Daily Notes

The switch MUST track the particular hardware device that is connecting( wirelessly) to the mobile phone, as it must route the call there. In fact, every time a call is initiated, ended, or handed off from one site to another, the switch is directly involved, so it's a simple matter to record this information. However, the handoff information is not retained in the billing record. It would get quite cumbersome!

As this data is a financial record, I would expect it to be kept for a matter of years, just as receipts and invoices are kept by any business. However, I don't have certain information on that. I would think a simple letter to the cellular company would establish this.

While I am sure that the records are quite accurate, I am not a switch engineer. If you need expert testimony on the reliability of the call records, I think a switch engineer would be the most qualified person. If you wish, I can try to locate a someone. If you need testimony on the accuracy of the locations that can be inferred from such data, I
can help there. I have been troubled by the apparent delusions of expertise of some police departments in handling this kind of information. It is a complex subject, and I have seen unwarranted conclusions drawn from such data. If the call records are pivotal for a case, a qualified engineer should be consulted BEFORE any conclusions are made. It really is more complex than it looks. Let me go on a bit more.

One thing to be aware of - when you talk to someone at customer service OR the legal compliance department (whatever they call it), please remember, these folks are NOT technical people, but many THINK they are. They are not a reliable source of technical information. I've acted as expert witness a few times, and found that these people can often be quite pompous and idiotic. Part of their job is to shield the engineering departments from having to respond to endless questions, which can take up quite a bit of time. This is understandable, but it can result in them giving out wrong information, because they get on the phone with someone in engineering, and don't understand what is told them. So, they 'fill in' the gaps of their understanding, thus garbling the message. For example, the explanation you sent me from this is nonsense. I can only GUESS what was originally meant by the engineering department, now that it's been filtered through these folks.

Your best bet is to have a subpoena issued when you need the information. THEN the information should come - in writing - from the engineering folks. If you are able to get a subpoena issued, make sure that it requests information from a qualified engineer.

Regards,

Mark

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From R.C. Levine

There is no billing-related reason to keep a record of every cell or sector that a wireless handset passed through during a call. In the less usual instance of an inter-city handover during the call, the last cell in system A used before the handover, and the first cell used in system B immediately after the handover are in the individual billing station detail or automatic message accounting data (from system A and B respectively), but not other cells. I agree with Mark that you are not likely to find the history of every cell in billing data.

All cellular switches that I am familiar with (Lucent, Nortel, Ericsson and Motorola) have a capability that may be able to help you to a degree. These switches have the optional capability to record detailed call "history" including all sorts of switching related data (typically on hard disk) during a call. This can include the time and the identification numbers of the two cells involved in every handover within the call, as well as other technical information about the
condition of the radio channel (e. g., signal strength, digital bit error rate). This is provided by the manufacturer so the service provider's technical people can debug problems with radio coverage at the boundary between cells, etc. The problem is that this data only exists for past calls if the technicians had the history capture software running for that call, and furthermore if they preserved that information up to the present day.

There is also another aspect that occurs in legal cases involving cellphone: the fact that a call is being handled by one particular sector of a particular cell at a certain time does not indicate physical location with a degree of accuracy suitable for locating the wireless handset precisely. The boundaries of the sectors/cells are inherently a
little "fuzzy" -- that is to say that, for various reasons, the handover will not always occur at exactly the same spot on the path of a subscriber who is moving from one cell into another. (That is why the FCC has pressed for new and more accurate radio-location methods to facilitate finding a subscriber in distress who has made a 911 call.) To be more comprehensive I should note that in some cases the particular geography of certain cell boundaries may allow a much more accurate location to be correctly inferred. For example, consider a city with a river running through it, and only one bridge crossing the river in a region where two cells on opposite sides of the river have a common boundary approximately lying along the centerline of the river. (That is the preferred way to configure two cells on both banks of a river.) In this geographical situation, we can infer that when the subscriber was handed over from an earlier cell on one side of the river to a later cell on the opposite side, that he must have crossed via the bridge (in contrast to swimming....),

Also, some service providers have various types of FCC mandated locating facilities in place ranging from multi=antenna triangulation capability (moderate but not good accuracy) up to having certain subscribers' handsets incorporate a GPS satellite receiver and then periodically reporting their latitude, longitude and altitude above sea level (but this is currently somewhat rare, may not report anything when the handset is in a bad location for GPS radio reception like on a downtown sidewalk between tall buildings, the technicians may not have recorded cell history for that call, and they may not have saved it, etc.) [GPS=global positioning system, satellite navigation]

Another thing that you may wish to consider in conjunction with the presentation of a cell identification number is to present evidence from experts and cellular service providers own technical people regarding the radio coverage area of each cell and the margin of accuracy with which one can assert that a particular handset is within the nominal cell or sector coverage area. Most wireless systems have a sizable technical staff dedicated to continually
patrolling the streets and pedestrian areas to prepare geo.