Understanding the advantages of vswitches

Gain insight into the advantages of vswitches. To correctly understand the working principle and superiority of a vswitch, we must not mention some mainstream exchange technologies of the vswitch. On the basis of these exchange technologies, the vswitch achieves better performance than the hub, this article introduces several mainstream exchange technologies. Later, we will introduce some precautions for switch purchasing at the end of this article to help you make proper purchase.

Switch Switching Mode

Currently, vswitches use three packet exchange modes: pass-through, storage-forward, and fragment isolation when transmitting data packets from the source and target ports.

Pass-through switch Switch Mode

The ethernet switch configuration using the pass-through switching mode can be understood as a line matrix telephone switch with vertical and horizontal traffic * between ports. When a packet is detected on the input port, it checks the packet header, obtains the destination address of the packet, and starts the internal dynamic search table to convert it to the corresponding output port, connect the data packet to the corresponding port to implement the switching function.

Because it only checks the packet header, usually only 14 bytes), does not need to be stored, so the cut-in method has the advantage of low Latency and fast switching speed. The so-called delay Latency) it refers to the time it takes for a packet to enter a network device and leave the device ).

It has three main disadvantages: first, because the data packet content is not saved by the Ethernet switch, it is impossible to check whether the transmitted data packet is incorrect and the error detection capability is not provided; second, because there is no cache, the input/output ports with different rates cannot be directly connected, and packet loss is easy.

If you want to connect to a high-speed network, such as providing a Fast Ethernet 100BASE-T), FDDI, or ATM connection, you cannot simply "Connect" the input/output ports ", because there is a speed difference between the input and output ports, the cache must be provided. Third, when the port number of the Ethernet switch increases, the switching matrix becomes more complex and becomes more difficult to implement.

Storage and forwarding Switch Exchange Mode

Storage forwarding Store and Forward) is one of the most widely used technologies in the computer network field. The controller of the Ethernet switch first caches the incoming data packets from the input port and first checks whether the data packets are correct, and filter out conflicting packet errors. After confirming that the package is correct, retrieve the destination address, find the output port address to be sent through the search table, and then send the package out.

Because of this, the storage and forwarding method is insufficient when the data processing latency is large, but it can detect errors of data packets entering the switch, it also supports switching between input/output ports at different speeds, which can effectively improve network performance. Another advantage of this switching mode is that it supports switching between ports at different speeds to ensure collaboration between high-speed ports and low-speed ports. The solution is to store 10 Mbps low-speed packages and then forward them to the port at Mbps.

Fragment Free)

This is a solution between a pass-through and a storage and forwarding. Before forwarding, it checks whether the length of the data packet is 64 bytes (512 bits). If it is smaller than 64 bytes, it indicates a false packet or a residual frame), the packet is discarded; if the value is greater than 64 bytes, the packet is sent. This method processes data faster than the storage and forwarding method, but is slower than the pass-through method. However, it is widely used in low-end switches because it can avoid Frame Forwarding.

A switch that uses the switch switching mode generally uses a special cache. This cache is a kind of FIFO ofirst In First Out), where bits enter from one end and then come Out from the other end In the same order. When a frame is received, it is saved in FIFO. If a frame ends with a length less than 512 bits, the content in the FIFO frame will be discarded.

Therefore, there is no Frame Forwarding problem in a common direct-through forwarding switch, which is a very good solution. Data packets are cached and saved before forwarding to ensure that collision fragments are not transmitted over the network, which can greatly improve the network transmission efficiency.