Common Functions And Applications Of Switches

- Oct 28, 2020-

Learning: The Ethernet switch understands the MAC address of the device connected to each port, and maps the address to the corresponding port and stores it in the MAC address table in the switch cache.


Forwarding/Filtering: When the destination address of a data frame is mapped in the MAC address table, it is forwarded to the port connected to the destination node instead of all ports (if the data frame is a broadcast/multicast frame, it is forwarded to all ports) .


Elimination of loops: When the switch includes a redundant loop, the Ethernet switch avoids loops through the spanning tree protocol, while allowing backup paths.


In addition to being able to connect to the same type of network, the switch can also play an interconnection role between different types of networks (such as Ethernet and Fast Ethernet). Nowadays, many switches can provide high-speed connection ports that support Fast Ethernet or FDDI, etc., which are used to connect to other switches in the network or provide additional bandwidth for key servers that take up a lot of bandwidth.


Generally speaking, each port of the switch is used to connect to an independent network segment, but sometimes in order to provide faster access speed, we can connect some important network computers directly to the port of the switch. In this way, key servers and important users of the network have faster access speeds and support greater information flow.

Switch mode


The switch exchanges in the following three ways:


1) Straight-through type:


The straight-through Ethernet switch can be understood as a line matrix telephone switch that crosses vertically and horizontally between ports. When it detects a data packet at the input port, it checks the packet header, obtains the destination address of the packet, activates the internal dynamic lookup table to convert it into the corresponding output port, connects at the intersection of input and output, and passes the data packet directly to The corresponding port realizes the switching function. Since no storage is required, the delay is very small and the exchange is very fast, which is its advantage. Its disadvantage is that because the content of the data packet is not saved by the Ethernet switch, it cannot check whether the transmitted data packet is wrong, and it cannot provide error detection capability. Because there is no buffer, input/output ports with different speeds cannot be connected directly, and packets are easily lost.

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2) Store and forward:


The store-and-forward method is the most widely used method in the field of computer networks. It stores the data packet of the input port first, and then performs CRC (cyclic redundancy check) check. After processing the error packet, it takes out the destination address of the data packet, and converts it into the output port through a lookup table to send the packet. Because of this, the store-and-forward method has a large delay in data processing, which is its shortcoming, but it can perform error detection on the data packets entering the switch and effectively improve network performance. It is especially important that it can support the conversion between ports of different speeds and maintain the cooperation between high-speed ports and low-speed ports.



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3) Fragment isolation:


This is a solution between the first two. It checks whether the length of the data packet is 64 bytes, if it is less than 64 bytes, it means it is a fake packet, and then discards the packet; if it is greater than 64 bytes, the packet is sent. This method also does not provide data verification. Its data processing speed is faster than store-and-forward, but slower than straight-through.


Switch application


As the main connection device of the local area network, the Ethernet switch has become one of the most popular network devices. With the continuous development of switching technology, the price of Ethernet switches has dropped sharply, and switching to the desktop has become a general trend.


If you have a large number of users, busy applications, and various servers on your Ethernet network, and you have not made any adjustments to the network structure, then the performance of the entire network may be very low. One of the solutions is to add a 10/100Mbps switch to the Ethernet, which can not only handle 10Mbps regular Ethernet data flow, but also supports 100Mbps fast Ethernet connection.

If the utilization rate of the network exceeds 40%, and the collision rate is greater than 10%, the switch can help you solve a little problem. Switches with 100Mbps Fast Ethernet and 10Mbps Ethernet ports can operate in full duplex mode and can establish a dedicated 20Mbps to 200Mbps connection.


Not only are the roles of switches in different network environments different, but the effects of adding new switches and increasing the switching ports of existing switches on the network are also different in the same network environment. Fully understanding and mastering the flow pattern of the network is a very important factor in whether the switch can function. Because the purpose of using a switch is to reduce and filter the data traffic in the network as much as possible, if a switch in the network is installed incorrectly and almost needs to forward all the received data packets, the switch will not be able to optimize the network. The effect of performance, on the contrary, reduces the data transmission speed and increases the network delay.


In addition to the installation location, if a switch is also blindly added to a network with a small load and a low amount of information, it may also have a negative impact. Affected by factors such as the processing time of the data packet, the buffer size of the switch and the need to regenerate new data packets, in this case it is more ideal to use a simple HUB than a switch. Therefore, we cannot assume that the switch has advantages over the HUB, especially when the user's network is not crowded and there is still a lot of usable space, using the HUB can make full use of the existing resources of the network.