What factors need to be considered when selecting a switch for a network camera?

Nowadays, the building intelligentization weak industry often uses switches, so how to choose switches? Especially in video surveillance, the choice of switches is particularly important. What are the main considerations for the quality of the switch? This article focuses on the basics and important parameters of the switch.

Switch classification

Network composition: access layer switches, aggregation layer switches, and core layer switches

OSI model: Layer 2 switch, Layer 3 switch, Layer 4 switch, etc., up to the Layer 7 switch.

Manageability of switches: Manageable switches and unmanaged switches. The difference is the support for SNMP, RMON and other network management protocols.

Select the switch mainly to refer to those factors

a, backplane bandwidth, two/three-layer switching throughput.

b. VLAN type and quantity.

c. Number and type of switch ports.

d. Protocols and methods that support network management. The switch is required to provide more convenient and centralized management.

e, Qos, 802.1q priority control, 802.1X, 802.3X support.

f. Support for stacking.

g, switch exchange cache and port cache, main memory, forwarding delay and other parameters.

h, wire-speed forwarding, routing table size, access control list size, support for routing protocols, support for multicast protocols, packet filtering methods, machine expansion capabilities, etc. are all parameters worth considering, and should be investigated according to actual conditions. .

The above factors to complete the switch selection need to refer to, then usually choose the switch we can judge by the following factors.

1. Backplane bandwidth: The backplane bandwidth of the switch is the upper limit of the amount of data that can be handled between the switch interface processor or the interface card and the data bus. The backplane bandwidth marks the total data exchange capability of the switch, in Gbps, also called the switching bandwidth. Therefore, only the modular switch (with scalable slots, which can flexibly change the number of ports) has this concept. Fixed port switches do not have this concept, and the backplane capacity and switching capacity of fixed port switches are equal. The backplane bandwidth determines the upper limit of the bandwidth of the connection between each board (including the boards that are not installed in the expandable slot) and the switching engine. Due to the different architectures of modular switches, backplane bandwidth is not fully effective at representing the true performance of the switch. Fixed port switches do not have the concept of backplane bandwidth.

2. Exchange capacity and forwarding capability. Since the switching engine is the core of packet forwarding for modular switches, this metric can truly reflect the performance of the switch. For a fixed port switch, the switching engine and the network interface template are integrated. Therefore, the forwarding performance parameter provided by the manufacturer is the forwarding performance of the switching engine. This indicator is the key to determining the performance of the switch. For devices supporting Layer 3 switching, the manufacturer will provide the Layer 2 forwarding rate and the Layer 3 forwarding rate respectively. Generally, the Layer 2 capability uses bps, the Layer 3 capability uses pps, and the modular switch with different architectures. These two parameters. The meaning is different. However, for the average LAN user, only concerned with these two indicators can be, it is a key indicator to determine the performance of the system. For large campus and metro users, it is meaningful to discuss the switch architecture and the third-tier optimization algorithm.

3. Backplane bandwidth calculation. The backplane bandwidth is the upper limit of the amount of data that can be handled between the switch interface processor or the interface card and the data bus.

Calculation formula: number of ports × corresponding port rate × 2 (full duplex mode), 24 ports of 100 megabytes + 2 ports of Gigabit, 24 * 2 * 100 + 2 * 2 * 1000 = 8.8 Gbps

4. Calculation method of line rate packet forwarding rate

(1) Backplane bandwidth (exchange capacity)

Examine the total bandwidth that all ports on the switch can provide. The calculation formula is the number of ports * the corresponding port rate * 2 (full duplex mode), if the total bandwidth ≤ nominal backplane bandwidth, then the line speed is on the backplane bandwidth.

(2) packet forwarding line speed

Packet forwarding rate = number of Gigabit ports × 1.488 Mpps + number of 100 Mbps ports * 0.1488 Mpps + number of ports of the remaining types * Corresponding calculation method.

5, the origin of the parameter 1.488Mpps

So, how is 1.488Mpps obtained? The measure of packet forwarding line rate is based on the number of 64-byte packets (minimum packets) sent per unit time. For Gigabit Ethernet, the calculation method is as follows: 1,000,000,000bps/8bit/(64+8+12)byte=1,488,095pps Description: When the Ethernet frame is 64byte, consider the 8byte header and Fixed overhead of 12-byte frame gap. Therefore, the packet forwarding rate of a line rate Gigabit Ethernet port when forwarding a 64-byte packet is 1.488 Mpps.

Fast Ethernet's wire-speed port packet forwarding rate is exactly one-tenth of that of Gigabit Ethernet, which is 148.8kpps. For 10 Gigabit Ethernet, the packet forwarding rate of a wire-speed port is 14.88 Mpps.

For Gigabit Ethernet, the packet forwarding rate of a wire-speed port is 1.488 Mpps.

For Fast Ethernet, the packet forwarding rate of a wire-speed port is 0.1488 Mpps.

For Ethernet, the packet forwarding rate of a wire-speed port is 0.01488 Mpps.

6, packet forwarding rate. The packet forwarding rate marks the size of the switch's ability to forward packets. It refers to how many packets (Mpps) a switch can forward per second, that is, the number of packets that the switch can forward at the same time. The packet forwarding rate reflects the switching capability of the switch in units of packets. Calculation method = number of gigabit ports × 1.488 Mpps + number of hundred mega ports × 0.1488 Mpps + number of ports of other types.

7, line speed exchange. What is the line-speed switching: line-speed switching refers to the ability to implement bottle-free data exchange in accordance with the data transmission speed on the network communication line. The implementation first implements protocol parsing and packet forwarding through dedicated hardware according to the ASIC chip, instead of completing the software according to the CPU of the switch. The implementation of wire-speed switching also relies on distributed processing technology, in which the data streams of multiple ports of the switch can be processed simultaneously. Therefore, the LAN switch can be regarded as a parallel processing device used by the CPU, RISC, and ASIC.