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4. SWITCH OPERATION
4.1 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.
4.2 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.
4.3 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 increase the network throughput and availability.
4.4 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 the network traffic to its respective
domain, reducing the overall load on the network.
The Switch performs "Store and forward" therefore, no error packets occur. More reliably, it reduces the re-transmission
rate. No packet loss will occur.
4.5 Auto-Negotiation
The STP ports on the Switch have built-in
“
Auto-negotiation
”
function. This technology automatically sets the best possible
bandwidth when a connection is established with another network device (usually at Power On or Reset). This is done by
detect the modes and speeds at the second of both device is connected and capable of, both 10Base-T and 100Base-TX
devices can connect with the port in either Half- or Full-Duplex mode. 1000Base-T can be only connected in Full-duplex
mode.
