There are various modes of communication systems that are classified based on different criteria. One common classification is based on the nature of the communication channel. In this classification, the modes of communication systems are categorized into line communication and space communication, point-to-point communication and broadcast communication, and digital communication and analog communication.

Line Communication and Space Communication:
Line communication refers to the mode of communication where signals are transmitted over a physical medium, such as a wire or a cable. Examples of line communication include telephony, telegraphy, and fax machines. In line communication, the signals are transmitted in a sequential manner, one after the other.

On the other hand, space communication refers to the mode of communication where signals are transmitted through free space, without the need for a physical medium. Examples of space communication include radio waves, microwave communication, and satellite communication. In space communication, the signals are transmitted through electromagnetic waves, which can propagate through space.

Point-to-Point Communication and Broadcast Communication:
Point-to-point communication refers to the mode of communication where signals are transmitted between two specific points or locations. Examples of point-to-point communication include telephone calls and video conferencing. In point-to-point communication, the transmission is usually private and intended for a specific recipient.

In contrast, broadcast communication refers to the mode of communication where signals are transmitted from one point to multiple points. Examples of broadcast communication include television and radio broadcasting. In broadcast communication, the transmission is intended for a wide audience and can be received by multiple recipients simultaneously.

Digital Communication and Analog Communication:
Digital communication refers to the mode of communication where signals are represented as discrete values or digits. Examples of digital communication include computer networks, email, and digital television. In digital communication, the signals are encoded into binary digits (0s and 1s) and transmitted using digital modulation techniques.

Analog communication, on the other hand, refers to the mode of communication where signals are represented as continuous waveforms. Examples of analog communication include traditional telephony, AM/FM radio, and analog television. In analog communication, the signals are transmitted using analog modulation techniques, where the amplitude, frequency, or phase of the carrier wave is varied to encode the information.

In conclusion, the modes of communication systems are classified into line communication and space communication, point-to-point communication and broadcast communication, and digital communication and analog communication. Each classification represents a different characteristic of the communication system and is used in different applications.