Re: [asterisk-biz] Mobile extensions from Asterisk - HLR registration?

John -

Naturally, if you find such a service, I am eager to know about.

To address your closing questions, the mechanics of standard GSM
roaming are something like this:

* SP-B assigns your MSISDN E.164 when you are provisioned. All calls
placed to the MSISDN get routed to SP-B's HLR and then forwarded from
there to a hidden temporary E.164 called the MSRN, which is assigned
by a VLR somewhere. (More on the VLR next.)

* Where ever you roam, even within SP-B's own network, you never deal
with the HLR directly. Instead, you deal with VLRs. When you
register with a network, the VLR assigns you an MSRN and reports the
{MSRN,ISMI} pairing to SP-B's HLR so that inbound calls are routed
correctly. Note that all calls are routed as roaming calls through
VLRs, even when you are within your home network.

* In the proposed service, when you "roam" to SP-A, SP-A assigns you
a local MRSN. SP-A then contacts SP-B's HLR and reports the
{MSRN,IMSI} pairing. To do this, SP-A needs to appear to SP-B's HLR
as a VLR. From an implementation standpoint, this probably means
operating a full-featured SIP-GSM/MAP gateway and having peering
agreements with GSM carriers.

* As long as SP-A's roaming registration is in effect, all calls
placed to your MSISDN get forwarded to SP-A's MRSN by SP-B's HLR,
then, presumably, terminated in whatever device or third-party
network you have registered with SP-A.

* The most recent {MSRN,IMSI} registration is effective. To my
knowledge there is no mechanism for conflicts.

[That's a slight simplification, but any real GSM operator is welcome
to correct any of that if I got it wrong or left our something really
important for this discussion. I've punted on the SMS part of the
question, which includes a whole extra layer of routing among the
SMSCs, but has a similar theme to it.]

You only need one GSM carrier to step forward and act as SP-A,
assuming it doesn't get them black-balled from the GSM Association.
The ideal candidate would be a company that already operates both
VoIP routing services and a PLMN-connected GSM VLR. It could be a
valuable service. If I weren't neck deep in a lawsuit with Martone
Radio Technology, I might be out raising capital to do this myself,
since we will eventually need a service like this to act as a roaming
clearinghouse for OpenBTS systems.

-- David

On May 20, 2009, at 8:00 AM, John Todd wrote:

>
> I've posed this question in person to people with some frequency over
> the last few years, and the answer has always been "No, I don't know
> of such a service." but I'll try on the list and see what I get.
>
> I think it would be a great asset to the Asterisk community to have a
> service provider (let's call them "SP-A") who is a mobile carrier who
> offered the following method: if I register a SIP entity with their
> servers, they would then register with the HLR of my mobile carrier
> ("SP-B") and act as if I was roaming into a mobile network operated
> by SP-A. SP-B would then take all calls and text messages destined
> for my mobile device and send them to SP-A. SP-A in turn would then
> relay those calls and messages to my Asterisk server, via SIP and/or
> XMPP.
>
> I would have pre-registered my mobile number with SP-B and
> authenticated that I was the owner of that mobile number. SP-A would
> hopefully charge very little for the calls - perhaps a slight premium
> on what I'd expect for a SIP carrier.
>
> This would, I believe, quickly make Asterisk a roaming-capable
> solution for mobile devices. Local Asterisk servers would be able to
> (as an example) detect dual-mode devices and then route calls in the
> office in the appropriate manner. Bluetooth could be used as the
> "trigger" for non-dual-mode phones. I have faith that Asterisk
> developers and administrators would descend upon this type of service
> like locusts. The trick would be to make it purchase-able by
> individuals, and not as some large-scale process that involved sales
> contracts and NDAs and the like. This needs to be a web form, a
> credit card/paypal account, and some good documentation.
>
> Potential problems: what if my mobile phone is registered with SP-A or
> some other provider already? Who gets the messages? How do HLRs
> manage multi-registration conflicts?
>
> JT
>
>
> ---
> John Todd email:jtodd@digium.com
> Digium, Inc. | Asterisk Open Source Community Director
> 445 Jan Davis Drive NW - Huntsville AL 35806 - USA
> direct: +1-256-428-6083 http://www.digium.com/
>
>
>
>
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David A. Burgess

OpenBTS on the web:
http://www.kestrelsp.com/OpenBTS
http://openbts.blogspot.com
http://www.gnuradio.org/trac/wiki/OpenBTS

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