Chapter Summary


Hubs only allow one device to transmit a frame at a single point in time, whereas LAN switches allow multiple frames to be transmitted at the same time. LAN switches also support the use of full duplex transmission, allowing a single device to send and receive frames over the same cable at the same time. These facts, along with the fact that switches buffer frames to avoid collisions, mean that networks that are built with switches have much more capacity than do similar networks built with hubs.

A switch makes a forwarding and filtering decision for each frame it receives. It compares the destination address of the frame to the MAC address table. If a match is found, the entry in the MAC address table lists the port out which the switch should forward the framethat's called the forwarding decision. By not sending the frame out the rest of the ports, the switch has filtered frames, which is known as a filtering decision.

Switches build the MAC address table by examining the source MAC address field of incoming frames, placing the MAC address and the incoming port number in an entry in the table. This process is called learning.

The IEEE has created many new and improved versions of Ethernet over the years. Interestingly, many of the details remain the samethe headers and trailers in particular, including the addresses. The one thing that has been vastly improved has been the transmission speed. 100 Mbps Fast Ethernet is installed in almost every network, Gigabit Ethernet is common for servers, and 10 GigE is now available for high-bandwidth applications.




Computer Networking first-step
Computer Networking First-Step
ISBN: 1587201011
EAN: 2147483647
Year: 2004
Pages: 173
Authors: Wendell Odom

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