Computer Networks can be classified into two classes regarding the transmission technology they use. They are broadcast network and point-to-point networks.
Broadcast networks have a single communication channel that is shared by all the machines on the network. Short messages, called packets in certain contexts, sent by any machine are received by all the others. An address field within the packet specifies for whom it is intended. Upon receiving a packet, a machine checks the address field. If the packet is intended for itself, it processes the packet; if the packet is intended for some other machine, it is just ignored.
Broadcast systems generally also allow the possibility of addressing a packet to all destinations by using a special code in the address field. When a packet with this code is transmitted, it is received and processed by every machine on the network. This mode of operation is called broadcasting. Some broadcast systems also support transmission to a subset of the machines, something known as multicasting. One possible scheme is to reserve one bit to indicate multicasting. The remaining (n－1) address bits can hold a group number. Each machine can "subscribe" to any or all of the groups. When a packet is sent to a certain group, it is delivered to ail machines subscribing to that group.
Point-to-point networks consist of many connections between individual pairs of machines . To go from the source to the destination, a packet on this type of network may have to first visit one or more intermediate machines. Often multiple mutes, of different lengths are possible, so routing algorithms play an important role in point-to-point networks. As a general rule (although there are many exceptions), smaller, geographicaily localized networks tend to use broadcasting, whereas larger networks usually are point-to-point.