A required technology for next-generation networks-IP multicast is mature

With the development of broadband, the increasing demand for multimedia services has stimulated the popularization and development of IP multicast technology and become an indispensable key technology for the next generation of networks. Currently, the IP multicast technology is quite mature, which means that operators and enterprises can use this technology to obtain economic benefits.

Mature IP multicast networking

1. Multicast technology between host and multicast Router

IGMP is the only protocol available. The router uses this Protocol to communicate with the host to understand multicast groups on the LAN, the host sends a message to the vro to tell the vro。 which group it wants to listen. Currently, the mature version is 2, and the IETF workgroup is developing Version 3.

2. Routing Protocol

For large IP Multicast Networks, layer-3 IP routing protocols are generally divided into intra-domain multicast protocol and Inter-Domain multicast protocol. The domain is managed by the operator or enterprise, and Inter-Domain multicast is achieved through the Inter-Domain multicast protocol.

1) Intra-domain Multicast Routing Protocol

Including DVMRP, PIM-DM, PIM-SM, MOSPF, and CBT.

With the advancement of technology and the choice of the market, the PIM-SM protocols stand out and become a widely supported multicast protocol. The "display addition" feature of this Protocol only transmits packets to networks that require multicast packets. At the same time, the network delay from Multicast Source to receiver is small, these two factors make it the preferred choice for intra-domain multicast protocols. In addition, Cisco, which has the largest market share, only supports PIM-SM and PIM-DM, is not suitable for large networks due to its "broadcast" feature, therefore, Cisco also recommends this protocol as the intra-domain multicast protocol.

2) Inter-Domain Routing Protocol

MBGP has extended BGP to make it suitable for Routing Switching of multiple protocols, but it is currently mainly used for multicast. This Protocol adds the status of route information. Each route can be marked as a unicast or multicast route. In this way, the route information and status of Multicast can be maintained to solve the problem of Inter-Domain multicast routing.

To achieve Inter-Domain multicast, in addition to using MBGP to solve routing problems, for PIM-SM domain interconnection but also to assist with MSDP, the same as its name, the Protocol is mainly used to solve the problem of Multicast Source discovery between different domains. Through the discovery of multicast sources, domains can know each other's multicast sources in each domain, thus establishing a multicast distribution tree from the multicast source to the multicast receiver.

3. Requirements for Ethernet Switches

The emergence of multicast technology also puts forward certain requirements for Ethernet switches. When stacking an Ethernet switch, if only multicast packets are used as broadcast packets for flooding transmission, unnecessary traffic in the LAN is bound to occur. There are two mature technologies available to solve this problem: IGMP eavesdropping and CGMP. They are designed to solve the problem that the old vswitch cannot know the distribution of multicast group members. IGMP eavesdropping is to enable the switch to have a layer-3 awareness, and intercept IGMP messages sent between the host and the router to determine the location of the group members. CGMP enables the vswitch to understand group member distribution through Protocol interaction between the vro and the vswitch, but CGMP is a Cisco proprietary protocol.

Multicast high-level protocol

IP multicast cannot ensure reliable data transmission, and may cause packet loss, disorder, and duplication. Different protocols are developed for different types of applications.

1. common protocols in streaming media applications

The Application of streaming media is an important application of multicast, such as audio and video playback, video conferencing, and remote teaching. A complete set of protocols are supported for such applications.

RTP is a transmission protocol for multimedia data streams over the Internet. It can either use unicast or multicast as the underlying transmission protocol. RTP is designed to work in one-to-one or one-to-multiple scenarios. It mainly provides time information and implements stream synchronization. Generally, UDP is used to transmit data. RTCP is part of the RTP protocol and provides traffic control and congestion control services.

RTSP is an open standard jointly proposed by RealNetworks and Netscape. It extends the existing Web architecture and provides a controllable on-demand audio and video service. It is an application layer protocol, similar to HTTP. HTTP transmits HTML, while RTP transmits multimedia data.

RSVP is a Resource Reservation Protocol on the Internet. It uses RSVP to reserve some network resources, that is, bandwidth. It can provide QoS for streaming media transmission to a certain extent. RSVP technology has been challenged in terms of scalability. Therefore, it is only applicable to small intranets.

2. Reliable Multicast Protocol

In streaming media applications, it is not very sensitive to a small number of lost multicast packets. However, for data multicast applications, the reliability of multicast is very important. Such as recovery of multicast packets, consistent number of packets received by all multicast recipients, consistent sequence, and real-time performance. Research in this area is a hot topic, and there are no unified standards. IETF is working hard to launch standards, and many organizations are actively developing their own protocols.

Common protocols include SRM, MDP, and Bimodel Multicast.

Reliable Multicast has broad application prospects, reliable media stream release, satellite channel information release, airport air control system, stock market release, data update of large-scale distributed websites, Distributed Database Synchronization, distributed object messaging transmission, military battlefield command system, even online games all have application fields of this technology.

Application Status and Future of Multicast Technology

Focusing on the outstanding performance of multicast technology and broad application prospects, many service providers are taking the lead, making a huge profit. FastWeb in Italy, HKBN in Hong Kong and BredbandsbolagetB2 in Sweden are among the best. Generally, operators provide teleconference, television, and video-on-demand services, and video conferencing and other video stream services to commercial users. In practice, in the case of multicast, you can send TV programs to 30 thousand users, without causing a surge in network traffic. If unicast technology is used, the required network bandwidth is unimaginable.

At present, IP multicast technology still faces some problems in commercial applications, such as charging methods and methods for multicast services and monitoring of multicast networks; identity Authentication of multicast members; how to ensure the QoS of multicast; and what business model is used to promote multicast services to users. However, it is foreseeable that people are increasingly aware of the advantages and advantages brought by Multicast technology. Multicast technology will surely become one of the indispensable network technologies in people's work and life.

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