Detailed video conference transmission and terminal purchase
At present, there are various video terminals on the market, ranging from high-performance products for professional markets to low-end products with prices.
Video conference transmission
Currently, there are mainly two kinds of network environments that are ubiquitous. One is a circuit-switched network, such as ISDN, DDN, and PSTN. The other type is packet-switched networks such as ATM, IP, and Frame Relay.
Using ISDN lines
For most individual users and small business users, the use of ISDN line access is a more economical and practical choice. ISDN uses the public telephone network to provide users with end-to-end digital channel connections for carrying various telephony services including voice and non-voice. ISDN lines are used to transmit conference television on ISDN channels at rates from 384kb/s to 2Mb/s. Since the ISDN charges the communication according to the used B channel (64 kb/s), the domestic communication rate of the 1B channel is equal to the ordinary telephone communication rate (according to the most widely used circuit switching method).
For users with less traffic and shorter communication time, the غير مجاز مي باشدt of using ISDN is far lower than the غير مجاز مي باشدt of renting a DDN leased line or frame relay circuit, and it has the characteristics of high speed, low investment, and easy networking, and can meet the basic conference TV. System application requirements. However, the nationwide ISDN network is still in the stage of continuous upgrading, and reliability and stability are insufficient compared to the dedicated line.
Rent DDN Line
Large enterprises and institutions often have high requirements for video effects. At this time, they can choose the access mode of the DDN private line. The use of DDN dedicated lines has high transmission quality, small network delay, high circuit reliability, high network security, and convenient networking. Although DDN has the above advantages, because the digital circuit provided by DDN is a semi-permanent connection, that is, regardless of whether the user transmits data, the connection is maintained, so the غير مجاز مي باشدt is relatively high, not suitable for users with shorter communication time, but only suitable for long Time-to-point and multipoint-to-point communication links, because the DDN line charges by the number of point-to-point. If some group users' subordinate departments are connected to the company's headquarters, they can use a multi-site DDN private network, but if subordinate departments also need to communicate frequently, if you use point-to-point connections, the subordinate departments of the company will form a network. Network, so that the user's غير مجاز مي باشدt is too high.
System using PSTN
For ordinary individual users, if you want to try a video conference, you can try PSTN access. The PSTN public telephone network is currently the most widely used network system. Its advantages are wide coverage, ease of use, low price, and easy networking. However, the network speed can only reach 56 kbps, the line quality is poor, and the transmission rate is low. Therefore, the voice and image transmission for video conference is far from enough. The software-based videoconferencing system can achieve a 4f/s image transmission rate. The biggest drawback is that the image quality is too bad, which will greatly affect the quality of the conference. Generally, it is rarely used.
Use ATM network
If you want to get good video effects, and access to the ATM network is very convenient, ATM network access is also an option. ATM is an asynchronous transmission mode, which combines the advantages of circuit switching and packet switching. It can transmit wide-band signals of any speed and can transmit voice, data, image and video signals. The most important feature of this technology is QoS guarantee. This solution is recommended for units with line conditions and high quality requirements. Its features are good image quality and convenient networking (it is not necessary to connect all TV conference terminal lines. MCU) High reliability. However, the equipment غير مجاز مي باشدts are high and an ATM network is required for access.
IP network based system
The most simple and easy way to access is the IP network. IP-based networks employ packet-switching techniques because packet switching does not guarantee orderliness and fixed delays, and therefore does not guarantee a fixed delay and bandwidth. In order to better solve the service quality of real-time communication, protocols such as UDP/IP, RTP, RTCP, and RSVP are adopted. The video conference system applied to broadband IP networks such as ADSL and FTTB+LAN has achieved very good results. In today's ubiquitous IP networks, this type of network is convenient and inexpensive. However, since the packet-switched IP network follows the principle of best effort delivery, the video conferencing effect of this access method is worse than that of ISDN, DDN, and other dedicated lines. But its good غير مجاز مي باشدt performance has been favored by more and more users, especially for small and medium-sized enterprises and individuals with sufficient network bandwidth.
Using satellite access
The satellite network has the incomparable performance advantages of terrestrial networks in the mid- and long-distance video conferences. It can cover remote areas such as seas and mountains, has high transmission rates and good security, and is flexible and convenient for the venue construction and relocation. It is a multinational corporation. It is a good choice, satellite broadband video conferencing system supports multi-channel conference video, documents and data integrated transmission broadcast. The disadvantage of this scheme is that it is expensive. In addition to the channel fee for renting satellites, the construction غير مجاز مي باشدt of each satellite ground station is about 200,000 yuan. At the same time, satellite communication has a large delay and is not suitable for video conferencing systems with high real-time requirements.
Frame relay mode
Frame relay access mode is also a professional conference access mode. Frame relay technology is mainly used to transfer data services. Frame relay frames are suitable for encapsulating data units of local area networks and transmitting burst services. It is a method of wide area network communications. This kind of network has high efficiency, large network throughput and low communication delay. The frame relay user's access rate is from 64 kbit/s to 2 Mbit/s, and can even reach 34 Mbit/s. Frame Relay-based networks are expensive, but video effects are good.
Video conference terminal purchase method
Facing the complicated video market of the brand, users can choose what they want to buy and sell at a reasonable price. Simply speaking, they can be considered from the three aspects of product audio and video effects, their own application requirements, and the system application environment.
Audio and video effects are the most direct performance of a video conferencing product. It is also the most intuitive experience for users to use the product. Currently, there are "software" products and "hardware" products on the market. Although the two are similar in function, there are still some differences in the effects of video and audio.
In terms of video and audio decoding capability, whether it is based on a closed platform or a development system platform, "hardware" products use dedicated DSP processors to perform corresponding codec operations, and its coding and decoding operation efficiency, especially the coding efficiency is better than simply relying on The "software" product of the CPU is one of the biggest differences between "software" and "hardware" products. In addition, the current pure "software" products generally only support the application in the IP environment, and the general professional "hardware" products also support applications under various network environments such as ISDN, DDN, and satellite on the basis of IP.
Whether a product can be used satisfactorily by the user, in addition to the product's own performance, there is an application environment. In practical applications, due to the differences in the application industry and the environment, the user's focus on the terminal products should also be different. In general, excellent audio and video effects and stability should be the primary considerations for users when they are applied in government offices; when they are applied in the field of education, interactive real-time, abundant multimedia courseware transmission capabilities, and hypermedia Accessibility functions such as information interaction should be the focus of attention of users; in enterprise-level applications, due to the diversity of enterprise network environment and video products, the interoperability of products in enterprise-level applications and the richness of network interfaces should be highly regarded by users. .
In addition to environmental factors, users should also fully consider their actual application needs when purchasing products. With the maturation of videoconferencing technology, the industry trends that followed are overwhelming. However, some users have blindly pursued the trend in purchasing products, neglecting their actual needs and causing a waste of capital. In order to ensure the value of the selected products, users should follow the following principles when purchasing products:
1. It is necessary to specify the application purpose, select the type of product that meets the demand on the basis of its own professional needs, and simply considering the غير مجاز مي باشدt or catching up with the trend is not desirable.
2. Considering existing equipment comprehensively, if the user already has certain communication facilities, the purchased products should be compatible with the existing equipment as far as possible, and make full use of the existing facilities so as to save input غير مجاز مي باشدts;
3, in addition to paying attention to the quality of the product performance, but also pay attention to product after-sales service, especially in the construction of a certain scale of the system, product selection must consider the selected product manufacturers technical support capabilities, various network engineering Networking experience, spare parts size, etc., to minimize maintenance troubles in daily applications.
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