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Cell Phone Number Portability Finally A Reality?
graphicartist82 writes "MSNBC is running an article about the upcoming deadline for cell phone companies to let customers keep their numbers when switching companies. FCC Chairman Michael Powell has already extended the deadline once, but plans to stay with the Nov 24th, 2003 deadline. Companies like Verizon Wireless and T-Mobile have committed to meeting the deadline. I, for one, would love this. I've had the same cell phone number for years now -- it's where everybody knows how to get a hold of me. Other companies are now offering better services in my area where they weren't before. If I can keep my number and get a better service, I'm all for it! (Even if I have to pay a fee like the article suggests)."
> It can't be that hard if most of Europe has it,
Actually - yes it can. It is technically complex and hard to impliment properly / reliably - It only seems easy because the problems have been solved.
There are some minor differences in the way that call routing works between GSM and the various USA systems. But these are generally small - they all sit on top of SS7 and getting calls through to the location is done by essentially the same Processes in the SS7 SCCP TCAP and MAP layers. If GSM can make it work then the USA will be able to too.
What is more of a problem is the lack of consistency in the way that number portability is implimented. SS7/SCCP/TCAP/MAP doesn't explicitly provide for portability - so it has to be "bolted on" and not every territory does it the same.
Sometimes you want to originate a call or send an SMS and you need to know which network hosts the handset. (Usually you want to do this because you're providing a service in a country (EG Hong Hong) where the carriers are always squabbling and won't neccesarily route your call through to the right network)
Anyway, some territories (eg HongKong) have implimented number portability by means of a centralised common database - and if you provide a service and have multiple trunks into each network (as we do) then you have to negoiate access to that Database and treat it as a whole extra layer before you even start connecting to the network proper. Even then there can be messy differences between territories in the detail of how these databases work.
Other places (EG the UK) do it completely different. Here there is an extra Database associated with every HLR ( Home Location Register - one of the key Databases involved with routing calls to mobiles). When a number is ported, the GTTS (Global Title Translation Service - converts phone numbers into the point codes which underly the SS7 network) in the originating network SCCP still returns the point code of the original operator's HLR - practically speaking it has to or the routing tables would become impossibly large. When that HLR receives a "sendRoutingInfo" message it first checks in its portability database and if the number has been ported elsewhere, then it forwards the message to the new HLR - which will query the current VLR and provide the routing info. This has the advantage that it is transparent to everyone else on the SS7 network , but has the disadvantage that if you actually want to know which network you're paying to receive the call - it's harder to find out. The other disadvantage of this system is the admin is more awkward. Potentially you could be relying on three different companies to make your network change work. All the UK phone companies are a bit of a admin. shambles even at the best of times.
We're busy designing and implimenting various SMS configured voice conferencing services - and this single issue is more complex than just about all the rest put together.
What will be interesting will be to see how the USA has decided to solve the problem. It will face essentially the same choices as countries with GSM - and the same tradeoffs.
AJB