A brief summary of industrial switch technology

A brief summary of industrial switch technology

Industrial switches, Ethernet switch equipment used in the industrial control field, use the transparent and unified TCP/IP protocol, which has no essence in terms of data link layer, network layer, protocol layer, etc. between itself and the business network The difference, the editor of Feichang Technology will introduce the industrial switch technology in detail for everyone. If you are interested, let's take a look!

General summary and introduction of industrial Ethernet switch products:

(1) Switch-through forwarding technology: (Cut-through)

Once the switch interprets the destination address of the packet, it starts to send the packet to the destination port. Usually, when the switch receives the first 6 bytes of the data packet, it already knows the destination address, so it can decide which port to forward the data packet to. The advantages of the cut-through forwarding technology are fast forwarding rate, reduced delay and improved overall throughput. The disadvantage is that the switch has already started data forwarding before it has completely received and checked the correctness of the data packet. In this way, in an environment with low communication quality, the switch will forward all complete data packets and error data packets. This actually brings a lot of junk communication packets to the entire switching network, and the switch will be misunderstood as a broadcast storm. In short, the cut-through forwarding technology is suitable for a network environment with better network link quality and fewer error packets.

Switch store and forward technology: (Store-and-Forward)

Store-and-forward technology requires the switch to decide how to forward after receiving all data packets. In this way, the switch can check the integrity and correctness of the packet before forwarding. The advantage is: no incomplete data packet forwarding, reducing potential unnecessary data forwarding. The disadvantage is that the forwarding rate is slower than the direct forwarding technology. Therefore, the store-and-forward technology is more suitable for the network environment with ordinary link quality.

(2) Delay: (Latency)

Switch delay refers to the time interval from when the switch receives a data packet to when it starts to copy the data packet to the destination port. There are many factors that affect the delay, such as forwarding technology and so on. Switches using cut-through forwarding technology have a fixed delay. Because the straight-through switch does not care about the overall size of the data packet, but only determines the forwarding direction based on the destination address. Therefore, its delay is fixed and depends on the decoding rate of the destination address in the first 6 bytes of the data packet by the switch. Since the switch adopting store and forward technology must receive the complete data packet before it starts to forward the data packet, its delay is related to the size of the data packet. The data packet is large, the delay is large; the data packet is small, the delay is small.

(3) Management function: (Management)

The management function of the switch refers to how the switch controls the user's access to the switch and how much the user can see the switch. Usually, switch manufacturers provide management software or meet third-party management software to remotely manage the switch. General switches meet SNMP MIB I / MIB II statistical management functions. However, more complex switches will support the RMON active monitoring function through the built-in RMON group (mini-RMON). Some switches also allow an external RMON probe to monitor the network status of optional ports.

(4) Single/multiple MAC address types: (Single- versus Multi-MAC)

Each port of a single MAC switch has only one MAC hardware address. Each port of a multi-MAC switch is bundled with multiple MAC hardware addresses. Single MAC switches are mainly designed to connect end users, network shared resources or non-bridged routers. They cannot be used to connect hubs or network segments that contain multiple network devices. Multi-MAC switches have enough memory for multiple hardware addresses on each port. Each port of a multi-MAC switch can be regarded as a hub, and a multi-MAC switch can be regarded as a hub of a hub. The size of the memory buffer of each manufacturer's switch is different. The size of the Buffer capacity limits the exchange address capacity that the switch can provide. Once this address capacity is exceeded, some switches will discard data packets from other addresses, and some switches will copy the data packets to each port without switching.

(5) External monitoring support: (Extendal Monitoring)

Some switch manufacturers provide a "monitoring port" that allows an external network analyzer to be directly connected to the switch to monitor network conditions.

(6) Extension tree: (Spanning Tree)

Since the switch is actually a multi-port transparent bridging device, the switch also has the inherent problem of bridging devices—"Topology Loops". When a data packet of a certain network segment is transmitted to another network segment through a certain bridge device, and the returned data packet returns to the source address through another bridge device. This phenomenon is called "topological ring". Generally, the switch adopts the extended tree protocol algorithm to let each bridge device in the network know each other, and automatically prevents the topology ring phenomenon. By disconnecting a certain port in the detected "topological ring", the switch achieves the purpose of eliminating the "topological ring" and maintaining the integrity of the topology tree in the network. In network design, "topological ring" is often recommended for the selection of redundant backup links for critical data links. Therefore, switches with extended tree protocol support can be used to connect key resources in the network for switching redundancy.

(7) Full Duplex: (Full Duplex)

The full-duplex port can send and receive data at the same time, but this requires the switch and the connected device to support full-duplex operation. The switch with full-duplex function has the following advantages:

1. High throughput (Throughput): Twice the communication throughput of simplex mode.

2. Collision Avoidance: No collision is sent/received.

3. Improved Distance Limitation: As there is no collision, it is not limited by the length of the CSMA/CD link. The length limit of the communication link is only related to the physical medium.

The protocols that currently support full-duplex communication are: Fast Ethernet, Gigabit Ethernet and ATM.

Virtual Local Area Network (VLAN)

The development of switching technology has also accelerated the application of new switching technology (VLAN). By dividing the enterprise network into virtual network VLAN network segments, network management and network security can be strengthened, and unnecessary data broadcasting can be controlled. In a shared network, a physical network segment is a broadcast domain. In a switched network, the broadcast domain can be a virtual network segment composed of a group of arbitrarily selected layer 2 network addresses (MAC addresses). In this way, the division of work groups in the network can break through the geographical restrictions in the shared network, and is completely divided according to management functions. This grouping mode based on workflow greatly improves the management functions of network planning and reorganization.

Workstations in the same VLAN, no matter which switch they are actually connected to, the communication between them is as if they were on separate hubs. The broadcast in the same VLAN can only be heard by the members in the VLAN, and will not be transmitted to other VLANs, so that unnecessary broadcast storms can be well controlled. At the same time, if there is no routing, different VLANs cannot communicate with each other, which increases the security between different departments in the enterprise network. Network administrators can comprehensively manage the exchange of information between different management units within the enterprise by configuring routes between VLANs. The switch divides the VLAN according to the MAC address of the user workstation. Therefore, the user can freely move and work in the corporate network, no matter where he accesses the switching network, he can communicate freely with other users in the VLAN.

VLAN can be composed of mixed network type equipment, such as: 10M Ethernet, 100M Ethernet, etc., can be workstations, servers, hubs, network uplink backbones, etc.

The management of VLAN requires more complex specialized software. It meets the functions of VLAN division and monitoring of the entire network through comprehensive management of management objects such as users, MAC addresses, switch port numbers, and VLAN numbers, as well as other extended management functions. The more common VLAN division method is based on MAC address. But there are also switches from some manufacturers that provide more VLAN division methods: MAC addresses, protocol addresses, switch ports, network application types, user permissions, and so on.

When choosing a switch, users should carefully examine the VLAN function of the switch they choose, and choose a switch that meets the requirements and is easy to manage according to the actual needs of their own enterprise. At the same time, we should pay special attention to the incompatibility between VLANs of switches of different manufacturers.