The document discusses data communication and computer networks. It covers three key topics: 1) Communication standards and models like the OSI reference model that define protocols for computer networks. 2) Network types including LANs, MANs, WANs and examples of common topologies. 3) Hardware and infrastructure that enable communication, such as modems, hubs, routers and different connection methods.

3. OSI Reference Model Layer Name Purpose 7 Application Layer Application-to-application communication 6 Presentation Layer Manage data representation conversions 5 Session Layer Establish and maintain communication channel 4 Transport Layer Guarantee end-to-end integrity of transmission 3 Network Layer Route data between network addresses 2 Data Link Layer Move data from one network address to another 1 Physical Layer Put data onto and off of the network media 10-

4. ISO Website 10-

11. Data Communications Links the General Systems Model Elements Standards Management Information processor Environment Input Transformation Output 10-

14. Users Manager 1 Secretary 1 Secretary 2 Workstation 1 Workstation 2 Workstation 3 Workstation 4 Manager 2 Network Server Hard Disk Letter Quality Printer Plotter A Local Area Network 10-

15. Common LAN Topologies Star 10-

16. Common LAN Topologies Ring 10-

17. Common LAN Topologies Bus 10-

18. Satellite Earth station Earth station Telephone company central office Telephone company central office Telephone company central office Telephone company central office Local loop Microwave tower Microwave tower IXC circuit (interexchange channel) IXC circuit (interexchange channel ) Local loop Wide Area Network 10- User’s modem User’s modem

21. Legend : Computer Terminal A Network of Terminals 10-

22. Legend: Central Computer Distributed Computer A Distributed Processing Network 10-

24. Data Communications with a Modem Modem Channel Modem A modem is always required between a telephone and a digital computer 10- Computer Computer

32. A Network with Mobility Capability MSS = mobile support station MU = mobile units MU MU MU MU MU MU MU MU MU MU MU MU MSS MSS MSS MSS Fixed host Fixed host Fixed host Fixed host Fixed network 10- Highlights in MIS