Review For Exam 2 School of Business Eastern Illinois University © Abdou Illia, Spring 2003 (Week 7, Monday 2/24/2003)

Network Architecture Models ( Layered Communications ) School of Business Eastern Illinois University © Abdou Illia, Spring 2003 (Week 3, Wednesday 1/29/2003) Encapsulation and Deencapsulation

3 Summary Questions 1. (a) What is indirect communication ? (b) Why is it necessary ? (c) What is encapsulation ? (d) What happens as soon as a layer on the source computer creates a message ? 2. ………………………. 3. At which layer a Trailer is usually added. 4. Compare Hybrid TCP/IP layering and Windows 98 layering.

4 Hybrid TCP/IP-OSI Model LayersSample protocols for Web access ApplicationHTTP TransportTCP InternetIP Data LinkEthernet, PPP PhysicalEthernet, Modem standards, Telephone standards

5 Layered Communication n Application programs on different computers cannot communicate directly – Because they are on different machines. – So, they communicate indirectly through layers cooperation Browser Trans Int DL Phy User PC Web App Trans Int DL Phy Webserver HTTP Request

6 Layer Cooperation on the User PC n Application layer passes HTTP-request to transport layer Application Transport Internet Data Link HTTP Request PhysicalUser PC

7 Layer Cooperation on the User PC n Transport layer creates a TCP segment – HTTP request is put in the data field – A TCP header is added n So, Transport layer “encapsulates” HTTP request within a TCP segment HTTP Request TCP-H TCP Segment Data Field TCP Header

8 Encapsulation n Encapsulation is: – Embedding a received message in a new message – Delivering a received message in the data field of a new message n Example: TCP encapsulates HTTP request in the data field of a new massage called TCP Segment HTTP Request TCP-H TCP Segment Data Field TCP Header

9 Layer Cooperation on the User PC n The internet layer passes the IP packet to the Data Link layer – Internet layer messages are called packets Application Transport Internet Data Link IP packet PhysicalUser PC

10 Layer Cooperation on the User PC n Data Link Layer Encapsulates IP Packet within a PPP Frame – Data Link layer messages are called frames – PPP frame has IP packet in data field – PPP frame has a PPP Trailer and a PPP Header PPP Frame Encapsulating an IP Packet PPP-T IP packet PPP-H

11 PPP-T Layer Cooperation on the User PC n Recap: Adding Headers and Trailers: Application Transport Internet Data Link HTTP msg Physical User PC HTTP msg TCP-H HTTP msg TCP-H IP-H HTTP msg TCP-H IP-H PPP-H

12 Layer Cooperation on the Webserver n Situation reverse to Situation on User PC (Deencapsulation) Application Transport Internet Data Link PhysicalUser PCWebserver

13 Hybrid TCP/IP and Windows Layering Hybrid TCP/IP-OSI Layering Microsoft Windows 95/98 Layering ApplicationClients and Services TransportProtocols (TCP/IP, IPX/SPX, NetBEUI, etc.) Internet Data LinkAdapters (Dial-up adapters, Network Interface Card, etc.) Physical

Internetworking School of Business Eastern Illinois University © Abdou Illia, Spring 2003 (Week 4, Wednesday 2/5/2003)

15 Summary Questions 1. Name the two most known Medium Access Control Protocols found in LANs. How they differ? 2. (a) What are the primary reasons for internetworking two or more networks ? (b) What are the basic functions of a bridge ? 3. How does a Transparent bridge operate? Answer: (1) Observes traffic to create routing tables (backward learning), (2) When a message arrives at a port, looks at routing table to know where to send the message. 4. …………………………………………………………… ………………………………………… 2b) Filtering messages, Forwarding messages, conversion between different frame formats

16 Medium Access Control Protocols used in LANs n Ethernet or CSMA/CD – Most common form of LAN today. – Star-wired bus is most common topology – Many standards (form 1Base5 to 1000BaseT) n Token Ring – For LAN that use Ring topology – Offered at speeds of 4, 16 and 100 Mbps. – More expensive components than CSMA/CD – Losing ground quickly to CSMA/CD.

17 Ethernet and Token ring n Created to answer two questions: – How to identify sending & receiving computers in LANs? – Which computer should send? At what time? n Ethernet answer: – Adding Sender’s & Receiver’s MAC address to packets – Implement a rule known as CSMA/CD n Token ring answer: – Adding Sender’s & Receiver’s MAC address to packets – Implement a Token passing method: a Token circulate in the ring. Only the computer that get the token will send.

18 Internetworking ? n Connecting separate Networks using internetworking devices (bridges, routers, hubs, switches) n Reasons for internetworking: – LAN performance decrease due to growth => Break & Interconnect – Need to access resources available on another network – Need to share software & hardware between networks n Will focus on – Interconnecting LANs to LANs – Interconnecting LANs to WANs

Internetworking (Part II) School of Business Eastern Illinois University © Abdou Illia, Spring 2003 (Week 4, Friday 2/07/2003)

20 Summary Questions 1. How a Source-routing bridge differ from a transparent bridge ? Answer: With Source-routing bridges packets must contain the exact path of LAN-Bridge-LAN-Bridge… Source-routing bridges are found with Token ring LANs. On the other hand Transparent bridges use Routing tables to forward messages and are used to connect two Ethernet LANs or to connect an Ethernet LAN to a Token ring LAN 2. What is the purpose of a discovery frame ? Answer: Allows a station to discover the path of LAN-Bridge-LAN-Bridge.. when Source-routing bridges are used. 3. In what situation does one use a Remote bridge ? (Slide #4 in Internetwkg 2) 4. What are the basic functions of a router? (See slide #7 in Internetworking 2) 5. ………………………

21 Summary Questions 6. 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: 7. 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 School of Business Eastern Illinois University © Abdou Illia, Spring 2003 (Week 5, Monday 2/10/03)

23 Summary Questions 1. Distinguish between digital and analog signals 2. Distinguish between digital and binary transmission 3. What is the difference between the bit rate and the baud rate? in Fundamentals of Data & Signals

24 Bits and Baud n Baud Rate = Number of clock cycles/sec – In this example, 4 baud (not 4 bauds/second) – Note: Number of clock cycles, not actual line changes n Bit Rate = Number of bits/second – In this example, 8 bits/second n Bit Rate = Baud Rate * Bits per clock cycle Second Possible Change Not Made

25 Equations n # of states – 2 Bits per clock cycle = Number of possible states (Eq. 1) n Bit rate – Bit rate = Baud Rate * Bits per clock cycle (Eq. 2) n Exercise (See next slide)

26 Exercise A) If a transmission line has a Baud rate of baud, and if there are eight possible line states, what is the Bit rate? B) If you wish to send two bits per clock cycle, how many possible states must you have?

Fundamentals of Data & Signals (continued) School of Business Eastern Illinois University © Abdou Illia, Spring 2003 (Week 5, Wednesday 2/12/03)

28 Summary Questions 1. What is the main advantage of digital signals over analog signals ? Answer: It’s easier to remove noise from digital signals (Slide #4 in Fundamentals of Data & Signals -continued) 2. What are the Tree main components (characteristics) of signals ? Answer: Amplitude, Frequency and Phase 3. What is the bandwidth of a signal ? (See slide # 10 in Fundamentals of Data & Signals - continued) 4. (a) Name one technique for converting digital data into digital signals. (b) Name 3 techniques for converting digital data into analog signals 4a) NRZ-L or Differential Manchester. 4b) Amplitude modulation, Frequency modulation, Phase modulation

Conducted and Wireless Media School of Business Eastern Illinois University © Abdou Illia, Spring 2003 (Week 6, Monday 2/17/03)

30 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 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 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.

Conducted and Wireless Media (Part 2) School of Business Eastern Illinois University © Abdou Illia, Spring 2003 (Week 6, Friday 2/21/03)

32 Summary Questions n a) Wireless transmission can experience propagation problems due to shadow zones and multipath interference. Explain. n b) Describe the elements in a typical Wireless LAN. See other questions in PPT notes titled “ Additional questions about Conducted and Wireless Media”

33 Wireless LAN ( standard) Switch Client PC Server Wired LAN Access Point A Access Point B UTPRadio Link Handoff If mobile computer moves to another access point, it switches service to that access point Laptop CSMA/CA+ACK