Do you know these basic concepts of network bandwidth?

A netizen asked for help, the image of the network surveillance camera will be frozen, but the bandwidth is calculated by itself. A network camera occupies 8M bandwidth, a switch 100M, access 11 units, theoretically 100 ÷ 8 = 12.5 units, a total of 11 Is the network bandwidth enough for Taiwan, but the network is still stuck, and ask why?

Regarding the cause of stuttering, we have already written related articles before. If you are interested, you can turn over historical articles. The cause can usually be found externally, but what should you do if external factors are ruled out?

In view of these confusions, we must first understand the basic concepts of network monitoring and related equipment.

What is the video stream and frame rate?

Video code stream is the data flow used in unit time after the video file is encoded. Also called video bit rate. Is an important part of video picture quality (taken from Baidu Encyclopedia).

The unit time of the bitstream in our surveillance video is 1 second. 1 second = 1000 milliseconds (used below).

Does the video image flow at a constant speed like flowing water? Definitely not. It passes through frames. Frames are data transmission units. The more frames per second (in fps), the smoother the displayed motion will be. High frame rates result in smoother, more realistic video animations.

If the video is 25 frames per second, there is a time interval between each frame. The time interval can be calculated as 40 milliseconds.

Then we can know that the average bit rate of sending and sending intervals is smaller than the bit rate when sending video frames.

Frames are also divided into I frames, P frames, and B frames. The I-frame is usually the first frame of each video segment, and its account is the largest.

What are full and half duplex?

Full-duplex transmission means that the switch can receive data at the same time as sending data. The two are synchronized. This is like a wide road running from east to west, which allows two carriages to pass through. When carriage A runs from east to west, carriage B When driving from west to east, two cars can travel simultaneously without affecting each other. In this example, the wide road represents a full-duplex link. Current switches support full duplex. The advantage of full duplex is that it has low latency and high speed.

Half-duplex means that only one action takes place in a period of time. For a simple example, a single wooden bridge can only allow one person to pass at the same time. This is the case when there are two people coming from both ends of the river Only one person stops at the bridgehead, waits for another person to come over, and then continues to walk. In this example, the single-wood bridge represents a half-duplex link. Early interphones and early hubs were half-duplex products. When the data traffic is heavy, the links working in half-duplex mode will have collisions and error packets, which will eventually affect the working performance. So half-duplex has gradually withdrawn from the arena of history.

The difference between full-duplex mode and half-duplex mode in the network card

1. In full-duplex mode, the 8 network wires must be connected to the corresponding line sequence position of the crystal head respectively;

2. In the half-duplex mode, only 4 wires need to be connected. According to the T568B standard, four wires in the line sequence position of 1, 2, 3, and 6 are generally used. Four lines. Orange-white and orange are used to send data, and green-white and green are used to receive data.

3. In full-duplex mode, the network cable can reach a speed of more than 100 megabits. In half-duplex mode, the speed that the network cable can reach is usually about 10 megabytes.

4. The network cable in full-duplex mode can work in full-duplex mode or half-duplex mode; but the network cable in half-duplex mode cannot work in full-duplex mode.

5. In the half-duplex mode, the two additional lines can be used to connect to the telephone line. For example, the "white blue, blue" line can be used as a telephone line. In LAN network wiring, this way can save wiring costs, and a twisted pair can be used as a network cable and a telephone line at the same time.

What is the network port speed?

The network interfaces we are using today are all Ethernet interfaces. The network interface interface speed determines the data transmission bandwidth of the interface. Generally, the interfaces used are 10Mbps, 100 Mbps, 1000 Mbps and other types of speed.

Common Ethernet interface types are RJ-45 interface, RJ-11 interface, SC fiber interface, FDDI interface, AUI interface, BNC interface, and Console interface. But we usually say that the network port speed is RJ-45 interface, which is the crystal head of the network cable.

Interfaces with different speeds may also be successfully connected, and their working rates need to be negotiated. If the 100 Mbps auto-negotiation interface is connected to the 10 Mbps auto-negotiation interface, the negotiated working rate is 10 Mbps. Therefore, the interface rate is not necessarily the operating rate. Generally, the operating rate will be less than or equal to the interface rate.