1. Slide No. 1 Chapter 1, Unit c Data Communications H Telecommunications H LANs, WANs and Intranets

2. Slide No. 2 Chapter 1, Unit c Telecommunications H Hardware H Software H Impact

3. Slide No. 3 Chapter 1, Unit c Telecommunications n Two computers linked together through the telephone system n in a computer network computers are linked together with high-speed cables

4. Slide No. 4 Chapter 1, Unit c Telephone System n very extensive n most every household has a telephone or the very least a line a few hundred feet away n cheap n used for voice transfer n voice is a continuous series of analog signals (electrical representations of sound)

5. Slide No. 5 Chapter 1, Unit c Computers n use digital parallel transmission n a bunch of bits (8) move around a once

6. Slide No. 6 Chapter 1, Unit c Translation n for computer data to transmitted over an analog telephone line - must be converted form digital data to analog signals n the device that allows computer to connect to telephones is a modem

7. Slide No. 7 Chapter 1, Unit c Modem n modulation/demodulation n modulation-transfer the data from computer buses in parallel fashion to serial form so that one binary digit at a time can be released to the phone line n demodulation-accepts the serial data from the phone line and transforms them back into parallel form

8. Slide No. 8 Chapter 1, Unit c Rate of Transmission n or transmission speed of a modem n measured in bits per second (bps) n early modems - 300 bps n newer models - 14,400 or 28,800 bps n a text of type page is about 2800 chars - at 14,400 can send a full page of text in 2 seconds

9. Slide No. 9 Chapter 1, Unit c Data Transfer Rates Compared n Data transfer rate (bps) n 1,200 n 2,400 n 9,600 n 14,400 n 28,800 n Time to send a 20 page wp document n 10 min. n 5 min. n 1.25 min. n 50 sec. n 25 sec.

10. Slide No. 10 Chapter 1, Unit c Types of Modems n internal/external n fax modem - the sending fax machine makes a digital image (pixels) of the document and converts it to analog - the receiving fax converts the analog to digital n when received the document is just a bunch of black and white dots to the computer - need OCR software

11. Slide No. 11 Chapter 1, Unit c Protocols n how to behave - standards n modulation protocols - specifies all the details for communication n set by international standards org. n one example is the rate at which they exchange data n V.34 - regulates the 24,400 n V.32bis - regulates the 14,400

12. Slide No. 12 Chapter 1, Unit c Protocols n modems can communicate only if both follow the same protocol n fall back - two modems communicate and establish a protocol they both share - so they can fall back to slower rate

13. Slide No. 13 Chapter 1, Unit c Video Teleconferencing n allows people to communicate face to face over long distances by combining video and computer technology n need video camera, microphone and television monitor n specially equipped computers allow callers to see each other on their computer networks

14. Slide No. 14 Chapter 1, Unit c Channels n communication channel - the physical link between two computer n two important characteristics are n transmission medium n transmission mode

15. Slide No. 15 Chapter 1, Unit c Transmission Media n wire media n wireless media

16. Slide No. 16 Chapter 1, Unit c Wire Media n Twisted pair - simple, inexpensive, but slow and susceptible to errors n Coaxial Cable - faster and stronger, more expensive n Fiber-Optic - glass fibers smaller than a human hair are used - light pulses rather than electrical signals are sent

17. Slide No. 17 Chapter 1, Unit c Wireless Transmission n Cellular telephone system - n microwave transmission - longer distances, straight-line transmission - cannot pass through buildings or mountains n satellite transmission - uses satellites in space

18. Slide No. 18 Chapter 1, Unit c Bandwidth n relates to the data transfer capacity of the medium n measured in kilobits per second (Kbps), megabits per second (Mbps) or gigabits per second (gbps) n from slow to fast - twisted pair, coax then fiber optic

19. Slide No. 19 Chapter 1, Unit c Transmission Mode n enables the receiving computer to know where one byte ends and next byte begins. n Synchronous/asynchronous transmission

20. Slide No. 20 Chapter 1, Unit c Digital Telephony n most of the long distance telephone service is already digital n local service is still analog n ISDN - Integrated Service Digital Network - interim solution - can transmit digital over twisted pair - no conversion necessary - ( digital modem) n you can have this service but costs extra

21. Slide No. 21 Chapter 1, Unit c Telecommunications Software n Telecommunications software is software that transforms a computer into a terminal capable of connecting to a multi-user computer system by means of the telephone

22. Slide No. 22 Chapter 1, Unit c Features of Communications Program n directs the modem to dial the telephone number n choose the communications settings n emulate many computer terminals n enable user to store and print received data

23. Slide No. 23 Chapter 1, Unit c Uses of Telecommunications n Telecommuting n E-mail n BBSs - bulletin board systems n on-line information services n teleconferencing

24. Slide No. 24 Chapter 1, Unit c Computer Network n Computer Networks need direct, high- speed connections n These connections have more much more bandwidth than a standard telephone line

25. Slide No. 25 Chapter 1, Unit c LANs n Local Area Network n direction connections n doesn’t use wires owned by telephone company n can connect from two to hundreds of computers

26. Slide No. 26 Chapter 1, Unit c LAN Hardware n Cable - twisted pair, coaxial and fiber optic cables n NIC card (Network Interface Card) n Hub or Cable Interface Unit - sends and receives signals on the network cable n can connect LANs together by using a bridge, router or gateway.

27. Slide No. 27 Chapter 1, Unit c Network Topology n The physical layout n star n ring n bus

28. Slide No. 28 Chapter 1, Unit c Network Models n Client/server (CS network) n peer-to-peer

29. Slide No. 29 Chapter 1, Unit c WANs n Wide Area Networks - distance is more than a mile and as much as half the globe n require special media (normally provided by telephone companies) n require special hardware

30. Slide No. 30 Chapter 1, Unit c WAN Hardware n Special-purpose telephone wires, fiber- optic cables, microwaves, or satellites n dedicated, private, or leased line n multiplexors - combines computers signals and passes them on and one on the other end takes them apart and sends them directly n routers- sends data the right way n front-end processors

31. Slide No. 31 Chapter 1, Unit c Intranets n Network within an organization n “private” web n keeps the learning curve low when moving either back to the “real” web or if you move from the “real” web to an intranet