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Saturday, 28 April 2012

Sniffer for detecting lost mobiles


The sniffer is a small base station, it includes transceiver section. It should operate at a frequency that is much different from the frequency of the current cell in which the operation of detection is being carried out. Some of the main important things are the frequency that has to be generated by the transceiver section is around 900MHz range which is a VHF range and it is necessarily to design the oscillator circuit for that frequency range .Another important is the cooling that has to be provided to the circuit while designing the circuit that is to be operated at 900MHz range of frequency. Hence proper design of base station is an important thing in the design of the sniffer. Mobile phones as well as the base station has low power transmitter is also transmitting at low power. The transmitter of the sniffer has to be a low power transmitter. This helps in the process of reducing the interference of the device with the devices that are in the other cells.

Working Of The Sniffer Device

The sniffer is basically a transceiver that works in the frequency which is in the special unused range that is operated by the service provided or it can designed to operate at a frequency that is of much different frequency than the one that is being used by the nearby cells as there may be possibility of interference by the device with the devices in the nearby cells. The working for the device is as follows. The fig 2 &3 shows the working of the sniffer ; as given in the fig2 it gives the normal operation of the mobile with the base station and there is a BTS that acts as a middle man in the process of communication between the mobile and the MTSO which is popularly known as MSC or Mobile Switching Centre .There is always a two way communication between devices and before the establishment of the communication the authentication of the SIM card that has the IMSI or the International Mobile Subscriber Identifier

.This IMSI number helps in the authorization of the user. The second authentication is the authentication of the handset, which is done in EIR or the Equipment Identifier Register. This register is located at the MSC and it contains the IMEI number of the lost handset and if the signal is obtained from the normal one then the two way communication is established. The IMEI of the lost mobile phone number once has been reported to the service provider, who keeps in track of the record of lost mobile phones. The MTSO or the MSC which keeps in track of all the mobile phones with IMEI number and the IMSI number has the information of the lost mobile phones location which means the location of the cell where the lost device is because of the two way communication with the device the BTS of the lost device is known to MSC. From this information regarding the cell in which the device is located the sniffer device is introduced.

After the information regarding the IMEI number of the lost device is provided by the MTSO or MSC .This is then fed into the sniffers main memory the sniffer's located in particular cell gets into action of detecting the lost device. The sniffer uses a frequency that is different from the one that is being used by the base station and the located nearby cells .The base station disconnects the connection with the lost mobile phone, as there is a request regarding this action from the EIR part of the MSC. This causes the lost device to search the BTS to get locked with since each base station does not have authorization capability the lost device send appropriate connection request signal. Now when the sniffer device is being deployed and this device has in built authorization capability the lost device finds the sniffer to get itself locked to the frequency of the sniffer .


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