Network Monitoring system for voice and video

With the development of computer network technology, multimedia technology, computer vision and pattern recognition technology, a digital and intelligent multimedia Remote digital monitoring system came into being, that is, the digital monitoring system based on IP, realizes the leap from the traditional analog monitoring to the digital monitor quality. Compared with the traditional analog monitoring system, several main advantages of digital remote Monitoring system are: Remote monitoring can be realized by means of network, remote control center at different locations or the same branch control center can simultaneously adjust the audio and video data of one or several monitoring sites, so as to achieve distributed audio frequency access and audio and video data sharing, At the same time, can communicate with the monitoring personnel, can control the remote monitoring site of the gimbal, camera and other peripheral equipment.

China has a leading audio and video communication technology hundred RUI Technology Decade focused on "Anychat" audio and video development platform, through the use of advanced video codec technology and AAC audio codec technology, improve peer-to-peer data transmission technology. The reliable transmission of video and audio in real-time, distributed transmission and control instruction is a key problem of remote digital monitoring system, anychat can solve this kind of problem. This paper designs and realizes the remote digital audio frequency monitoring system, uses IP multicast technology as the solution of the distributed audio and video persistence and sharing, and discusses the different transmission technologies of the video, audio voice and control data, and gives the concrete realization method.

1. Overall structure of the system

The remote monitoring system generally consists of three parts: front-end monitoring field, communication equipment and back-End Sub-control center. The entire system is based on client/server (client/server) mode.

(1) The front-end monitoring site by the monitoring site host and some peripheral equipment composition. Peripherals include cameras, motorized lenses, PTZ, shields, monitors, multifunction decoders and alarms. Monitoring the field host running customer front-end software to achieve real-time video, audio data acquisition, compression, decompression (audio) (video transmission unidirectional, audio transmission is bidirectional) and packaging transmission, compressed video (tone) frequency data is stored (can also be in the center). Storage for cyclic storage, timed storage, manual storage, and motion video detection boot storage. Receive control commands from the Central Control Center (also available locally), with three variables (aperture, focal length and focus) on the gimbal motion (top, bottom, left, right, and automatic) motorized lenses.

(2) Communication equipment refers to the use of transmission channels and related equipment, communication network for LAN and WAN.

(3) The back-end device is composed of several control center computers. Each computer runs server-side software, receives from the front-end compression video (tone) frequency, display (playback), through the network to the front-end PTZ, camera control; Using multicast technology to realize distributed video persistence and sharing video share: Each central control center host can simultaneously monitor multiple front end, namely "point to Multipoint" Different control hearts can also monitor the same front end, that is, "multipoint to a point."

2. Design and implementation of network transmission module

(1) Characteristics of system Transmission data types and selection of communication protocols

The system transmits the data: the control data, the audio, the video data, the back-end Division control center transmits the control signal through the network to the Monitoring field host peripheral equipment gimbal and the camera, realizes the gimbal movement (upper, lower, left, right, automatic) the camera aperture, the focal length and the focus three variable, requests the control signal transmission accurate; , the data volume is large, the data error rate and data loss rate are allowed in the transmission, but the real-time requirement is very high. In addition, in the monitoring system, in order to realize the distributed access and data sharing of audio and video, multi-point transmission of audio and video is necessary. To achieve the above objectives? The first is the choice of communication protocol, TCP/IP protocol is widely used network protocol, its network model defines four layer (i.e. network interface layer, network layer, Transport layer, application layer) network communication protocol. The transport layer consists of two protocols: Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). IP is an international interconnection protocol located at the network level. TCP protocol is connection-oriented, provides reliable streaming service, UDP is non-connected, provides datagram service, TCP uses to provide confirmation and time-out retransmission, sliding window mechanism and other measures to ensure the reliability of transmission, it is these measures increase the network overhead. If using TCP to transmit the apparent (tone) frequency data, a large amount of data capacity causes retransmission. Make the network load large and will increase the delay; The UDP protocol is the simplest transmission protocol, does not provide the reliability guarantee, because UDP protocol does not carry on the data confirmation and the retransmission country, greatly improves the transmission efficiency, has the high efficiency fast characteristic; Ipv4 defines the transmission of three IP packets: unicast, broadcast, and multicast.

In order to realize the multi-point transmission of the video (tone) frequency data in the system, if unicast is used, the same audio and video data should be sent multiple times, which causes the sender to bear heavy load, delay long, and network congestion; If broadcast, each site in the network will receive data, no matter whether the node needs data, increase the non-receiver Multicast is a network technology that allows one or more senders (multicast sources) to send a single packet to multiple receivers (at once, at the same time). A multicast source sends a packet to a specific multicast group, and only the address belonging to that multicast group can receive the packet. Because no matter how many destination addresses, only a single packet is transmitted across any link in the network. Therefore, multicast improves the efficiency of network transmission, and greatly saves the network transmission. The multicast method is only available for UDP. In summary, the use of TCP/IP Transmission control signal, that is, signaling channel, the use of UDP/IP transmission audio and video signals, namely data channels.

IP multicast relies on a special group of addresses-the "migration address", which is the Class D address. The range is between 224.0.0.0-239.255.255.255 (where 224.0.0.0-224.0.0.255 is the reserved address), and the Class D address is the transient address for dynamic allocation and recovery. The multicast address can only be used as the address of a host, and cannot appear in any source address. Each multicast group corresponds to a class D address that is dynamically assigned. Multicast features: The membership of the multicast group is dynamic, the host can join or leave the multicast group at any time, the members of the host group in the location and the number of old unlimited.

(2) WINSOCK2 implementation of IP multicast under Windows

Multicast communication is based on Windowssocket in the Windows environment. Windows Sockets provides two different IP multicast implementations: Windows Sockets provides two different ways to implement IP multicast: Winsock1 and Winsock2. The VC 6.0 development tool is implemented in Windows2000 platform, and the programming of multicast communication based on Winsock2 is realized in this system.

Send side (front end, client) implementation steps:

(1) Load the Winsock2 library and complete the initialization of the Winsock2: Wsastarup (Makeword (2,2).

Network Monitoring system for voice and video