Multicast business technology and development ideas (1)

BSR	Custom Router(BootStrap Router)
IGMP	Internet Group Management Protocol(Internet Group Management Protocol)
IP	Internet Protocol(Internet Protocol)
MBGP	Multi-Protocol Border Gateway Protocol(Multi-protocol Border Gateway Protocol)
MSDP	Multicast Source sending protocol(Multicast Source Discovery Protocol)
PIM-DM	Protocol Independent Multicast-Intensive Mode (Protocol Independent Multicast-Dense Mode)
PIM-SM	Protocol Independent Multicast-Sparse Mode (Protocol Independent Multicast-Sparse Mode)
RP	Collection point(Rendezvous Point)
RPT	PIM-SM protocol sharing Tree (Rendezvous Point Tree)
SPT	Shortest Path Tree(Shortest Path Tree)

1. Introduction to the core technology of Multicast

In many cities, the access from the Metropolitan Area Network to the core is achieved by broadband, and an IP-based non-blocking Data bearer platform is built. Broadband networks allow people to communicate more smoothly on the wide information highway. People are no longer limited to traditional point-to-point communication, but eager for multi-point communication. Multicast technology provides good technical support for multi-point communication.

In an IP network, the multi-point communication service can be implemented using the traditional unicast technology. We use the network TV service as an example to describe its implementation process. Figure 1 on the left shows the working principle of unicast multi-point communication. In three steps, the video server sends the video stream to the final 30 recipients through the router. First, through the unicast routing protocol, the router master the network topology information to form a unicast route table. Then, the video server copies 30 video packets and sends them to 30 recipients. Finally, the router forwards the packets to the receiver based on the unicast route table.

As the number of end recipients increases, the load on video servers and network devices increases sharply. We can optimize this communication mode. In the unicast model on the left of Figure 1, the stream path in the network forms a tree structure, each branch of this tree has multiple video streams with the same content at the same time, resulting in a waste of bandwidth. In fact, as long as a video stream is transmitted on every branch of the tree and copied at the branch of the tree, the video can be sent to all the recipients. We call this tree a distribution tree, multicast technology is built based on this idea. Figure 1 on the right shows the working principle of multicast multi-point communication. The Multicast Routing Protocol first forms a distribution tree and transmits a video stream on each branch of the distribution tree, in the process of copying at the tree branch, the video stream is finally transmitted from the server to all receivers.

For the distribution tree in Figure 1 with the source as the root and the receiver as the leaf node, we call it the source tree or the Shortest Path Tree SPT ). If multiple sources and recipients share a distribution tree, we call it a sharing tree.

The Application of multicast technology to carry out multi-point communication services has good scalability. No matter how many recipients increase, for a service, the server only needs to send one video stream, and only one video stream needs to be transmitted along the network path, it minimizes server and network load and saves costs.

Figure 1 multi-point communication example network TV business

Multicast Technology covers a wide range of content, including Address Allocation Management, group member management, intra-multicast routing, inter-multicast routing, and many other aspects. The following describes the multicast address and then the multicast communication model.