16.3 Ethernet versus ATM Networks

Recall from Chapter 14 that ATM uses fiber optic cables and specialized equipment (ATM switches) to enable computers to communicate at very high rates (Gbits per second). ATM networks were originally developed by the telecommunications industry to handle multimedia communications (combined video, voice, and data). Therefore, it is no coincidence that ATM works like voice telephone systems. Switches establish circuits between computers on a network (like a telephone call) and ATM network addresses use the same standard as telephone numbers - they have a local network number and then a prefix (like an area or country code) for communication between distant networks.^[3]

Notice that this circuit establishment is different from Ethernet. Like Ethernet, ATM encapsulates data into what are called ATM cells. However, ATM cells are not addressed in the same way as Ethernet frames. Instead of addressing a cell using the MAC address of the destination computer, ATM uses a number that identifies the circuit that the ATM network has established between two computers. Two computers will use the same circuit for the duration of their communication.

Although ATM uses a form of ARP (called ATMARP) to discover Machine Access Control (MAC) addresses, the approach that ATM takes is slightly different. Instead of allowing individual computers to respond to ARP requests, ATMARP uses a central server to keep track of IP → MAC address associations. This central server responds to all ARP requests on a given ATM network.

Although there are some differences between Ethernet and ATM, the digital evidence on each is similar. There are log files, MAC addresses, ARP tables, and encapsulated data travelling through the network cables - all of which can be a source of digital evidence.

^[3]ATM addresses contain information that is used for routing so there is some network layer functionality in ATM. However, for the purposes of this text it is sufficient to think of ATM as the physical and data-link layers.