1. 1 Chapter 7 Networking: Computer Connections

2. Basic Components of a Network Sending device Communications link Receiving device

3. Data Transmission Methods Digital transmission Distinct pulses 0’s and 1’s

4. Data Transmission Methods Analog transmission Continuous electrical signal Carrier wave Amplitude Frequency -- height of each wave -- number of times the wave repeats per second

5. Data Transmission Devices Modem (MOdulator/DEModulator) Capable of 56,000 bps (56 Kbps) bps = bits per second Receive speed limited to 53 Kbps Transmit speed limited to 31 Kbps ← FCC restrictions

6. Data Transmission Devices ISDN Digital data Speeds of 128,000 bps Connect and talk on the phone at the same time Requires an adapter & upgraded phone service Expensive to set up + requires monthly fees -- Integrated Services Digital Network

7. Data Transmission Devices DSL Conventional telephone lines DSL modem: converts digital  analog Many times faster than 56K modem Computer and voice share phone line Must be within 3 miles of telephone company switching office – Digital Subscriber Line

8. Data Transmission Devices Cable modems Coaxial cables Does not interfere with cable TV Up to 10 million bps Always on Shared capacity: More users mean slower Security problem

9. Data Transmission Devices Cellular Modems Useful for people on the move Slow speed

10. Transmission Types Asynchronous transmission Start/stop transmission Low-speed communications

11. Transmission Types Synchronous transmission Blocks of data transmitted at a time More complex and expensive Faster transmission

12. Transmission Types Simplex One direction only Half-duplex Either direction Only one way at a time Full-duplex Both directions at once

13. Communications Media Bandwidth = range of frequencies that medium can carry Wire pair (twisted pair) Inexpensive Telephone systems

14. NOISE Electrical interference Anything that disrupts the signal High voltage equipment Lightning Even the sun can cause noise

15. Communications Media Shielded twisted pair Protective sheath Reduces noise Increases speed

16. Communications Media Coaxial cable Higher bandwidth Less susceptible to noise Cable TV systems

17. Communications Media Fiber optics Transmits using light Higher bandwidth Immune to electrical noise More security

18. Communications Media Microwave transmission Line-of-sight Relay stations High speed Weather can cause interference

19. Communications Media Satellite transmission Microwave transmission Satellite acting as relay Long distance

20. Satellite Transmission Uplink – signal travels from the earth to the satellite Downlink – signal travels from the satellite to the earth Geosynchronous orbit – communication satellites stay positioned over the same point on the earth

21. Protocols Set of rules to exchange data What form of data transmission will be used? What is the transmission speed? What duplex setting is needed? Without a protocol, computers cannot communicate with each other

22. Protocols Standards Assists with coordination TCP/IP Transmission Control Protocol/Internet Protocol Permits any computer to communicate with the internet

23. Network Topologies Topology = the physical layout of a network Star network Central computer (hub) Prevents collisions Node failure—no effect on overall network Hub failure—network fails

24. Network Topologies Ring network Circular connection in one direction No danger from collisions Node failure — entire network fails

25. Network Topologies Bus network All nodes attached to a single line Collisions result in re-send Node failure—no effect on overall network

26. Wide Area Networks Large geographical area Dial-up service Temporary connection POTS Dedicated service Permanent connection Own dedicated circuits Leased lines

27. Network Software File transfer software (FTP) Download – copy a file from another computer to your computer Upload – copy a file from your computer to another computer

28. Local Area Network Components PCs Network cable Network Interface Card (NIC)

29. Connecting LANs Bridge Connects LANs with similar protocols Router Directs traffic to best path Gateway Connects LANs with varying protocols

30. Uses of Networks E-mail Facsimile (FAX) Groupware Teleconferencing and video conferencing

31. Uses of Networks Electronic Fund Transfers ATM Telecommuting Online services The Internet