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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical FW: How do I log on while in flight?
This was very informative... not to mention interesting. (see below) -----Original Message----- From: John Fraizer [mailto:[email protected]] Sent: Thursday, June 27, 2002 9:01 PM To: Jacob M Wilkens Cc: [email protected] Subject: RE: How do I log on while in flight? On Thu, 27 Jun 2002, Jacob M Wilkens wrote: > > I'm fairly certain the cell networks won't crash - as demonstrated in some > calls made last fall. It's more like they won't be able to bill for the time > or keep track of your calls. > > -----Original Message----- > From: [email protected] [mailto:[email protected]]On Behalf Of > Scott Weeks > Sent: Thursday, June 27, 2002 5:01 PM > To: Leigh Anne Chisholm > Cc: [email protected] > Subject: RE: How do I log on while in flight? > > > I was mainly thinking of satellite systems, but failed to remember the > latency problems associated with them so the videoconferencing example > wouldn't work. (not enough coffee today... :) So for latency tolerent > apps does satellite work well when traveling at air speeds? If the > footprint doesn't cover the entire area traveled how well does hand off > from one 'cell' to another work? What do the big boys like the president > and corporate execs use? > > Also, that the cellular network could crash if cell phones are used at > altitude seems like a big security hole to me. > > scott > > Jacob, Since Sue H. has my posting privs nuked (since last fall), I can't post this to the entire list but, I can explain the reasoning behind not using cell phones on aircraft from the cellular carrier point of view. In a previous life, I was an engineer for a very large cellular carrier in the southern US. It has absolutely NOTHING to do with not being able to track the call or bill for the time. If the mobile and the MTSO (mobile telephone switching office) are able to agree on which site has the call during call initiation, the call can be established. If it is establisted, it is logged. Once it is logged, it can be billed. On the analog cell system, the cell site has one of more signaling channel and what is called a scanning receiver. In addition to these, there are regular channels. The signaling channel is used to initiate calls to/from the mobile. The MTSO keeps track of the LKA (last known area) of the mobile. When a call is placed to that mobile, the MTSO will send a message on the signaling channel of the cellsite that the mobile was last known to be in. This message says "mobileID #nnn-nnn-nnnn, I have a call for you. If you're there, TX on channel XXX with a SAT tone of YYY." The cellsite then listens on channel XXX for a carrier with a SAT tone of YYY. If it hears the mobile there, it then says "OK. I hear you there. Cause the mobile phone to ring and let the guy know he ha a call." The phone rings. If the user answers the call, it tells the cellsite over channel XXX, which in turn tells the MTSO. The MTSO then tells the cellsite, over the signaling channel, "OK. You listen on channel ZZZ for me with a SAT tone of QQQ. If you hear me, let me know over the signaling channel and we'll establish a two-way link and tie your call up." The "handoff" process is very similar. The MTSO is asking all of the surrounding cellsites to listen for you on channel XXX with a SAT tone of YYY and tell it how strong it hears you. When there is a cellsite that claims to hear you better than the site you're currently using, the whole "listen for me, I'll listen for you and we'll use these SAT tones to authenticate ourselfs" process goes on to hand your call off to the new cellsite. This is all fine and dandy and will work, although sub-optimum, with the mobile airborn. The problem comes from a process called "foreign carrier detect." If a cellsite hears someone on its scanning receiver, it reports this to the MTSO. The MTSO knows what calls it is tracking and which cellsites should be adjacent to and hearing those calls. If a cellsite is hearing a call that, by design, it should NOT be hearing, the MTSO will alarm for "foreign carrier detect" and shut that channel down on that cellsite. The reason is that the MTSO thinks that it is some "foreign carrier" that could cause problems for a REAL call. It doesn't want that so, it shuts that channel down with a FCD alarm to prevent it. Since the original analog system consisted of 600-so channels, divided equally between the A-wireless and B-wireline carriers, the systems were designed to share channels. It re-used channels throughout the network, only it did so at distances at which two cellsites using the same channels would not hear each other or each others client mobiles. Now, you put one of those mobiles in the air and not only can it hear every cellsite that is using the particular voice channel but, every scanning receiver at every cellsite in a network is most likely going to hear the airborne mobile and start a cascading foreign carrier detect shutdown of channels, network-wide. As the mobile is handed off from site to site, it is likely that it is going to use a different channel and then THAT channel gets put out of service because of a FCD alarm. To add to it, it is not system specific. Depending on the size of the MSA (metropolitin service area) or RSA (rural service area) footprint, there may be as many as 4 or 5 cellular network carriers effected in this cascading failure by a SINGLE airborne mobile. So, now you know one of the more UNKNOWN reasons why it is not legal to use a cell phone while airborne. It is a great way to DoS the network and the carriers, subscribers, and FCC don't want that. I would greatly appreciate it if you would post this to the list since, as I stated to begin with, I don't have post access to NANOG. --- John Fraizer EnterZone, Inc
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