Introduction to multicast technology 1. Prospects and applications in multicast technology in the construction and operation of broadband networks, business is the forefront, which is the fact that the core has become an indisputable, in which the multicast business is one of the most potential future business. An unprecedented emphasis. With the continuous development of broadband technology, traditional data services such as FTP, HTTP, SMTP can not meet people's demand for information, while video on demand, distance teaching, news release, online TV, etc. will become the major operators to fight for development. New business. These new services are characterized by a server (we call this server as media stream server) in publishing information, and the number of receivers is large, there may be thousands, and the specific number is not fixed. In this way, we can use the traditional client server (C / S) model to solve it, follow the following ideas: 1. Start the media stream playback process on the media stream server, as a server; 2. Client whenever you want to accept When a media stream server is data, by giving the IP address of the media stream server, establish a connection with the media stream server (such as TCP connection, etc.); 3. Media stream server maintains a list of customers, using a rotation The way the media stream is sent to each customer. It is not difficult to see that such a solution has two flaws. When the number of customers is large, the media stream server may not bear, because this media stream is different from traditional narrowband services (such as http, etc.), it needs very High bandwidth to transmit, and the server must also maintain information about each customer; 2. Serious waste of network resources, the same data may spread online, there are many links in some bandwidth, may cause serious communication Bottle diameter. At this time, we naturally remember the multicast. This technology is best suited for these new services above. Because multicast communication has the following advantages: 1. Media stream server does not have to know the existence of a client, it only plays the media stream to play out, and only play one; 2. Media stream data is only transferred online A copy, even thousands of clients; 3. The client does not have to register with the media stream server, if you want to receive the data of a media stream server, just join the data played by the media stream server. Monogram group. 2. The multicast archived multicast protocol is divided into group member relationship protocols between host-routers and the multicast routing protocol between routers - routers. The membership relationship agreement includes IGMP (Interconnect Network Group Management Protocol). The multicast routing protocol is divided into domain multicast routing protocols and domain multicast routing protocols. The domain multicast routing protocol includes protocols such as PIM-SM, PIM-DM, DVMRP, and domain multicast routing protocols include protocols such as MBGP, MSDP. At the same time, in order to effectively suppress multicast data, IGMP Snooping, HGMP and other two multicast protocols are introduced.
Where IGMP is responsible for establishing and maintaining group membership information of the router's linear segment. The domain multicast routing protocol According to these multicast group member relationship information for IGMP, constructs a multicast route algorithm to make a multicast packet for multicast packets. Domain multicast routing protocols issued routing information with multicasting capabilities between each autonomous domain, and multicast source information, so that multicast data is forwarded between domains. 3. Multicast IP address IP multicast address is used to identify an IP multicast group. IANA assigns the D-class address space to IP multicast, which ranges from 224.0.0.0 to 239.255.255.255. As shown in Figure 1 (binary representation), the first four bits of the IP multicast address are 1110.
Eight groups (1) Eight group (2) Eight group (3) Eight group (4) 1110xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Figure 1 D-class multicast address has been divided into all D-class IP addresses: Figure 2 Shown
Figure 2 The multicast address is not difficult to see, from 224.0.0.0 to 224.0.0.255 Reserved as Network Protocol Use, Example: 244.0.0.1 All Master Group 244.0.0 All Multicast Router Group 244.0.0 All DVMRP Router Group 244.0 .0.5 All OSPF router groups in this range of multicast packages will not be forwarded to the local network, and the TTL value of the multicast package is not considered. The address is used as a management range address from 239.0.0.0 to 239.255.255.255, which is reserved as a private internal domain. As shown in Figure 3, Ethernet and FDDI MAC address 01: 5E: 00: 00: 00 to 01: 00: 5E: 7F: FF: FF is used to map three-layer IP multicast address to a Layer 2 address That is, the low 23 bits in the IP multicast address are put into the low 23 bits of the IEEE MAC address. The IP multicast address has 28-bit address space, but only 23 is mapped to the IEEE MAC address, which will have 32 IP multicast addresses to map to the same MAC address.
Figure 3 Map of multicast addresses. Multicast operation status with the increasing popularity of broadband networks, the number of broadband Internet access is also expanded, according to statistics, so far, from the broadband access user has reached ####, through the line, DSL technology and A variety of access methods such as fiber optic Ethernet provides two megabits, 100 megabytes of broadband services have become reality, but only relying on traditional browsing can't take advantage of such large bandwidth, causing the backbone network only 20% -30 %. In the face of the status quo of network bandwidth and the number of users, how to develop "Killer Applicatong" that can produce profits, especially the multicast business, which is a top, gratifying, has started multicast on China NET. Soon, the corresponding business will soon. But we must also see that there is still a certain difficulty of current multicast operation, mainly lacking effective user management functions, specific: 1. Certification: The multicast protocol does not provide user authentication, users can freely Join and leave. 2. Billing: The multicast protocol does not involve the billing section, plus the multicast source cannot know when the user joins and leaves, and cannot count how many users have to watch the multicast program, so it cannot be accurate Billing. 3. Management is difficult: multicast source lacks effective management means to control the range and direction of the multicast information to transfer online. All difficulties show that there is an urgent need to optimize and improve multicast functions, so that it can adapt to the current operation status, so that the controllable group will be shipped. Multicast business management - controllable multicast controlling multicast mainly contains three aspects of source control, user control, and security control: Source Control: Source management refers to multicast services before the multicast stream enters backbone network. Control the device distinguish between legitimate and illegal media servers, forward legal multicast information flows, block illegal multicast information flow. At the same time, the multicast traffic issued by the source enters the network speed (CAR) and the priority (Mark) control. Thereby controlling the opening, type, bandwidth, and filtration of illegal sources. When the network is large, the work of manually configuring the source management information will become very complex and hinder the development of the network. In order to solve the above problems, Huawei company uses the ITellin / Quidway business management platform to implement multicast source management. Source management configuration, increase, and delete source control entries can be easily completed to ensure consistency of the entire network entry. As shown in Figure 4:
Figure 4 Multicast Source Manage User Control: User Control means that the second-layer device first verifies the user's multicast authority according to the Web, 802.1x and PPPoE. If verified, the Layer 2 device receives the user's IGMP add / leaving information, and establishes the corresponding forwarding table, allowing the user to receive the flow of multicast. Otherwise, discard the user's IGMP packet, prohibiting the user from receiving the traffic flow. And after passing, the iTellin / Quidway business management platform can establish a multicast access rule entry for the user, and users can only access authorized multicast services. When the user joins a group of multicast groups, the second-floor device first go to the Quidway business management platform for users' business certification. If the authentication is passed, the second layer device generates a multicast channel to the user; otherwise the user is prohibited from joining. Its authentication billing process is shown in Figure 5: Figure 5 User authentication billing process, two-layer equipment, Quidway business management system combines user authentication, authorization, and Figure 6 within the entire network:
Safety Control: In a standard multicast, the recipient can join any multicast group, that is, the branch of the multicast tree is uncontrollable. The source does not know the range and direction of the multicast tree, and the security is low. In order to achieve some of the protection of some more important information, it is necessary to control the scope of its diffusion, and Huawei's static multicast tree meets this requirement. Implement the configuration of static multicast trees to meet the safety needs of high-value users. The static multicast tree is the pre-configuration of the multicast tree, the range and direction of the multicast tree, does not receive other dynamic multicast members, so that the packets of the multicast source can spread within the specified range. Figure 7
V. Prospect As broadbandization has become the focus of construction information high-speed network architecture, many enterprise networks have realized broadband, and architectures the IP-based non-blocking data bearer platform. The broadband of the network is not only to communicate more smoothly on a wide information on the highway, but also people more and more expensive broadband networks bring more intuitive and richer multimedia information. Multicast technology provides the basis for transporting technology for multimedia services. The domain technology in multicast is basically mature, and the domain technology is still constantly being improved. Based on multicast technology, various broadband value-added services including streaming, video, and video are carried out. The smooth development of the business depends on effective business management, monitoring. As the main assignment unit, Huawei, China will strive to promote the development of multicast technology, and combine our understanding and experience in business operation management, providing continuously manageable controlled multicast solutions.
