The Seven Fundamentals of Call Routing

Cisco CallManager Administration presents several items in the Route Plan menu related to routing. However, this chapter describes routing concepts, not particular pages in CallManager Administration. By understanding the underlying concepts, you can better develop your enterprise's call routing infrastructure. For example, the Route Pattern Configuration page (shown in Figure 2-2) incorporates several routing concepts: route patterns, route filters, transformations, route lists, and partitions. This chapter does not directly deal with the Route Pattern Configuration page, but when you understand the components that make up the Route Pattern Configuration page, building an individual route pattern is straightforward. Figure 2-2 demonstrates how an excerpt from a single pagethe Route Pattern Configuration page in this caseincorporates several (but not all) routing concepts.

Figure 2-2. Route Pattern Configuration Page

CallManager uses seven major concepts to fulfill its responsibilities:

• Route patterns
• Route filters
• Dialing transformations
• Translation patterns
• Call hunting constructs
• Calling search spaces
• Partitions

Route patterns and route filters permit CallManager to fulfill its primary responsibility of locating a destination. Route patterns are the addresses you assign to devices. For instance, associating the route pattern 8XXX with a gateway means that when you dial a number between 8000 and 8999, your call routes out that gateway. Route filters are more esoteric. Used in conjunction with the special route pattern wildcard @, route filters restrict the scope of the @ wildcard.

Dialing transformations, along with several miscellaneous gateway and system settings, permit CallManager to modify dialed digits and calling numbers before the destination receives a call. Also, by modifying dialed digits before passing a call to another network, you can affect which destination the other network ultimately dials.

Translation patterns provide a level of routing indirection that can resolve complicated scenarios. They are another feature that helps the call routing component fulfill its primary responsibility of selecting a destination. You can think of a translation pattern as an alias for another route pattern.

Translation patterns allow you to do the following:

• Change the called number of a call from what the user dialed to a different number
• Change the calling number of a call from the original user's number to another identity
• Route the resulting call as it is had been dialed with different call routing rules.

Call hunting constructs are mechanisms that allow CallManager to intelligently route a single call to several deviceseither simultaneously or serially. CallManager supports two types of hunting constructs:

• Route lists Enable CallManager to choose from available gateways when placing a call to another network. Route lists are composed of route groups, which in turn are composed of gateways. When CallManager selects a route list as the destination for a call, it begins searching serially, according to the specified search order, for an available gateway from among the gateways that the route list's route groups contain. If a gateway is busy, temporarily unreachable, or nonexistent, CallManager chooses another gateway to which to route the call.
• Hunt lists Enable CallManager to offer calls to IP phones, either simultaneously or serially. When CallManager selects a hunt list as a destination for a call, it looks at the hunting algorithm associated with the hunt list for an available line from among the lines that the hunt list's line groups contain. Hunt lists provide a variety of ways to treat calls when a particular line is busy or not available.

Calling search spaces and partitions allow CallManager to provide individualized routing. These features allow you to configure networks to use toll restriction, enforce calling restrictions by user, or configure networks that serve independent organizations with fully or partially segregated routing plans.