November 25, 2023
ForewordHi everyone, I'm Mr. Lin, how do I select a switch? How to determine network structure for project? We have such questions in most projects. As one of most commonly used devices in low current, circuit breaker is one of most commonly used devices. Regarding its use and selection, we must know. In this issue, let's learn more about how to choose a switch in a project? Text1. Network Scale and Hierarchy
The scale of network and application layer of switch are taken into account, which are mainly divided into small and medium-sized networks, as well as large and medium-sized networks.
When you select a switch, you can select it using OSI reference model. If enterprise processes only data, it is recommended to use a layer 2 switch. If departments are separated to create isolation between departments, it is recommended to choose a layer 3 switch. If you need to configure features such as gateways and firewalls, a more advanced firewall layer switch is required.
How to plan a network hierarchy:
The network structure determines which hardware to use. Some small networks only have a basic layer and an access layer, so choosing a basic switch is relatively easy and load is light. For example, some small monitoring networks only in internal network. Then select layer 2 switch.
For example, following network: access layer and base layer only
Of course, in a large-scale network, it is difficult to coordinate and distribute only access layer and base layer, so a three-layer structure, a base layer and an aggregation layer, and an access layer are required. Functions such as separation of network management and network management require a layer 3 switch.
Some friends will ask if I can get four floors? Most networks only have three levels. The fewer layers in network structure, faster response of network. A simple network structure is beneficial in terms of response time and post-disaster maintenance.
Second, number of switch ports
The number of switch ports and number of physical ports supported by switch determine number of terminals or secondary receivers connected to switch, which must be selected according to actual needs. Of course, subsequent expansion of network must also be taken into account. The access port of switch is used to connect to intranet terminal, and uplink port is used to connect to upper equipment.
If number of points is around 16 and this number will not change much in long term, you can choose a 24-port switch. If number of points is over 16 or more and there are other network devices, you need to adjust number of ports at this time. For a certain amount of redundancy, you can choose a 48-port switch.
3. Port Options
Mainly port parameters to consider:
Port speed (100M, 1000M, 10G) and port type (RJ45, SFP/optical port, PoE network port, etc.). There are multiple optical ports, or multiple electrical ports, etc., number of ports is 100M and gigabit ports.
Fourthly, functional support of switch
Consider switch's functional support, whether it has a network management function, module redundancy, routing redundancy, four-layer switching, scalability, etc. At same time, security function of switch must be considered.
Specific examples include: access control, 802.1X authentication, loop detection, quadruple bind, IGMP snooping, etc.
5. Backplane Bandwidth
Backplane bandwidth, also known as switching bandwidth, is maximum amount of data that can be processed between switch interface processor and data bus, just like sum of lanes belonging to a flyover. Since all ports must communicate through backplane, bandwidth provided by backplane becomes bottleneck for simultaneous communication between ports.
When we buy a switch, we will see following parameters:
The greater bandwidth, greater available bandwidth provided to each port, and faster communication speed; lower bandwidth, less available bandwidth available to each port, and slower communication speed. In other words, bandwidth of backplane determines processing capability of switch: higher bandwidth of backplane, greater processing capability. If you want to implement full-duplex, non-blocking network transmission, you must meet minimum backplane bandwidth requirements.
The backplane bandwidth formula is as follows
Backplane bandwidth = number of ports x port speed x 2
Advice. For a layer 3 switch, only if speed and throughput of backplane meet minimum requirements is it a qualified switch, and both are indispensable.
How can a switch have 24 ports and speed of each port is gigabit?
Backplane bandwidth = 24 * 1000 * 2/1000 = 48 Gbps.
6. Package price
Data on network is made up of data packets, and processing each data packet requires resources. Speed (also known as throughput) refers to number of data packets that pass per unit of time without packet loss. Bandwidth is similar to traffic flow of an overpass and is most important parameter of a Layer 3 switch that determines specific performance of switch. If bandwidth is too small, it will become a bottleneck in network and have a negative impact on transmission efficiency of entire network.
The switch must be able to switch at wire speed, that is, switching speed reaches data rate of transmission line, in order to eliminate switching bottleneck as much as possible. For a basic layer 3 switch, if it is required to provide non-blocking network transmission, rate can be ≤ nominal packet rate of layer 2, and rate can be ≤ nominal packet rate of layer 3, then switch performs switching between layer 2 and layer 3 when it can reach linear speed.
The packet rate formula is as follows
Bandwidth (Mpps) = 10Gb ports x 14.88Mpps + Gigabit ports x 1.488Mpps + 100Mb ports x 0.1488Mpps.
If calculated bandwidth is less than your switch's bandwidth, it may reach data rate.
If there are 10Mb ports and 100Mb ports, they will be counted, and if there are none, they can be ignored.
For a switch with 24 gigabit ports, its fully configured throughput must be at least 24×1.488Mpps = 35.71Mpps to provide non-blocking packets when all ports are running at wired speed.
Seven, look at stamp
At moment, many non-brand switches are good, especially packet speed and backplane bandwidth, but they are not usable, so you still need to look at brand when buying a switch.
Huawei, Ruijie, H3C, Cisco and other enterprise grade switch brands are highly rated and each has its own strengths. As domestic brands, Huawei, Ruijie and H3C are rapidly developing into switch field. However, as an established company, Cisco has a very strong position and must be considered according to project and its own situation.