Can multicasting use TCP ?
No. Multicasting uses UDP (User Datagram Protocol) as its underlying transport protocol. TCP (transmission control protocol) uses frequent transmission of acknowledgement (ACK) packets between the receiver and the transmitter for flow control, and also to determine if packets have arrived safely, in order that dropped packets can be retransmitted. This form of feedback and retransmission does not scale well into the one to many case, although some forms of reliable multicast do use negative acknowledgements (NACKs) to signal the need for retransmission. UDP is a simpler protocol where there is no acknowledgement of the success or failure of the transmission of any packet, and no retransmission, at the transport layer. (In the jargon, UDP is called “best effort.”) Strictly speaking, therefore, multicast data transport is unreliable, and any reliability must be engineered-in at a higher level.
