Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request From: rpw3%rigden.wpd@sgi.com (Rob Warnock) Newsgroups: comp.dcom.telecom Subject: Re: A Couple Tech Questions About Cellular Phones Message-ID: <10094@accuvax.nwu.edu> Date: 25 Jul 90 11:35:00 GMT Sender: news@accuvax.nwu.edu Reply-To: Rob Warnock Organization: Silicon Graphics Inc., Mountain View, CA Lines: 43 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 514, Message 2 of 9 In article <9972@accuvax.nwu.edu> John Higdon writes: | Cliff Yamamoto writes: | > This may be a rumor, but I've heard that *all* cellular phones have | > the capability to have their microphones/xmitters activated by the | > switching office? | Not true. When your unit is address by the system, a two way audio | path is indeed enabled, but your transmitter is not turned on until | you answer the call. Uh, I think you have it backwards, John. Your transmitter turns on to answer the broadcast poll on the setup channel [sent to *all* cells, in order to find your phone], and you're switched to what will be the talk channel, *before* the local ringer on the addressed phone starts tweeting. It's the talk path (mic, earphone amplifier) that doesn't open 'til you hit SND. The "dead time" before the first ring you sometimes get when calling a cellular number is the broadcast poll while the system's trying to locate the mobile phone. (I have seen this time be as long as fifteen seconds.) When you [the caller] finally hear the ringing tone, the mobile has already got its transmitter on, tuned to the assigned talk channel, and is also ringing. I actually proved this to myself one day by setting my handheld near a field-strength meter (el cheapo Radio Shack FSM, with a ~1/4-wave piece of wire hanging out the top), and calling the handheld from a landline. The FSM went offscale *before* either the mobile phone started ringing or I heard ringing tone the calling phone. I have no idea whether there is any magic a cellular CO can do to create an "infinity tap" without causing ringing. I would doubt it, but, hey, bugs and Trojan horses *have* been known to exist in software, no? And cellular phones *are* controlled by the software in the phone's local microprocessor. Rob Warnock, MS-9U/510 rpw3@sgi.com rpw3@pei.com Silicon Graphics, Inc. (415)335-1673 Protocol Engines, Inc. 2011 N. Shoreline Blvd. Mountain View, CA 94039-7311