Review for Exam 3 School of Business Eastern Illinois University © Abdou Illia, Fall 2005

Local Area Networks School of Business Eastern Illinois University

3 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

4 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

5 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

6 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

7 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 using a printer server? Answer: You do not need special printers, because the printer is fed by a parallel cable in the normal way.

8 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.

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

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

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

12 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

13 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

14 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 are in LAN-Management.doc (Review section of course Website)

15 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 are in LAN-Management.doc (Notes’ section of course Website)

Wide Area Networks School of Business Eastern Illinois University

17 Wide Area Networks basics n A station is a device that interfaces a user to a network n A station can be: – a computer (for Data networks) – a telephone (For Voice networks)

18 Wide Area Networks basics n Data is transferred from node to node through the network n A Node is a transfer point for passing data through the network n A Node is often a computer, a router, or a telephone switch Q: What is the difference between a station and a node?

19 Wide Area Networks basics n The subnet is the underlying physical connection of nodes and communication lines that transfer data from one location to another. n A Subnet is a collection of nodes and different types of transmission media Q: How does the subnet differ from the network?

20 Circuit Switching Subnet n Usually used for Voice networks n A subnet in which a dedicated circuit is established between sender and receiver and all data passes over this circuit.

21 Virtual-Circuit Packet Switching Subnets n Amount of data broken into n packets n A virtual circuit (temporary path through the network) is determined n Note: The virtual circuit is not dedicated (not reserved) n All n packets transmitted through the virtual circuit n When transfer completed, virtual circuit dissolved Q:

22 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 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.

23 Summary Questions n 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 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 #18-19 in appropriate class notes

Telecommunications Systems School of Business Eastern Illinois University

25 Review: - Class notes titled “Telecommunications Systems, Part 1” (Slides 1-13) - Class notes titled “Telecommunication Systems, Part 2” (Slides 1-13)

26 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.

27 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 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.

28 Summary Questions 1.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. 2.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.

29 Summary Questions 3) On the user end, what elements are needed to establish a DSL connection? A DSL modem and a splitter to separate regular telephone line from the DSL data line. 4) 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? n a) Asymmetric speeds are good for Webservice because requests tend to be small but downloaded pages large. n (b) It is not good for videoconferencing, which needs high speed in both directions.

30 n Note: Reviewing Quiz 2 could also be helpful

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

Security School of Business Eastern Illinois University

33 Summary Questions n Name a few kinds of systems attacks Answer (Security, Slide #3): Denial of Service attacks, Malicious content attacks and Intercepting messages. n 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. n Name some techniques usually used to protect a communication against Intercepting messages. Answer: Symmetric key encryption/decryption and Public key encryption/decryption

34 Summary Questions n 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. n 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.

35 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.