The principle and main features of the switch

A switch is a network device used to forward electrical signals. It can provide an exclusive electrical signal path for any two network nodes connected to the switch. The most common switch is an Ethernet switch. Other common ones include telephone voice switches, optical fiber switches, and so on.

The main functions of the switch include physical addressing, network topology, error checking, frame sequence and flow control. At present, the switch also has some new functions, such as support for VLAN (virtual local area network), support for link aggregation, and some even have the function of a firewall.

Working at the data link layer, the switch has a high-bandwidth back bus and internal switching matrix. All ports of the switch are connected to this back bus. After the control circuit receives the data packet, the processing port will look up the address comparison table in the memory to determine the destination MAC (hardware address of the network card) and the NIC (network card) connection On which port, the data packet is quickly transmitted to the destination port through the internal switching matrix. If the destination MAC does not exist, it will be broadcast to all ports. After receiving the port response, the switch will "learn" the new address and add it to the internal MAC Address table. The switch can also be used to "segment" the network. By comparing the MAC address table, the switch allows only necessary network traffic to pass through the switch. Through the filtering and forwarding of the switch, the collision domain can be effectively reduced, but it cannot divide the network layer broadcast, that is, the broadcast domain. The switch can transmit data between multiple port pairs at the same time. Each port can be regarded as an independent network segment, and the network equipment connected to it enjoys the full bandwidth independently, without competing for use with other equipment. When node A sends data to node D, node B can send data to node C at the same time, and both transmissions enjoy the full bandwidth of the network and both have their own virtual connections. If a 10Mbps Ethernet switch is used here, then the total circulation of the switch at this time is equal to 2×10Mbps=20Mbps, and when a 10Mbps shared HUB is used, the total circulation of a HUB will not exceed 10Mbps. In short, a switch is a network device based on MAC address recognition and capable of encapsulating and forwarding data frames. The switch can "learn" the MAC address and store it in the internal address table. By establishing a temporary switching path between the originator and the target receiver of the data frame, the data frame can directly reach the destination address from the source address.

Learning: The Ethernet switch understands the MAC address of the device connected to each port, and maps the address to the corresponding port and stores it in the MAC address table in the switch cache.

Forwarding/Filtering: When the destination address of a data frame is mapped in the MAC address table, it is forwarded to the port connected to the destination node instead of all ports (if the data frame is a broadcast/multicast frame, it is forwarded to all ports) .

Elimination of loops: When the switch includes a redundant loop, the Ethernet switch avoids loops through the spanning tree protocol, while allowing the existence of backup paths.

In addition to being able to connect to the same type of network, the switch can also interconnect different types of networks (such as Ethernet and Fast Ethernet). Nowadays, many switches can provide high-speed connection ports that support Fast Ethernet or FDDI, etc., which are used to connect to other switches in the network or provide additional bandwidth for key servers that take up a lot of bandwidth.

Generally speaking, each port of the switch is used to connect to an independent network segment, but sometimes in order to provide faster access speed, we can connect some important network computers directly to the port of the switch. In this way, key servers and important users of the network have faster access speeds and support greater information flow.

Finally, briefly summarize the basic functions of the switch:

1. Like a hub, the switch provides a large number of ports for cable connection, so that the star topology can be used for wiring.

2. Like repeaters, hubs, and bridges, when it forwards frames, the switch regenerates an undistorted square electrical signal.

3. Like a bridge, the switch uses the same forwarding or filtering logic on each port.

4. Like a bridge, the switch divides the LAN into multiple collision domains, and each collision domain has an independent broadband, thus greatly improving the bandwidth of the LAN.

5. In addition to the functions of bridges, hubs and repeaters, switches also provide more advanced features such as virtual local area networks (VLANs) and higher performance.

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