1. Should consider Review-For-Exam4 for your Final Exam preparation
Review For Final
© Abdou Illia, Spring 2007

2. Network Architecture Models

3. OSI 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
Application
Data transport

4. Summary Questions
(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
Application programs used at the application layer of the OSI Model include word processing. T / F
Upper layers of the OSI Model are usually implemented in hardware devices. T / F

5. Internetworking

6. Summary 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?
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?

7. Fundamentals of Data & Signals

8. Summary Questions 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

9. Attenuation
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.
dB = 10 log10 (P2 / P1)
dB = 10 log10 (5/10)
dB = 10 log10 (0.5)
dB = 10 (-0.3)
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
Q: What is the bandwidth of a signal composed of frequencies from 50 Hz to 500 Hz ?
Answer: |500 Hz – 50 Hz | = 450 Hz

11. Conducted and Wireless Media

12. Summary 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.

13. School of Business
Eastern Illinois University
Local Area Networks

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 or other transmission media.
In print service with a print server device, 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 when File Server Access system is used?
Answer: Programs stored on file servers execute on client PCs, which have limited processing power. So, you must install programs small enough to run on a PC.

16. Servers 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

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

18. File Server Program Access
Before execution:
Program files and data files are stored on a file server
Programs and data files stored
on the
File
Server
Client PC
File Server

19. File 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
Downloaded to
Client PC,
Executed There
Client PC
File Server

20. Summary Questions
Answers are in Week9SummaryQuestionsS07.doc (Review section of course Website)
Your organization has 12 employees, each with his or her own stand-alone PC running Windows 98. Each computer has a 10 Mbps NIC that could work with coaxial cable or twisted pair.
a) List all the additional hardware and software you would have to buy to install a 100BaseTX LAN. 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 fed with parallel ports.
b) How many ports should the hub or switch have? Explain.

21. Software and Support Systems
Workstation Operating System on Client PCs
Network Operating System on Servers
Workstation Operating System
Client application programs
Network Operating System
Application programs:
Word processor
Spreadsheets
Accountability
Utility programs

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

23. Summary Questions
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

24. Automatic Inheritance of Access Rights
Assigning rights to users or group in a directory
Rights automatically inherited in lower directories
Simplifies rights assignment
Inherits Browse
And Read Rights
Assigned Browse
And Read Rights
Application
Word Processing
Database
Inherits Browse
And Read Rights
Oracle
QuickDB

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

26. Reviewing Exercise(ExtraS07)
Reviewing Exercise(ExtraS07).doc available in the Review section of the course web site will be very helpful.

27. School of Business
Eastern Illinois University
Wide Area Networks

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 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 Switched network?
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 ones that create 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 #18-19 in appropriate class notes

30. Reviewing Question #2 of the 3/22 Review Exercise (WAN) available in the Notes’ section of the course web site will be very helpful.
Reviewing Exercise(ExtraS07).doc available in the Review section of the course web site will be very helpful.

31. Telecommunications Systems
School of Business
Eastern Illinois University
Telecommunications Systems

32. Summary Questions
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.
(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.

33. Summary Questions
(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 no 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)

34. Summary Questions
What is the difference between a T-1 Trunk line and T-1 Leased line?
Answer: A T-1 trunk line only runs between two switches within the telephone network. T-1 Leased lines extend T-1 trunk line speeds to end-to-end circuits between 2 locations.
In T-1 Leased lines, what kind of twisted pair wire is used to connect a customer to the 1st telephone switch?
Answer: Data-grade TP which is a category 2 TP.

35. Summary Questions
On the user end, what elements are needed to establish a DSL connection?
A computer, a DSL modem, filter(s) to separate regular telephone line from the DSL data line, tel. line, software (OS, client application programs, TCP/IP), and an ISP
Several Internet access systems are asymmetric, with higher downstream speeds than upstream speeds. (a) Is this good for Webservice? (b) Is it good for videoconferencing?
a) Asymmetric speeds are good for Webservice because requests tend to be small but downloaded pages large.
(b) It is not good for videoconferencing, which needs high speed in both directions.

36. Reviewing Exercise(ExtraS07)
Reviewing Exercise(ExtraS07).doc available in the Review section of the course web site will be very helpful.

37. School of Business
Eastern Illinois University
Security

38. Virus Program (script, macro) that: Could be Attaches to files
Performs annoying actions when they are executed
Performs destructive actions when they are executed
Spreads by user actions (floppy disk, flash drive, opening attachment, IRC, etc), not by themselves.
Could be
Boot sector virus: attaches itself to files in boot sector of HD
File infector virus: attaches itself to program files and user files
Polymorphic virus: mutates with every infection, making them hard to locate

39. Q: Distinguish between viruses and worms
Does not attach to files
A self-replicating computer program that propagate across a system
Uses a host computer’s resources and network connections to transfer a copy of itself to another computer
Harms the host computer by consuming processing time and memory
Harms the network by consuming the bandwidth
Q: Distinguish between viruses and worms

40. Trojan horse A computer program When executed, a Trojan horse could
That appears as a useful program like a game, a screen saver, etc.
But, is really a program designed to damage or take control of the host computer
When executed, a Trojan horse could
Format disks
Delete files
Open some TCP ports to allow a remote computer to take control of the host computer
NetBus and SubSeven used to be attackers’ favorite programs for target remote control

41. Logic bomb
Piece of malicious code intentionally inserted into a software system
The bomb is set to run when a certain condition is met
Passing of specified date/time
Deletion of a specific record in a database
Example: a programmer could insert a logic bomb that will function as follow:
Scan the payroll records each day.
If the programmer’s name is removed from payroll, then the logic bomb will destroy vital files weeks or months after the name removal.

42. Review Questions 3
What kind of malware is a malicious program that could allow an attacker to take control of a target computer?
What kind of malware could harm a host computer by consuming processor time and random access memory?

43. Security Goals
If eavesdropping and message alteration attacks succeed, in which of the following ways the victims could be affected?
Data files stored on hard drives might be deleted
Data files stored on hard drives might be altered
Data being transmitted could be altered
Data being transmitted could be intercepted and used by the attacker
Users might not be able to get network services for a certain period of time
The network might slow down
Confidentiality = Main goal of implementing defense systems against eavesdropping and message alteration.

44. Security Goals
If a malware attack succeeds, in which of the following ways the victims could be affected?
Data files stored on hard drives might be deleted
Data files stored on hard drives might be altered
Data being transmitted could be altered
Data being transmitted could be intercepted and used by the attacker
Users might not be able to get network services for a certain period of time
The network might slow down
Integrity = Main goal of implementing defense systems against malware attacks.

45. Security Goals
If a DoS attack succeeds, in which of the following ways the victims could be affected?
Data files stored on hard drive might be deleted
Data files stored on hard drives might be altered
Data being transmitted could be altered
Data being transmitted could be intercepted and used by the attacker
Users might not be able to get network services for a certain period of time
The network might slow down
Availability = Main goal of implementing defense systems against DoS attacks.

46. Security Goals Confidentiality of communications Integrity of data
CIA is the key word in implementing security
Confidentiality of communications
Integrity of data
Availability of network services and resources

47. Summary 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.
(a)
(b)
(c)
(d)
(e)
Does public key encryption have a problem with secure key exchange for the public key? Explain.

48. Summary Questions What are the three main security goals
Answer: See slide #6
a) What parts of incoming messages do application firewalls examine? b) What do they look for?
Answer: a) Application layer messages.
b) They look for illicit content.
4. What is an IDS? What it is used for?

49. - The Internet - Central Network Management
School of Business
Eastern Illinois University
- The Internet - Central Network Management
See Review For Exam 4