Review For Final Should consider Review-For-Exam4 for your Final Exam preparation © Abdou Illia, Fall 2006.

Review For Final

Should consider Review-For-Exam4 for your Final Exam preparation

© Abdou Illia, Fall 2006

Network Architecture Models

3OSI Reference Model

7 layers

Each layer communicate with its peer layer, and with layer above and below it.

Different protocols at each layer

Upper layer deal with application issues, and are implemented in software

Lower layers handle data transport issues, and are implemented in software and hardware

App

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Dat

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ansp

ort

4Summary Questions

1. (a) Name the 7 layers of the OSI model, (b) Name 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 hardware devices. T / F

Internetworking

6Summary Questions

3. The local area network shown in Figure 8-18 (p. 269) has two hubs (X and Y) interconnecting the workstations and servers. What workstations and servers will receive the message if the following workstations/servers transmit (not counting the sender)?

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 workstations and servers will receive the message if the following workstations/servers transmit (not counting the sender)?

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

8Summary 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: Discrete (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 (2-64 states)

Binary: 2 states

9Attenuation

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 log10 (P2 / P1)

2. dB = 10 log10 (5/10)

3. dB = 10 log10 (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 ?

10Frequency, Bandwidth(See Fundamentals of Data & Signals – Continued for details)

Q: What is the frequency (in Hz) of a signal that repeats 80000 times within one minute ?

Answer: 80000 / 60 = 1333.33 Hz

Q: What is the bandwidth of a signal composed of frequencies from 50 Hz to 500 Hz ?

Answer: |500 Hz – 50 Hz | = 450 Hz

Conducted and WirelessMedia

12Summary Questions

What does cross talk interference mean ? How can crosstalk interference be reduced ?

If transmission wires are placed side by side, electromagnetic radiation is emitted by one wire and picked up by the other. Twisting pair of wire reduce crosstalk interference.

What categories of twisted pair are usually used in LANs ?

Categories 3, 4, 5, 6, 7, 8

What are the advantages and disadvantages of STP compared to UTP ?

Advantage: better level of isolation from interference. Disadvantage: cost

What is the main difference between Baseband coaxial cable and Broadband coaxial cable ?

Baseband transmit signals in a single channel, whereas broadband uses multiple channels.

What are the advantages of Optical fiber compared twisted pair and coaxial cable ?

Speed, No significant noise, No interference, Long distance

Can you transmit video signal over twisted pair wire ? Explain

Yes, you can (e.g. Digital Video Service or DVS). Noise used to be a limiting factor.

Local Area Networks

School of BusinessEastern Illinois University

14

Summary Questions

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

To what two devices does a print server usually connect?

Answer: To a printer via a parallel or USB cable and to a hub/switch via UTP

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 the computer where the print queue manager program is installed, which puts it in a print queue.

Do you have to use special printers for print service?

Answer: You do not need special printers, because all printers come with a parallel and/or USB port that could be used.

15

Summary Questions

Why does file sharing for programs make software installation easier with File Server Access?

Answer: A program only has to be installed once, on the file server, not on each client PC.

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.

16Servers

Single server Versus Multiple specialized Servers– Decision based on Cost, Optimization, Reliability, and Security

Optimization: – File servers need storage capacity and rapid access– Client/Server applications need very fast processors

17Servers

Print Server: basically NIC + a parallel or USB port + Random Access Memory + Intelligence to receive data and commands from print queue manager program.

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

18Servers

File Server: A server that acts like a very large hard disk shared by many client PCs

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

19File Server Program Access

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 ServerClient PC

Downloaded toClient PC,Executed There

20Summary 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 are in Week8SummaryQuestions.doc (Review section of course Website)

21Software 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

22Ethernet standards

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

23Summary 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 are in LAN-Management.doc (Review section of course web site)

24Summary 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

WordProcessingsDatabases

Answers are in LAN-Management.doc (Review section of course web site)

25Automatic Inheritance of Access Rights

Assigning rights to users or group in a directory Rights automatically inherited in lower directories Simplifies rights assignment

Application

Word Processing Database

Oracle QuickDB

Assigned BrowseAnd Read Rights

Inherits BrowseAnd Read Rights

Inherits BrowseAnd Read Rights

26Automatic Inheritance of Access Rights

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 BrowseAnd Read Rights

Inherit BrowseAnd Read Rights

Assigned BrowseAnd Execute Rights Oracle

Wide Area Networks

School of BusinessEastern Illinois University

28

Summary Questions

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 could be a computer, a router, or a telephone switch.

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.

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Summary Questions

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.

Name some criteria that routing decisions are based on

Answer: see slide #17 in appropriate class notes Name two routing algorithms/techniques.

Answer: see slide #18 in appropriate class notes

Telecommunications Systems

School of BusinessEastern Illinois University

31

Summary Questions1. 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.

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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? (c) How are 56K leased lines different than T1 in terms of speed?

(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.

(c) T1, which operate at 1.54 Mbps are faster than 56K (56 Kbps)

33Standard telephone line

ADC limits transmission speed

ADC needed because internal telephone system is digital

34

Reviewing Quiz 2 could also be helpful

The Internet

School of BusinessEastern Illinois University

36Summary Questions

1. a) Distinguish between IP address and host name. b) Which is the official address of a host? c) Does a server host need an IP address? d) Does your home PC need an IP address when you are on the Internet? e) Does a server host need a host name? f) Does your home PC need a host name when you are on the Internet?

2. Using the conversion system in slide #10, convert the following IP address to dotted decimal notation: 10101010 11110000 11001100 01010101. (Spaces are included to facilitate reading.)

37

Summary Questions3. What are the two parts in IP addresses?

4. a) Who assigns the Network part? b) The Local part?

5. a) When do we need DNS? b) What information do you send in a DNS request message? c) What information do you receive in a DNS response message?

a) We need a DNS server in order to provide servers’ IP addresses given their host names. (b) host name. (c) IP address host name

6. a) What is autoconfiguration? b) What information does a client computer get back, at a minimum, in an autoconfiguration response message? c) What other information may the client get back?

a) Refers to the process that allow a client computer to automatically get a temporary IP address from an autoconfiguration server. (b) The client computer gets back a temporary IP address to use for communications with other computers on the Internet. ( c) The client may also get the DNS server’s IP address, the default gateway’s (or router’s) IP address.

SecurityCentral Network Management

School of BusinessEastern Illinois University

See Review For Exam 4