TMCnews Featured Article
December 01, 2010
Number Portability Delivers True Least Cost Routing
By Susan J. Campbell, TMCnet Contributing Editor
Optimizing least cost routing has emerged as a challenging endeavor, one that is no longer exercised by a billing or switch technician on a part time basis. Least cost routing has increased in scope and complexity across the North American telephone network and the subsequent changes have presented new challenges to overcome.
In 1947, when area codes were first established, there were a total of 78 area codes throughout the nation. By 1990, only 36 area codes had been added, but the growth in wireless services generated the need for an additional 109 new areas codes in the 1990s so that 10,000 numbers could be used by carriers. By the year 2000, telephone numbers were dwindling in supply and the FCC (News - Alert) ordered that NPA-NXX number blocks (representing the area code and number pre-fix or switch code) be issued in 1000 blocks.
By number pooling – partitioning NPA (News - Alert)-NXX blocks – the supply of new numbers was dramatically increased. The challenge is that this process is more complicated for seven digit routing based on 1000 block partitions.In telephone routing tables, a dial code matched with a destination is called a translation. Least cost routing tables tend to have an average of three destinations per dial code. As a result, basic optimized least cost routing tables for domestic U.S. routing can have more than one and a half million translations. Local, intra-state and inter-state routing is also known as jurisdictional routing.
Decisions about call routing are based on both the calling and called number. The rating of the call depends on the location of the calling party. Intra-state calls cost more than inter-state calls. To optimize least cost routing, service providers must have two routing tables – one for intra-state calls and another for inter-state calls. The Automatic Number Identification (ANI) determines the jurisdictional routing of the calling party. It is common for the ANI to be an invalid value in VoIP calls.
Calls with an invalid ANI are rated at the higher intra-state rate if completed. When these calls are accepted, a third least cost routing table must be created. Local routing and the interconnection of local calls is usually charged at very low rates and offer another least cost routing optimization. The challenge for VoIP providers is the size of the table that defines the source and destination number combinations for each local calling area. The challenge is that VoIP service providers can serve customers anywhere in the U.S. and still be a local call.
A table defining such local calling areas would have a billion number combinations. To determine least cost routing, dial codes and the rates carriers charge to complete calls to those dial codes, are analyzed. Most carriers do not quote rates for U.S. termination by dial code, and instead quote in terms of OCN, LATA and Tier. As a result, these rates have to be normalized.
This process is one that is challenging for even the most talented technician. When number portability was mandated by the FCC, it helped to drive least cost routing. Every call that is made in North American starts with a query to the Number Portability Administration Center database to determine if the number has been ported. If so, the Location Routing Number (LRN) returned applies to the ported number and the call is routed according to the LRN, not the dialed telephone number. According to TransNexus (News - Alert), 40 percent of customer calls are to ported telephone numbers. This development has a dramatic impact on least cost routing. If this routing is based on dialed telephone numbers, then 40 percent of all calls will not be routed to the least cost provider. As a result, number portability correction can decrease total termination costs by more than 15 percent – delivering true least cost routing.
Susan J. Campbell is a contributing editor for TMCnet and has also written for eastbiz.com. To read more of Susan’s articles, please visit her columnist page.
Edited by Juliana Kenny