Shulou(Shulou.com)06/01 Report--

At present, the video surveillance system has completed a comprehensive upgrade from traditional analog video surveillance to digital video surveillance, and gradually developed to the high-definition network digital video surveillance stage, using the existing office network, industry private network, optical fiber private network, and even the Internet and wireless networks and other infrastructure to build regional security, production surveillance and other different purposes of high-definition network video surveillance system. Among them, the large-scale popularity of megapixel network cameras not only solves the embarrassing situation of the lack of clarity of the traditional analog video surveillance system, but also improves the convenience and security of the monitoring system.

Advantages of HD network video surveillance system

Advanced: using the existing integrated cabling network to transmit images, the real-time monitoring system needs less front-end equipment, simple connection, and only a set of software system is needed at the back end.

Reliability: the main equipment network camera adopts embedded real-time operating system, the required equipment is simple, and the image transmission is realized through integrated wiring network, the system reliability is quite high.

Performance-price ratio: the required equipment is extremely simple, and the control of the system is realized by the back-end software system, eliminating a large number of equipment in the traditional analog monitoring system, such as expensive matrix, picture splitter, switch, video-to-network host and so on. Because the image is transmitted through the integrated cabling network, a large number of video coaxial cables are saved and the cost is reduced.

Security: the system has set different levels of user rights, only users with the highest permissions can set or change the entire system, users without permissions can not receive images. In addition, the storage of image data is a proprietary format

Use and maintainability: the installation of the system is extremely simple, and the installation and use of the software system is also very easy to understand. In terms of maintainability, the wiring of the system is very simple, while the reliability of the main equipment is very high, the maintenance performance is good, and remote maintenance can be realized.

Expansion and extensibility: when you need to add monitoring points and monitoring hosts, you only need to add a camera or PC through the existing network, and there is no need to make any changes to the existing wiring system

A wide range of applications: regional monitoring, using the network to transmit real-time images, such as offices, buildings, etc.; cross-district remote monitoring, chain enterprises, large-scale factory computer rooms, remote elderly, child care, public buildings, unmanned environment monitoring, branch monitoring of financial institutions, traffic supervision, false alarm identification and so on.

The key factor affecting the quality of HD network video surveillance system-switch

There are many reasons for the phenomenon of picture delay and stutter in the high-definition network video surveillance system, but in most cases, the configuration of the switch is unreasonable, resulting in insufficient bandwidth, so how to configure the switch reasonably? What technical parameters should be considered when choosing a switch?

General idea: first, analyze the location and responsibility of the switch in the network architecture, and then combined with the scale and layout of video surveillance, calculate the technical parameters such as the port rate, backplane bandwidth and packet forwarding rate of each switch, and get the accurate data. finally, the switch is selected to form a high-definition network video surveillance solution.

First of all, we need to clarify some concepts:

1. Main technical parameters of switch

1) Port bandwidth

The switch has many different types of ports, each with its own dedicated bandwidth, such as 10Mbps, 100Mbps, 1000Mbps, 10000Mbps (10Gbps), and even 100Gbps. For example, the H3C S5120-28P-SI switch has 24 1000Base-T Ethernet ports and 4 1000Base-X SFP Gigabit Ethernet ports.

Backplane bandwidth

The backplane bandwidth of the switch is the maximum amount of data that can be handled between the switch interface processor or the interface card and the data bus. The backplane bandwidth indicates the total data switching capacity of the switch, in Gbps, also known as switching bandwidth. The average backplane bandwidth of a switch ranges from a few Gbps to hundreds of Gbps. The higher the bandwidth of the backplane of a switch, the stronger the ability to process data, but the higher the design cost.

Packet forwarding rate

Packet forwarding rate, also known as port throughput, refers to the packet forwarding capability of a router on a port, usually measured in pps (packets per second). Generally speaking, the packet forwarding rate of low-end routers is only a few K to dozens of Kpps, while high-end routers can reach dozens of Mpps (millions of packets per second) or even hundreds of Mpps.

two。 Calculation of backplane bandwidth and packet forwarding rate

The best performance of the switchboard requires the switch to achieve linear non-blocking transmission. How do we check whether the backplane bandwidth of a switch is sufficient?

Generally speaking, the method of calculation is as follows:

Line-speed backplane bandwidth

The formula for calculating the total bandwidth provided by all ports on the switch is:

Number of ports x corresponding port rate x 2 (full duplex mode)

If the total bandwidth ≤ is nominal backplane bandwidth, then the switch backplane bandwidth is line-speed.

Layer 2 packet forwarding line speed

Layer 2 packet forwarding rate = number of gigabit ports × 1.488Mpps + number of 100 megabit ports * 0.1488Mpps+ number of ports of other types * corresponding calculation method

If this rate can be ≤-denoted layer 2 packet forwarding rate, then the switch can achieve line speed when doing layer 2 switching.

Layer 3 packet forwarding line speed

Layer 3 packet forwarding rate = number of gigabit ports × 1.488Mpps + number of 100 megabit ports * 0.1488Mpps+ number of ports of other types * corresponding calculation method

If this rate can be ≤ nominal layer 3 packet forwarding rate, then the switch can achieve line speed when doing layer 3 switching.

How did 1.488Mpps get it?

Gigabit port wire speed (packet forwarding rate is 1.4881 MPPs; 100 megabit port wire speed packet forwarding rate is 0.14881MPPS, this is the international standard, but how to get it?

In the process of transmission, a specific packet will add 64 leading characters and a 96bit frame gap in front of each packet, that is, a 64-byte packet, originally only 512 bit, but in the process of transmission, there will actually be 512+64+96=672bit, that is, the actual length of a packet.

Gigabit port line speed packet forwarding rate 1000Mbps / 672 ≈ 1.488095Mpps

100-megabit port line speed packet forwarding rate 100Mbps / 672 ≈ 0.14881Mpps

Therefore, the following data can be obtained:

For 10 Gigabit Ethernet, the packet forwarding rate for a wire-speed port is 14.88Mpps.

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

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

For the POS port of OC-12, the packet forwarding rate for a wire-speed port is 1.17Mpps.

For the POS port of OC-48, the packet forwarding rate for a wire-speed port is 468MppS.

Therefore, if the above three conditions can be met, then we will say that this switch is truly linear and non-blocking.

Standard definition: a video format (D1/DCIF/CIF) with a physical resolution below 720p (1280mm / 720). Specifically, it refers to VCD, DVD, TV programs and other "standard definition" video formats with a resolution of 400 lines or less, that is, standard definition.

The difference between Standard definition, HD, and full HD

High definition: a physical resolution of 720p or more is called high definition. (English expression: HighDefinition) abbreviation: HD,720p refers to a video with a vertical resolution of 720line progressive scanning, which is used as an entry-level standard for HD; equivalent to 2.5 D1 resolutions.

Full HD: physical resolution up to: 1920 × 1080, abbreviated as: Full HD, horizontal resolution of sub-1080P/1080I display equipment reaches 1080 lines, from the visual effect, 1080p is the highest standard TV signal, and its image quality can reach or close to the level of 35mm wide-screen movies. The image resolution of 1080p is equivalent to the resolution of 6 D1. 1080i refers to interlaced scanning of 1080 lines, and 1080p refers to progressive scanning of 1080 lines.

1. What is a high definition webcam?

We usually call it millions, 2 million pixel cameras:

Megapixel camera

720p actually refers to the resolution of 1280,720 pixels, that is, 1280 × 720,921600 pixels, which is generally called 720p or 720i as megapixel resolution. A camera with an image coding resolution above 1280 × 720 / 25fps is called a megapixel camera.

2 million pixel camera

1080p actually refers to the resolution of 1920,1080 pixels, that is, 1920 × 1080mm 2073600 pixels, which is generally called 1080p or 1080i with a resolution of 2 million pixels. A camera whose image coding resolution is above 1920 × 1080 / 25fps is called a 2 million pixel camera.

Switch in High definition Network Video Surveillance system

In terms of network topology, a medium-and large-scale high-definition network video surveillance system needs to adopt three layers of network architecture: access layer, aggregation layer and core layer.

Small systems need to adopt a two-layer network architecture: access layer and aggregation layer.

1. Selection of access layer switches:

The access layer switch is mainly connected to the front-end network high-definition camera and the convergence switch. Based on the 4m code stream of 720p network camera, how many 720p network cameras can be accessed by a 100-megabit access switch?

The actual bandwidth of our commonly used switch is 50% of the theoretical value, so the actual bandwidth of a 100 megabit port is in 50M-70M. 4M*12=48M, so it is recommended that one 100-megabit access switch can access up to 12 720p network cameras. At the same time, considering that the current network monitoring adopts dynamic coding, the peak bit stream of the camera may exceed 4m bandwidth, and the design of bandwidth redundancy is taken into account, so it is best for a 100-megabit access switch to be controlled within 8. Gigabit ports are recommended for more than 8.

two。 Selection of aggregation layer switches:

The convergence layer switch is mainly connected to the lower layer switch and the monitoring center core switch. In general, the aggregation switch needs to choose the layer 2 switch with gigabit upload port.

Calculated on the basis of 720p network camera 4m code stream, there are six 720p network cameras on each access layer switch at the front end, and the convergence switch is connected to five access layer switches. The total bandwidth under the aggregation layer switch is 4M*6*5=120M, so the convergence switch and core switch cascade port should be selected gigabit port.

3. Selection of core layer switches:

The core layer switch is mainly connected to the aggregation layer switch, the uplink monitoring center video surveillance platform, storage server, digital matrix and other equipment, which is the core of the whole HD network surveillance system. In the selection of the core switch, we must consider the bandwidth capacity of the whole system and how to configure the core layer switch improperly, which will inevitably lead to the video screen can not be displayed smoothly. Therefore, the monitoring center needs to choose a full gigabit core switch. If there are many points, the VLAN should be divided, and the three-layer all-gigabit core switch should be selected.

Give examples to illustrate

If five IPCAM are connected to a switch, we usually use an 8 × × × switch, then does this 8 × × × switch meet the requirements? Then we calculate at least three aspects of the capabilities of this switch.

1. Backplane bandwidth: number of ports × port speed × 2 = backplane bandwidth, 8 × 100 × 2=1.6Gbps

two。 Packet switching rate: number of ports × port speed / 1000 × 1.488 Mpps / 8 × 100 / 1000 × 1.488=1.20Mpps. The packet switching rate of some switches sometimes calculated can not meet this requirement, so it is a non-line-speed switch. When carrying out large capacity throughput, it is easy to cause delay.

3. Cascade port bandwidth: IPCAM code stream × number = the minimum bandwidth of the upload port, 4.5 × 5=22.5Mbps/S. Generally speaking, when the IPCAM bandwidth exceeds 45Mbps, 1000m cascade port is recommended.

2. Other matters needing attention in type selection:

1. For the convenience of management, WEB managed switch is optional.

2. Because of the large video traffic, the line-speed switch is optional.

3. Video data is sudden, and the larger the switch cache, the better.

4. The flow control function of the switch

5. Aggregation switches and core switches are recommended to choose well-known enterprise products.

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