Data Link protocols determine how signals and data flow between nodes on the same physical network. One of the most important aspects of any Data Link technology is its method of medium access control. In this unit, we saw that Ethernet's MAC technique allows nodes to compete for access to the shared medium. Token-passing networks, such as Token Ring and FDDI, give each node a periodic opportunity to transmit.

Ethernet, the dominant Data Link protocol, comes in several versions and speeds. Basic Ethernet, the most common version, provides 10-Mbps throughput over UTP. Fast Ethernet delivers 100 Mbps over UTP, and Gigabit Ethernet offers 1,000 Mbps (1 Gbps) over STP or optical fiber. Ethernet networks are most commonly configured in a star network topology.

LAN software architectures are entire suites of layered protocols from major vendors such as Microsoft, Novell, and Apple. Each of these suites defines and uses its own proprietary protocols. However, each one typically supports some of the protocols of the others, and all support de facto standards, such as TCP/IP and NetBIOS. These shared protocols can be used to provide communication between networks based on different LAN architectures.

We also looked at two ways communication flows throughout a LAN: peer-to-peer and client/server. Peer-to-peer communication is when the nodes attached to the network are basically equal, and any node can initiate communication with any other node on the network. With client/server networking, a server is present in the network for processing client requests. Information is typically generated by the client in the form of a request to the server. The server responds with a reply to each specific request of the client.

To see how all of these layers and protocols work together, we looked at a brief example of information flow between a client and server. We reviewed how protocol headers are generated by a client computer as information is moved from an application, through communication processes, and down to the NIC. The NIC generates a frame that encapsulates the packet, message, and request. The frame is then transmitted across the communication channel. At the receiving end, information in each protocol header is used to send the request up through the protocol layers to the receiving application. Each protocol header is processed and removed (decapsulated) by the client's peer process on the receiving side.

[ Previous Section ] [ Unit Contents ] [ Next Unit ]