Multicast technology, some knowledge about multicast

There are many more professional explanations online. In my own conclusion, multicast is the transmission method used when you know which group a certain receiver is in, but you don't know which machine it is.

The biggest difference between multicast and broadcast is that broadcast data can only be transmitted within the broadcast domain, and cannot cross the broadcast domain. Multicast data, on the other hand, can span the broadcast domain. What is a broadcast domain? In most cases, a VLAN is a broadcast domain.

If you need to send data to multiple receivers at the same time, you need to copy multiple copies of the data from the source data sending terminal and send them to the receivers separately. If the target is 10,000 receivers, 10,000 copies of data need to be copied, and the source data sending terminal will be miserable.

When using multicast to send data, the devices in the network can determine which members join the multicast, which means that the task of data replication can be handed over to thousands of switches and routers in the network, which greatly improves the utilization of network resources.

Multicast uses the IGMP control protocol used between the host and the router, and the IM control protocol used between the router and the router, so that the receiver can join and leave the group very flexibly, so that there is a flexible option to transmit data to the receiver in need.

This is because multicast uses the UDP protocol, so there is no packet replenishment mechanism, and if the reliability requirements are high, multicast cannot be used.

Multicast has the potential to cause network storms, so routers on the Internet do not enable the PIM protocol by default, so they cannot directly transmit multicast packets. To transmit multicast data over the Internet, we need to establish a tunnel and transmit it in tunnel mode.

1. Unicast: Communication between network nodes is like a conversation between people.

Detailed explanation: 1. Unicast is a "one-to-one" communication mode between hosts, and the switches and routers in the network only carry out data replication without replication. If 10 clients need the same data, the server needs to pass each other one by one, repeating the same work 10 times. However, due to its ability to respond in a timely manner to each customer, all web browsing is now based on the IP unicast protocol.

Routers and switches in a network select a transmission path based on their destination address to deliver IP unicast data to their designated destination.

Differences in definitions:

Unicast requires a separate data channel between the client and the server, while multicast enables a point-to-multipoint network connection between the sender and each receiver.

Multicast solves the problem of inefficiency in unicast and broadcast modes, and multicast routers use the multicast routing protocol to establish a tree route for multicast packets, and the transmitted information is replicated and distributed at the farthest fork in the road.

Functional differences:

Advantages of unicast:

1.The server responds to the client's request in a timely manner.

2.The server sends different data for different requests from each customer, making it easy to achieve personalized services.

Disadvantages of unicast:

1.The server is overwhelmed in a streaming application with a large number of customers and a large amount of traffic per client.

2.The existing network bandwidth is a pyramid structure, and if all unicast protocols are used, the network backbone will be overwhelmed.

Advantages of Multicast:

1.Clients that require the same data flow join the same group to share a data flow, saving the load on the server. It has the advantages of broadcasting.

2.Since the multicast protocol replicates the data stream according to the needs of the recipient**, the total service bandwidth of the server is not limited by the bandwidth of the customer access side. So the services it provides can be very rich.

3.This protocol, like the unicast protocol, allows transmission over the Internet broadband network.

Disadvantages of multicast:

1 Compared with the unicast protocol, there is no error correction mechanism, and it is difficult to compensate for packet loss and error packets, but it can be compensated by a certain fault-tolerant mechanism and QoS.

2 Although the current network supports multicast transmission, it still needs to be improved in terms of customer authentication and QoS, and these shortcomings have mature solutions in theory, but they need to be gradually promoted and applied to the existing network.

From the point of view of the sender and receiver of the message.

Unicast: 1v1

Multicast: 1-to-many

Multicast technology covers a wide range of contents, from address allocation and group member management to multicast packets**, route establishment, reliability, and many other aspects. This section first introduces the overall structure of the multicast protocol architecture, and then introduces the representative protocols and mechanisms from several aspects, such as multicast addresses, multicast member management, multicast packets**, intra-domain multicast routing, and inter-domain multicast routing.

There are two ways of traditional IP communication: the first is between a source IP host and a destination IP host, i.e., unicast; The second is between one source IP host and all other IP hosts in the network, i.e., broadcast. If you want to send information to multiple hosts in your network instead of all of them, you can either broadcast or have the source host send IP packets unicast to multiple destination hosts in the network.

When the broadcast mode is adopted, it will not only send information to unwanted hosts and waste bandwidth, but also cause serious broadcast storms due to route loopback. When unicast mode is adopted, a lot of bandwidth will be wasted due to the retransmission of IP packets, and the load on the server will also be increased. Therefore, the traditional unicast and broadcast communication methods cannot effectively solve the problem of single-point transmission and multi-point reception.

IP multicast refers to the sending of packets to a certain subset of nodes in the network in the form of best-effort in an IP network, which is called a multicast group. The basic idea of IP multicast is that the source host sends only one piece of data, and the destination address in this data is the multicast group address. All receivers in a multicast group can receive the same copy of the data, and only the hosts in the multicast group (the destination host) can receive the data, not other hosts on the network. Multicast groups are identified by Class D IP addresses ( .