LNP Obstacle Course

Local number portability (LNP) is a bureaucrat's dream and an engineer's nightmare. Although it may achieve the goal of leveling the playing field for competitive LECs, it is of debatable value for wireless consumers and provides an enormous challenge to the integrity of telecom networks. Currently, the wireless industry is challenging both the need for wireless number portability and, as a backup plan, the implementation deadlines.

Most wireless carriers will have to implement some support for number portability, even if their own numbers never are required to be portable, because they must be able to route to ported wireline phone numbers. For example, a wireless carrier in New York City routes a call to a phone number that is managed by NYNEX. That wireline customer could port his phone number to a competitive local exchange carrier (CLEC), which would require all nearby switches (including wireless) to be able to query a number portability database to obtain routing instructions prior to completing a call to that number.

LNP impacts are limited to nearby switches because, as the name implies, portability is "local." A New York City subscriber can port his number to one of several carriers in New York City, but not to a carrier in a different city. This reduces the impact of portability by requiring that switches only know about local blocks of numbers that have been ported.

The LNP capability for wireless switches is being provided in a TIA standard that is close to publication. Currently known by its project number (PN-3980A), it soon will become a TIA interim standard. It provides a query message (number portability request or NPREQ) that can be sent from an MSC to a number portability database to obtain the local routing number (LRN) associated with a ported directory number. If the number is not ported, no routing information is returned, resulting in use of the directory number as the routing number.

LNP Concerns One concern about LNP is network load (and its impact on reliability). Processing a local call in an area that provides flat-rate local calling is relatively simple. Digit analysis confirms that a local number has been dialed, and the call is routed. Wireline switches have no need for database queries nor even for billing record generation. LNP changes eventually may force a database query on most local calls. This is truly a massive change in the processing requirements for wireline switches and will effectively reduce their call-processing capacity. Wireless carriers may shed no tears because they are used to IS-41 (or similar) queries on a significant portion of calls. Although LNP also will increase the processing load on wireless switches, it will not be as much as for wireline switches. This will erode the cost differential further between the two services.

Another aspect of LNP that may reduce network reliability significantly is the administration of number changes. Whenever a subscriber ports, both the old and new carriers have to report the change, and this has to be reflected in all copies of the local database. An error in this process (either hardware or software) could result in database inconsistencies and possible looping of calls. Software errors in particular hold a real risk that could deny service to an entire local calling area.

LNP Phase II Phase II of LNP requires wireless carriers to allow their customers to participate in porting. It is currently a battleground, with CTIA fighting for a delay, and Bell Atlantic Mobile fighting for elimination of the requirement entirely. Wireless carriers are upset because they say that LNP will have minimal benefit for their customers (at considerable cost to the carriers and, ultimately, to consumers) and because they think that the technical complexity was underestimated. Most wireless customers do not widely circulate their phone numbers and, therefore, would suffer little if the number had to change when changing carriers. There are, however, some wireless companies that think that portability will be beneficial, including Omnipoint and various resellers. They obviously think that the business benefits to their companies outweigh the technical challenges.

Despite this climate of uncertainty, standards development pushes ahead. TIA subcommittee TR-45.2 is developing PN-4186, which will provide a standard method for adherence to LNP Phase II requirements, if and when required.

One of the major impacts of LNP Phase II is to force the separation of the MIN and directory number. The directory number, by definition, has to be retained when a subscriber ports. If the MIN remains the same as the directory number, it would require a number portability database query every time a roamer appears in a system (even if he never makes a call). Because the MIN generally is hidden from the subscriber, having to modify the MIN whenever a phone is ported is not a large hurdle.

Adverse Effects The separation of MIN and mobile directory number (MDN) will have a negative effect on wireless carriers that are outside the LNP mandate (i.e. those in rural areas). When a 911 call is made, these carriers may not have access to the MDN. Yet, the FCC's Phase I 911 mandate requires the ability to perform callback (which requires the MDN), while the FCC's Phase II LNP mandate makes this difficult to achieve.

The separation of MIN and directory number will have many other effects. Employees will have to be retrained to recognize the distinction, and many applications will have to be reprogrammed. Carriers will have to allocate MIN and directory number resources separately. This will require a new administrator, which initially will have to determine all current allocations of MINs and educate the entire industry about the new procedures for obtaining blocks of MINs.

This new organization (currently being developed by CTIA) will have to be managed jointly with other countries in the North American Number Plan, most notably Canada. This is a significant undertaking, although the separation of MIN and MDN will have long-term benefits by reducing the impact of area-code changes and potentially facilitating international roaming.

Phase II of LNP also affects special features such as calling name presentation (CNAP), SMS and calling party pays (CPP). It also will accelerate the movement from MF tone-based signaling to SS7 ISUP interconnection.

CNAP usually is implemented via a database access to the home carrier (which may be wireless or wireline). However, if the number is ported, it is not so easy to identify the home carrier. If this information is not carried in an ISUP message from the home system, then a further number-portability query will be required before the appropriate calling name database even can be identified.

SMS will be affected because it will be difficult to identify the mobile to which to direct the message. Take, for example, a carrier that allows short messages to be sent via the Internet using messages addressed as MDN@carrier.com. The Internet can deliver the message to the carrier's domain, but the MDN will not always identify the specific HLR for the mobile, resulting in a requirement for an additional number portability query. This problem is somewhat limited because there is no need to deliver short messages sent to MDN@carrier.com when the MDN has been ported to a different carrier. (This is considered to be service portability, which is not covered by the LNP mandate.)

Another SMS problem occurs when a mobile originates a short message. In this case, it may specify the phone number of another mobile, which could belong to a different carrier. However, the MDN does not necessarily identify the carrier, resulting in yet another number portability query.

CPP has grown slowly in North America for a number of reasons. (See "Protocols" in the April 1 issue.) The LNP mandate will make most current CPP implementations obsolete, something that already has forced CTIA to rethink the service. Current implementations rely on a recognizable block of numbers, which is not permissible when a number may be changed from one carrier to another at will.

ISUP is generally agreed to be a better interconnection method than the older MF-tone based methods. However, the transition to ISUP has been slow because of the cost. LNP will change all that because it will help eliminate unnecessary database queries by carrying a flag that identifies whether an LNP query already has been performed.

LNP is an obstacle course for wireless carriers. Currently, the emphasis is on getting the appropriate functionality implemented to meet the deadlines. However, long-term concerns must include cost reduction, the reliability and performance of the network, and the feasibility of advanced services that are adversely affected by this FCC mandate.