Catholic University College of Ghana Fiapre-Sunyani

1. Catholic University College of GhanaFiapre-Sunyani Data Communications and Networks Internet INFORMATION TECHNOLOGY II Audrey Asante, Faculty of ICST

2. Computer communication is the transmission of data and information over a communications channel between two computers, which can be several different things. • Communications between computers can be as simple as cabling two computers to the same printer. It can be as complex as a computer at NASA sending messages through an elaborate system of relays and satellites to tell a computer on Mars how to drive around without hitting the rocks.

3. Depending on the context, for computer communications you might use the terms: • Data Communications for transmission of data and information over a communications channel Telecommunications for any long-distance communications, especially television Teleprocessing for accessing computer files located elsewhere

4. Communications Channel • A communications channel, also called a communications line or link, is the path that the data follows as it is transmitted from one computer to another.

5. COMPUTER NETWORK • A network is a system of interconnected computers, telephones, other communications devices that can communicate with one another and share applications and data

6. NETWORK MODEL • OSI (Open Systems Interconnect ) Reference Model • TCP/IP Reference Model

7. OSI MODEL

8. LAYERS’ FUNCTIONS Application (Layer 7) • This layer supports application and end-user processes. • Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. • Everything at this layer is application-specific. • This layer provides application services for file transfers, e-mail, and other networksoftware services.

9. LAYERS’ FUNCTIONS Presentation (Layer 6) • This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. • The presentation layer works to transform data into the form that the application layer can accept. • This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.

10. LAYERS’ FUNCTIONS Session (Layer 5) • This layer establishes, manages and terminates connections between applications. • The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. • It deals with session and connection coordination.

11. LAYERS’ FUNCTIONS Transport (Layer 4) • This layer provides transparent transfer of data between end systems, or hosts • The layer is responsible for end-to-end error recovery and flow control. • It ensures complete data transfer.

12. LAYERS’ FUNCTIONS Network (Layer 3) • The layer provides switching and routing technologies • Creates logical paths, known as virtual circuits, for transmitting data from node to node • Provides routing and forwarding functions • Transforms the Logical Names into Physical Addresses • Provides internetworking, error handling, congestion control and packet sequencing.

13. LAYERS’ FUNCTIONS Physical (Layer 1) • This layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level • It defines the electrical characteristics of the signals • It provides the hardware means of sending and receiving data on a carrier • It defines Network Interface Cards (NIC), cables, and connectors

14. TYPES OF NETWORKS • Local network • It is a privately owned communications network that serves users within a confined geographical area. The range is usually within a mile-an office, a building, a campus. There are two types-private branch exchanges (PBXs) and Local area networks • Metropolitan area network • It is a communications network covering a geographic area the size of a city or suburb. The purpose is often to bypass local telephone companies when accessing long-distance services.

15. Wide area network • It is a communications network that covers a wide geograhical area, such as a state or a country. The internet links together hundreds of computer WANs. Most telephone systems are WANs. • Global area network • It is a communications network that covers the world. An examples is the internet.

16. Advantages • Sharing of peripheral devices • Sharing of programs and data • Better communications • Security of information • Access to databases

17. DISADVANTAGES • More complexity adds new problems to handle. Less customization is possible for shared programs and folders. Everyone will have to follow the same conventions for storing and naming files so others can find the right files. Sharing is hard for some people

18. LAN • They are local networks consisting of a communications link, network operating system, microcomputers or workstations, servers, and other shared hardware.

19. TYPES OF LAN • Client/Server LAN • Peer-to-peer: they don’t rely on a server.

20. TOPOLOGY OF LANs • Topology is the logical layout or shape of a network. The five basic topologies are star, ring, bus, hybrid, FDDI, Mesh

21. STAR TOPOLOGY • All microcomputers and other communication devices are connected to a central server. If the server goes down, the entire network will go off because it handles the flow of information. The maximum number of network devices is 1,024 . This configuration is good for businesses that have large amounts of rapidly changing data, like banks and airline reservation . Standard twisted-pair Ethernet uses a star topology

22. ADVANTAGES OF STAR TOPOLOGY • The server prevents collisions between messages. • If a connection is broken between any communications device and the server, the rest of the devices on the network will continue operating. • It's easy to add and remove nodes.

23. DISADVATANGES OF STAR TOPOLOGY • They require more cabling than other topologies

24. RING TOPOLOGY • All microcomputers and other communication devices are connected in a continuous loop. Each device is connected directly to two other devices, one on either side of it. There is no central server. Electronic messages are passed around the ring until they reach the right destination. Messages travel around the ring, with each node reading those messages addressed to it.

25. Ring Topology • The most common type of cabling used for token ring networks is twisted pair. Transmission rates are at either 4 or 16 megabits per second

26. ADVANTAGES OF THE RING TOPOLOGY • Messages flow in only one direction. • There is no collisions • Requires less cabling. • They offer high bandwidth and can span large distances

27. DISADVANTAGES OF RING TOPOLOGY • If the connection is broken, the entire network stops working. • Ring topologies are relatively expensive and difficult to install • Moves, adds and changes of devices can affect the network • Much slower than an Ethernet network under normal load

28. BUS TOPOLOGY • All communications devices are connected to a common channel called the bus or backbone. There is no central server. Each communications device transmits electronic messages to other devices. If some of those messages collide, the device waits and tries to retransmit. Ethernet 10Base-2 and 10Base-5 networks are bus networks.

29. Disadvantages • If a connection in the bus is broken, the entire network may stop working. • Extra circuitry and software are needed to avoid collisions between data • Can't connect a large number of computers this way. It's physically difficult to run the one communications line over a whole building, for example.

30. ADVANTAGES OF BUS NETWORK • It may be organized as a client/server or peer-to-peer network • Any one computer or device being down does not affect the others. • Bus networks are relatively inexpensive and easy to install for small networks.

31. MIXED/HYBRID TOPOLOGIES • The purpose of such topologies is to avoid some of the inconveniencies of the simple topologies and to use more effectively their advantages. • In such topologies, there at least one station, which belongs to the both topologies. Its role is to transform the signals and the protocols of the both networks.

32. RING – BUS TOPOLOGY • An interesting example is the mixed topology, based on token ring (optical cable) and star topology is very often used. • The optical ring can cover more long distances (between different buildings), and within each building – the topology can be either star or bus.

33. RING – BUS TOPOLOGY

34. FDDI • Fiber distributed data interface uses fiber-optic cable with an adaptation of ring topology using not one but two token rings. It is costly and fragility because fiber-optic cables are fragile. It overcomes the vulnerability by sending data on a clockwise and a counterclockwise ring:

35. in the event of a break data is wrapped back onto the complementary ring before it reaches the end of the cable, maintaining a path to every node along the resulting "C-Ring • In addition to covering large geographical areas, FDDI local area networks can support thousands of users.

36. ADVANTAGES OF FDDI • High speed • Because of the adaptation of two token rings, if one should fail, the network can continue operating with the second ring.

37. MESH TOPOLOGY This is a network topology in which devices are connected with many redundant interconnections between network nodes. There are two types of mesh topologies: • full mesh • partial mesh.

38. FULL MESH TOPOLOGY • Every node has a circuit connecting it to every other node in a network. • Very expensive to implement but yields the greatest amount of redundancy • If one of those nodes fails, network traffic can be directed to any of the other nodes. • Full mesh is usually reserved for backbone networks

39. PARTIAL MESH TOPOLOGY • Less expensive to implement and yields less redundancy than full mesh topology. • With partial mesh, some nodes are organized in a full mesh scheme but others are only connected to one or two in the network. • Partial mesh topology is commonly found in peripheral networks connected to a full meshed backbone.

40. COMPONENTS OF LAN • Connection or cabling system: Cabling or connection system is either wired or wireless. Wired connections may be done by twisted-pair, coaxial or fiber-optic cables. Wireless connections may be infrared or radio-wave transmission. Wireless are essential if computers are portable.

41. Transmission media just means the physical materials that are used to transmit data between computers.

42. Twisted wire(phone line) • Advantage:Easy to string Cheap Disadvantage:Subject to interference = static and garble. attenuation

43. Fiber optic line (glass fibers) • Advantage: SmallerLighter Faster (speed of light!)No interference • Disadvantage: ExpensiveHarder to install and modify

44. Wireless(infrared, light, radio) • Advantage: Flexible Portable • Disadvantage:Slower data transfer than hard-wired methodsSubject to interference

45. Microwave • Advantage:Speed of light Uses a few sites • Disadvantage: Line-of-sight only

46. Satellite • Advantage: Always in sight • Disadvantage: Expensive uplink and downlink facilities

47. Signals • Two types of signals are used for data transmission:Digital and Analog.

48. A digital signal is a stream of 0's and 1's. So this type is particularly appropriate for computers to use. An analog signal uses variations (modulations) in a signal to convey information. It is particularly useful for wave data like sound waves. Analog signals are what your normal phone line and sound speakers use.

49. Coaxial cable(round insulated wire) • Advantage:Not susceptible to interference Transmits faster • Disadvantage:Heavy & bulky Needs booster over distance • Cross talk

50. COMPONENTS OF LAN cotn • Microcomputers with network interface cards. For communication to go on between two or more computers, they should have network interface cards • Network Operating System: NOS manages the activities of the network. Example Windows Server 2003 • Other shared devices: printers, fax, scanners, peripherals