3.8 Implementing Selective PSTN Breakout

This topic describes how to implement selective PSTN breakout in a multisite environment.

  • Gateway selection by local route group feature
    1. Matched route pattern refers to systemwide route list.
    2. Route list refers to a Local Route Group.
    3. Device pool of calling device is configured with route group to be used for the referenced Local Route Group.
    4. Eliminates the need for multiple (site-specific) route lists, route patterns, partitions, and CSSs.
    5. One Local Route Group (Standard Local Route Group) exists by default.
    6. Additional Local Route Groups can be added.

There are two ways to select the local gateway for PSTN calls. One way is to configure a site-specific set of route patterns, partitions, CSSs, route lists, and route groups. If you apply a site-specific CSS at the end, you use a site-specific route group. This implementation model was the only model that was available before Cisco Unified Communications Manager Version 7.

Cisco Unified Communications Manager Release 7 introduced the local route group feature. With local route groups, all sites that share the same PSTN dial rules can use the same route pattern (or set of route patterns). The route pattern (or set of route patterns) is put into a systemwide route list, and this route list includes the local route group. At the device pool of the calling device, one of the configured route groups is configured to be the Standard Local Route Group for this caller. In this model, the route group that is used is determined by the device pool of the calling device and not by its CSS. The local route group feature simplifies dial plans because it eliminates the need for duplicate CSSs, partitions, route patterns, and route lists. Since local route groups have been introduced, they are the preferred method for local gateway selection.

Beginning with Cisco Unified Communications Manager Release 10, you can have more than one local route group. Assume that you add three local route groups (LRG1 to LRG3) to the Standard Local Route Group (which exists by default). At each route list, you can now refer to one of the four local route groups. At each device pool, you can set the local route group for each of the four local route groups. The ability to configure multiple local route groups increases flexibility because you can use the local route group feature in scenarios where some matched patterns should use a different local route group than others.

Configuring IP Phones to Use Local PSTN Gateway

In a multisite deployment, there are typically multiple PSTN gateways (usually one per site). Selective PSTN breakout ensures that local gateways are used to access the PSTN.

IP phones located in the main site use the main-site gateway for PSTN access. Remote phones use their local gateway:

  • Single 9.@ route pattern
  • Route list configured to use local route group
  • Phone device pool configured with route group to be used by phone
  • Main site device pool and remote site device pool refer to different route groups

From a dial plan perspective, you create one 9.@ route pattern (assuming that the NANP is used). This route pattern is in a partition that is part of a global CSS that is used by all phones. The route pattern refers to a systemwide route list that is configured to use the local route group. At the site-specific device pools, the Standard Local Route Group is set to the route group that includes the site-specific gateway.

In the example, there would be a device pool for the main site and a device pool for the remote site. There would be a main site route group, including the main site gateway, and a remote site route group, including the remote site gateway. IP phones at the main site and at the remote site can now be configured with the same CSS. They will all match the same route pattern and therefore will use the same route list. Based on the local route group feature, however, they will always use their local PSTN gateway for PSTN breakout.