H.320 and H.323 Conference Technical System Technical System
CWW.NET.CN September 24, 2003 09:56 Communication World Network
Railway Communication Information Co., Ltd. Yang Tao
From the history of video conferencing technology, the current video conferencing system can be carried out in accordance with the two major frameworks of ITU-T, thereby forming two different construction schemes. H.320 is the earlier video conferencing standard for ITU-T, which is fully established on a series of video conferencing proprietary technology and standards, and H.323 standard is established in general, open computer network communication technology based. On, there is a broad development prospect. Since ITU-T approved this standard in 1996, the technical and markets of video conferences have revolutionized. More and more manufacturers compete for the development of new H.323 new products, more and more users use H.323 technology and products to construct their own video conferencing system. First, video conferencing technical system 1. H.320 Standard H.320 is developed in 1990 and is one of the early recommendations of video conferences, mainly for narrowband ISDN. Since the narrowband ISDN network is a circuit-switched network, the H.320 standard is mainly satisfied with the characteristics of the circuit exchange, so the H.320 standard video conference is widely used for circuit switched networks such as VSAT, DDN, ISDN. The circuit exchange is characterized by connection, transmission rate, and time delay, time delay, low error rate, so the quality of video conferencing is easy to guarantee. However, its disadvantage is that the connection is fixed, except for the ISDN network, other network applications must be permanent connection, low bandwidth utilization, poor openness, and set join are not convenient. Since 1993, the video conference network introduced in my country has adopted H.320 standard video conference, and is built on VSAT, DDN, E1 line, ISDN, etc., greatly limiting further expansion of video services. . 2. H.323 Standard H.323 Standard covers communication with an IP-based network (LAN, EXTRANET, and Internet), establishing H.323 standards to allow multimedia products and applications of different vendors Interoperability. For a wide range of IP-based multimedia communication applications, H.323 standards are very important components. In addition, this standard also allows direct connection to PPP-based networks via ISDN and POTS. In 1996, ITU approved the H.323 specification. The standard has a wide range, covering a variety of separate equipment, personal computer technology, and point-to-point and point-to-point video conference. This standard solves many issues such as calls and session control, multimedia and bandwidth management in video conferencing. Second, the network structure 1. The H.320 standard single MCU star network and two-stage MCU network (main from) single MCU star network refers to a star network structure with a plurality of conference television terminals using a MCU device. When the meeting TV terminal is more than one MCU, a single MCU cannot connect all conference television terminals. At this time, the network expansion is to be achieved by the cascading MCU to increase the network capacity, and constitute the main slave structure. Each from the MCU is fixed to the main MCU, so the stability of the network is very poor. From the topology, this single star structure will cause the entire network to unstabilize due to the problem of the main MCU. In principle, MCU's cascading can not be restricted, but the network does not meet the minimum time delay and synchronization of the meeting at level 3, so in the application, only single MCU star network and two-level MCU networking ( The main point is from two. User layer access is generally connected to an E1 line mode or ISDN 2b D. There are advantages and disadvantages in two ways, and the line ensures good stability and image quality, but the network utilization rate is low; ISDN is affected by the line, but the access is flexible. The H.320 conference television system is stricter than network bandwidth requirements. For example, when there is 10 venues at a meeting, if each venue can see each other, 10 × 11/2 = 55 channels are required.
Therefore, when the network terminal reaches a certain number, it is difficult to intercontrol and circuitry, so that it is not suitable for large-scale meetings. 2. Based on H.323 Standard System Advantage H.323 Conference Television System The MCU Networking and H.320 differ in that the MCU in H.323 is only a network structure in the logical sense, and there is no fixed connection between them. Rendering a tree structure during the transfer meeting, but the converted MCU does not occupy the port resource. According to the second edition of H.323, there are two types of GK networking and MCU networking. The GK is a component of the H.323 system, which features a call control service to the H.323 node. All H.323 nodes in this area must register on the gatekeepers in the domain. The basic services provided by GK are: address translation, bandwidth management, license control, regional management. Multiple GK networking can form a mesh structure or a master-slave structure. Each GK status in the mesh structure is equal, and the address resolution, regional management of the connected MCU is managed separately. The master-slave structure GK network consists of a top GK and multiple domain GK, which makes it easy to upgrade the network. The top GK is resolved in the domain GK, and the domain GK is responsible for the connected MCU parsing, regional management, etc., but in this manner, it is centrally managed and stabilizes. H. 323 The bandwidth configuration of the conference television system is divided into bandwidth requirements in the domain and bandwidth requirements between the major regions. For a region, if the maximum number of MCUs is 100 384kbit / s terminals, at this time, at this time, the actual utilization rate of the IP network is calculated, each MCU's access bandwidth should be at least 100 × 384 / 0.8 = 48 Mbit / s. For different regions, the level can be taken from the MCU to save bandwidth. According to the operator's experience data, the average number of people in each domain is three people, calculated according to the average minimum number of sites, can save three points The bid of the bid, so the minimum bandwidth between the regions is 16 Mbit / s. Third, H.32O and H.323 Conference Organization Process In the H.320 conference TV system, due to the MCU and the MCU, the terminal and the MCU are staticly fixed. Therefore, the main MCU treats the connection from the MCU as a terminal, and each terminal establishes a call one by one with the connected MCU, and joining the meeting in order. In the H.323 conference television system, due to the MCU and the MCU, the terminal and the MCU are not staticly fixed, so the organizational process is more complex, there is a problem between terminal and MCU. When a meeting is held, the terminal is still first connected to the connected local domain MCU, and other domain terminals can be added to this MCU to participate in the meeting or this terminal overflows to the neighbor MCU to participate in the meeting. On the selection of routes, if the terminal is divided, you can select the MCU where the end side is located as the convener, and the other terminals are connected to this MCU. For invitations and addition to other terminals in the meeting, if the number of MCU ports in the conference is full, the terminal will be directed to the adjacent MCU to establish a connection. For the participation terminals, the MCU should be used without crossing the GK domain, and will participate in the local domain of the MCU. H.323 Conference Television System The organizational process forms a point-to-point meeting, a multi-point meeting, and a video conference between cross-regions. 4. Network Quality Assurance Technology H.320 Conference Television System The bearing network needs to be synchronized and guaranteed by the transmission indicator. The clock synchronization can be used in two ways of internal clock or external clock to meet the MCU three clock requirements. Domestic transmission indicators are recommended according to ITU-T N.86, ITU-T N.90 recommends the limit of channel performance: Domestic / International Conference TV circuit When transmitting 2048 kbit / s, bit error rate (BER) should Less than 10-6, error-free seconds (EFS) should be greater than 92%.
H.323 Conference Television System is transmitted by IP packet network, so IP network transmission h.323 conference television system should include indicators such as packet loss, delay, jitter, bit error rate. The maximum delay of speech is 0.25, and the maximum time slime should be less than 10 ms. The acceptable bit rate is less than 10-1; the maximum time delay of the movable image is 0.25 s, the maximum time slime should be less than 10 ms, acceptable bit error rate Less than 10-2, 1. H.323 Conference Television System In practical application QoS protection (1) Connect the network element consisting of all service network components using IP exclusive network or VPN technology, ensuring that between MCU and MCU, between MCU and gatekeeper, gatekeeper Communication between the gatekeeper. (2) The H.323 data can be encapsulated by the H.323 proxy server, providing QoS mechanisms. Use directional routes to route H.323 data to a private network with QoS assurance. H.323 Proxy Server has two primary subsystems: gatekeepers and gateway agent subsystems. Gateway agent subsystem: Provide H.323 traffic control, bandwidth control, QoS mechanism, and reliable communication links to external networks. Neighboring agent subsystem: Provide user authorization, call detailed record, local area network exit bandwidth management, and number of conferences, H.323 call routing, address directory. Orientation Routing: For QoS, administrators configure a separate network and separated from the public network. The H.323 proxy server makes full use of the advantages of the independent network through ASR (special application routes). (3) Neighborhood Double Registry Mapping Since the terminal is hidden after the H.323 proxy server, even after the firewall, the terminal is not being used when the H.323 proxy server is registered on the GK subsystem. The terminal other than the H.323 proxy server is directly called, and must be forwarded through the H.323 proxy server. If there is a number of terminals after a H.323 proxy server, a question that is forwarded on the H.323 proxy server, which is an address resolution problem. Here, there are two solutions to handle H.323 through the firewall: firewall supports H.323 protocol (such as CheckPoint 4.1 or more): We can put H.323 proxy servers after the firewall. The firewall cannot support H.323 Dynamic Access Protocol: The proxy server can be used in the firewall to provide a simple access control scheme. Because only H.323 proxy servers are node servers, this node is interacting with the equipment outside the firewall, so it is easy to establish an access control list on the firewall to pass the H.323 proxy server. If the firewall does not support the H.323 dynamic access protocol, we can place the H.323 proxy server and the firewall. The reason for indirect transmission signals through a H.323 proxy server: can resolve the server's security mechanism; can represent the H.323 terminal to undertake QoS signal; can complete the route task of special applications to improve H.323 transmission quality. 2. Using VPN-MPLS to implement flow control and QoS assurance virtual private network (VPNS) to be used to distinguish between network traffic. The service provider can apply the MPLS to create a new VPN, which has the MPLS capability of the VPN that is unconnected, with confidentiality with the frame relay and multi-level IP services, making MPLS's VPN operation more efficient, service provider More cheap manageable IP services can be available. The MPLS-based VPN based on the third layer is built into a peer-to-peer mode, which is essentially better extended compared to traditional VPNs and more beneficial to build and manage.
In addition, many value-added services, such as video applications and data storage, network business, voice services, etc., can be easily deployed through a special MPLS VPN, which is the service provider's transmission network to identify each VPN as A secure connection IP network. V. H.320 and H.323 system Interior H.320 protocol is based on a multimedia communication standard based on narrow-tape ISDN network, is a circuit-exchanged network; H.323 protocol is a multimedia communication standard for group-switched networks. Both are based on the network-based multimedia communication standard. The compression algorithm of the audio and video used is the same, through the comparison of the H.320 protocol and the H.323 protocol conference TV standard, can be achieved by Gateway (Gateway) The conversion between these two different protocols. 1. Interoperability between the two conference systems (1) H.320 terminal and H.323 endpoint pair points; (2) H.320 terminal adds H.323 Conference on MCU; (3) H.323 Terminal Add H.320 The MCU meeting; (4) H.320 on the MCU meeting and the meeting of the MCU on the H.323. 2. The interworking H.320 video conferencing system of network management has basically no true network management, just for the terminal, MCU has a remote dial-up control feature, which can remotely dial-up configuration and maintenance terminals remotely with the modem, implementation and booking meetings, master Conference control and other functions. H.323 Video Conference System Network Management Ability than H.320 video conferencing systems, the H.323 video conferencing system network management is based on SNMP (simple network management protocol) in the TCP / IP protocol, including Terminal, MCU Management, configuration, and maintenance can be implemented by SNMP. In response to the above situation, the distributed structure is proposed in a manner, as shown in Figure 2. When the area is involved, it can be interconnected by the gateway. Through a custom private server connected to the MCU of H.320 through the IP, the MCU in the network is managed, including a predetermined meeting, a grouping conference, etc. Realize the control of the MCU to the MCU, thereby achieving centralized management of the entire network.
