The differences and characteristics of unicast, multicast and broadcast

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There are three kinds of communication modes in the current network: unicast, broadcast, multicast, in which the multicast time is the most late, but also has the advantages of unicast and broadcast, the most promising development.

1. Unicast:
A one-to-one communication mode between hosts, where switches and routers on the network only forward and not replicate data. If 10 clients need the same data, the server needs to be routed one at a time, repeating the same work 10 times. But because it can respond to each customer in a timely manner, so now the Web browsing all are using unicast mode, specifically, IP unicast protocol. Routers and switches in the network select the transmission path according to their destination address, and the IP unicast data is routed to its designated destination.
The advantages of unicast:
1 The server responds to client requests in a timely manner
2 The server for each customer requests not send data, easy to achieve personalized service.

The disadvantage of unicast:
1 server for each client to send data stream, server traffic = client number x client traffic, in a large number of customers, each client flow large streaming media applications in the server overwhelmed.
2 The existing network bandwidth is the pyramid structure, the inter-city provincial backbone bandwidth is only equivalent to the sum of all its user bandwidth of 5%. If all use unicast protocol, will cause network backbone overwhelmed. The current Peer-to-peer application has already blocked the backbone. It is almost impossible to expand the backbone by 20 times times.

2. Broadcasting:
Host a pair of all modes of communication, the network for each of the signals sent by the host to the unconditional replication and forwarding, all the host can receive all the information (whether you need it or not), because it does not choose the path, so its network cost can be very low. The cable network is a typical broadcast network, our TV is actually receiving the signal to all channels, but only one channel to restore the signal to the screen. Broadcasting is also allowed in the data network, but it is limited to the LAN range of the two-tier switch, prohibiting broadcast data across routers, and preventing broadcast data from affecting large-area hosts.
Advantages of broadcasting:
1 network equipment simple, easy maintenance, low cost of cloth network
2 because the server does not have to send data to each client separately, so the server traffic load is very low.

Disadvantages of broadcasting:
1 Unable to provide personalized service for each customer's request and time timely.
2 The network allows the server to provide data bandwidth is limited, the client's maximum bandwidth = Service Total bandwidth. For example, cable TV client line support 100 channels (if the use of digital compression technology, the theory can provide 500 channels), even if the service provider has greater financial resources to configure more sending equipment, into the fiber backbone, can not exceed this limit. That is to say, there is no way to provide more diverse, more personalized services to many customers.
3 broadcast is prohibited from being allowed to be transmitted on Internet broadband Internet.

3. Group Broadcast:
A pair of communication modes between hosts, that is, a host that joins the same group can receive all of the data in this group, and the switches and routers in the network only copy and forward their required data to the person who needs it. The host can request to join or exit a group from the router, and the routers and switches in the network have the option to copy and transmit the data, that is, transfer the group to only those hosts that join the group. This allows the data to be transmitted at one time to multiple hosts that need to be joined to the group, while ensuring that no other traffic is affected by other hosts that do not require (not joined) the group.
The advantages of multicast:
1 clients that need the same data stream join the same group to share a data stream, saving the load on the server. Have the advantages of broadcasting.
2 because the multicast protocol replicates and forwards 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 client's access port. IP protocol allows for 2亿6千多万个 multicast, so its services can be very rich.
3 This protocol, like unicast protocol, allows transmission on internet broadband Internet.

The disadvantage of multicast:
1) compared with the unicast protocol, there is no error correction mechanism, which is difficult to make up after the packet loss, but can be compensated by a certain fault-tolerant mechanism and QoS.
2 The current network although all support multicast transmission, but in the customer authentication, QoS and so on need to improve, these shortcomings theoretically have a mature solution, just need to gradually spread to the existing network.