Planet ISW-511S15 [24/28] Switchoperation

4. SwITCh OpeRATION

4.1 Address Table

The Industrial Fast Ethernet 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. This information comes from the learning

process of Industrial Fast Ethernet Switch.

4.2 Learning

When one packet comes in from any port. The Industrial Fast Ethernet

Switch will record the source address, port no. And the other related

information in address table. This information will be used to decide

either forwarding or ltering for future packets.

4.3 Forwarding & Filtering

When one packet comes from some port of the Industrial Fast Ethernet

Switch, it will also check the destination address besides the source

address learning. The Industrial Fast 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 Industrial Fast 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, then

this packet will be ltered. Thereby increasing the network throughput

and availability.

4.4 Store-and-Forward

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

Store-and-Forward Industrial Switch stores the incoming frame in an

internal buffer, do the complete error checking before transmission.