Path: utzoo!attcan!uunet!lll-winken!netsys!vector!nobody From: brian@umbc3.UMD.EDU (Brian Cuthie) Newsgroups: comp.dcom.telecom Subject: Re: Another Cellular Phone Question Message-ID: Date: 12 Oct 88 04:10:07 GMT Sender: chip@vector.UUCP Lines: 69 Approved: telecom-request@vector.uucp (USENET Telecom Moderator) X-TELECOM-Digest: volume 8, issue 161, message 7 X-Submissions-To: telecom@bu-cs.bu.edu (TELECOM Digest Coordinator) X-Administrivia-To: telecom-request@vector.uucp (USENET Telecom Moderator) In article eckert!john@rutgers.edu (John H. Hall) writes: >X-Administrivia-To: telecom-request@vector.uucp (USENET Telecom Moderator) > >In article westmark!dave@rutgers.edu (Dave Levenson) writes: >>In article , weinstoc@SEI.CMU.EDU (Chuck Weinstock) writes: >>> If I call a number associated with a cellular phone, how does the >>> cellular phone operator know which phone to ring and where it is... >> >>When you dial a number assigned to a cellular mobile telephone, all >>of the cell-sites in the mobile phone user's home region broadcast >> ...description of how cellular phones work in their "home region" deleted ... > >Okay, what's a home region? > My city? > My state? > My LATA? > Any place in any cell run by the cellular service I subscribe to? ^^^^^^^ BINGO ! > >While my home and business are stationary, my car is mobile. > >Assume I live in Rochester NY, and drive to Florida on vacation. >If someone in Rochester calls me at my cellular phone: > > 1. How does it get routed to the cellular system (home region?) > through which I happen to be driving? > > 2. Does the caller have any way of knowing that he's > making (and presumably paying for) a long-distance call? > It's actually much simpler than you would imagine. To call a cellular phone in system that is not it's "home" system, you must dial the "roamer" port. A phone is said to be "roaming" when it has latched on to a system that is not the same as the one programmed into the phone. This is what causes the ROAM light on the phone to be activated. To place a call to a roaming phone, you dial the roam port for the system in which the phone is currently active. You will usually then get a second dial-tone. At the tone, you dial the full 10 digit number of the phone when it is in it's home system. The system then pages the phone and the rest works as normal. It makes more sense when you realize that the phone is programmed with it;s home system ID and it's home NPA and phone number. Thus, let's assume I live in baltimore maryland and my cell phone number is 301 555-1234. If I were in phila and I was on the Cell One system there it's roam port is 215 350-ROAM. To place a call to me while I was in phila you would do the following: 1. dial 1-215-350-7626. 2. wait for tone 3. dial 301-555-1234 4. things work as normal from here. You can see from this example that the long distance charges are paid by the caller. He of course knows it's a toll call when he dials it. Incidentally, the big problem with roaming is that you must know what city I'm in (usually not too big a problem, unless traveling) and you must know which system I am using (since most market areas are served by two systems). There is, of course, a LARGE security problem since the system in which you are roaming has no way of validating your phone's ESN. This is left as an excersize for the ambitious student (ie, don't expect me to spill the beens to the world). cheers, brian