Thanks for the reply, Ben.

I have looked at Robin Walkers site, but I was hoping for something more detailed as to what exactly goes on once you power up the modem.
AFAIK, basically the uBR detects the modem and forwards the connection requests to the DCHP server. The DCHP server verifies the MAC address is allowed on the network and what service config file it should be sent. The config is sent and an IP address given. However it's all the techy details I'm unsure about.
Andy.