All animals are equal but some animals are more equal than others.
-George Orwell, Animal Farm, 1945.
In Chapter 4 we discussed how network packets are routed from a host application to a Mobile End System attached to a CDPD network. However, we did not cover any details about how the mobile device attaches itself to the network, and in doing so, how it shares the precious airlink resources with other mobile devices on the channel.
In CDPD, mobile devices attach to the network infrastructure via radio frequency channels. However, this requires many steps, from the creation of an analog waveform on a transmitter to transporting data packets. To perform these operations, the CDPD system relies on a collection of layered protocols. This collection of protocol layers that span the physical channel to the network layer is called the A-Interface.
In this chapter, we shall delve into some of the logistics, protocols and procedures associated with getting a Mobile End System onto the network via the A-Interface.