Introduction to Data Communications and Networking

1. Introduction to Data Communications and Networking

2. Data Communications • Data • Information presented in whatever form is agreed upon by the parties creating and using the data • Data communication • Exchange of data between two devices • Via some form of transmission medium • Fundamental characteristics of data communication • Delivery • Accuracy • Timeliness

3. Standards: agreed-upon rules • Standards is essential in • Creating/maintaining open and competitive markets • Guaranteeing national/international interoperability • Two categories -Proprietary standards: closed standards -Nonproprietary standards: open standards

4. Standards Organizations • Standards are developed by • Standards creation committees • Forums • Regulatory agencies • Standards committees & forums • Standards committees are slow moving • Forums are made up of interested corporations • Forum are able to speed acceptance of a particular technology

5. Standards Organizations • ISO • Voluntary international organization • Technical recommendations for data communication interfaces • Composed of each country’s national standards orgs. • Based in Geneva, Switzerland (www.iso.ch) • ITU-T • Formerly, CCITT formed by UN • Technical recommendations about telephone, telegraph and data communications interfaces • Composed of representatives from each country in UN • Based in Geneva, Switzerland (www.itu.int) • IEEE • The largest engineering society in the world • Professional society; also develops mostly LAN standards • standards.ieee.org • ANSI • Private non-profit corporation in the US • Coordinating organization for US (not a standards- making body) • www.ansi.org

6. Internet Standards • EIA • Non-profit organization in the US • IETF (Internet Engineering Task Force) - evolution of Internet architecture and smooth operation of internet • Develops Internet standards • No official membership (anyone welcome) • www.ietf.org • IRTF (Internet Research Task Force) - research groups working on topics related to Internet protocols

7. Layered Network Architecture • Used by Network model layers • Sets of standardized rules to define how to communicate at each layer and how to interface with adjacent layers Layer N+1 Layer N+1 Layer N Layer N Layer N-1 Layer N-1 sender receiver

8. Network layers – the OSI stack application email Service interfaces

9. Network layers – the OSI stack • That data is offered to the service interface • Data transfer is therefore vertical • Protocols communicate horizontal(through protocol-specific control information)

10. Data Communications Circuits • Message: Information(data) to be communicated • Source • Transmitter • Receiver • Transmission medium: Physical path by which a message travels • Destination

11. Two- station Data Communications Circuit

12. Data Communications Circuit Arrangements

13. Data Flow • Simplex • Unidirectional • As on a one-way street • Half-duplex • Both transmit and receive possible, but not at the same time • Like a one-lane road with two-directional traffic • Walkie-talkie, CB radio • Full-duplex • Transmit and receive simultaneously • Like a two-way street, telephone network • Channel capacity must be divided between two directions

14. Data Communications Networks • Network: A set of devices (nodes) connected by communication links • Node: Computer, printer, or any device capable of sending and/or receiving data • To be considered effective and efficient, a network must meet a number of criteria

15. Type of Connection

16. Network Topologies • Point-to-point • Dedicated link between two devices • The entire capacity of the channel is reserved • Ex: Microwave link, TV remote control • Multipoint • More than two devices share a single link • Capacity of the channel is either • Spatially shared: Devices can use the link simultaneously • Timeshare: Users take turns

17. Multipoint Topology

18. Star Topology • Dedicated point-to-point link only to a central controller, called a hub • Hub acts as an exchange: No direct traffic between devices • Advantages: Less expensive, robust • Disadvantages: dependency of the whole on one single point, the hub

19. Bus Topology • One long cable that links all nodes • tap, drop line, cable end • limit on the no. of devices, distance between nodes • Advantages: Easy installation, cheap • Disadvantages: Difficult reconfiguration, no fault isolation, a fault or break in the bus stops all transmission

20. Ring Topology • Dedicated point-to-point link only with the two nodes on each sides • One direction, repeater • Advantages: Easy reconfiguration, fault isolation • Disadvantage: Unidirectional traffic, a break in the ring cab disable the entire network

21. Mesh Topology • Dedicated point-to-point link to every other nodes • A mesh network with n nodes has n(n-1)/2 links. A node has n-1 I/O ports (links) • Advantages: No traffic problems, robust, security, easy fault identification & isolation • Disadvantages: Difficult installation/reconfiguration, space, cost

22. Hybrid Topology • Example: Main star topology with each branch connecting several stations in a bus topology • To share the advantages from various topologies

23. Network Classifications

24. LAN • Usually privately owned • A network for a single office, building, or campus with 10 to 100 computers • Common LAN topologies: bus, ring, star • An isolated LAN connecting 12 computers to a hub in a closet

25. MAN • Designed to extend to an entire city • Cable TV network, a company’s connected LANs • Owned by a private or a public company

26. WAN • Long distance transmission, e.g., a country, a continent, the world • Enterprise network: A WAN that is owned and used by one company

27. Backbone Networks (BN) - less than few kms • a high speed backbone linking together organizational LANs at various locations

28. Internetwork • Internetwork (internet) : two or more networks are connected by internetworking devices • Internetworking devices: router, gateway, etc. • The Internet: a specific worldwide network

29. Internetwork Example • A heterogeneous network : four WANs and two LANs

30. Protocols • Protocol : rule • A set of rules that govern data communication • For communication to occur, entities must agree upon a protocol • Key elements of a protocol • Syntax: structure or format of data • Semantics: meaning of each section in the structure • Timing: when and how fast data should be sent

31. TCP/IP Three Layer Model • three layer model and its example • Application Layer : www • Transport Layer • TCP(UDP) : reliable (unreliable) transfer from the point of users • Network Access Layer : • IP, Ethernet : from the point of networks

32. Three Layer Model • Application Layer : application • Support for different user applications • e.g. e-mail, file transfer • transport layer : end-to-end : from the point of users • reliable data exchange for end-to-end data communication • independent of network being used • independent of application • Network Access Layer : from the point of networks • exchange of data between the computer and the network • sending computer provides address of destination : IP • may invoke levels of service • dependent on type of network used (LAN, packet switched etc.)

33. Four-Layer TCP/IP Model • Process Layer • Support for user applications • e.g. http, SMPT • Host-to-host Layer (TCP) • Reliable delivery of data • Ordering of delivery • Internet Layer (IP) • Systems may be attached to different networks • Routing functions across multiple networks • Implemented in end systems and routers • Network Access Layer • Exchange of data between end system and network • Destination address provision : IP address • Invoking services like priority

34. Signals, Noise, Modulation and Demodulation

35. Modulation Techniques • Amplitude Modulation • Frequency Modulation • Phase Modulation • Pulse Modulation

36. Amplitude Modulation • Uses a higher frequency carrier • Most efficient use of frequency • Time and Frequency Domain • Susceptible to Noise

37. Higher Frequency Carrier Signal time Carrier time

38. Time Domain Signal time Carrier time

39. time Time Domain Continued

40. Frequency Domain Unmodulated watts Carrier Signal frequency Baseband watts Modulated Carrier Signal frequency Baseband Baseband

41. Frequency Modulation • Uses a higher frequency carrier • Usually more bandwidth • Time and Frequency Domain • Resistant to some Noise

42. Time Domain time

43. Frequency Domain Unmodulated watts Carrier Signal frequency Baseband watts Modulated Carrier Signal frequency

44. Phase Modulation • Uses a higher frequency carrier • Fairly efficient use of frequency • Time and Frequency Domain • Used mainly for data

45. Time Domain (Instantaneous View) Unmodulated Carrier Modulated Carrier Phase Input

46. Information Capacity, Bits, and Bit Rate • Information capacity represents the number of independent symbols that can be carried through a system in a given unit of time. • The most basic digital symbol used to represent information is the binary digit, or bit. Therefore, it is often convenient to express the information capacity of a system as a bit rate. • Bit rate is simply the number of bits transmitted during one second and is expressed in bits per second (b/s).

47. M-ary Encoding • M-ary is a term derived from the word binary. M simple represents a digit that corresponds to the number of conditions, levels, or combinations possible for a given number of binary variables. • It is often advantageous to encode at a level higher than binary where there are more than two conditions possible. • Example: a digital signal with four possible conditions is an M-ary system where M = 4. if there are eight conditions possible, M = 8 and so fort.

48. M-ary Encoding • The number of bits necessary to produce a given number of conditions is expressed mathematically: N = log2M N – number of bits necessary M – number of conditions possible, with N bits

49. Baud & Minimum Bandwidth • Baud is often misunderstood and commonly confused with bit rate (bps). • Bit rate refers to the rate of change of a digital information signal, which is usually binary. • Baud is also a rate of change; however, baud refers to the rate of change of a signal on the transmission medium after encoding and modulation have occurred. • Baud is a unit of transmission rate, modulation rate, or symbol rate.

50. Baud & Minimum Bandwidth • Mathematically baud is the reciprocal of the time of one output signaling element, and a signaling element may represent several information bits. Baud is expressed: baud = symbol rate (baud per second) ts = time of one signaling element (seconds)