Network Layer Cake Model

The purpose of this module is to mention the "network layer cake model" and its implications. The layer cake model, in essence, divides up networking activity into a number of layers: the physical level, the link level, the network level, the transport level, the applications level etc.

The purpose of this model is to clarify the fact that each layer exists on different kinds of network, and that (within reason) the different kinds of network can be mixed and matched.

To take some practical examples of this, an Ethernet (a kind of physical network) can carry many different kinds of networking protocol: Internet (IP), Novell, Appletalk, DECNET etc. and furthermore, a given type of networking protocol can be carried over different kinds of physical network (IP for example can be carried over Ethernet, point-to-point links, even over radio). To add even more complication, some networking protocols can be encapsulated in other protocols, with the encapsulation being stripped off elsewhere. The most complex situation that we encounter is the Particle Physics DECNET network, that is carried over an X25 network, which in turn is carried over the IP network!!

That was a whirlwind tour of the layer cake model, and not particularly well explained I fear, but I haven't time for a full exposition. Suffice it to say that within the Department, we make use of the following combinations:

Over Ethernet (chiefly twisted pair, but some thin co-axial):
- IP (Internet protocols)
- Novell protocol (LAN protocol)
- Appletalk protocol
- DECNET protocol
- LAT (DEC local terminal protocol)
- etc.
Over Localtalk/Phonenet
- Appletalk protocol
- IP (Internet protocols)
- (DECNET may be feasible, but we don't use it)

In addition, the university maintains a campus highway using FDDI (100Mbit/s) which carries many of these protocols, and interconnects with the rest of the campus (Appletalk, Novell) or with the rest of the known universe (Internet). I won't try to go into detail about how the Particle Physics DECNET arrangements work.