From: die@pig.jjm.com (Dave Emery)
Date: Thu, 11 Aug 94 19:38:37 PDT
To: lrh@crl.com (Lyman Hazelton)
Subject: Re: Satellite Cellphones
In-Reply-To: <Pine.3.87.9408111315.A417-0100000@crl.crl.com>
Message-ID: <9408120242.AA24719@pig.jjm.com>
MIME-Version: 1.0
Content-Type: text/plain


> 
> On Wed, 10 Aug 1994, Dave Emery wrote:
> 
> > 							Dave Emery
> 
>   Your understanding of how IRIDIUM(r) will work is incorrect.  It most 
> certainly WILL be the NORMAL operating mode for a subscriber unit (cell 
> phone, if you will) to talk to another subscriber unit by only going 
> through satellite links.  The caller will be authenticated via a "home" 
> equivalent to the MTSO switch, but the call itself will NOT go through 
> the switch (or any other) unless it is to a phone number which is not a 
> subscriber unit. ONLY in that case will the call be routed through the 
> MTSO equivalent.

	Thanks for the correction - there is not a lot published about
the system that I'm aware of (at least in technical journals I see) so I'm
apparently out of date on how the current system works.

	But your qualification about going to a phone number which is
not a subscriber is a very big one.  No doubt IRIDIUM service will cost
more per minute than some current ripoff prime time AMPS cellular costs
and even perhaps in the outrageous INMARSAT ($>6.00 minute) range and is
unlikely to replace all but a small fraction of current wired phones and
terrestrial cell phones, let alone the hordes of PCS and cable company
phone connections coming in the near future.  So on a statistical basis
an IRIDIUM subscriber is rather unlikely to be calling another IRIDIUM
subscriber.  I will grant you that if IRIDIUM becomes competitive in
remote areas that a certain amount of remote area to nearby remote area
traffic will be IRIDIUM transported, but my guess is that nevertheless
most IRIDIUM traffic will be to numbers outside the system and thus go
via the MTSO equivalent. 

	This does raise the point, however, about what the IRIDIUM system
plans to do about pirates who wait for an IRIDIUM to IRIDIUM call to set
up and then take over the uplink with higher power (probably just using high
gain steerable antennas would do this fine) and talk on someone else's nickel.

	I imagine that if the satellite actually demodulates the digital
voice/data stream to baseband and switches it as digital data rather
than rf that it would be possible to incorperate cryptographic
authentication of the packets and have the satellite borne switch check
all its packet streams for valid user id.  But of course this adds a
weight and power penalty to the satellites...  Do you know if this
problem been thought of and addressed or is it being assumed to be as
impossible as AMPS cellular spoofing apparently seemed to be to the
developers of that system ?

> 
>   Your thoughts about caller authentication are correct.  I don't know if 
> IRIDIUM is planning to do this correctly or not.

	It had better.
							Dave Emery