Evaluate the advantages and disadvantages of the switch from the overall structure, performance and function

Exchange (switching) is the need to transmit information at both ends of communication, using manual or equipment automatic completion method, the information to be transmitted to meet the requirements of the corresponding routing of the technology collectively. A generalized switch is a device that completes the information exchange function in a communication system.

In http://www.aliyun.com/zixun/aggregation/11991.html "> Computer network System, the concept of exchange is proposed for the improvement of shared working mode." The Hub Hub We've been introducing is a shared device, the hub itself can not identify the destination address, when the same LAN in the host to the B host transmission data, packets in the hub-structured network is transmitted by radio, each terminal by verifying the address of the packet header information to determine whether to receive. In other words, in this mode of operation, the network can only transmit a set of data frames at the same time, if the collision has to try again. This approach is to share network bandwidth.

The switch has a very high bandwidth back bus and an internal exchange matrix. All the ports on the switch are hooked up on this back bus, after the control circuit receives the packet, the processing port finds the Address table in memory to determine the port on which Nic (NIC) is hooked on the destination Mac (the hardware address of the network card), and transmits the packet quickly to the destination port through the internal exchange matrix. If the Mac does not exist to broadcast to all ports, the receiving port responds and the switch "learns" the new address and adds it to the internal MAC address table.

Using a switch can also "segment" The network, through the control of the MAC Address table, the switch allows only the necessary network traffic through the switch. Through the switch filtering and forwarding, can effectively isolate the broadcast storm, reduce the occurrence of false packets and wrong packets, avoid sharing conflicts.

With the gradual deepening of network application, the Telecom class switch, especially the three-layer switch, has become the focus of the market contention. However, in different functions, a wide range of switch equipment, users how to remove the fog, to find their own application characteristics of the product? This not only requires users to start from the traditional switch evaluation indicators, consider the price of products, but also pay special attention to whether the product can provide some of the latest features with high value-added support.

Generally speaking, the evaluation of the advantages and disadvantages of the switch from the overall structure, performance and function of the three aspects. The overall architecture refers to the port density of the switch device, the maximum speed of the port support, the value of the exchange capacity and other basic performance parameters, so that the user can grasp the positioning and grade of the equipment in general.

In addition to the performance of the switch to meet the RFC2544 recommended basic standards, that is, throughput, delay, packet loss rate, with the increase in user business and application of in-depth, but also added some additional indicators, such as the number of MAC address, routing table capacity (three-tier switch), ACL number, LSP capacity, the number of support VPN. Take the number of MAC addresses as an example. The number of MAC addresses refers to the number of MAC addresses that can be stored in the MAC Address table of the switch, and the more MAC addresses are supported, the higher the rate of data forwarding.

function is the most direct indicator

For a general access layer switch, simple QoS guarantees, security mechanisms, support network management policies, spanning tree protocols, and VLANs are essential functions, but if carefully analyzed, some features can be further subdivided under simple representations, which are the main causes of product differences, It is also an important way to embody the value-added of products.

Application-Level QoS Assurance

In order to provide more flexibility for users in practical applications, the QoS policy of the switch must support multi-level packet priority setting, which can be prioritized for MAC address, VLAN, IP address and port respectively. At the same time, the switch also has the ability of good congestion control and traffic limit, support DiffServ differentiated service, can distinguish different application flow according to source/Aim MAC/IP intelligence, meet the demand of real-time multimedia application. At present, some of the switches in the market, although also known as a QoS guarantee, but in fact only support the single level of priority settings, for the user's actual application to bring a lot of inconvenience.