【 Weak current College 】 detailed IP video conference technology---Power By 【 China power house network 】

Summary: this article from the standard IP video conferencing, IP video conference system with traditional video conference systems, IP video conference system, how to ensure quality IP video conference, video conference areas of future trends, detailed look at IP video conference technology.

Keywords: video conferencing, H.323 protocol, IP video conferencing, IP video conferencing quality.

Video conferencing is through the Terminal and network, so that the participants can be in different places on the same topic to discuss, among not only can hear speakers sound and you can see the speaker's image and background, and you can exchange the data on the subject. Text. Chart and other information, so participants can get richer than the phone conference information, along with the VLSI circuits and computer technology, set computer interactivity. Network of distribution and synchronization of multimedia information for multimedia conferencing system broke through the computer. Communication. TV and other traditional boundaries, as it provides a new interactive services.

Currently, the global video conferencing equipment demand soared, particularly since the "SARS" events occur, in order to ensure the security, many large corporations through video conferencing, remote teleconference, Web conferencing, and other means of commercial activities.

N-ISDN or PSTN based video conference system while also can transmit a variety of media information, but it is the use of existing private or common communications network, using a simple time division multiplexing (TDM) in the same channel multi-channel information on transport, and not from the multimedia communication system structure. Connect and control protocol for departure, the design of the system of communication processes and media information interactive control capabilities are very limited.

As the Internet and intranet development and popularization of PC desktop systems, the transmission network of interactive video conferencing infrastructure is based on circuit-switched of N-ISDN or PST based on packet switching type of IP network transition, dedicated conference rooms to personal desktop development. IP video technology to the traditional meeting of models produced unprecedented impact, and to provide a more efficient and better means of communication, triggered a new revolution in the field of communications. IP video technology with low operating costs and high-quality communications services, a clear advantage, based on the IP video solutions are widely applied to our business decisions, distance learning, telemedicine, etc. This article focuses on IP video conference system.

First, the standard IP video conference

In order to solve various vendor interoperability issues between products, and establish global unified videoconferencing standards, International Telecommunication Union (ITU) of the Telecommunication Standardization sector (ITU-T) since 1990, developing has issued a series of standards for video conferencing, forming a set of related video conference full standard system. Currently, video conference system can be based on two main frame ITU-T recommends H.323 and H.320.

1990 launched H.320 standard is first generation videoconferencing standards, mainly applies to the narrowband ISDN (N-ISDN) network and dial-up VPN, concentrated on defining the ISDN video conferencing as well as the speed of 2Mbps 56kbps ~ video conference, is now developing the most sophisticated technology and systems.

1996 launch of H.323 defines a LAN, Intranet and Internet video conferencing framework proposal. It enables compliance with standards of different manufacturers with the system, you can communicate with each other on a LAN, a video conference development of new directions. H.323 defines LAN on video communications equipment, procedures and protocols. H.323 uses Internet Protocol compatible IETF RTP/RTCP standard, and plan to use a variety of packet switching network (PSN) protocols, including TCP/IP and Novell SPX/IPX protocol. H.323 protocol is a standard IP video conferencing.

Initially, because the IP protocol is not very common, based on the ISDN line, in line with the agreement of products covers H.320 major proportions, with few years of the universal application of the IP Protocol and the rapid development of the Internet, especially for broadband network foreseen, in line with the H.323 protocol products since 2000, the overall proportion of markets has risen dramatically. With IP technology continues to improve and upgrade, international standards, IP video services and applications will gradually expand, application based on the H.323 platform will become increasingly widespread.

H.323 standard covers the packet switching network, audio, video and data communications, resolve the point-to-point and multipoint video conferences such as the call session control, multimedia and bandwidth control. T.120 protocol H.323 reference to process data exchange.

In H.323 recommendations, the image decoding format with H.263, H.261, H263 +. H.263 and H.263 + to images provide greater compression rate, to be able to provide low bit rate than H.261 better image quality, and therefore more suitable for the IP network applications

Audio coding format must be compatible with the G.711 voice coding, you can also choose to use the G.723.1, G.722, G.728, G.729 or MPEG-1 speech coding standard.

IP network video conferencing system uses packet switching technology for packet switching does not guarantee order and fixed time delay, and therefore are not guaranteed a fixed delay and bandwidth. In order to better address the real-time communication service quality, the use of UDP/IP, RTP, RTCP, RSVP, and other protocols.

H.323 has the following main advantages. H.323 protocol is designed to run on the common network architecture, network-independent. H.323 protocolDiscussion provides network bandwidth management function, to be able to network with h.323 connections and H.323 applications available to limit the total amount of bandwidth. H.323 provides connections are based on circuit-switched or ISDN video conferencing tool. H.323 support multipoint and multipoint Conference broadcast (multicast). H.323 implementation of the different manufacturers of multimedia products and application interoperability, etc.

II. IP video conference system with traditional video conference system comparison

Previous traditional video conference system is based on a special line of protocols that need fixed H.320 routing and QoS assurance of video conference system. Mainly uses ISDN or E1 access. While the image quality of the sound ideal, but the user-end equipment and MCU (multipoint control unit) of expensive, small businesses and individual users will not be accepted.

Since H.323 and H.320 agreement protocols (IP video conference system protocol) in the video, audio compression protocol on basically the same, therefore, in the same bandwidth situations, H.323 videoconferencing (IP video conference system) and H.320 videoconferencing quality basically the same.

For ISDN access desktop H.320 videoconferencing, user terminal needs and fixed ISDN line binding that cannot be moved, in addition, if the convening of a meeting across provinces, users also need to pay long distance charges, not only in inconvenience to the users, also increased the burden on users. And H.323 videoconference system (IP video conference system) you do not have these problems because, for Internet users, there is no question of long distance charges, and, as long as H.323 video conferencing users are installed on the PC client software, compression card and camera, and a successful landing on the Internet, the Gatekeeper (gateway) registered, can by MCU (multipoint control unit) convene meetings anytime, anywhere, is very flexible and convenient. The user saves a tremendous amount of investment and maintenance costs, greatly improving the efficiency of the enterprise's information and communication; on the other hand also for operators to attract users, development of new value-added services.

III. IP video conference system composed of

According to recommendation H.323 IP video conferencing system from Conference Terminal (Termial), gateway (gateway), gap (gatekeeper) and IP networks, and multipoint controller (MCU).

The Terminal is the provision of one-way or two-way real-time communication client. All voice communication terminal support, optional support for video and data communications.

Gateway for achieving and non-terminal of H.323.

Gatekeepers perform secure data network integrity features, including address conversion, access control and bandwidth management.

High speed IP networks: as home users increased demand on Internet as well as for information exchange and higher requirements for high-speed IP network will get a fast development, through the re-laying 5 cable, users can gain access 10M even 100M bandwidth, you can fully support Conference TV business. Use of VLAN switches instead of hubs, support IGMP router, via frame relay and ATM network transfer images, guaranteed bandwidth, you can better guarantee the transmission quality video conference.

Multipoint controller is used to support three or more points on a network, from the necessary multipoint controller (MC) and zero or more multipoint processor (MP). MC determines all terminal of audio and video processing power and control conference resources. MP mix, Exchange and processing of audio, video and data streams.

Multipoint session is divided into a centralized, distributed and mixed multipoint session three modes.

Centralized multipoint session must be equipped with MCU. All of the Terminal to ad-hoc manner to the MCU sends audio, video, data and control flow. MC Central Management Conference. MP for audio mixing and video mixing and data distribution, and ECHO participated in the meeting of the Terminal. Centralized multipoint meetings allow all come from different manufacturers of H.323 Terminal to join the meeting.

Decentralized multipoint session using Multicast technology. Participation in meetings of H.323 terminal will be audio, video streaming radio to other participation in the meetings of the Terminal, control the information you send in a point-to-point manner MC. Receiving terminal is responsible for processing the received audio and video streaming. Decentralized multipoint Conference put on a network resource consumption is low, and can significantly reduce costs. It called on the network configuration supports network broadcast.

Hybrid multipoint session combines centralized and decentralized multi-point conferencing multipoint characteristic. Participation in meetings of H.323 terminal will be audio, video, stream select one to send ad-hoc mode, the rest of the MC to broadcast to all H.323 Terminal.

By MCU can be centralized multipoint conferences and mixed multipoint conferencing, you can achieve greater flexibility.

In addition, H.323 defines "loose contact" Conference to support large-scale meetings. In this mode, the participants were divided into active participants and passive participants, active participants are divided into permanent and temporary members. Passive participants will only be able to watch the Conference. Through temporary members and passive participant role change, allow more participants to express their views. IV. how to ensure quality IP video conference

In recent years, based on the H.323 IP video conferencing system is a great development, already the public operating conditions, and the realization of this condition, the service quality is the key.

Thanks to the H.323 protocol itself is not mature, IP video conference of public operators bring certain difficulties. IP video conference of public operators, must solve user management, business management, billing management and video switching of interoperability issues. Because the Internet is a connectionless network, onlyProvides a hosted business-try to transfer (best effort) business. That is, the network does not guarantee that the data stream to the application to provide the required bandwidth, there is no guarantee that the data flow of transfer delay and loss ratio, and other quality indicators. For data services and other non-transmission of real-time business, try to meet the requirements, but for audio or video and other real-time communications applications, the network must have a certain end-to-end QoS hosting business. How to improve real-time performance, ensure that the communication of QoS, IP video system key technical requirements, is also a technical difficulty.

In the IP video conferencing, QoS policies can be divided into two levels: network level and the operational level. The following two levels from the view of how to ensure that the IP video conferencing quality (QoS).

1. ensure that the IP video system QoS method

The Internet ensure that the IP video system QoS there are two ways, as follows:

(1) excessive engineering method (overengineering)

The network planning sufficient bandwidth so that any time to obtain acceptable QoS. This method is very simple, there is no need to RSVP and admission control function, but requires the deployment of a sufficient number of routers and high speed link, ensure that even in a busy network resources also have sufficient allowance. It can be used to network resources, network cheap maximum traffic and predictable.

(2) integrated services Internet method

By IETF integrated services (IntServ) working group definition. It needs to define a call admission control features, such as the resource reservation protocol RSVP. Use RSVP message, endpoint applications can make data transfer whole must retain the network resource (such as bandwidth, buffer size, etc.), and also determines the transport en router, take this scheduling policies, you can stream data on each QoS control in turn.

2. network design for QoS Assurance

(1) network

Metro IP network is typically used by the core layer, the tandem layer and access layer composition, the node tandem layer over a high-speed link to connect to the core layer. In Metro IP network, the router connection on routing hops, guarantee network any two nodes communicate routing hops between a maximum of 4 jumps, configure a high-performance router, depending on experience, in a light transmission of a packet jump its delay typically 10ms, this value is not determined by the length of the lines and the performance of the router (the router for more than 75), packet core network in normal delay probably around 50ms. From this perspective, the delay is not a business affecting IP video quality.

(2) route oscillation problems and solutions

Route Oscillation causes is divided into two areas. One is due to the link state change causes a routing change, if you use IS-IS or OSPF route discovery, because the problem depends on the Hello packet detection, detection once is not enough, you also need to test a few times. In General, from the link to the new route selected take several seconds to several tens of seconds, this problem occurs in the backbone of the Internet will greatly affect the quality of real-time multimedia services that mainly through the use of MPLS FRR ability to protect it. Another route oscillation problems mainly loose network design, for a large number of values selected road or large numbers of Route ReLookup or routing status update oscillation of the main programme to prevent problems is to design the network requires that all flow directions and routing needs to monitor explicitly be inspected.

Oscillation is a very difficult to solve, because the principle of the router (relative to the switch), there are always some time may be at a busy time, this may lead to a single router latency increases to more than 100ms, downtime, multimedia conferencing system quality decline occurred. Produce this condition sometimes not necessarily due to excessive traffic on the line, there may be 20% ~ 30% of the bandwidth is such a thing occurs. This is mainly due to the router's Buffer settings. Improvement of the programme is the router's Buffer settings specifically for conferencing system that is optimized, but there are potential efficiency of traditional IP service. Best is to use two network separately from the service, there is a decision of a problem.

(3) network congestion

In addition to the oscillation, network congestion on IP video conferencing business also has a significant impact. So we designed a network, to prevent the emergence of network congestion. When you deploy the congestion management, use the following steps:

(A) the determination of whether the WAN congestion phenomenon

(B) depending on the need to manage the communication type, network topologies and design programmes to determine target. In determining what needs to be made, consider whether the target is located several criteria:

Can be identified by all traffic types to establish a fair distribution of bandwidth;

For business from IP video communication sent out, will be able to specify strict priority. This may hurt also supported, but not an emergency communications business interests;

To customize the bandwidth assigned to the service of all the network resources are shared between applications. Each application has a specific, identified good bandwidth requirements.

(C) use the selected kind of queue policy configuration interface, and observe the results.

3.IP video business itself QoS implementations

How to improve real-time performance, ensure that the communication of QoS, IP video conference key technical requirements. At this point, based on the H.323 videoConference system with IETF's real-time protocol and network technology. First of all, the voice signals using real-time Transport Protocol, RTP encapsulation. However, RTP itself does not provide any guarantee QoS mechanisms, to ensure that the communication of real need IP network itself has the enhanced ability.

(1) RTP function and design ideas

RTP Protocol for audio, video and other real-time data to provide end-to-end delivery service, you can transfer to a receiving endpoint recovery time signal required timing and order information, and to send and receive both sides and network operators to provide QoS monitoring tool for reducing the demand for network bandwidth. RTP can greatly reduce your bandwidth consumption. You can also make video RTP session in tolerance a small amount of packet loss, to avoid packet retransmission caused by the delay. RTP actually consists of two protocols.

RTP itself: to transmit real-time data. It features provide payload type indicates, data grouping ordinal, data sent timestamp and identifies the data source.

RTCP real time signal for delivery: delivery of quality parameters, provide QoS monitoring mechanisms; while shipping conference communication participants information to has no explicit member control and call the establishment of "relaxation" Conference communications provides control mechanism.

H.323 protocol use RTCP SR and RR packets of QoS for monitoring.

SR: mainly used for multiple RTP stream, such as audio and video synchronization between closely related, and H.225.0. And stream synchronization-related fields is NTP RTP timestamp and timestamp.

RR: user monitoring QoS indicators, including indicators of long and short-time when indicators. If packet loss rate is higher than the set value, you should lower media rate. Such as receiving report interval longer than the set value, it should be based on the RR packet loss rate in the field to determine whether the network congestion, and if so, should lower media rate. If continuous 3 receive report arrival jitter value increases, the sender should take measures.

(2) guarantee QoS specific means

In order to maintain a certain quality of service, when monitoring to QoS indicators declined to H.323 terminal when certain measures. In fact, these measures do not keep existing Qos and follow a certain order to reduce the quality of various media, in a given bandwidth and load conditions still able to provide acceptable services. First of all to consider lowering the quality of the video signal, then the data, audio and control signals. Measures can be divided into two groups: short-time response and long-term response. The former is designed to address a package of short-term loss and delay increase short-term issues; the latter is used to network congestion worsening situation.

(A) to dynamically adjust image bandwidth

People on the image and sound sensitivity is not the same, when the image stream a delay, jitter, the decoded image performance for ber, dropped frames; when voice stream a delay, jitter, decoded voice interrupted. From the impression on the image some more tolerant of error. To improve QoS, you can use RTP/RTCP report, get on the network status information, such as packet loss rate, jitter, latency, according to the information dynamically adjust image bandwidth. When network conditions are not good, you can notify encoder, reduce image bandwidth, the bandwidth priority ensure sound; when the network status, notification encoder, improve image bandwidth.

(B) lip sync

Receiver: for receiving voice and image of synchronization, Terminal received pronunciation, the image data is placed into the buffer and image buffering for voice, scheduled from speech voice out of the buffer, if the package out of voice packets time stamp with the image, the corresponding image package decoding. The benefit is given voice of sensitivity.

Sender: play-time stamp. The sender should give the packet hits the timestamp on the one hand, the packet (RTP packets) timestamp, on the other hand, is a data control package (RTCP packet) of timestamp.

Based on the H.323 IP video conferencing system will become the broadband IP network to a potential significant value-added services. But it's the ultimate goal is the public service, of households enjoy video services. But IP video conference system for public operators, many of the issues involved, the service quality is the implementation of IP video conference key, so the IP video system design, to unify the design of good service quality. Because IP video conferencing is an emerging technology, itself still in development, a lot of technology to further research and discussion.

5. video conference areas of future trends

As the communications network operators, broadband business expansion as well as in ensuring network quality of service for core broadband backbone technology, we can foresee that the network transmission capacity will be further enhanced, thereby promoting H.323 videoconference system (IP video conference system) of rapid development. Video conference system for the future development trend include the following:

(1) codec conversion from hardware to software

As a result of computer processing speeds and affiliated card processing speeds increase, many require special equipment for data processing can be handled by a computer and its built-in universal Board to complete, in effect, there is no significant difference between

(2) product protocol type conversion from H.320 to H.323

Initially, because the IP protocol is not very common, based on the ISDN line, in line with the agreement of products covers H.320 major proportions, with few years of the universal application of the IP Protocol and the rapid development of the Internet, especially for broadband network foreseen, in line with the H.323 protocol products since 2000, the overall proportion of markets has risen dramatically. Estimated in 2003, based on the H.323 protocol product sales will exceed the H.320 products.

(3) market focus to low-cost average user market transfer

Due to network conditions, skills, DHProduction process and other factors in this period of change, the video conferencing system from high-priced private market to low-cost average user market. Now including POLYCOM, VCON and other large companies have equivalent strength is in the personal user market.

(4) streaming media broadcasting technology more and more applications in video conference system

Streaming media broadcasting technology will increasingly applied to video conference system. At present, the streaming media technology and IP video sessions are in hot pursuit by the industry, both for Visual/audio technology is an important component of their mutual integration between the two is open up a broad application space. Now, video conference, you can apply online Roadshow, live interviews, live broadcasts, online stock as well as distance learning services, mainly for the transmission of multimedia information, users are rarely interaction between the application of this technology is on traditional video conference function extensions.

(5) virtual cooperation application services will be video conferencing for the enterprise one of the core features

Most multinational groups and branches of larger enterprises in use video conferencing system, in addition to meeting features, the most frequent is a virtual cooperation, such as remote project management, customer service, technical training, and so on, this kind of application is particularly evident in the knowledge-based enterprises.

Finally, IP video conferencing areas of focus to make the market priced transfer user market. From the communications market development we can see that most of the product's target market user are from high-end users to low-cost user gradually shifted. Due to the technical level and the improvement of the production process, the cost of these products, and gradually reduce as the application area of expansion, the scale effect in this area. In this way, the video conferencing system from high-priced private market to low-cost market gradually over an ordinary user.