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Several dial plan solutions exist for multisite deployments with both centralized call processing and
distributed call processing.
• Access and site codes: By adding an access code and a site code to directory numbers of remote
locations, you can do call routing based on the site code instead of directory numbers. As a
result, directory numbers do not have to be globally unique, although they do need to be unique
within a site. Configuration requires route patterns, translation patterns, partitions, and Calling
Search Spaces (CSS). Adding access and site codes simplifies internal dialing for users in a
multisite environment.
Chapter 4: Implementing a Dial Plan for Multisite Deployments
• Implementing PSTN access: PSTN access within a CUCM cluster is implemented
using route patterns, route lists, route groups, and partitions and CSSs. When implementing
TEHO, the same dial plan configuration elements are used; however, more
entities have to be configured, which makes the configuration more complex. TEHO
reduces the operating cost of long-distance dialing.
• Implementing PSTN backup: The IP WAN used in a multisite deployment with
centralized call processing is backed up by Media Gateway Control Protocol (MGCP)
fallback, Cisco Unified Survivable Remote Site Telephony (SRST), or CUCM Express
in SRST mode, and Call Forward Unregistered (CFUR). PSTN backup ensures that
calls will go through the PSTN in the event of a WAN link failure.
Implementing Access and Site Codes
Configuring access and site codes includes implementing site codes for on-net calls and
setting digit manipulation by configuring route patterns, translation patterns, partitions,
and calling search spaces.
Implementing Site Codes for On-Net Calls
In Figure 4-1, two sites have overlapping and nonconsecutive directory numbers. To
accommodate unique addressing of all endpoints, site-code dialing is used. Users dial an
access code (8 in this example), followed by a three-digit site code. A designer can choose
another site code access code as well. When calling the phone with directory number 1001
at the remote site, a user located at the main site has to dial 82221001. For calls in the other
direction, remote users dial 81111001. When distributed call processing is used, each
CUCM cluster is only aware of its own directory numbers in detail. For all directory
numbers located at the other site, the call is routed to a CUCM server at the other site based
on the dialed site code.
Digit-Manipulation Requirements When Using Access and Site Codes
When you use site codes in multisite environments with distributed call processing, as
shown in Figure 4-2, the access and site code have to be stripped from the Dialed Number
Identification Service (DNIS) on outgoing calls. If access and site codes are configured
before the . in the route pattern, they can be easily stripped using the discard digit instruction
on the route pattern or route list. For incoming calls, you have to add the access code and
appropriate site code that are used to get to the caller's site. You can do this easily by using
translation patterns. Note that the ANI can also be properly manipulated on the outgoing
CUCM servers at the main site.
mplementing Access and Site Codes
Figure 4-1 Access and Site Codes Solve Issues with Directory Numbers Used at Different Sites
Figure 4-2 Digit-Manipulation Requirements When Using Access and Site Codes
Chapter 4: Implementing a Dial Plan for Multisite Deployments
NOTE If the WAN link is not functional, additional digit manipulation would be
required to route the call through the PSTN, because the PSTN does not understand the
Site Code.
Access and Site Code Requirements for Centralized Call-
Processing Deployments
If overlapping directory numbers exist in a centralized call-processing deployment, access
and site codes are implemented in a different way, as shown in Figure 4-3.
Figure 4-3 Centralized Call Processing Deployments: Access and Site Codes
This figure shows two sites with centralized call processing. Directory numbers in the main
site and the remote site partially overlap. Again, access and site codes are used to solve the
problem of overlapping directory numbers.
However, in this case, partitions and CSSs need to be deployed in a way that phones at the
remote site do not see directory numbers of main-site phones, and vice versa. In this case,
a translation pattern is added for each site.
The translation pattern of each site includes the access and site code of the respective site.
Phones at each site have a CSS assigned, which provides access to the directory numbers
of the local site and the translation pattern for the other site or sites. The translation patterns
are configured with a transformation mask that strips the access code and site code. Further,
each translation pattern must have a CSS, which provides access to only those directory
implementing PSTN Access
numbers that are located at the target site of the respective translation pattern. This way, all
phones can dial local directory numbers and site-code translation patterns for accessing
other sites. After an intersite number is dialed that consists of the access code, site code, and
directory number, the directory number is extracted by the translation pattern. Then the
number is looked up again in the call-routing table using a CSS that has access only to the
directory numbers of the site, which was identified by the site code.