Sunday, June 08, 2014

GSM Normal Burst Power/Time Template

The image (below) is of the power/time template to illustrate a GSM Normal Burst (GSM05.01/05.02). A single burst when transmitted may contain up to 114-bits of useful speech data. Given the speed at which GSM radio signals traverse the ether calculated in micro-seconds to be received at a destination handset and processed by that handset in milli-seconds and converted into audible speech within one or seconds opens possibilities for examiners to demonstrate the power of mobile communications.

For instance, an attacker communicating a single 'provocative' word consisting of 80-bits in a normal burst to an accomplice could be:

D               E              T              O              N             A              T               E
01000100 01000101 01010100 01001111 01001110 01000001 01010100 01000101

The entire timing of this event may last no longer that 2 seconds. When you get time try a simple test to see how many clearly audible words you can speak within 2 seconds and what messages can be communicated in that time. Moreover, the clock for recording call records can be operated in 1000-ths of a second separated into 5 x 200-ths of a second. Whilst it is possible to see a call detail record showing a 0-second call duration and it is generally accepted there is no meaningful communication taking place, what about call that lasts 1, 2 or 3 seconds?

The knowledge tool to demonstrate the GSM Normal Burst power/time template, the power output of MS and BTS etc can be found in 3GPP TS 05.05 V8.20.00 (2005-11) Release 99.

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