Planet GSW-2401, User Manual

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Chapter 3
SWITCH OPERATION
3.1 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. This information comes from the learning process
of Ethernet Switch.
3.2 Learning
When one packet comes in from any port, the 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 filtering for future packets.
3.3 Forwarding & Filtering
When one packet comes from some port of the Ethernet Switching, it will also check
the destination address besides the source address learning. The Ethernet Switching 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 Switching 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 filtered. Thereby increasing the network
throughput and availability.
3.4 Store-and-Forward
Store-and-Forward is one type of packet-forwarding techniques. A Store-and-Forward
Ethernet Switching 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 efficiency and stability.
The Ethernet 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. An
Ethernet Switching can be easily configured in any Ethernet network environment to
significantly boost bandwidth using conventional cabling and adapters.
Due to the learning function of the Ethernet switching, 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 filter packets whose destination address is
on the same segment as the source address. This confines network traffic to its respective
domain, reducing the overall load on the network.