Whether an individual picks up the phone to make a call in-state or out-of-state, a rather complicated call routing process is simultaneously occurring.

According to Jim Dalton, CEO and founder of least cost routing leader TransNexus (News - Alert), this background process is called “jurisdictional routing,” or the method of routing calls locally, intra-state (which refers to calls between two points that are within the same state), or inter-state (which refers to calls made from one point in one state to another point in a secondary state).

The ANI (Automatic Number Identification) determines the jurisdictional routing, or telephone number of the calling party. First created by AT&T (News - Alert) for internal long-distance billing purposes, ANIs permit subscribers to display the billing telephone number of a calling individual. Therefore, even if a number is blocked or used over VoIP, a caller’s phone number and line type are captured by the ANI service.

Local routing, another form of jurisdictional call routing, is determined by the number blocks, or NPA-NXX-X, of the calling and called parties. Costing much less than intra-state calls, local call interconnection delivers another form of least cost routing optimization.

VoIP providers face a unique challenge when it comes to local call routing, in terms of the size of the table that defines the source and destination combinations for each local calling area. While Local Exchange Carriers serve limited geographic areas, VoIP service providers possess a softswitch that can serve customers anywhere in the U.S.

In fact, according to Dalton, a table combining all the local calling areas in the U.S. would actually have over a billion NPA (News - Alert)-NXX-X combinations.

Of course, we are all familiar with the fact that calls to others across the state border will cost more when compared to local calls. Therefore, for a service provider to optimize their least cost routing, they must have two routing tables on hand – one for intra-state calls and another for inter-state calls.

To find out more, visit TransNexus’ website or bookmark the Least Cost Routing channel, exclusively on TMCnet.To find out more about TransNexus, visit the company at ITEXPO West 2011. To be held Sept. 13-15 in Austin, Texas, ITEXPO (News - Alert) is the world’s premier IP communications event. Visit TransNexus in booth #819. Don’t wait. Register now.

Tammy Wolf is a TMCnet web editor. She covers a wide range of topics, including IP communications and information technology. To read more of her articles, please visit her columnist page.

Edited by Carrie Schmelkin