
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 URI
dialing is followed.
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 URI
dialing is followed.
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 Expressway 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.
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 Expressway 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 Expressway is automatically triggered to transform the
number into an ENUM domain as follows:
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
Expressway that the E.164 number we have dialed is mapped to the SIP URI of
Expressway that the E.164 number we have dialed is mapped to the SIP URI of
fred@example.com
.
8.
The Expressway 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.
Configuring Zones and Search Rules for ENUM Dialing
To support ENUM dialing, you must configure an ENUM zone and related search rules for each ENUM service used by
remote endpoints.
remote endpoints.
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Cisco Expressway Administrator Guide