In computer networking, unicast refers to transmitting information from one sender to a one receiver. So unicasting involves only two nodes in a network. The single receiver in unicasting is identified by a unique address. On the other hand, Multicasting refers to transmitting information in a single transmission to a group of receivers. Multicasting is commonly implemented as IP (internet Protocol) Multicasting.
What is Unicasting?
When it comes to computer networking, unicasting refers to transmitting information from a single sender to a single receiver. Unicasting uses session based IP delivery protocols such as Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). In unicasting, each receiver or client connects to the server consuming additional bandwidth. The client has a direct relationship with the server. For example, consider a situation where you request the URL http://www.cnn.com from your computer. This request should be received only by the CNN server else the network will be filled with unwanted requests sent to other computers in the network. Therefore unicast transmission is essential to networks and is supported by Ethernet and IP networks. Some examples of unicast transmissions are http, smtp, telnet, ssh and pop3. Unicasting is used when a private or unique resource is requested by a client. But unicasting is not suitable when transmitting information to lot of clients since the sender has to make separate connections with every receiver. This will consume computing resources in the sender and will consume a large bandwidth in the network.
What is Multicasting?
As mentioned earlier, multicasting refers to transmitting information to a group of receivers in a single transmission. In multicasting, source is required to transmit a data packet only once. The nodes in the network such as routers make the necessary copies of the transmitted data packet, so that it could be received by multiple receivers. The intermediate routers send the packets to receivers who have registered with them indicating the interest to receive data from that particular sender. IP multicasting is one of the commonly used multicasting implementations. Furthermore, the source does not need to know the addresses of the receivers that it is going to multicast and there is no direct relationship between the sender and the receivers. Multicasting is not suitable for bulk data transferring and not generally used in a large scale on the internet since only small sections of the Internet are multicast-enabled.
What is the difference between Unicasting and Multicasting?
The main difference between unicasting and multicasting is on how they communicate with receiver. In unicasting, information is transmitted to a single receiver by a single sender and the receiver has a direct relationship with the sender. In multicasting, information is sent to multiple receivers in a single transmission and there is no direct relationship between the senders and receivers. Unicasting is used when a private resource is requested by a client and it is not suitable for transmitting information to lot of clients since it will consume a large bandwidth of the network. On the other hand, multicasting does not make direct connections with the receivers, hence does not consume network bandwidth as unicasting.