Basic knowledge of switches

Many new client/server applications and the advent of multimedia technology, resulting in traditional shared network is far from satisfying the requirements, which also promote the emergence of LAN switches.

Definition of a switch

The LAN switch has many ports, each with its own dedicated bandwidth, and can connect to different network segments. The communication between each port of the switch is simultaneous and parallel, which greatly improves the information throughput.

To further improve performance, each port can also connect to only one device.

To achieve interconnection between switches or connections to high-end servers, LAN switches typically have one or several high-speed ports, such as 100M Ethernet ports, FDDI ports, or 155M ATM ports, to ensure the transmission performance of the entire network.

Second, the characteristics of the switch

Users who share a local area network through a hub are not only sharing bandwidth, but also competitive bandwidth. Communication and information processing can be delayed because individual users need more bandwidth to reduce the available bandwidth of other users or even be forced to wait.

By using the network differential segment technology of the switch, the users of a large shared LAN can be divided into many independent network segments, reducing the number of users competing for bandwidth and increasing the available bandwidth of each user, thus alleviating the congestion of the shared network.

Because the switch can send the information quickly and directly to the destination can greatly improve the speed and bandwidth, to protect the user's previous investment in the media, and provide good scalability, so the switch is not only the ideal replacement for the bridge, but also is the ideal replacement for hubs.

Compared to bridges and hubs, switches improve performance in the following ways:

(1) The information throughput of the switch is improved by supporting the parallel communication.

(2) Dividing a traditional user on a large local area network into a number of working groups, each port connecting a device or connecting a workgroup, effectively resolving the crowding present image. This method is called the network differential segment (Micro one segmentation) technology.

(3) The emergence of virtual network (Virtuai LAN) technology brings more flexibility to the use and management of switches. We'll focus on the virtual Web later.

(4) port density can match the hub

A typical network system has one or several servers, and most of them are ordinary clients. Clients need access to the server, which causes the server's communication and transaction processing capabilities to be key to the overall performance of the network.

The switch mainly improves the performance of the entire network by increasing the speed of the port connecting to the server and the corresponding frame buffer, thus satisfying the requirements of the users.

Some high-end switches also use FULL-DUPLEX technology to further improve the bandwidth of the port. The previous network equipment basically uses half-duplex work way, namely when a host sends the data packet, it cannot receive the packet, when receives the packet, cannot send the data packet.

Because the use of Full-duplex technology, that is, the host in the packet sent at the same time, can also receive packets, the normal 10M port can be turned into 20M ports, the normal 100M port can become 200M port, which further improve the information throughput.

Third, the operation principle of the switch

The traditional switch is essentially a multiport network bridge with flow control capability, that is, the traditional (two-layer) switch.

The routing technology is introduced into the switch, which can complete the network layer routing, so it is called three-layer exchange, which is the new development of the switch.

The working principle of switch (two-layer exchange)

Switches, like bridges, are networked devices that work at the link level, each with a bridging capability, each port connecting a LAN or a high-performance Web site or server, and learning to learn about device connectivity for each port. All ports are controlled by a dedicated processor and forwarded by the control management bus.

At the same time, we can use specialized network management software to manage centrally.

In addition, switches in order to improve the speed and efficiency of data exchange, generally support a variety of ways.

(1) Store forwarding:

This method is used for all conventional network bridges.

Before they send the data frames to other ports, the received frames are completely stored in the internal memory, inspected and then sent to other ports, so that the delay is equal to the time of receiving a complete data frame and the sum of processing time.

If the cascade is long, it can cause serious performance problems, but this method filters out the wrong data frames.

(2) Approach:

This method only examines the target address of the data frame, which allows the data frame to be transmitted almost immediately, thus greatly reducing the delay.

The disadvantages are:

The error frame will also be passed out. If the probability of the error frame is small, the cut method can be used to improve the transmission speed. However, when the probability of the error frame is large, the storage and forwarding method can be used to reduce the retransmission of the error frames.