GSM gateways in the US?!?

Mon Jul 25 06:00:52 UTC 2005

At 10:43 PM -0400 on 7/24/05, Robert M. Enger wrote:
>I've seen cellular service agreements that discuss "all more almost 
>all usage originating from a single cell site".
>Apparently, they discourage using fixed-location cell adapters to 
>jack-in to the cellular network.
>
>I suppose one could use directional antennas on the roof, and target 
>two or more of the cellular provider's
>cell cites, alternating calls amongst the sites.  You couldn't just 
>use PBX routing though.  You'd have to
>distribute the calls from each fixed-location adapter across 
>multiple cell-sites, so an antenna switcher would be needed.
>(If you're real close to a cell site, you probably can't get an 
>antenna sufficiently directional to ensure that you use a distant 
>tower...)
>
>Seems like a lot of work.  If you have enough mobiles to make this 
>worthwhile, I'm surprised that the carrier
>won't cut you a deal to encourage you to stay with them (rather than 
>shopping other carriers for better deal/discounts).
>If your account really matters, maybe they'll let you set up some 
>VoIP trunking into their MTSO.  That would be low cost.
>
>
>At 08:56 PM 7/24/2005, Roy wrote:
>
>>Here is once such vendor of cellular-PSTN gateways,
>>
>  >http://www.mobilecomms-technology.com/contractors/gsm/eurotech1/

(this is somewhat off-topic, but does relate to North American 
Networks in a vague sense...)

There are two methods that are obvious to terminate calls into mobile 
(GSM) networks in North America:

Outbound (enterprise-to-mobile):

1) Purchase a PRI-to-GSM channel bank adapter (use Google search 
terms "pri gsm" for more details) and link it into your PBX, or 
Asterisk server, or what-have you.  Then, buy 23 GSM SIM cards from 
Carrier C, who offers "free" mobile-to-mobile termination.  Then, buy 
cell phones for all your employees on Carrier  C.  Put specific 
routes into your PBX/Asterisk/ENUM routing engine so that anyone 
dialing any employee's cell number gets routed to the next available 
channel on the PRI gateway instead of going out to the PSTN.  The 
calls lose meaningful caller ID (it shows up as the number on the GSM 
chip in that semi-random channel) but administrators gain some 
ease-of-use at a  low introductory price.  As you mention, it may be 
against the policy of the carrier to route calls in this way.
    This is a popular method to do international VoIP-to-mobile 
termination in many smaller nations with restrictive telephony laws. 
Ethernet cables are often seen running out of windows in office parks 
to a parked van with lots of antennas.  The van stays for a day or 
so, before it shows up on the "abnormal usage" alarm list for the 
closest cell tower, and then vanishes off to the next IP teat.

or

2) Buy all your employees cell phones on Carrier C.  Then, contact 
Carrier C and negotiate a direct PRI into their mobile network, 
hopefully at a very low rate per month.  Put specific routes into 
your PBX/Asterisk/ENUM routing engine so that anyone dialing any 
employee's cell number gets routed to the next available channel on 
the PRI that goes to Carrier C's network.   You'd better be doing a 
boatload of mobile calls, otherwise this is very cost-ineffective due 
to just the local loop costs, not to mention any service charges.  I 
have spoken to at least two companies who have done this with various 
carriers (not necessarily GSM) but they were Fortune 100 firms which 
may give them the clout to make this happen, while smaller companies 
may just be out of luck.

Inbound (mobile-to-enterprise):

1) (using method 1 above)  It is unlikely that your employees will be 
able to efficiently use this method to call INTO the office, since it 
is unreasonable to ask everyone to remember all 23 numbers on the GSM 
channel bank.  Recall that if a line is busy, there is no "hunt" 
feature.  (I could be proven wrong with this, since I know there is a 
GSM "forward-on-busy" configuration option, but I have NEVER seen it 
work correctly on any of the three GSM networks I've tried in the 
United States, and it's an ugly, ugly hack.)

or

2) (using method 2 above)  You would need to negotiate with Carrier C 
to install specific routes for your office trunk prefixes such that 
any calls originating inside of Carrier C's network would get pumped 
over the PRI instead of being delivered via LD or ILEC handoff.   I 
don't know if this is possible, but it does make one yearn for a 
dynamic and filterable way to "announce" e.164 information to 
carriers (and on this segue, go to the voip-peering list to hear more 
tales of woe and sorrow about the lack of scale-able inter-carrier or 
inter-enterprise dynamic routing protocols.)

Both methods (1 and 2) require that the administrator know every 
mobile number that has been allocated to employees, for either 
outbound routing or outbound announcement.

Ideally, it would be great to be able to hand off these calls into 
and out of mobile carrier's networks via native IP (SIP, most likely) 
since it saves everyone money and possibly increases security of 
transport by having fewer entities "touch" the media stream. 
However, that seems unlikely due to FUD and politics at this time. 
Anyone knowing of a mobile carrier who will accept enterprise traffic 
to their voice network via SIP over private or public SIP 
interconnection should let me know... I've not encountered such 
enlightenment yet.

JT