What is compressed mode, what is it's function, and what impact does it have on the network?

Compressed mode is when the mobile goes into a slotted transmit mode whereby it opens up an idle period (transmission gap) where it can monitor another carrier or technology (GSM). The impact is that to maintain the same bit rate, it halves the SF, and therefore increases power level causing higher interference to the network. If the SF cannot be halved then the bit rate of the bearer decreases. If they seem knowledgably, ask them if they know what messages and events trigger and configure compressed mode on/off. 2D event for on, 2F for off.  Messages would for configuration would be RADIO BEARER RECONFIGURATION, TRANSPORT CHANNEL RECONFIGFURATION or PHYSICAL CHANNEL RECONFIGURATION.