The transmission means, is that sending a signal from one location to another. Transmission technologies refer to the physical layer protocol such as modulation, demodulation, line coding, error control etc. The transmission technology can be categorized broadly into two types:
• Broadcast networks have a single communication channel that is shared or used by all the machines on the network. Short messages called packets sent by any machine are received by all the others.
• Broadcast systems generally use a special code in the address field for addressing a packet to all the concerned computers. This mode of operation is called broadcasting.
• Some broadcast systems also support transmission to a subset of the machines known as multicasting.
• Upon receiving a packet, a machine checks the address field. If the packet is addressed to it then the packet is processed, otherwise the packet is ignored.
• Point to point networks consists of many connections between individual pairs of machines. To go from the source to the destination a packet on these types of network may have to go through intermediate computers before they reach the desired computer.
• Often the packets have to follow multiple routes, of different lengths.
• Hence routing algorithms are very important in the point-to-point networks.
• An important general rule is as follows:
Small, localized networks (e.g. LAN) tend to use the broadcasting; whereas networks located over wide geographical areas (such as WAN) use point-to-point transmission.