Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request From: John Gilmore Newsgroups: comp.dcom.telecom Subject: Re: A Couple Tech Questions About Cellular Phones Message-ID: <10573@accuvax.nwu.edu> Date: 7 Aug 90 10:57:46 GMT Sender: news@accuvax.nwu.edu Organization: TELECOM Digest Lines: 54 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 10, Issue 549, Message 6 of 8 rpw3%rigden.wpd@sgi.com (Rob Warnock) wrote: > I have no idea whether there is any magic a cellular CO can do to > create an "infinity tap" without causing ringing. The US cellular telephone standard defines a way to "ping" a cellular phone without making it ring. The ping is transmitted like an incoming call; the phone wakes up, transmits by radio to its local cell, saying "I'm here", but does not ring. In other words, your phone responds to the cellular base station, without giving any external indication (to you) that it is doing so. I don't think the standard specifies an audio path to the microphone/speaker during this operation, but individual models might 'extend' the standard that way. With this feature, the movements or current whereabouts of your phone can be tracked at will by the cellular company. Anytime the phone will accept an incoming call, it will answer these pings. And if The Phone Company is any guide, the cellular companies will have chummy relationships with cops of all stripes, finking on their paying customers (without requiring warrants), to curry favor with governments. Not to mention helping out the occasional private investigator who knows a friendly technician who... Cellular base stations typically have a lot of directional antennas fanning out in a circle, e.g. twelve antennas, each covering 30 degrees of arc from the base. When your cellular phone transmits to the base, it compares the reception on the various antennas to know where you are in the cell (e.g. who to hand you off to as you get fainter). By comparing the reception in several base stations (an operation they already do all the time, for handoffs), they can probably pin your location down to within a few blocks. Suppose three cells can hear your phone (one strongly, two faintly). This gives them three pie-shaped areas, all spreading from base stations to you. The intersection of these areas is likely to contain you. This works even with two bases, and can be made a lot more accurate using the signal strength as well as the direction. Even if only one cell can hear you, the direction and strength give a pretty good guide to where in the cell you are -- and they *know* your phone is in that cell as opposed to being in Peoria. If I ever get a cellular phone, this 'ping' will be one of the first things I reprogram... [I used to have a copy of the cellular standard document, "EIA IS-3", but it's been a few years since I dug it out. I got it for $32 plus from Global Engineering Documents at +1 800 624 3974. It may have been revised since then ('87); they will check if you ask them. I recommend that anyone with a technical interest in cellular get it; it's the real live protocol that runs over the radio.] [What I have been calling a "ping" they have another name for, which I forget. Something like a "service check" or "maintenance request"...]