How the switch works and the kind of distinction

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.

1, the definition of the 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 100MB Ethernet ports, FDDI ports, or 155MB ATM ports, to ensure the transmission performance of the entire network.

2, 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) The port density can be compared with the hub, the general network system is 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.

3, 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. Switch (two-layer switching) Working principle switch and bridge, is a networking device that works at the link layer, each port has bridging capabilities, each port can connect to a LAN or a high-performance Web site or server, and can learn about the device connectivity for each port through self-learning. 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 disadvantage is that 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.

4, the configuration of the switch

The following is an example of Cisco's Catlystl900 Switch, which describes the general configuration process for switches.

For a new Catlystl900 switch, use its default configuration to work. This is because it is a hardware device that will install software in Flashmemory, when power is added, it first has to carry on a series of self-test, after testing all ports, the switch is in working state. At this time its exchange table is empty, it can learn from the various ports of the device connectivity, and the device's MAC address recorded in the exchange table, when there is information exchange, the switch according to the exchange table for data forwarding.

However, to facilitate network management, the Catlystl900 switch itself has a MAC address, which allows it to assign an IP address and a screen code. The network administrator must connect a terminal or emulation terminal through the serial port of the switch to assign an IP address to it, the default value is 0. 0. 0. 0. After you specify an IP address, your network administrator can manage it remotely over the network. The configuration interface of the Catlystl900 switch is the menu form, with all ports belonging to the same VLAN under the default configuration, and in many cases no modification is required.

(1) The computer serial port through RS 1232 cable and cata1yst1900 console port connection, running simulation terminal software, Catalyst 1900 after the start.

(2) Enter the main menu after entering the carriage.

(3) Press "S" key, enter System configuration menu: (Configure system name, location, date).

(4) In the main menu, press "N" key to enter the network Management menu.

(5) Configure IP placement.

(6) Configure SNMP parameters.

5, the type of switch

A switch is a data link layer device that connects multiple physical LAN segments to a large network, and network-like switch transmission and overflow is based on MAC address transmission. Because the switch is hardware implemented, the transfer speed is very fast. When transferring packets, the switch either uses a storage---forwarding exchange or a broken-----through exchange Mode. There are many types of switches, including ATM switches, LAN switches, and different types of WAN switches.

ATM Switches

The ATM (asynchronous Transfer Mode) switch provides high-speed exchange of information and scalable bandwidth for Workgroups, enterprise network hubs, and many other areas. ATM switches support Voice, video, and text data applications and can be used to exchange fixed-length information units (sometimes called elements). A corporate network is made up of multiple LANs connected by an ATM hub link.

LAN switch

LAN switches are used for the mutual connection of multiple LAN segments, which make dedicated, conflict-free communication between network devices, while supporting conversations between multiple devices. LAN switches are primarily used for high-speed exchange of data frames. Interconnect a 0Mbps Ethernet network with a 100Mbps Ethernet via a LAN switch.