Introduction to Unicast, Broadcast, and Multicast

Latest reply: Dec 4, 2019 01:16:26 262 1 4 0

Hi, all.

The following describes three transmission modes of TCP/IP communication: Unicast, broadcast, and multicast, and their advantages and disadvantages.


A one-to-one communication mode between the server and the client. Switches and routers on the network only forward data and do not replicate data. If 10 clients require the same data, the server needs to transmit the same data one by one and repeat the same work 10 times. The routers and switches in the network select a transmission path according to the destination address and transmit the IP unicast data to the specified destination. Unicast can respond to each customer in a timely manner. Therefore, Internet applications, such as web browsing, use the IP unicast protocol.

Advantages of Unicast

  • The server responds to the request from the client in a timely manner.

  • The server sends different data for different requests of each customer, which is easy to implement personalized services.

Disadvantages of unicast

  • The server sends data streams to each client. Server traffic = client quantity × client traffic.

  • In the streaming media application where the number of customers is large and the traffic of each client is large, the server is overloaded.

  • The existing network bandwidth is a pyramid structure. The inter-city backbone bandwidth is only 5% of the total bandwidth of all users. If only 5% of customers on the network use the unicast protocol, the backbone network will be overloaded.


A pair of communication modes between the server and the client. The network performs unconditional replication and forwarding of signals sent by each host. All hosts can receive all information (regardless of whether you need it or not). Therefore, the network cost can be low because the host does not need to select a path. The cable TV network is a typical broadcast network. Our TV is actually receiving signals from all channels, but only the signals of one channel are restored to images. Broadcast data is also allowed to exist on the data network, but it is restricted to the LAN of the Layer 2 switch. Broadcast data cannot be transmitted through the router to prevent broadcast data from affecting a large number of hosts.

Advantages of Broadcasting

  • The network equipment is simple, the maintenance is simple, and the network deployment cost is low.

  • Because the server does not need to send data to each client separately, the server traffic load is extremely low.

Flaws in broadcasting

  • Personalized services cannot be provided in a timely manner based on the requirements and time of each customer.

  • The network allows the server to provide limited bandwidth for data. The maximum bandwidth of the client is = of the total service bandwidth. As a result, more diversified and personalized services cannot be provided to many customers.

  • Broadcast packets cannot be transmitted on the Internet broadband network.


The communication mode between the server and the client is "one to one group". That is, the clients that join the same group can accept all the data in the group. The switches and routers on the network only copy and forward the required data to the required ones. The client can request the router to join or exit a group. The routers and switches in the network selectively copy and transmit data, that is, only the data in the group is transmitted to the clients that join the group. In this way, data can be transmitted to multiple hosts that need to be added to the group at a time, and another communication of other hosts that do not need to be added to the group is not affected.

Advantages of Multicast

  • The client that requires the same data flow joins the same group to share a data flow, which saves the load of the server.

  • The multicast protocol replicates and forwards data streams according to the needs of receivers. Therefore, the total service bandwidth of the server is not limited by the bandwidth of the client access end. The IP protocol allows more than 260 million (268435456) multicast. Therefore, the IP protocol provides abundant services.

  • The multicast protocol is the same as the unicast protocol and can be transmitted on the Internet broadband network.

Disadvantages of Multicast

  • Compared with the unicast protocol, there is no error correction mechanism. It is difficult to make up for the error packet after packet loss. However, the error tolerance mechanism and QoS can be used to compensate for the error.

  • Although the existing networks support multicast transmission, they need to be improved in terms of customer authentication and QoS. These disadvantages theoretically have mature solutions and need to be gradually applied to existing networks.

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Admin Created Dec 4, 2019 01:16:26 Helpful(0) Helpful(0)

Nice sharing
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