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NS3503-16P-4C User Manual
5. SWITCH OPERATION
5.1 Address Table
The Switch is implemented with an address table. This address table is composed of many entries. Each
entry is used to store the address information of some nodes on the network, including MAC address,
port no, etc. This information comes from the learning process of the Ethernet Switch.
5.2 Learning
When a packet comes in from any port, the Switch will record the source address, port number and the
other related information in the address table. This information will be used to decide either forwarding or
filtering for future packets.
5.3 Forwarding & Filtering
When a packet comes from a port of the Ethernet Switching, it will also check the destination address
besides the source address learning. The Ethernet Switching will look up the address table for the
destination address. If not found, this packet will be forwarded to all the other ports except the port from
which this packet comes. These ports will transmit this packet to the network it is connected. If found,
and the destination address is located at a different port from which this packet comes, the Ethernet
Switching will forward this packet to the port where this destination address is located according to the
information from the address table. However, if the destination address is located at the same port as
this packet, then this packet will be filtered, thereby increasing the network throughput and availability.
5.4 Store-and-Forward
Store-and-Forward is one type of packet-forwarding technique. A Store-and-Forward Ethernet Switching
stores the incoming frame in an internal buffer and does the complete error checking before
transmission. Therefore, no error packets occur. 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 existence hubs, which nearly
always improves the overall performance. An Ethernet Switching can be easily configured in any
Ethernet network environment to significantly boost bandwidth using the 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 is 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 and reduces the overall load on the
network.
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