Planet FSD-803PE [21/24] Appendix b

APPENDIX B

SWITCH OPERATION

Address Table

The Switch is implemented with an address table. This address table composed of many

entries. Each entry is used to store the address information of some node in network,

including MAC address, port no, etc. The information comes from the learning process of

Ethernet Switch.

Learning

When one packet comes in from any port, the Ethernet Switch will record the source

address, port no. and the other related information in address table. These information

will be used to decide either forwarding or ltering for future packets.

Forwarding & Filtering

When one packet comes from some port of the Ethernet Switch, it will also check the

destination address besides the source address learning. The Ethernet Switch will lookup

the address table for the destination address. If not found, this packet will be forwarded

to all the other ports except the port which this packet comes in. And these ports will

transmit this packet to the network it connected. If found, and the destination address is

located at different port from this packet comes in, the Ethernet Switch will forward this

packet to the port where this destination address is located according to the information

from address table. But, if the destination address is located at the same port with

this packet comes in, when this packet will be ltered. Thereby increasing the network

throughput and availability

Store-and-Forward

Store-and-Forward is one type of packet-forwarding techniques. A Store-and-Forward

Ethernet Switch stores the incoming frame in an internal buffer, do the complete error

checking before transmission. Therefore, no error packets occurrence, it is the best choice

when a network needs efciency and stability.

The Switch scans the destination address from the packet header, searches the routing

table provided for the incoming port and forwards the packet, only if required. The fast

forwarding makes the switch attractive for connecting servers directly to the network,

thereby increasing throughput and availability. However, the switch is most commonly

used to segment existing hubs, which nearly always improves overall performance.

A Ethernet Switch can be easily congured in any Ethernet network environment to

signicantly boost bandwidth using conventional cabling and adapters.

Due to the learning function of the Ethernet switch, the source address and corresponding

port number of each incoming and outgoing packet are stored in a routing table. This

information is subsequently used to lter packets whose destination address is on the

same segment as the source address. This connes network trafc to its respective

domain, reducing the overall load on the network.

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