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First, video surveillance system introductionThe video surveillance system is an integral part of the security system. It is a comprehensive system with strong defense capabilities. Video surveillance is widely used in many applications because of its intuitiveness, convenience, and rich information content. In recent years, with the rapid development of computer, network and image processing and transmission technology, video surveillance technology has also made great progress.
1. Networked video and audio integrated information service
In the Internet environment, IP technology provides technical consistency for data transmission and information exchange at different levels of information services, and can effectively support two-way asymmetric information services. Therefore, based on IP and IPv6. Driven by the convergence of information networks, the information services carried by the network have been further integrated, forming a comprehensive information business environment with different business models.
In the one-way broadcast service, since the broadcast TV network is gradually achieving IP-based and Web-based network convergence, the AV broadcast service can achieve more flexible two-way interactive functions in the context of a converged information network. One-way broadcasts provide a potential value-added business model.
In the two-way interactive service, with the convergence of traditional telecommunication networks for computer Internet, various multimedia information services have gradually become the main development trend of communication services, and the asymmetry of two-way services can be provided by IP networks. Technology such as multicast and multicasting can be used to achieve a flexible business model.
In particular, the video surveillance service has become a key business realized by the integration of information network. From the traditional video surveillance service applied in the security field, video surveillance has been extended to real-time two-way video and audio communication and media communication services. The integrated business form. In recent years, video surveillance has broken through the existing connotations and achieved an extension to a wider range of two-way interactive services.
Therefore, in the process of researching interactive video and audio services, this paper will explore the more effective and efficient interactive video and audio service forms based on IP and Internet from the video surveillance service, and research its supporting technologies.
2. Analysis of the development status of video surveillance technology
In the domestic and international markets, the main products are digitally controlled analog video surveillance and digital video surveillance. The former technology development is very mature, stable performance, and has been widely used in practical engineering applications, especially in large and medium-sized video surveillance projects; the latter is the newly emerging computer technology and image video compression as the core The new video surveillance system, which solves the shortcomings of the analog system and rises rapidly, but needs further improvement and development. At present, video surveillance systems are in the stage of hybrid application of digital analog systems and digital systems and will gradually transition to digital systems. The following is a brief introduction and analysis of these two types of systems:
(1) Digital signal controlled analog video monitoring system
The monitoring system is divided into two types: microprocessor-based video switching control plus multimedia management of PC and PC-based switching control of matrix host and multimedia management of the system. However, the main advantages of the analog monitoring system are the following:
1 Usually only suitable for small-area area monitoring analog video signal transmission tools are mainly coaxial cable, while coaxial cable transmission analog video signal distance is not more than 1Km, twisted pair distance is shorter, which determines the analog monitoring Suitable for single buildings, small residential areas, and other small areas;
2 The poor expansion capability of the system For the already established system, if a new monitoring point is to be added, it is often taken care of, and new equipment is difficult to add to the original system;
3 Can not form an effective alarm linkage In the analog monitoring system, because the various parts operate independently, the mutual control protocols are difficult to communicate, and the linkage can only be carried out within a limited range.
Although the system has developed to a very high level, it has no potential to be tapped, and its limitations must exist. To meet higher requirements, digitalization is the only way.
(2) Digital video surveillance system
With the development of multimedia technology, video compression coding technology, network communication technology and the rapid rise of digital video surveillance systems, there are two types of digital video surveillance systems on the market today, one is a video surveillance system with digital video recording equipment as its core. The superiority is mainly manifested in: many functions, simplified system structure, and digital multimedia remote network monitoring are not limited by distance, which is beneficial to the system to realize multimedia information inquiry. However, with the development of PC-based video surveillance video recording system, some shortcomings are exposed in the actual engineering use process, mainly the instability of the system work;
The other is a video surveillance system with an embedded video web server as its core. It is a dedicated computer system that is application-centric, software and hardware can be cut, and adapts to the comprehensive requirements of the application system for functions, reliability, cost and volume. The advantages and disadvantages of this monitoring system are:
1 system is a dedicated system, so the system is small, the instructions are streamlined, and the processing speed is fast;
2 system data is placed in ROM/FLASHMEMORY, the calling speed is fast, will not be changed, and the stability is good;
3 system processing has good real-time performance and stable performance;
â—‹ 4 file management system is more suitable for a large amount of video data;
â—‹5 This type of system is currently relatively rare in more than four roads;
â—‹6 is also unsatisfactory in terms of network functions, audio and video synchronization.
Second, the principle of instant messaging system
InstantMessenger (IM), a technology that enables people to identify online users and exchange messages with them in real time. A typical IM works like this: When someone in the buddylist logs in online at any time and tries to make a communication request, the IM system sends a message to alert the user, then establishes a communication session and types the message text. communicate with.
The emergence of instant messaging is inextricably linked to the Internet. Technically, IM is based entirely on the TCP/IP network protocol family, and the TCP/IP protocol family is the technical basis for the entire Internet.
First, user A enters his own username and password to log in to the instant messaging server. The server authenticates the user by reading the user database. If the username and password are correct, the user A's IP address and the version number of the IM client software are registered. The TCP/UDP port number used, and then the user A login success flag is returned. At this time, the status of user A in the IM system is Online (Online Presence).
Secondly, according to the contact list (BuddyList) stored by the user A on the IM server, the server sends the related information of the user A online to the PC of the instant communication contact who is also online, including online status, IP address, IM. The TCP port number used by the client, etc., the instant messaging software on the instant messaging contact PC will pop up a small window on the PC desktop to prompt.
In the third step, the instant messaging server returns the contact list and related information stored by the user A on the server to his PC, and the information includes the online status, the IP address, the TCP port number used by the IM client, and the like. Information, when the IM client on User A's PC receives it, it will display these contact lists and their online status.
Next, if user A needs to communicate with user B, he will directly send information to user B's PC through the IP address and TCP port number of user B sent from the server, and user B's IM client software. After receiving it, it will be displayed on the screen, and then user B will directly reply to user A's PC, so that the instant messages of both parties will not be transmitted through the IM server, but through point-to-point direct communication through the network. This is called peer-to-peer communication. (PeerToPeer). In a commercial instant messaging system, if the peer-to-peer communication between user A and user B is difficult to establish or slow due to reasons such as firewall, network speed, etc., the IM server also provides a message relay service, that is, all the instant messages of user A and user B are sent first. Go to the IM server and forward it to the other party. In the early IM system, the UDP protocol was adopted for communication between the IM client and the IM server. The UDP protocol is an unreliable transmission protocol, and in the direct communication between the IM clients, the TCP protocol with reliable transmission capability is adopted. With the development of user requirements and technology environment, current mainstream instant messaging systems tend to adopt the TCP protocol between instant messaging clients, instant messaging clients and instant messaging servers.
Third, the realization of instant messaging system
1. Overview of the overall architecture design of the system
Figure 1 System overall architecture The system is based on the thin client C/S mode, adopts a server-centric star structure in the architecture, and innovatively characterizes the monitoring field end and the monitoring center end C. That is to say, in the system, all the monitoring field ends and the monitoring center end are clients with respect to the architecture of the entire system, and their communication needs to be verified and relayed by the server. At the same time, the login of the user of the monitoring center, due to this architecture mode, must also be verified by the server in order to successfully log in, and then obtain the right to monitor.
The role of the S-end of the system is very important, because the system adopts the thin client mode, so the server side has to perform more functions: confirmation of user login, verification and connection of remote monitoring host, verification and connection of field host, data Storage, parsing of data packets, construction of connections for video communication lines, and more. It can be said that the entire server is the core of the normal operation of the entire system, and its stability is directly related to the normal operation of the entire system.
The connection of the communication line utilizes the API provided by Skype. TOM-Skype is an Internet voice communication tool jointly launched by TOM Online and Skype TechnologiesS.A. TOM-Skype uses state-of-the-art P2P technology to provide ultra-clear voice calls and end-to-end encryption to ensure secure communications. The characteristics of modern system development are reproducibility. The video communication line of this system architecture takes this into consideration very well, making full use of the characteristics of Skype, which not only ensures the simple and effective development of video communication lines, but also improves the video communication. Line performance and stability. It can be said that this is also a major feature of this system.
2, the superiority of system architecture design
(1) Security
The overall architecture of the system determines the security of the entire system. Because the monitoring site and the monitoring center are unified client-side, all client logins must be verified by the server. At the same time, the relevant data packets of the communication protocol must also be parsed and transferred by the server. In particular, the entire video communication line is also verified after the server parses the data packet of the relevant protocol. In this way, the security of the entire architecture is concentrated on the S-side to be effectively guaranteed, and the security requirements of the video communication system are outstandingly completed.
(2) Networking
Because the system adopts the design and development mode of remote monitoring of IP network, it breaks the geographical and quantitative boundaries of the deployment area and equipment expansion to some extent. System networking will share the hardware and software resources of the entire network system and the sharing of tasks and workloads.
(3) Economic simplicity
Whether it is a PC or a workstation or a mainframe, it only needs to be monitored by an installation file of the system plus a USB camera. It does not require users to install other software or video capture cards.
(4) Scalability
The definition of an open client greatly improves the scalability of the entire system. By developing different clients, the functional characteristics of the entire system can be extended, and all of the premise is that only the server-centric verification relay is required. .
(5) Openness
It is precisely because the system uses data transmission over an IP network, so that through the network camera, analog camera and video server, the system can be connected to the IP network for data transmission. On the other hand, the system can provide information via PDAs, PDAs, and other devices that can be connected to PC servers and network storage. This open system provides better scalability, integration and economics.
(6) The advanced nature of the interface
Since the video communication line of the system is implemented by the API provided by Skype, and Skype itself provides the voice connection function of the mobile phone and the telephone, in the 3G network era, when the video surveillance technology of the mobile phone is mature, the system is provided by Skype. The API can extend the range of video surveillance equipment to mobile phones, and adapt to the requirements of the 3G era to further meet the higher requirements of users.
Fourth, the conclusion
The core of this paper is a system design problem, which includes the design ideas and implementation methods of the terminal, network and monitoring center. The development strategy of the video communication module based on the Skype instant communication tool can effectively save network resources, realize small delay, reduce the probability of network congestion, and better ensure the real-time performance and service quality of digital video transmission.
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