Cisco Cisco Expressway Maintenance Manual
This transformation can be applied to the alias at two points in the routing process: as a pre-search transform, and as
a zone transform.
a zone transform.
■
Pre-search transforms are applied before any Call Policy is applied and before the search process is
performed (see
performed (see
■
Zone transforms are applied during the search process by each individual search rule as required. After the
search rule has matched an alias they can be used to change the target alias before the search request is sent
to a target zone or policy service (see
search rule has matched an alias they can be used to change the target alias before the search request is sent
to a target zone or policy service (see
Search rules
Search rules are used to route incoming search requests to the appropriate target zones or policy services.
The Expressway's search rules are highly configurable. You can:
■
define alias, IP address and pattern matches to filter searches to specific zones or policy services
■
define the priority (order) in which the rules are applied and stop applying any lower-priority search rules after
a match is found; this lets you reduce the potential number of search requests sent out, and speed up the
search process
a match is found; this lets you reduce the potential number of search requests sent out, and speed up the
search process
■
set up different rules according to the protocol (SIP or H.323) or the source of the query
■
limit the range of destinations or network services available to unauthenticated devices by making specific
search rules applicable to
search rules applicable to
■
use zone transforms to modify an alias before the query is sent to a target zone or policy service
Note that multiple search rules can refer to the same target zone or policy service. This means that you can specify
different sets of search criteria and zone transforms for each zone or policy service.
different sets of search criteria and zone transforms for each zone or policy service.
The Expressway uses the protocol (SIP or H.323) of the incoming call when searching a zone for a given alias. If the
search is unsuccessful the Expressway may then search the same zone again using the alternative protocol,
depending on where the search came from and the Interworking mode (Configuration > Protocols > Interworking).
search is unsuccessful the Expressway may then search the same zone again using the alternative protocol,
depending on where the search came from and the Interworking mode (Configuration > Protocols > Interworking).
About Pre-Search Transforms
The pre-search transform function allows you to modify the alias in an incoming search request. The transformation is
applied by the Expressway before any Call Policy is applied and before any searches take place.
applied by the Expressway before any Call Policy is applied and before any searches take place.
■
It applies to all incoming search requests received from neighbor, traversal client and traversal server zones,
and endpoints on the public internet.
and endpoints on the public internet.
■
It does not apply to requests received from peers (which are configured identically and therefore will have
already applied the same transform).
already applied the same transform).
Each pre-search transform defines a string against which an alias is compared, and the changes to make to the alias
if it matches that string.
if it matches that string.
After the alias has been transformed, it remains changed and all further call processing is applied to the new alias.
Pre-search transform process
Up to 100 pre-search transforms can be configured. Each transform must have a unique priority number between 1
and 65534.
and 65534.
Every incoming alias is compared with each transform in order of priority, starting with that closest to 1. If and when a
match is made, the transform is applied to the alias and no further pre-search checks and transformations of the new
alias will take place. The new alias is then used for the remainder of the
match is made, the transform is applied to the alias and no further pre-search checks and transformations of the new
alias will take place. The new alias is then used for the remainder of the
■
Further transforms of the alias may take place during the remainder of the search process as a result of
(also known as Administrator Policy). If this is the case, the pre-search transforms are re-applied to the
new alias.
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Cisco Expressway Administrator Guide