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Cellular Phone Forum / General / GSM / April 2008Mobile Laptop on EDGE/GPRS
We will be installing GPRS/EDGE cards in company laptops. Our application requires that the card pass the cell tower's ID to the laptop so our laptop can know which cell tower it's currently connected to. Is this possible? > We will be installing GPRS/EDGE cards in company laptops. Our > application requires that the card pass the cell tower's ID to > the laptop so our laptop can know which cell tower it's > currently connected to. Is this possible? It should be possible, given a few assumptions. When you say "which cell tower it's currently connected to", will these devices be actually connected (with a circuit-switched connection), attached with an active GPRS session, or in idle mode (camped on a cell but not interacting with it)? Reading the cell ID should be straightforward in idle mode, but will be trickier if the laptop is talking to something else /through/ the card at the time. You may have to momentarily suspend that connection/session, in order to have a brief conversation with the card itself. Some networks in some parts of the world broadcast a textual cell name (a "cell broadcast" or "area info" message) as well as a unique numeric cell ID. With most modern GSM modem cards, reading both should be possible. But good luck if you're looking for software "off-the-shelf" to do these things. John Thanks, John: > When you say "which cell tower it's currently connected to", > will these devices be actually connected (with a > circuit-switched connection), attached with an active GPRS > session, or in idle mode (camped on a cell but not interacting > with it)? We are interested in knowing which cell tower we are connected to, just prior to initiation of the GPRS session. Connection will be telemetry data, no voice. The mobile laptop with GPRS card will be camped on a cell site but not interacting with it. Then our server will attempt to initiate a connection to it. The GPRS network will find our laptop. Our laptop needs to know at that time (or immediately before) which cell site it is connected to so it can report that in its response back to the server. We prefer connections to be TCP-IP rather than circuit-switched. Does all this sound possible? > Reading the cell ID should be straightforward in idle mode, but > will be trickier if the laptop is talking to something else > /through/ the card at the time. You may have to momentarily > suspend that connection/session, in order to have a brief > conversation with the card itself. That should be fine. We only need to know the cell ID when in idle, waiting for a request from our server. That's the ID we will report back through our laptop application after the connection is made. > Some networks in some parts of the world broadcast a textual > cell name (a "cell broadcast" or "area info" message) as well > as a unique numeric cell ID. With most modern GSM modem cards, > reading both should be possible. Can you refer me to a Website where this information is available? We'll need to write the S/W to get the cell site ID from the card. We'll also need to be able to do a lookup of the cell site ID to determine its physical location. > But good luck if you're looking for software "off-the-shelf" to > do these things. Many thanks, Henry > We are interested in knowing which cell tower we are connected > to, just prior to initiation of the GPRS session. Connection [quoted text clipped - 6 lines] > to the server. We prefer connections to be TCP-IP rather than > circuit-switched. Does all this sound possible? Assuming your modem card supports the necessary commands, this will be easy. Below is an annotated log of a session with a Siemens S55 phone. I'll start by using "AT+CREG?" to ask about phone registration status. AT+CREG? +CREG: 0,1 OK I'm now changing the "+CREG" behaviour to report cell ID as well, and also give me unsolicited results. By "unsolicited results" I mean that the phone will report all changes of cell ID automatically, when they happen, without my entering any more commands. AT+CREG=2 OK I'll ask again about registration status, and this time the LAC and cell ID will be reported as well. AT+CREG? +CREG: 2,1,"1030","639E" OK LAC (location area code) is 1030 hex (4144 decimal), and cell ID is 639E hex (25502 decimal). +CREG: 1,"1030","1401" The above is an unsolicited result code, showing me that the phone has now camped on another cell (same LAC, but cell ID is now 5151 decimal). I'll now ask which network I'm using. This will show my SIM's home network, because the second argument in the "+CREG:" result above, "1", says that the phone is currently registered on the home network (rather than roaming). AT+COPS? +COPS: 0,0,"Telstra" OK Now I want to see the registered network in numeric format, so I'll ask for that. AT+COPS=0,2 OK AT+COPS? +COPS: 0,2,"50501" OK The operator part of the result consists of a 3-digit country code "505" (MCC = Australia), and a 2-digit network code within that country (MNC = Telstra). Note that some countries (North America) use a 3-digit MNC as well as a 3-digit MCC). The reason I'm showing the MCC + MNC detail is that the cell ID is only guaranteed to be absolutely unique if it consists of the whole MCC + MNC + LAC + ID string, eg "505 01 1030 639E" +CREG: 1,"1030","639E" That was another unsolicited result showing that the phone changed cell again. Now I'll ask the phone to scan all possible channels (takes a while) and give me a list of all visible carriers. AT+COPS=? +COPS: (2,"Telstra",,"50501"),(3,"vodafone AU",,"50503"),(3,"YES OPTUS",,"50502) OK > Can you refer me to a Website where this information is > available? We'll need to write the S/W to get the cell site > ID from the card. We'll also need to be able to do a lookup > of the cell site ID to determine its physical location. Any version of GSM 07.07 (or the later 2G/3G replacement, 3GPP 27.007) will give you the full syntax of the above commands. They're widely available on the net, including free official downloads from www.etsi.org or www.3gpp.org John John, that was extremely helpful. Thank you very much. One final question, that I now realize I should have asked earlier but didn't think it would be an issue. The purpose of obtaining the cell ID is so that we can determine approximate location of the tower and our client connected to it. I was just told, however, that the networks keep tower locations secret. If that's true we would be unable to determine tower location even if we have the cell ID. Do you know if this is the case? Henry. >> We are interested in knowing which cell tower we are connected >> to, just prior to initiation of the GPRS session. Connection [quoted text clipped - 97 lines] > > John >John, that was extremely helpful. Thank you very much. > [quoted text clipped - 6 lines] >would be unable to determine tower location even if we have the cell ID. Do >you know if this is the case? Perhaps this might be of some help. http://www.sitefinder.ofcom.org.uk/ Chris Hi Chris, Thanks, but I didn't see a way to look up individual tower locations on that site, but it's for the U.K. anyway. I've been told that U.S. carriers keep their tower locations secret. The only way I've found to get tower location info so far is to use Websites that cellular users contribute to, where they report the locations and cell IDs of towers using their cell phones. That seems like it's bound to be incomplete and full of inaccuracies. Hope there's a better way. Henry. >>John, that was extremely helpful. Thank you very much. >> [quoted text clipped - 14 lines] > > Chris >Hi Chris, > [quoted text clipped - 8 lines] >That seems like it's bound to be incomplete and full of inaccuracies. Hope >there's a better way. OK. Sorry, I didn't realise you were in the US. Chris > John, that was extremely helpful. Thank you very much. > [quoted text clipped - 7 lines] > unable to determine tower location even if we have the cell > ID. Do you know if this is the case? For the USA, I don't know if you can look up that info anywhere. If you're working in a limited area, some GSM devices can help you find cell locations for yourself. I have Siemens phones, and Wavecom and Falcom (Wavecom engine) modems which let me read TA (timing advance). This will give distance to the cell with an accuracy of about 550 metres. Do some intensive automated logging with GPS correlation from a moving device, and you can quickly build up a good picture of where the cells are. Here's a Wavecom modem, using "AT+CREG=2" to tell me about cell ID changes, and "AT+CCED=1,4" (a Wavecom proprietary command) to tell me the last-negotiated TA value: +CREG: 1,"1030","639E" AT+CCED=1,4 OK +CCED: 8 TA = 8, so I'm about 4 to 4.5 km from this cell. Now I'll do a free "supplementary services" command to force the modem to interact with the network. This automatically refreshes the TA value (the distance to the cell). AT+CLIP? +CLIP: 0,1 OK I didn't get a fresh "+CCED:" unsolicited result, so the TA value remains at 8 (valid TA range is 0 through 63). +CREG: 1,"1030","1401" We've had a change of serving cell, so I'll do: AT+CLIP? +CLIP: 0,1 OK and get +CCED: 4 discovering from this that this new cell is about 2 km away. Unfortunately, there isn't a GSM standard command for reading TA, so you're reliant on your device manufacturer providing one. On the Siemens phone, I use a variant of the Siemens proprietary "AT^SSTK" command. John > For the USA, I don't know if you can look up that info anywhere. I agree - so far I haven't found an open database of GSM tower locations in the U.S. except for a couple user-contributed ones such as: http://www.navizon.com/navizon_v-gps.asp which I doubt are accurate or complete for all GSM service providers. > If you're working in a limited area, some GSM devices can help > you find cell locations for yourself. I have Siemens phones, [quoted text clipped - 4 lines] > and you can quickly build up a good picture of where the cells > are. In my case, however, I have to determine my geographic location independently of GPS. All I need to do is to relate a GSM tower's cell ID to a location very roughly. But even that rough tower location data seems to be unavailable. I assume a way around this would be to purchase an API from every service provider, but this involves considerable expense, and there is no assurance that all providers would be willing to do this. So ONLY the network service providers can sell tower-based geo-location services (ie - triangulation) because they alone have the tower location data? Henry > In my case, however, I have to determine my geographic > location independently of GPS. All I need to do is to relate > a GSM tower's cell ID to a location very roughly. But even > that rough tower location data seems to be unavailable. I was thinking that you might be able to map the locations for yourself as a separate exercise, prior to your implementing your proposed main system. This would involve writing an additional purpose-built application to initially correlate GPS, cell ID and TA data as a foundation for the real application. How feasible this is would depend on the geographical area you want to cover. Obviously, covering a significant part of a country the size of the US in this way would be completely out of the question (except for a large organization like google). > I assume a way around this would be to purchase an API from > every service provider, but this involves considerable [quoted text clipped - 4 lines] > geo-location services (ie - triangulation) because they alone > have the tower location data? I agree that the secrecy is likely motivated by purely commercial concerns. John Yep, it would be a huge job to map (and then keep updated) the towers ourselves because we need to be operable throughout the U.S. But thank you for all the good info, John. I've learned a lot! Henry >> In my case, however, I have to determine my geographic >> location independently of GPS. All I need to do is to relate [quoted text clipped - 26 lines] > > John >John, that was extremely helpful. Thank you very much. > [quoted text clipped - 6 lines] >would be unable to determine tower location even if we have the cell ID. Do >you know if this is the case? I don't think they advertise them, but most cells towers are pretty ugly looking things. In addition you get the distance from the tower from the timing advance. So while they don't advertise the location, the actual locations are in fact, hard to hide. >Henry. > [quoted text clipped - 99 lines] >> >> John |
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