Research Pre GSM Modem Protocol

Here we are collecting informations about the modem protocol. At the moment all the research is don on the european UMTS version of the Palm Pre. The CDM version is likely to be pretty similar to the UMTS variant with regards to the protocol.

What we are doing to get used to the protocol is to strace the different applications that talk to the modem and log everything that goes over /dev/modemuart to the actual modem. From this wire protocol traces we are working backwards to the actual protocol and packet format.

Packet Start

A new packet starts with: 0x7A

Packet End

A packet ends with: 0x7E

Escaping

For the packet end marker there is an escaping sequence inside the packet. It is used 0x7D 0x5E instead.