WNP Clutch

Real-time number-porting operations are complicated enough without number pooling.

The wireless number portability (WNP) implementation deadline is looming ever closer for wireless carriers. The November 2002 date is unlikely to be moved unless courts rule against it, the FCC (www.fcc.gov) has a complete change of heart, or some major problems erupt in wireline local number portability (LNP).

The LNP mandate already requires wireless carriers to perform queries to a number-portability database (NPDB) to route calls to ported landline phone numbers in major metropolitan areas. The November 2002 deadline will allow wireless numbers also to be ported, either to or from another wireless carrier or a landline carrier. The major change required by this phase of number portability is the separation of the MIN and mobile directory number (MDN) to allow wireless systems to identify the true home carrier at the time of registration. Every wireless phone that is ported to another carrier will have an MDN that is unchanged and a MIN (or IMSI) that has been reprogrammed to point to the HLR of the new serving wireless carrier.

The challenge of WNP has increased substantially because of another mandate — number pooling. This uses the WNP infrastructure, but for a totally different purpose. The LNP mandate is intended to increase competition by allowing (largely landline) consumers to obtain service from a competitive carrier without the barrier of changing their phone numbers. Pooling, however, is intended to increase the efficiency of phone-number usage. It does this by peeling off blocks of 1,000 numbers from underused blocks of 10,000 assigned to one carrier. Because routing is to these larger blocks, the entire group of 1,000 numbers has to be ported in one operation. In fact, it gets more complicated. A few of the 1,000 numbers already may be in use (a so-called contaminated block), and they must be ported back to the original carrier immediately.

Theoretically, pooling can be accomplished using the LNP infrastructure. However, pooling radically increases the numbers that are ported at one time and makes number-portability databases larger and more cumbersome. Now queries have to ask if the number is ported and, if not, if is it within a block of 1,000 pooled numbers. If not, default routing will apply. To combat this change in ported-block size, the Number Portability Administration Center (NPAC) must reorganize its databases with efficient data representation.

Real-time porting operations are complicated enough, but the real challenge occurs behind the scenes when a customer attempts to port one or more numbers. When a customer is persuaded to port his phone to another carrier, the service-order-entry system has to initiate a local service request to the old serving carrier. This carrier has the choice of accepting it or challenging it. If the port request is accepted, the new carrier must inform the NPAC when the port is scheduled to occur. The NPAC then will download the porting information to the local service-management systems that are used by carriers to provision the real-time NPDBs. To make matters more complicated, while this one number is being ported, it's possible the 1,000-number block that its phone number resides in is being pooled.

Although carriers are planning for these radical changes, it still is questionable whether it is beneficial to apply the LNP or pooling mandates to wireless. Given the high levels of churn in the wireless industry and establishment of at least three competitors in most markets, it is hard to believe that changing phone numbers has been much of a barrier.

The LNP mandate can't guarantee a smooth porting process for the consumer. Often, when changing between digital systems, he will have to purchase a new phone or purchase a long-term contract. MIN reprogramming will be needed. Further, 911 callback may not be possible when ported phones are in an area outside the LNP mandate because these systems may retain the current assumption that the MIN is the same as the MDN.

Nobody questions the need for number conservation; the question is whether number pooling is the best approach. The basic problem appears to be that rate centers, the fundamental billing and routing unit in the North American Number Plan, are too small in many cities. Consolidating rate centers allows carriers to distribute one block of numbers to all customers within this larger area, making it possible to use numbers that previously were stranded in a rate center with low growth. This could be much more beneficial than pooling but requires action at the state level and could reduce intra-LATA long-distance revenue to ILECs.

Wireless carriers likely will continue to fight WNP and number-pooling, but they also must plan to implement the mandates, because there is no guarantee that any more extensions will be granted, let alone exemptions.

Crowe (crowed@cnp-wireless.com) is a wireless-standards consultant and editor of Cellular Networking Perspectives, a wireless-standards and -technology bulletin.