Talk about LAN switch

The internal structure of LAN switch

The excellent performance of the LAN switch comes from its unique internal technical structure. However, different exchange modes or different types of exchange are also closely related to the internal structure of LAN switch. Therefore, the understanding of the internal structure of the LAN switch equals to understand the technical characteristics and working principle of the LAN switch. At present, the internal technology structure of LAN switch mainly has the following kinds.

1. Shared-Memory Architecture

The structure relies on a full port high performance connection provided by the central LAN switch engine, and the core engine completes checking each input packet to determine the connection route. This way requires a lot of memory bandwidth and high management costs, especially with the increase in LAN switch ports, the need for greater memory capacity, faster, the price of central memory becomes very high, making LAN switch memory become the main bottleneck of performance.

2. Cross-bus architecture

Cross-bus structure can establish direct point-to-point connection between ports, this structure is very good for simple single point (Unicast) information transmission, but it is not suitable for multicast transmission of point-to-point. Because broadcasting and multicast transmission are very common in the actual network application environment, the standard crossover bus method can bring some transmission problems. For example, Port B and Port C can wait only when port a transmits data to Port D. When port a broadcasts messages to all ports, it may cause the destination port to queue up. This will consume a large amount of bandwidth in the system and thus affect the performance of the LAN switch transmission. and to connect N ports, you need the NX (n+1) Cross bus, so that the cost will also increase with the number of ports increased sharply.

3. Hybrid cross-bus architecture

In view of the defects of the standard crossover bus, a hybrid crossover bus implementation method is proposed. The design idea of this method is to divide the whole cross bus matrix into small cross matrix, which is connected by a high performance bus in the middle. The advantage of this structure is that it reduces the number of crossover buses, reduces costs, and reduces bus contention. But the bus that joins the cross matrix becomes the new performance bottleneck.

4. Ring-Bus structure

This structure supports up to four switching engines in a single ring and allows Exchange matrix interconnection at different speeds, as well as loops and loops connected through the switching engine. Because of the ring structure, it is easy to gather bandwidth. When the number of ports increases, the bandwidth increases accordingly. Unlike the previous structures, the structure has a separate control bus for collecting bus status, processing routing, flow control, and cleaning data bus. In addition, a management module can be added to the ring bus to provide complete SNMP management features. At the same time, you can choose the third-tier switching function according to the need. The biggest advantage of this structure is that it has the advantages of strong scalability, low cost, and effectively avoids the bus bottleneck caused by system expansion.

Second, the main technology of LAN switch

LAN switch because of the use of virtual circuit switching mode, the technology can be in each input, output ports between the different bandwidth, or in the absence of transmission bottlenecks, the completion of high-speed data transmission between the ports, thus greatly improving the network information points of the data transmission, optimization of the network system. The main difference between LAN switch and hub hardware is that the backplane bus and switch engine are more than two parts, which indicates that the technical content of LAN switch is generally high. So to fully understand the LAN switch, you must be aware of the main technical characteristics of the LAN switch. The following is a description of the major technologies used in LAN switches.

1. Programmable ASIC (Specific purpose integrated circuit)

This is a dedicated integrated circuit chip designed to optimize the second-tier switching process, it is also the core integration technology of the current networking solution, which integrates multiple functions on the same chip, making it easy to design, high reliability, low power consumption, higher performance and lower cost. The programmable ASIC chip, which is widely used in the LAN switch, is an ASIC chip which can be edited by the manufacturer or even the user according to the application needs, and is one of the important application technologies in the LAN switch application.

2. Distributed pipeline

With distributed pipelining, multiple distributed forwarding engines can transmit their packets quickly and independently. In a single pipeline, multiple ASIC chips can handle multiple frames at the same time. This concurrency and pipelining can improve forwarding performance to a new level. Achieve line-speed performance on-demand (Unicast), broadcast (broadcast), and multicast (multicast) on all ports. Therefore, the adoption of distributed pipeline is an important reason for the improvement of the switching speed of LAN switch.