Periodic signal

1. Periodic signal • A signal is periodic if and only if s(t + T) = s(t) for all values of t • T is the period of the signal.

2. Analog signal • An analog signal is a continuously varying electromagnetic wave that may be propagated over a variety of media, depending on spectrum.

3. Digital signal • A digital signal is a sequence of voltage pulses that may be transmitted over a wire medium.

4. Characteristics of a periodic signal • Amplitude • instantaneous value of a signal at any time. • Frequency • the inverse of the period (1/T), or the number of repetition of the period per second; it is expressed in cycles per second, or hertz (Hz). • Phase • measure of the relative position in time within a single period of a signal.

5. Spectrum and bandwidth • Spectrum of a signal is the range of frequencies that it contains. • Bandwidth of a signal is the width of the spectrum in which most of the energy in the signal is contained.

6. Transmission • Data transmission occurs between transmitter and receiver over some transmission medium. • Transmission media may be classified as guided or unguided.

7. Guided media • With guided media, the wave are guided along a physical path; example of guided media are: • twisted pair • coaxial cable • optical fiber

8. Unguided media • Unguided media provide a means for transmitting electromagnetic waves but do not guide them; examples are propagation through: • air • vacuum • seawater

9. Direct link • The term direct link is used to refer to the transmission path between two devices in which signals propagate directly from transmitter to receiver with no intermediate devices, other than amplifier or repeaters used to increase signal strength.

10. Point-to-Point • A guided transmission medium is point-to-point if it provides a direct link between two devices and those are the only two devices sharing the medium.

11. Point-to-Point Transmitter/ receiver Amplifier or repeater Medium 0 or more Transmitter/ receiver Medium

12. Multipoint • In a multipoint guided configuration, more than two devices share the same medium.

13. Multipoint Transmitter/ receiver Transmitter/ receiver Transmitter/ receiver Transmitter/ receiver …. Amplifier or repeater Medium Medium 0 or more

14. Simplex transmission • In simplex transmission, signals are transmitted in only one direction; one station is transmitter and the other is receiver.

15. Half-duplex transmission • In half-duplex transmission, both station may transmit, but only one at a time.

16. Full-duplex transmission • In full-duplex transmission, both station may transmit simultaneously. In this case the medium is carrying signals in both direction.

17. Telecommunication Devices • Modems • Fax modems • Special purpose modems • Multiplexers • TDM • FDM • Communication processors

18. Telecommunication Carriers & Services • Common carriers • AT&T • MCI • Sprint • Value added carriers • Telnet • SprintNet

19. Switched Lines • Switched line is a standard telephone line that uses switching equipment to allow one transmission device to be connected to other transmission devices.

20. Dedicated Line • Dedicated line is a line that provides a constant connection between two points.

21. Private Branch Exchange • PBX is a communications system that can manage both voice and data transfer within a building and to outside lines. • PBX can store calls • PBX can transfer calls • PBX can serve as a connection between different office devices

22. Wide Area Telecommunication Service • WATs is a billing method for heavy users of voice band media.

23. Integrated Services Digital Network • ISDN is a technology that uses existing common carrier lines to simultaneously transmit voice, video, and image data in digital form.

24. Network Topology • Ring • Bus • Star • Hybrid • Hierarchical

25. Type of Networks • LAN • WAN

26. Communication Protocol • Open System Interconnection (OSI) • Transmission Control Protocol/Internet Protocol (TCP/IP) • System Network Architecture (SNA) • Ethernet • X.400 • X.500

27. SOI • Physical layer • transmits the data from one node to another. • Data link layer • format the data into a record called a frame and performs error detection. • Network layer • causes the physical layer to transfer the frames from node to node.

28. OSI • Transport layer • enable the user and host nodes to communicate with each other. • Session layer • initiate, maintains, and end each session. • Presentation layer • formats the data so that it can be presented to the user or the host.

29. OSI • Application layer • controls user input from the terminal and executes the user’s application program in the host computer.

30. Data Transfer Modes • Packet switching • Frame relay • Voice over frame relay • Asynchronous transfer mode (ATM)

31. Internet • The internet is the world’s largest computer network. • It is a collection of interconnected networks, all freely exchanging information.

32. Internet Protocol • The set of conventions used to pass packets from one host to another is known as the internet protocol (IP) • TCP (transport control protocol is widely used.

33. Ways to connect to internet • LAN • SLIP ( serial line internet protocol) or PPP (point to point protocol) • On-line service

34. World Wide Web (www) • WWW is a collection of over 30,000 independently owned computer that together as one in an internet service.

35. Web Browser • Web browser creates a unique, hypermedia based menu on your computer screen that provide a graphical interface to the the Web.

36. Hypermedia • Connects the data on pages, allowing users to access topics in whatever order they wish. • Allows you to bring up pictures, graphs and other displays with sound and motion.

37. Web Search Engine • Web search engines take the place of the card catalog. • They are software programs that allow you to search for information on the Web.

38. Intranet • An intranet is an internal corporate network built using internet and Web standards.

39. Cryptography • Cryptography is the process of converting a message into a secret code and changing the encoded message back to regular text. (digital signature)

40. Firewalls • The most popular method of preventing unauthorized access to corporate computer data to construct is known as a firewall. • Firewalls can be a set of filtering rules or specially configured hardware.

41. Zone • edu = educational sites • mil = military • gov = government • net = networking organizations • nom = individuals • org = organization • com = commercial

42. Telnet and FTP • Logon to another computer and access its public files. • Copy a file from another computer to your computer.

43. E-mail (store and forward) • To send text, binary files, sound, and images to others.

44. Amplitude Shift Keying (ASK) • To encode binary data by varying the amplitude of signal.

45. Frequency Shift Keying (FSK) • To encode binary data by varying the frequency of signal.

46. Phase Shift Keying (PSK) • To encode binary data by transition or shift from one phase to another.

47. Bit Synchronization • Coordination of signal measurement timing is called bit synchronization. • There are two methods of bit synchronization: • Asynchronous • Synchronous

48. Asynchronous Bit Synchronization • Massages begin with a start bit so that the receiving device can synchronize its internal clock with the timing of the massage. • Asynchronous transmissions are normally short, and the end of message is signaled by a stop bit. • Media is idle and the sender’s and receiver’s clocks are not synchronized when no data is being transmitted.

49. Synchronous Bit Synchronization • Clocks of the sender and receiver are synchronized by one of the following methods: • guaranteed state change • separate clock signal • oversampling

50. Baseband & Broadband Transmissions • Baseband: these transmission use the entire media bandwidth for a single channel. Most LAN use baseband signaling. • Broadband: these transmission provide the ability to divide the entire media bandwidth into multiple channels.