ECIS560: Lecture 2

1. ECIS560: Lecture 2 Fundamentals of Telecommunications

2. Data Communications • exchange of digital information between two devices using an electronic transmissionmedium

3. Types of Signals • Analog signals • used for voice communication • has a continuous waveform • Digital signals • discrete • not continuous • 0’s and 1’s

4. Digital vs. Analog Amplitude Analog Transmission Time 1 1 1 1 (+) voltage Amplitude 0 0 0 0 0 (-) voltage Time Digital Transmission

5. Advantages of Digital Signals • Can be converted to decimal number • Used for error detection and encryption • Language of computers • Easier to recover after distortion • Signals weaken due to resistance in a medium • Waveform shape gets distorted

6. Converting Analog to Digital • Pulse Code Modulation (PCM) • Like getting a ticker quote every 10 minutes • Approximates the actual signal curve • In PCM • Measure the signal height every 1/8000th of a second • 8 bits used to report the height at each measurement • 8*8000=64,000 bits per second to provide approximation of analog signal • 64Kbps represents a single voice line in digital telecommunications

7. Digital to Analog Conversion • Needed to transmit computer signals over telephone lines • Analog signal characteristics • Amplitude • Intensity of the wave (height) • Wavelength • Distance between comparable points on the wave • Frequency • Number of up and down cycles per second (Hz) • Phase • Relative state of the amplitude

8. Amplitude Modulation

9. Frequency Modulation

10. Multiplexing • Allows multiple signals to be sent over same medium at same time • Modes of multiplexing • Frequency Division (FDM) • Time Division (TDM)

11. Frequency Division Multiplexing X X X X X X X X X X Y Y Y Y Y Y Y Y Y Y Z Z Z Z Z Z Z Z Z Z • originally designed so multiple voice • streams could be placed on same telephone line • Multiple analog signals superimposed but on • different frequency spectra • Involves pair of multiplexers

12. Time Division Multiplexing X X X X Y Y Y Y X Y Z X Y Z X Y Z Z Z Z Z • Each signal allotted a time slot • Creates a composite stream with slots dedicated to data sources • If data source is not sending, slot goes unused – wasteful • Instead, use statistical TDM in which slots are dynamically allocated • If there is big demand, buffers are used.

13. Transmission Media • the physical path along which the data is carried • Types • twisted pair • coaxial • fiber optics and free space • satellite • terrestrial

14. Bandwidth • Measure of data that can flow in unit of time • Analog involves range of frequencies • 300-2400 Hz for telephone wires • Digital involves bits per second • Varies from medium to medium

15. Transmission Media • Twisted Pair • pair of wires twisted along entire length • usually copper with an insulating coat • Unshielded Twisted Pair (UTP) popular with LANs • CAT3 (voice) and CAT5 are common • CAT5 used for both voice and data • 100Mbs transmission speed • Limited segment length – signals needs regeneration every 100 meters

16. Transmission Media • Coaxial cable • thick insulated copper wire • Longer segment lengths • can carry up to 200 Mb/second • less interference due to shielding • Uses FDM to transmit 1000s of voice channels and 100s of TV channels • Not popular in LANS • More difficult to work with than UTP

17. Transmission Media • Fiber Optics cable • thousands of little fiber optic strands • May be glass or plastic • Thickness of a human hair • Inner core surrounded by glass (cladding) • Can be single mode or multimode • Single mode • Expensive, bigger capacity, long segment length • 8/125 • Multimode • Cheaper, less capacity • 62.5/125 • Data transmitted as pulses of light • 500 Kb/sec to several GB/sec

18. A typical optic fiber • Core made of silica and germania • Optic cladding is pure silica • Mix of different refractive indices allows for • total internal reflection

19. Advantages of fiber optics • Nearly infinite capacity • Single fiber can carry 40000 telephone calls or 250 channels of television • High transmission rates at greater distances • Immune to interference and electricity • Does not corrode (being glass) • Smaller and lighter than coaxial or twisted pair • Extremely secure

20. Wireless Transmission • Directional • Focuses electromagnetic beam in direction of receiver • Terrestrial microwave • Satellite microwave • Omni directional • Spreads the electromagnetic signal in all directions • AM and FM radio • 3G networks • Smart watches

21. Terrestrial Microwave • Parabolic dish antenna sends signal to receiving dish • Line-of-sight • Typically on towers to avoid obstacles • Frequencies in the gigahertz range

22. Telecommunications satellites • Space-based cluster of radio repeaters (called transponders) • Link • terrestrial radio transmitters to satellite receiver (uplink) • Satellite transmitters to terrestrial receivers (downlink)

23. Orbits • Mostly geostationary (GEO) • Circular orbit • 22,235 miles above earth • Fixed point above surface • Almost always a point on Equator • Must be separated by at least 4 degrees

24. Satellite services • Wide Area Broadcasting • Single transmitter to multiple receivers • Wide Area Report-Back • Multiple transmitters to a single receiver • Example VSATs (very small aperture terminals) • Also have microwave transmitters and receivers • Allows for spot-beam transmission (point- to-point data communications) • Can switch between beams upon request (Demand Assigned Multiple Access –DAMA) • Multi-beam satellites link widely dispersed mobile and fixed point users

25. C-band, Ku-band, Ka-band • Most GEO satellites operate in the C-Band frequencies • Uplink at 6 GHz • Downlink at 4 GHz • Ku-band also used • Uplink at 14 GHz • Downlink at 11 GHz • Above bands best suited for minimal atmospheric attenuation • Few slots left… forcing companies to look at Ka band (uplink:30 GHZ , downlink: 20 GHz)

26. Optical Transmission • Cutting edge • Uses modulated monochromatic light to carry data from transmitter to receiver • Optical wavelengths are suited for high rate broadband communications • Laser-based (up to 1000 times faster than coaxial)

27. Data Transport Networks • connect variety of computers and other devices • could be devices in same building • local area networks • could be devices in different countries • packet switching networks

28. Local Area Networks • LANs are typically confined to smaller distances • Within a room or building • Owned by a single entity • Includes ownership of all computers, media, software • LANs have topologies • Star, Bus, Ring, etc. • Ethernet architecture very common

29. Ethernet • Developed by Xerox (Metcalfe) and later submitted to IEEE by consortium (Digital, Intel, Xerox) • Uses variety of media • Bus topology • Data throughput varies from 10Mbps to 100Mbps to 1Gbps

30. WANs • US telephone system uses circuit switching • Call placed, circuit established to destination phone through number of switches • Digital phone system • Voice converted to digital through PCM and then multiplexed • 64kbps capacity reserved for each call • No other traffic reduces this capacity during the call • Data files do not need such a circuit established • Data files sent through a packet switching network

31. Packet Switching Network Host DC Host node Host Berlin NY node node Cairo PADs Host node

32. Frame Relay (56K-45M bps) • Dedicated, packet-switched service • Sends data in variable length packets – also called frames • Variable length makes it efficient • Works best when a few branches/subsidiaries need to share files with each other

33. Asynchronous Transfer Mode • A type of transport service on WANs • Handles all types of data… including voice and video… on single network • Most Fortune 1000 companies have some form of ATM • Unlike TCP/IP, ATM is connection-oriented • Sender, receiver set fixed path on network before sending data • Information arrives in order it was sent

34. ATM : How does it work? • ATM network transfers data in small fixed-length packets – 53 bytes each • Packets are known as cells… all cells with same source/destination follow same network path • Real-time data takes precedence over other types.. Voice always get priority over email cells • Small, constant cell size allows more efficient network usage – less delay at ATM switch • “Cell tax” make Gigabit Ethernet more attractive

35. Telephone Systems • T-1 Carrier Services • Developed in the 1960s to increase data speeds on regular copper lines • Involves 2 pairs of Cu wire – one for sending and one for receiving • Digital system – so it uses PCM • 24 channels of 64kbps each (1.5Mbps) • Can have T-2 (28 T-1 lines) T-3, T-4

36. Synchronous Optical Network • SONET uses fiber optic cables for data transmission • Difference between T-1 and SONET lies in transmission speeds • SONET has maximum speed of 10000 Mbps • Much better error detection • Most organization lease SONET lines for Internet access

37. Virtual Private Networks (VPNs) • Secure, encrypted connection between two points on the Internet • VPNs encrypt and encapsulate information into IP packets • IP packets sent across internet through process known as tunneling • Used mostly to replace existing company’s international networks

38. Point-to-Point Tunneling (PPTP) • Protocol developed by Microsoft and other independent vendors • Uses Internet as the connection between remote users and LAN or between LANs • PPTP wraps other protocols into an IP protocol (the basis for the Internet)

39. Tunneling • Process of routing one protocol through another • Like an astronaut traveling between space ships • Astronaut (the non-IP message) needs to get from spacecraft A (LAN 1) to spacecraft B (LAN 2) • Puts on a space suit (the wrap) • Travels through vacuum (IP)

40. PPTP contd. • PPTP allows creation on private link on the internet • No need for dedicated lines • Is the basis for most VPNs • Less expensive than frame relay and ATM • Less secure… encryption is weak

41. Next Class • Research Question • Wi-Fi or Bluetooth? • Quiz 2 • GP1 due • Please remember to turn in “Intent to Submit” to Entrepreneurship Center before January 17th deadline.