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Practical TCP/IP and Ethernet Networking- P21: One of the great protocols that has been inherited from the Internet is TCP/IP and this is being used as the open standard today for all network and communications systems. The reasons for this popularity are not hard to find. | 182 Practical TCP IP and Ethernet Networking Figure 10.6 Fast Ethernet hub interconnection 10.6 Switches Ethernet switches are an expansion of the concept of bridging and are in fact intelligent self-learning multi-port bridges. They enable frame transfers to be accomplished between any pair of devices on a network on a per-frame basis. Only the two ports involved see the specific frame. Illustrated below is an example of an 8 port switch with 8 hosts attached. This comprises a physical star configuration but it does not operate as a logical bus as an ordinary hub does. Since each port on the switch represents a separate segment with its own collision domain it means that there are only 2 devices on each segment namely the host and the switch port. Hence in this particular case there can be no collisions on any segment In the sketch below hosts 1 7 3 5 and 4 8 need to communicate at a given moment and are connected directly for the duration of the frame transfer. For example host 7 sends a packet to the switch which determines the destination address and directs the package to port 1 at 10 Mbps. Figure 10.7 8-Port Ethernet switch LAN system components 183 If host 3 wishes to communicate with host 5 the same procedure is repeated. Provided that there are no conflicting destinations a 16-port switch could allow 8 concurrent frame exchanges at 10 Mbps rendering an effective bandwidth of 80 Mbps. On top of this the switch could allow full-duplex operation which would double this figure. 10.6.1 Cut-through vs store-and-forward Switches have two basic architectures cut-through and store-and-forward. In the past cut-through switches were faster because they examined the packet destination address only before forwarding the frame to the destination segment. A store-and-forward switch on the other hand accepts and analyzes the entire packet before forwarding it to its destination. It takes more time to examine the entire packet but it allows the switch to catch certain .
