Review For Final (Week 16, Monday 12/6/2004) Should consider Review-For-Exam4 for your Final Exam preparation

Network Architecture Models

3 OSI Reference Model n 7 layers n Each layer communicate with its peer layer, and with layer above and below it. n Different protocols at each layer n Upper layer deal with application issues, and are implemented in software n Lower layers handle data transport issues, and are implemented in software and hardware Application Data transport

4 Summary Questions 1. (a) Name the OSI layers that deal with application issues ? (b) Name the OSI layer that deal with data transport issue ? Answer: See previous slide 2) Application programs used at the application layer of the OSI Model include word processing. T / F 3) Upper layers of the OSI Model are usually implemented in physical devices. T / F

Internetworking

6 Summary Questions 3. The local area network shown in Figure 8-21 (p. 273) has two hubs (X and Y) interconnecting the workstations and servers. What workstations and servers will receive a copy of a packet if the following workstations/servers transmit a message: Workstation 1 sends a message to workstation 3: Workstation 2 sends a message to Server 1: Server 1 sends a message to workstation 3: 4. Replace hub Y with a switch. Now what workstations and servers will receive a copy of a packet if the following workstations/servers transmit a message: Workstation 1 sends a message to workstation 3: Workstation 2 sends a message to Server 1: Server 1 sends a message to workstation 3:

Fundamentals of Data & Signals

8 Summary Questions 1. Distinguish between digital and analog signals Answer: (see class notes for details):  Analog: Continuous waveform, State of signal (voltage level, etc.) varies continuously among an infinite number of states  Digital: Non-continuous waveform, State of signal remain constant during each clock-cycle, Few possible states 2. Distinguish between digital and binary transmission Answer: Digital: Few possible states Binary: 2 states

9 Attenuation n A signal starts at a transmitter with 10 watts of power and arrived at a receiver with 5 watts of power. Calculate the loss of power in dB. 1. dB = 10 log 10 (P2 / P1) 2. dB = 10 log 10 (5/10) 3. dB = 10 log 10 (0.5) 4. dB = 10 (-0.3) 5. dB = -3 Q: What is the decibel loss of a signal that starts at 50 watts and experiences a 10-watt loss over a given section of cable ? Q: What is the decibel loss of a signal that loses half its power during the course of transmission ?

10 Frequency, Bandwidth (See Fundamentals of Data & Signals – Continued for details) Q: What is the frequency (in Hz) of a signal that repeats times within one minute ? Answer: / 60 = Hz or 1.33 Mhz Q: What is the bandwidth of a signal composed of frequencies from 50 Hz to 500 Hz ? Answer: |500 Hz – 50 Hz | = 450 Hz Q: What is the bandwidth of a signal composed of frequencies from -50 Hz to 500 Hz ? Answer: |500 Hz – (-50) Hz | = 550 Hz

Conducted and Wireless Media

12 Summary Questions n What does cross talk interference mean ? How can crosstalk interference be reduced ? If transmission wires are placed side by side, electromagnetical radiation is emitted by one wire and picked up by the other. Twisting pair of wire reduce crosstalk interference. n What categories of twisted pair are usually used in LANs ? Categories 3, 4, 5, 6, 7, 8 n What are the advantages and disadvantages of STP compared to UTP ? Advantage: better level of isolation from noise. Disadvantage: cost n What is the main difference between baseband coaxial cable and broadband coaxial cable ? Baseband carries digital signals, whereas broadband carries analog signals. n What are the advantages of Optical fiber compared twisted pair and coaxial cable ? Speed, No significant noise, No significant interference, Long distance n Can you transmit video signal over twisted pair wire ? Explain You can, but noise is going to be a serious factor.

Local Area Networks School of Business Eastern Illinois University

14 Summary Questions n What are the four factors to take into account in deciding how many servers to use to implement a LAN’s services? Answer: Optimization, reliability, security, cost n To what two devices does a print server connect? Answer: To a printer via a parallel cable and to a hub or switch via UTP n Where does a print job go when it leaves the client PC (not counting the hub or switch)? Answer: The print job first goes to a file server, which puts it in a print queue. n Do you have to use special printers for print service? Answer: You do not need special printers, because the printer is fed by a parallel cable in the normal way.

15 Summary Questions n Can anyone access shared files? Answer: No. Only those who have access rights. n Why does file sharing for programs make software installation easier? Answer: A program only has to be installed once, on the file server, not on each client PC. n Why is storing program files on a file server limiting? Answer: Programs stored on file servers execute on client PCs, which have limited processing power.

16 Servers n Single server Versus Multiple specialized Servers – Decision based on Cost, Optimization, Reliability, and Security n Optimization: – File servers need storage capacity and rapid access – Client/Server applications need very fast processors

17 Servers n Print Server: basically NIC + a parallel port + Random Access Memory + Intelligence to receive data and commands from print queue manager program. n Note: Possible to connect printer directly to file server, but people might have to walk far to get their printout. Newer printers have built-in NICs & print server hardware

18 Servers n File Server: A server that acts like a very large hard disk shared by many client PCs n Advantages: Single program installation, Sharing programs and files with access rights. Operates according to the File Server Program Access System seen during Classes 2&3

19 File Server Program Access n For execution, – Program and data files are downloaded (copied) to the Client PC – Processing on the client PC, not on the file server – File server merely stores programs and data files File Server Client PC Downloaded to Client PC, Executed There

20 Summary Questions Your organization has 12 employees, each with his or her own stand-alone PC running Windows 98. a) List all the additional hardware and software you would have to buy to install a simple PC network. Be very sure that you list all the things the organization will have to buy. The organization wishes to use electronic mail, word processing, file sharing, and print sharing with four existing printers. b) How many ports on the hub or switch will your organization use? Explain. c) Suppose that a decision have been made to implement the 100BaseTX Ethernet standard. What does it mean in terms of the characteristics of the following components: Hub/Switch, NICs, Wiring. Answers in Review section of course website (Check the Week9 Summary Questions’ link)

21 Software and Support Systems - [Individual] Operating System - Utilities - Network Operating System - Application programs: - Word processor - Spreadsheets - Accountability - Utilities [Individual] or standard Operating System on Client PCs Network Operating System on Servers

22 Ethernet standards Q: If a LAN is described as 10BaseT, list everything you know about that network?

23 Summary Questions 1. (a) What is LAN management ? (b) Name some common management activities. 2. a) What are access rights? b) How does the use of groups simplify the assignment of access rights? c) How does automatic inheritance simplify the assignment of access rights? d) How does explicit assignment modify automatic inheritance? Answers in Review section of course website (Check the LAN Management link)

24 Summary Questions 3. Directory Applications has Subdirectories Databases and WordProcessings. The Network administrator assigns user Lee to the group Outer. The administrator assigns Outer the access rights R, S, and T in Directory Applications. (Don’t worry about the meaning of R, S, and T. They are simply types of rights.) The administrator assigns Outer the access rights S, U, and V in Subdirectory Databases. a) What access rights does user Lee have in Directory Applications? Explain. b) What access rights does user Lee have in Directory Databases? Explain. c) What access rights does user Lee have in Directory WordProcessings? Explain. Applications WordProcessings Databases Answers in Review section of course website (Check the LAN Management link)

25 Automatic Inheritance of Access Rights n Assigning rights to users or group in a directory n Rights automatically inherited in lower directories n Simplifies rights assignment Application Word ProcessingDatabase OracleQuickDB Assigned Browse And Read Rights Inherits Browse And Read Rights Inherits Browse And Read Rights

26 Automatic Inheritance of Access Rights n Blocking of Inheritance – If rights explicitly assigned in subdirectory, inheritance is blocked – Only assigned rights are effective Application Word Processing Database (Browse and Execute Only) QuickDB Assigned Browse And Read Rights Inherit Browse And Read Rights Assigned Browse And Execute Rights Oracle

Wide Area Networks School of Business Eastern Illinois University

28 Summary Questions n How does the subnet differ from the network? Answer: The network include: the subnet(s), the stations, the OS & other application software, and the other networking devices & transmission medium needed to connect the stations to the subnet n What is the difference between a station and a node? Answer: A station is the device that interfaces a user to the network. A node is a transfer point for passing data through the network. A node can be a computer, a router, or a telephone switch. n What are the main characteristics of Circuit Switched networks? Answer: In Circuit Switched networks: (1) a dedicated circuit is established between sender and receiver, (2) circuit capacity is reserved during the duration of each communication, at each node (switch) and on each transmission line; (3) no routing decisions are necessary since circuit is dedicated.

29 Summary Questions n What are the main characteristics of Virtual Circuit Packet Switching? Answer: (1) Data sent in packets, (2) all packets follow the same virtual circuit, (3) the virtual circuit may be shared with packets from other conversions, (4) no routing decisions except the first one that creates the circuit. n Name some criteria that routing decisions are based on Answer: see slide #17 in appropriate class notes n Name two routing algorithms/techniques. Answer: see slide #18 in appropriate class notes

Telecommunications Systems School of Business Eastern Illinois University

31 Summary Questions 1. When a standard telephone line is used to connect to a network: (a) What device limits the speed? (b) Where is this device located? (a) The analog-to-digital converter (ADC). (b) It is located at the telephone company’s switch at the end of your local loop access line. 2. (a) In using a V.90 modem, what does the ISP need? (b) What does the telephone company need? (a) A digital leased line to the telephone carrier (and some internal equipment). Note: The ISP does not have a V.90 modem. If it did, it could only transmit at 33.6 kbps, and the receiver could only receive at 33.6 kbps. (b) The telephone company does not have to do anything differently. Note: the telephone company does not have to install ADCs. These are already there. You use ADCs and DACs every time you make a voice telephone call.

32 Summary Questions 3. (a) How are 56K Leased lines and standard telephone lines different in terms of operation? (b) How are they different in terms of speed and cost? (a) With Standard telephone lines you need to dial a telephone number to connect. The connection is not permanent (active only during a call). With 56K Leased line, there is no need to dial a telephone number, and the connection is always active. (b) 56K Leased lines are faster and more expensive.

33 Standard telephone line n ADC limits transmission speed n ADC needed because internal telephone system is digital