Understand the main structure and technology of LAN switches

LAN switches are quite common. So I studied the main structure and technology of LAN switches and shared them here. I hope they will be useful to you. The superior performance of LAN switches comes from its unique internal technical structure. Different switching modes or different switching types are also closely related to the internal structure of LAN switches. Therefore, understanding the internal structure of a LAN switch is equivalent to understanding the technical characteristics and working principles of the LAN switch. Currently, LAN switches use the following internal technical structures.

1. Shared Memory Structure

This structure depends on the high-performance connection of the full port provided by the central LAN switch engine, and the core engine checks each input packet to determine the connection route. This method requires a lot of memory bandwidth and high management costs. Especially with the increase of LAN switch ports, the memory capacity is required to be larger and the speed is faster, and the price of central memory becomes very high, this makes the LAN switch memory a major bottleneck for performance implementation.

2. Cross-bus structure

The cross-bus structure can establish direct point-to-point connections between ports. This structure is good for simple single-point Unicast) information transmission, but it is not suitable for point-to-point Broadcast Transmission. In the actual network application environment, the broadcast and multicast transmission modes are very common, so this standard cross-bus mode will bring about some transmission problems. For example, when port A transmits data to Port D, port B and port C can only wait. When port A broadcasts messages to all ports, it may cause queuing of the target port. This will consume a large amount of system bandwidth, thus affecting the transmission performance of LAN switches. In addition, to connect N ports, N × N + 1) Cross bus is required, so the implementation cost will also rise sharply as the number of ports increases.

3. Hybrid cross-bus structure

In view of the defects of the standard cross bus, a hybrid cross bus implementation method is proposed. The design idea of this method is to divide the integrated cross Bus Matrix into small cross matrices, and connect them through a high-performance bus in the middle. This structure reduces the number of Cross buses, reduces costs, and reduces bus contention. However, the bus connected to the cross matrix has become a new performance bottleneck.

4. Annular bus structure

This structure supports a maximum of four switching engines in a ring, supports Switching Matrix interconnection at different speeds, and intercommunication between the ring and the ring through the switching engine. Because the ring structure is used, it is easy to aggregate bandwidth. When the number of ports increases, the bandwidth increases accordingly. Different from the preceding structures, this structure has an independent control bus used to collect bus status, process routes, control traffic, and clean up the data bus. In addition, the management module can be added to the ring bus to provide complete SNMP management features. You can also select the layer-3 switching function as needed. The biggest advantage of this structure is its strong scalability, low implementation cost, and effectively avoids the bus bottleneck caused by system expansion.

Main technologies of LAN switches

Because a LAN switch uses a virtual line exchange method, it is technically possible to use different bandwidths between input and output ports, or without a transmission bottleneck, the high-speed transmission of data between ports greatly improves the data transmission of network information points and optimizes the network system. The main difference between LAN switches and hubs in hardware is that there are more Backplane Buses and exchange engines. This shows that LAN switches have a high technical level. Therefore, to fully understand LAN switches, you must understand the main technical features of LAN switches. The following describes the main technologies used in LAN switches.

1. Programmable ASIC for specific purposes integrated circuits)

This is a dedicated IC chip dedicated for optimizing Layer 2 switching processing. It is also the core integration technology of the current networking solution. It can integrate multiple functions on the same chip, it has the advantages of simple design, high reliability, low power consumption, higher performance and lower cost. The programmable ASIC chip widely used in LAN switches is an ASIC chip that can be edited by manufacturers or even users based on application needs, it is one of the important application technologies in LAN Switch Applications.

2. Distributed Pipeline

With the distributed pipeline, multiple distributed forwarding engines can quickly and independently transmit their respective data packets. In a single pipeline, multiple ASIC chips can simultaneously process multiple frames. This concurrency and pipeline can increase the forwarding performance to a new level. Achieve On-Demand Unicast, Broadcast, and Multicast on all ports. Therefore, the adoption of distributed pipelines is an important reason for the increase in the exchange speed of LAN switches.

3. dynamically Scalable Memory

For advanced LAN switching products, high performance and high quality features are often built on an intelligent storage system. The dynamic Scalable Memory technology enables LAN switches to dynamically expand the memory capacity based on the needs of data streams during operation. To this end, part of the memory has been directly associated with the forwarding engine in the layer-3 LAN switch mode, so that it can add more interface modules. In this way, including their respective forwarding engines, the memory will be extended accordingly. At the same time, you can also dynamically construct the cache through pipeline ASIC processing to increase memory usage. This also prevents packet loss when the system processes large burst data streams.

4. Advanced queue mechanism

In fact, no matter how good the performance and quality of network devices are, no one will be affected by the Data congestion on the connected network segment. The traditional method is that the traffic through a port must be stored in the cache of only one output queue. No matter how high its priority is, it must also be handled in the first-in-first-out mode. When the queue is full, any excess parts will be discarded. When the queue grows, the latency will also increase. Obviously, the traditional queue mechanism makes it very difficult to run real-time transaction processing and multimedia applications. To this end, many network equipment vendors are developing Advanced Queuing technologies to provide different service levels on an Ethernet segment and control latency and jitter. The advanced queue mechanism can be that each port has a queue mechanism of different levels, which can better distinguish different traffic levels, so that the network system can better match with high-performance applications. Data packets such as multimedia and real-time data streams are put into high-priority queues. After the Weighted Fair queuing algorithm is used, data packets can be processed in high-priority queues more frequently, it does not ignore low-priority queues. In addition, traditional application users do not notice changes in response time and throughput, while those who use emergency applications can receive timely responses.

5. Automatic traffic classification

In network transmission, some data streams are more important than other data streams. The layer-3 LAN switch has adopted the automatic traffic classification technology to distinguish different types and levels of data traffic. Practice has proved that after the automatic traffic classification technology is used, the layer-3 LAN switch can instruct the data packet assembly line to differentiate user-specified data streams, thus achieving low-latency and high-priority transmission, it not only provides effective control and management channels for special data traffic, but also avoids network traffic congestion.

6. Intelligent permission Control

As we all know, layer-3 LAN switches can provide multiple security mechanisms for network systems. For example, after using a traffic classifier, administrators can restrict any identified data streams, this includes limiting access to the server and eliminating useless protocol broadcasts. This is the so-called intelligent permission control technology, which provides the technical basis for the breakthrough technology in the network technology field-wire speed firewall technology.

7. Dynamic Traffic Monitoring

Although advanced technologies such as traffic classification, priority processing, and resource retention of LAN switches can greatly reduce the management burden on network administrators, they cannot complete network traffic monitoring. Dynamic Traffic Monitoring is actually a protection mechanism that monitors traffic and network congestion conditions and dynamically responds to these situations to ensure that all network elements end users and networks themselves) they can all be controlled by administrators and achieve optimal operation. Many layer-3 LAN switches use the 802.1p service level to prioritize congestion over the LAN. To avoid congestion, some layer-3 LAN switches even adopt more advanced technologies to dynamically monitor the size of the output queue, so as to detect whether a port will become congested in time. By controlling the queue size and congestion, the network can maintain the limit required for latency-sensitive data streams.

8. Vector Processing Technology

Vector processing is one of the third-layer LAN switches, mainly used to speed up data frame processing. As the third-layer LAN switch architecture not only adds the third-layer control capability on the second layer, but also adds multi-faceted vector control, thus enhancing the vector processing function. Vector processing of layer-3 LAN switches has the following advantages: Fast Frame processing speed. Because LAN switches support ASIC-based data packet classification, forwarding, and interpretation technologies, frame decoding by software is minimized. Compared with pure software design, this method can achieve high performance, and has highly adaptive function control, vector processing works with programmable ASIC to support future standards with minimal overhead. For example, IPv6 support is already part of Vector Logic; enhanced management functions, multidimensional vector processing also include built-in Network Management Agents and RMON.

9. multi-chip CPU

In a high-reliability LAN switch, one or more dedicated high-performance RISCReducedInstructionSetComputer: Short Instruction Set Computer) processors are absolutely required. In fact, the combination of a frame processor FPFrameProcessor using a RISC processor and Vector Logic provides unparalleled performance. An independent application processor (APApplicationProcessor) can assist FP. Like FP, AP is also a high-performance CPU. In addition to Frame Forwarding, the AP controller also has high-level bridging and routing, such as Spanning Tree and OSPF protocols, as well as SNMP and HTTP operations. Therefore, the advantage of using AP and FP is obvious, because management and computing work does not affect data forwarding, so as to achieve high throughput and low latency.

In short, through the above technical analysis, we can easily see that high performance, security, ease of use, manageability, stackability, service quality and fault tolerance are one of the main technical features of LAN switches. With the development of multimedia services such as video conferencing, real-time multicast, network calls, program-controlled switching, and automatic call forwarding, the LAN exchange technology will develop rapidly in the direction of high bandwidth, security, service quality and intelligent technology.