Review For Final

(Week 15, Monday 12/5/2005)

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

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

lica

tion

Dat

a tr

ansp

ort

4Summary 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

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 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

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: 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

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 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 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 noise. Disadvantage: cost

What is the main difference between baseband coaxial cable and broadband coaxial cable ?

Baseband carries digital signals, whereas broadband carries analog signals.

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

Speed, No significant noise, No significant interference, Long distance

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 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 connect?

Answer: To a printer via a parallel cable and to a hub or 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 a file server, 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 the printer is fed by a parallel cable in the normal way.

15

Summary Questions

Can anyone access shared files?

Answer: No. Only those who have access rights.

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.

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 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 (Check the Exam3 Review Guide in the 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 (Check the Exam3 Review Guide in the Review section of course Website)

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 (Check the Exam3 Review Guide in the Review section of course Website)

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

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

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.

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

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.

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.

33Standard telephone line

ADC limits transmission speed

ADC needed because internal telephone system is digital

Security

School of BusinessEastern Illinois University

35

Summary Questions

Name a few kinds of systems attacks

Answer (Security, Slide #3): Denial of Service attacks, Malicious content attacks and Intercepting messages.

Distinguish between Denial-of-Service (DoS) attack and Distributed Denial-of-Service (DDoS) attack

Answer (Security, Slides #4, 5): In DoS attack, the attacker sends a stream of messages to the victim (usually a server) from a single computer connected to the network. In DDoS, the attacker hacks into multiple clients and plants Zombie programs on them. Then, he sends commands to Zombie programs which execute the attacks.

Name some techniques usually used to protect a communication against Intercepting messages.

Answer: Symmetric key encryption/decryption and Public key encryption/decryption

36Summary Questions

Jason sends a message to Kristin using public key encryption. (a) What key will Jason use to encrypt the message? (b) What key will Kristin use to decrypt the message? (c) What key will Kristin use to encrypt the reply? (d) What key will Jason use to decrypt the reply? (e) Can the message and reply be long messages? Explain.

Answer:

a) Jason will encrypt the message with Kristin’s public key.

b) Kristin will use her own private key to decrypt the message.

c) Kristin will use Jason’s public key to encrypt the reply.

d) Jason will use his own private key to decrypt the reply.

e) No, public key encryption can only encrypt short messages.

Does public key encryption have a problem with secure key exchange for the public key? Explain.

Answer: There is no problem distributing the public key, because it does not have to be distributed securely. You can even find companies’ public keys on their website.

37

Summary Questions

1. Briefly describe the various types of malicious content attacks

Answer: See slide #6 (in Security 2 class notes)

2. What headers and messages do Packet filter firewalls examine?

Answer: See slide #10 (in Security 2 class notes)

3. a) What part of a packet do Application firewalls examine? b) What do they look for?

Answer: a) Application layer messages.

b) They look for illicit content.