Discover The Real Key Points For Switch Selection

As one of the most commonly used devices in the field of communication and information, how do you choose a switch to achieve optimal performance? Read this article to find out the key points to pay attention to when selecting a switch.

Switching mechanism

Current switches are mainly divided into box type and frame type.

Box switches can be understood as an iron box. Generally, box switches have fixed configuration, fixed number of ports, fixed power modules, fans, etc.; therefore, box switches are not scalable. In order to improve scalability, box switches can support stacking technology, which can logically form multiple box switches into one switch. Under normal circumstances, box switches are used in the access layer or aggregation layer of a network.Frame switches are based on the chassis, and interface cards, switch cards, power modules, etc. can be independently configured according to requirements. The scalability of frame switches is generally based on the number of slots. Frame switches are generally used in the core position of a network.

Therefore, when selecting equipment, you can choose box switches or frame switches according to the actual use level of the switch.

Function

Switches are classified according to the working protocol layer: switches can be divided into layer 2 switches and layer 3 switches.

Layer 2 switch: a switch working on the second layer data link layer of the OSI reference model, with main functions including physical addressing, error checking, frame sequence and flow control. Layer 2 switches work at the data link layer and can process data frames.

Layer 3 switch: a device with Layer 3 switching function, that is, a Layer 2 switch with Layer 3 routing function, but it is an organic combination of the two, not simply superimposing the hardware and software of the router device on the LAN switch. The Layer 3 switch works at the network layer and can process data packets.

Number of ports

• Number of switch ports: the number of ports that a switch can provide. For each model of box switch, it is basically fixed, generally providing 24 or 48 access points and 2-4 top-connection ports.

• Frame switches are related to the number of configured boards, generally referring to the maximum number of ports that each frame can support when configuring the highest density interface board.

• When choosing a switch, you need to base it on the current business situation and future scalability. The number of switch ports represents the number of terminals you need to access.

• Take a switch with 48 access points as an example. If 1 terminal occupies one port, then one switch can connect 48 terminals. If it is a company with 200 people, then 5 such switches are needed.

Port rate

Switch supports port rate: The current switch provides port rates of 100Mbps, 1000Mbps, 10Gbps, 25Gbps, 40Gbps, 100Gbps, 200Gbps, 400Gbps, etc. The unit of the switch port rate is bps (bit per second), that is, how many bits per second.

Switching capacity

• Switch switching capacity: also known as backplane bandwidth or switching bandwidth. The switching capacity is the maximum amount of data that can be handled between the switch interface processor (or interface card) and the data bus.

• The backplane bandwidth marks the total data exchange capacity of the switch, in Gbit/s. The higher the switching capacity of a switch, the stronger the ability to process data, but at the same time the design cost will be higher. Twice the sum of the number of ports of all port capacities should be less than the switching capacity, so as to achieve full-duplex non-blocking switching.

• The switching capacity is related to the switch format: for bus switches, the switching capacity refers to the bandwidth of the backplane bus.

• For switch matrix switches, the switching capacity refers to the total interface bandwidth of the switch matrix.

• This switching capacity is a theoretical calculation value, but it represents the maximum switching capacity that the switch can achieve. The current switch design ensures that this parameter will not become the bottleneck of the entire switch.

Packet forwarding rate

Switch packet forwarding rate: The packet forwarding rate is also called interface throughput, which refers to the data packet forwarding capacity on a certain interface of the communication device, and the unit is usually pps (packet per second). The packet forwarding rate of the switch is generally the result of actual measurement, representing the actual forwarding performance of the switch.

Packet forwarding rate calculation method: The measurement standard of the packet forwarding rate is the number of 64-byte data packets (minimum packets) sent per unit time as the calculation basis. When calculating the packet forwarding rate, the fixed overhead of the preamble and frame gap needs to be considered.

By default, the frame gap is the maximum value of 12 bytes, and users are advised to use the default configuration. If the user modifies the frame gap of the interface to a smaller value, the receiving end may not have enough time to receive the next frame after receiving a data frame, resulting in failure to process the forwarded message in time and packet loss.

We know that the length of the Ethernet frame is variable, but the processing power used by the switch to process each Ethernet frame has nothing to do with the length of the Ethernet frame. Therefore, when the interface bandwidth of the switch is constant, the shorter the Ethernet frame length is, the more frames the switch needs to process and the more processing power it needs to consume