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What are the important parameters and indicators of the PoE switch?

About PoE switches, we often hear some professional terms, such as backboard bandwidth, packet forwarding rate, power supply, line speed forwarding, and so on. What do they mean?

Today, CCIT, a manufacturer of wireless network equipment, has a common understanding of the important indicators of PoE switches to help you understand the technical parameters of the vendor's name so that users can choose their own PoE switch products.

What is the line speed?

The line speed refers to the bit number per second on the switch's port, the unit is BPS (bit per second, that is, how many bit per second, a bit is a binary number 0 or 1). In our common examples, for example, 100M's network card means that the network card has a network speed of 100Mbps; for example, the telecommunication broadband is the broadband of 50M, and the speed of the port line is 50Mbps for us.

It should be noted that we should not confuse line speed with file download speed. The speed calculation on a computer for file downloads is based on a byte (byte) rather than a bit. We usually say that the download speed can reach 2M per second meaning 2M byte/s, that is, 2M Bps, the capital B is Byte, and the lowercase B indicates bit. So what's the difference between byte and bit? In fact, it is also very simple, 1byte=8bit, that is, 8 times the relationship.

What is the backboard bandwidth?

The backboard bandwidth (Backplane Bandwidth) of the switch, also known as the switching bandwidth, is the largest amount of data that can be swallowed between the switch interface processor or the interface card and the data bus.

The backplane can be understood as a data bus inside the switch or router, and the data exchange between the device ports is transmitted on the bus. If a network is figurative of a transportation system, each network equipment is equivalent to a different city, and the backplane is like a highway connected to all the cities in the system, and the traffic flow between each city needs to pass through the highway. The backboard bandwidth is the largest non blocking traffic on the highway, and of course, unlike the complex traffic conditions on the actual freeway, we have to assume that the vehicles on the freeway are running at a constant maximum speed.

Backboard bandwidth is the physical property of the backboard, which marks the total exchange capacity of the switch, also called the exchange bandwidth, the unit is Gbps, and the backboard bandwidth of the general switch ranges from a few Gbps to hundreds of Gbps. The higher the bandwidth of a switch's backplane, the stronger the ability to process data, but the higher the cost will be.

what is the throughput?

Throughput (also known as the packet forwarding rate) refers to the number of data transmitted by a network, device, port or other facility in a unit time (bits, bytes, etc.), that is to say, the throughput is the maximum data rate that the device can receive and forward without a frame loss.

Throughput is a limiting indicator, that is, when a network device is fully equipped at all ports and operates at the highest line speed of the port. The throughput of a switch is equivalent to the sum of traffic flows in and out of all cities in the system, that is, the forward rate of two-way (duplex) packets on all ports of the switch, if it is still compared to the highway traffic system mentioned in the different cities mentioned earlier.

The size of the throughput is mainly determined by the internal and external hardware of the network device and the efficiency of the program algorithm, especially the program algorithm. For the equipment that needs a lot of operation, the low efficiency of the algorithm will reduce the amount of communication.

The difference between throughput and bandwidth

Throughput and bandwidth is a very easy to mix concept, although both units are Mbps, but the meaning of the two can be seen from their respective English names - throughput: throughput; bandwidth: Max net bitrate.

When we discuss the bandwidth of the communication link, it usually refers to the number of bits that can be transmitted per second in the chain road, which depends on the link clock rate and channel coding, which is also called the line speed in the computer network (the concept mentioned at the beginning of this article). We can say that the bandwidth of Ethernet is 50Mbps.

However, we need to distinguish between the number of available bandwidth (bandwidth) on the link and the number of bits (throughput) that can be transmitted per second in the actual link, usually using the word "throughput" to represent the performance of a system. In this way, because the actual transmission is affected by a variety of inefficient factors, a pair of link connections with a bandwidth of 50Mbps may only reach the throughput of 10Mbps. This means that an application on a host can send data to another host at 10Mbps speed.

What is the packet forwarding rate?

For network equipment, in addition to the important index of throughput, message forwarding rate, which is often said packet forwarding rate is another main index to measure the performance of network devices. Packet forwarding rate generally refers to the full duplex throughput of 64 byte packets, which includes both throughput and packet forwarding rate.

The meaning of packet forwarding rate is the number of packets forwarded per second, the unit is PPS, that is, packet per second.

There is a corresponding relationship between the packet packet and byte byte, that is, 1packet=64byte. Why is it 64? This is the definition of packets. The 1 packets in the network contain 64 bytes at least, and these 64 bytes refer to simple data. Of course, the transmission of data packets in the network is not only a bare data packet, but also the frame headers of 8byte and the frame gap of 12byte for each packet, so each packet will need to transmit a 64+8+12 common 84byte.

Next, calculate the maximum packet forwarding rate with a 1000Mbps wire speed port.

1000Mbps=1000000000bps/ (84*8bit) 1488095pps=1.488Mpps

According to this algorithm, we can get the packet forwarding rate of the following commonly used line speed ports:

Ten thousand megabyte speed port packet forwarding rate 14.88Mpps

Gigabit line speed port packet forwarding rate 1.488Mpps

100 megabytes speed port packet forwarding rate 0.1488Mpps

PoE power supply power

Since it is a PoE switch, the parameter that must be seen about its power supply performance is the PoE power supply, including the PoE power supply standard and the total PoE power two aspects. The PoE power supply standard has AF and at standards. The former allows the maximum power supply of the port to be 15.4W and the maximum power supply of the permitted port is 30W, so the PoE switch supporting the at standard is better.

The total PoE power is usually specified in the product specification, which represents the maximum power supplied by the entire PoE switch. The greater the general total power, the better the PoE switch, for example, the same 16 PoE switches, the total power of 400W is better than the total power of 280W, but it also needs to be selected according to the actual demand.

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