I'm in the midst of an assignment and we have to report on the protocols for GSM (phase 2+ or G2.5) used by mobile phones. Specifically, we have to draw the transfer of packets between the phone and base station when sending an SMS. I'm guessing that there is a protocol standard for this but as yet I haven't managed to find it.

Does anyone have any experience/knowledge in this area and might be able to guide me as to where to look?

Any help MUCH appreciated