July 27, 2007

Realities of Number Portability

In the PSTN world Number Portability is an important consumer right albeit a recently gained one. Without number portability, new entrants will be very much disadvantaged. But the right is severely restricted. I am not sure the reasons for the stipulated restrictions, but my suspicion is they were politically motivated. One of the important restrictions is that the line corresponding to a phone number must terminate in the same rate area even after a port. This has implications even when VoIP is involved.

That point is important for us to note, because the moment a VoIP service assumes a PSTN number, that service takes on many aspects and restrictions of PSTN. For example, if a subscriber moves from one location to another which is outside of the current rate area, the number can not be ported to the new area, even if the service provider is operating in both the areas. Granted, many VoIP service providers maintain the old number, legally the number is not ported. Instead the service provider assumes the ownership of the number and “loans” to the subscriber. So a service provider has to select one of the two conflicting options – give ownership of the number to the subscriber and allow that subscriber to port the number to another carrier or assume ownership of the number, allow the subscriber to use it from any location, but then the subscriber cannot port it to another carrier. This is an important point because most of the VoIP carriers have opted for the second option. In the case of SunRocket, its customers are facing difficulty because of this – they are not able to port “their” number to another service provider because it as not “theirs” to begin with.

This is a cautionary note for those subscribing to services that offer phone numbers for life whether they are now part of “God” company or they are a stable CLEC. PSTN number is like a cake, you an not have it and eat it too. So consumers have to pick one or the other.

Posted by aswath at July 27, 2007 11:12 PM
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There was actually a technical reason for the restriction on porting within the same rate center. On interLATA or intraLATA toll calls, the IXC is responsible for performing the LNP query and identifying the terminating LEC; the originating LEC is responsible for identifying the call as an IXC-handled call and handing it off to the proper IXC. On local calls, the originating LEC is responsible for performing the LNP query and identifying the LEC of the destination number. With the restriction that numbers can only be ported within the rate center, the originating LEC can do the local-toll differentiation based on the dialed number. Without that restriction, the originating LEC would have to do an LNP query on every call, because the Location Routing Number would be needed to do the local-toll differentiation.

That additional database and signaling network query load is not trivial. In addition, the restriction allowed LNP to be transitioned in by rate center - as a rate center was opened for portability, the class 5 switches in that rate center began doing queries on local calls, and the IXCs began doing queries on toll calls into that rate center. Without that restriction, LNP would have had to be flash cut - every class 5 switch in the NANP would have had to start LNP queries on every call as soon as any number could be ported, because class 5 switches don't have knowledge of what NPA-NXXs are in what distant rate centers.

Posted by: DG Lewis at July 30, 2007 11:01 AM

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