A switch has the amazing property (particularly for the already-overworked network administrator) that its table is built automatically, dynamically, and autonomously - without any interference from a network administrator or from a configuration protocol. In other words, switches are self-learning. This capability is accomplished as follows:
As illustrated in Figure 1, modern Ethernet LANs use a star topology, with each node connecting to a central switch. Up until this point, we have been unclear about what a switch actually does and how it works. The role of the switch is to receive incoming link-layer frames and
As discussed earlier, weve referred to Ethernet as if it were a single protocol standard. But in fact, Ethernet comes in many different flavors, with somewhat bewildering acronyms such as 10BASE-T, 10BASE-2, 100BASE-T, 1000BASE-LX, and 10GBASE-T. These and many other
When the nodes are interconnected with a hub (as opposed to a link-layer switch), as shown in Ethernet Figure 2, the Ethernet LAN is a true broadcast LAN - that is, when an adapter transmits a frame, all of the adapters on the LAN receive the frame. Because Ethernet can employ
We can learn a lot about Ethernet by examining the Ethernet frame, which is illustrated in Figure 1. To give this discussion about Ethernet frames a tangible context, lets consider sending an IP datagram from one host to another host, with both hosts on the same
Ethernet has pretty much taken over the wired LAN market. In the 1980s and the early 1990s, Ethernet faced many challenges from other LAN technologies, including token ring, FDDI, and ATM. Some of these other technologies succeeded in capturing a part of the LAN market for
Because there are both network-layer addresses (for instance, Internet IP addresses) and link-layer addresses (that is, MAC addresses), there is a need to translate between them. For the Internet, this is the job of the Address Resolution Protocol (ARP).
Nodes that is hosts and routers have link-layer addresses. Now you might find this surprising, recalling from "The Network Layer" that nodes have network-layer addresses as well. You might be thinking, why in the world do we need to have addresses at both the network and link
Remember that two desirable properties of a multiple access protocol are (1) when only one node is active, the active node has a throughput of R bps, and (2) when M nodes are active, then each active node has a throughput of nearly R/M bps. The ALOHA and CSMA protocols have
The second broad class of multiple access protocols are random access protocols. In a random access protocol, a transmitting node always transmits at the full rate of the channel, namely, R bps. When there is a collision, each node involved in the collision repeatedly retransmits its