The document discusses the key components of data communication systems including messages, senders, receivers, transmission mediums, and protocols. It describes different types of data flow as simplex, half-duplex, and full-duplex. It also discusses point-to-point and multipoint connections as well as common network topologies such as star, ring, bus, mesh, and hybrid.

1. DATA COMMUNICATIONS Nadir uz Zaman MCS-I

2. TELECOMMUNICATION The term telecommunication means communication at a distance. DATA The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data. DATA COMMUNICATIONS Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable.

3. Five components of Data Communication System The five components are : 1. Message: It is the information to be communicated. Popular forms of information include text, pictures, audio, video etc. 2. Sender: It is the device which sends the data messages. It can be a computer, workstation, telephone handset etc. 3. Receiver: It is the device which receives the data messages. It can be a computer, workstation, telephone handset etc. 4. Transmission Medium: It is the physical path by which a message travels from sender to receiver. Some examples include twisted-pair wire, coaxial cable, radio waves etc. 5. Protocol: It is a set of rules that governs the data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating.

4. Data flow (simplex, half-duplex, and full-duplex) 1. DATA FLOW: In communications, the path taken by a message from origination to destination that includes all nodes through which the data travels. 2. SIMPLEX: Simplex transmission allows data to travel only in a single, pre specified direction. An example from everyday life is doorbell the signal can go only from the button to the chime. Two other examples are television and radio broadcasting. 3. HALF DUPLEX: In half duplex transmission messages can move in either direction , but only one way at a time. A walkie-talkie is an example. 4. FULL DUPLEX: In full duplex mode the communication is from both the sides simultaneously. Example is cellular Phone (mobile phone).

5. Types of connections: point-to-point and multipoint Point to Point: A point-to-point link is a dedicated link that connects exactly two communication facilities (e.g., two nodes of a network, an intercom station at an entryway with a single internal intercom station, a radio path between two points, etc.). Point-to-point interfaces are used in serial communication. These types of connections are assumed to transmit solely to the station at the opposite end. The examples of Point-to-point are EIA/TIA 232, EIA/TIA 449, X.25, Frame Relay, T-carrier, and OC3 - OC192. Multipoint: A multipoint link is a link that connects two or more nodes It connects one station to several other stations. Point-to-multipoint are of two types • Point-to-multipoint Non-Broadcast • Point-to-multipoint Broadcast In Point-to-multipoint Non-broadcast, the communication is replicated to all the remote stations. Only specific, selected stations hear the replicated communication.

6. Categories of topology TOPOLOGY : Topology refers to the layout of connected devices. Network topology is defined as the physical interconnection of the various elements (links, nodes, etc.) of a computer network. Network Topologies can be physical or logical. Physical Topology means the physical design of a network including the devices, location and cable installation. Logical topology refers to the fact that how data actually transfers in a network as opposed to its design. i. STAR: In local area networks with a star topology, each network host is connected to a central hub. ii. RING: In Ring topology each computer is connected to the network in a closed loop or ring. iii. BUS: A type of network setup where each of the computers and network devices are connected to a single cable or backbone. iv. MESH: A type of network setup where each of the computers and network devices are interconnected with one another, allowing for most transmissions to be distributed, even if one of the connections go down. v. HYBRID: A network topology that uses two or more network topologies.

7. Categories of topology