1. Store and Forward:
Industrial switches running in store and forward mode must read the entire frame of data into memory and check its correctness before sending information. Although using this method takes more time than using a direct method, it can store and forward data, ensuring its accuracy. Due to the fact that industrial switches running in store and forward mode do not propagate erroneous data, they are more suitable for large local area networks.
2. Error control:
After receiving a complete frame on the port, the industrial switch compares the frame check sequence (FCS) of the last field of the datagram with its own FCS. The FCS verification process is used to help ensure that there are no physical or data link errors in the frame. If the frame verification is correct, the industrial switch will forward it; Otherwise, the data will be discarded.
3. Automatic caching:
The storage and forwarding industrial switch supports mixed connections of different Ethernet speeds by entering port cache. For example, when receiving a frame sent at a speed of 1Gb/s and forwarding it to a 100Mbps Ethernet port, storage and forwarding methods need to be used. When the speed of the input and output ports does not match, the industrial switch puts the entire frame content into the cache, calculates the FCS checksum, forwards the output cache, and sends out the frame.
4. Cut Through
One advantage of direct switching is that it is faster than storage and forwarding technology. The industrial switching machine that adopts the direct mode reads the frame header before receiving the complete data packet and decides which port to send the data to, without caching or checking the integrity of the data. This exchange method has two main characteristics: fast frame forwarding and invalid frame processing.
5. Fast frame forwarding:
As shown in the figure below, once the industrial switch finds the destination MAC address in the MAC address table, it immediately makes a forwarding decision without waiting for the remaining part of the frame to enter the port before making a forwarding decision.
Industrial switches that use a through method can quickly determine whether it is necessary to check more parts of the frame header for additional filtering purposes. For example, an industrial switch can check the first 14 bytes (source MAC address, destination MAC, Ethernet type field), as well as the next 40 bytes to achieve IPv4 layer 3 and layer 4 related functions.
6. Invalid frame processing:
For most invalid frames, industrial switches do not discard them through the passthrough method, and erroneous frames are forwarded to other network segments. If there is a high error rate (invalid frames) in the network, direct switching may have an adverse impact on bandwidth, damage, and invalid frames can cause bandwidth congestion. In congested situations, this type of industrial switch will cache like a storage and forwarding industrial switch.
7. Fragment Free forwarding
Fragmented forwarding is an improved mode of direct communication. Before forwarding the industrial switch, check if the frame is larger than 64 bytes (if smaller, discard) to ensure that there are no fragmented frames. The shard free method has better error detection than the through method, but in reality, it does not increase latency, making it more suitable for high-performance computing applications, i.e