point-to-point link
A point-to-point link connects a pair of individual machines. In this link, in order to get from the source segment to the receiver, a short message (also called a data packet or packet in some cases ) must first visit one or more intermediate machines.
Point-to-point transmission has only one sender and one receiver, sometimes called unicasting .
broadcast link
On a broadcast network, the communication channel is shared by all machines on the network. A packet sent by any machine can be received by any other machine. The address field of each packet specifies its intended recipient.
When a machine receives a packet, it checks the fields. If the destination address of the packet is the machine, the machine processes the packet. If it is another machine, the machine ignores the packet.
A wireless network is a common example of a broadcast link. The communication in an area is shared by all the machines in the area, and the division of the area depends on the wireless channel and the transmission machines.
If the address field of a transmitted data packet contains a special encoding, then every machine on the network will receive the packet and process it. This transmission mode is called broadcasting (boradcasting).
Some broadcast systems also support the mode of sending data packets to a group of machines. This transmission mode is called multicast (multicastin).