Review For Exam 2. Network Architecture Models (Layered Communications) Summary Questions

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1 School of Business Review For Exam 2 (Week 7, Monday 2/24/2003) School of Business Network Architecture Models (Layered Communications) Encapsulation and Deencapsulation (Week 3, Wednesday 1/29/2003) 3 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? At which layer a Trailer is usually added. 4. Compare Hybrid TCP/IP layering and Windows 98 layering.

2 Hybrid TCP/IP-OSI Model 4 Layers Sample protocols for Web access HTTP TCP IP Ethernet, PPP Ethernet, Modem standards, Telephone standards Layered Communication 5 programs on different computers cannot communicate directly Because they are on different machines. So, they communicate indirectly through layers cooperation Browser Trans Int DL HTTP Request Web App Trans Int DL Phy User PC Phy Webserver Layer Cooperation on the User PC 6 layer passes HTTPtransport layer request to HTTP Request User PC

3 Layer Cooperation on the User PC 7 layer creates a TCP segment HTTP request is put in the data field A TCP header is added So, layer encapsulates HTTP request within a TCP segment TCP Segment HTTP Request Data Field TCP-H TCP Header Encapsulation 8 Encapsulation is: Embedding a received message in a new message Delivering a received message in the data field of a new message Example: TCP encapsulates HTTP request in the data field of a new massage called TCP Segment TCP Segment HTTP Request Data Field TCP-H TCP Header Layer Cooperation on the User PC 9 The internet layer passes the IP packet to the layer layer messages are called packets IP packet User PC

4 Layer Cooperation on the User PC 10 Layer Encapsulates IP Packet within a PPP Frame 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 Layer Cooperation on the User PC 11 Recap: Adding Headers and Trailers: HTTP msg HTTP msg TCP-H HTTP msg TCP-H IP-H PPP-T HTTP msg TCP-H IP-H PPP-H User PC Layer Cooperation on the Webserver 12 Situation reverse to Situation on User PC (Deencapsulation) User PC Webserver

5 13 Hybrid TCP/IP and Windows Layering Hybrid TCP/IP-OSI Layering Microsoft Windows 95/98 Layering Clients and Services Protocols (TCP/IP, IPX/SPX, NetBEUI, etc.) Adapters (Dial-up adapters, Network Interface Card, etc.) School of Business working (Week 4, Wednesday 2/5/2003) 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

6 Medium Access Control Protocols used in LANs 16 Ethernet or CSMA/CD Most common form of LAN today. Star-wired bus is most common topology Many standards (form 1Base5 to 1000BaseT) 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. Ethernet and Token ring 17 Created to answer two questions: How to identify sending & receiving computers in LANs? Which computer should send? At what time? Ethernet answer: Adding Sender s & Receiver s MAC address to packets Implement a rule known as CSMA/CD 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. working? 18 Connecting separate Networks using internetworking devices (bridges, routers, hubs, switches) 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 Will focus on Interconnecting LANs to LANs Interconnecting LANs to WANs

7 School of Business working (Part II) (Week 4, Friday 2/07/2003) 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 wkg 2) 4. What are the basic functions of a router? (See slide #7 in working 2) 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:

8 School of Business Fundamentals of Data & Signals (Week 5, Monday 2/10/03) 1. Distinguish between digital and analog signals in Fundamentals of Data & Signals 2. Distinguish between digital and binary transmission What is the difference between the bit rate and the baud rate? 16 Bits and Baud 24 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 Bit Rate = Number of bits/second In this example, 8 bits/second Bit Rate = Baud Rate * Bits per clock cycle 1 Second 10 Possible Change Not Made

9 Equations 25 # of states 2 Bits per clock cycle = Number of possible states (Eq. 1) Bit rate Bit rate = Baud Rate * Bits per clock cycle (Eq. 2) Exercise (See next slide) Exercise 26 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? School of Business Fundamentals of Data & Signals (continued) (Week 5, Wednesday 2/12/03)

10 28 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 School of Business Conducted and Wireless Media (Week 6, Monday 2/17/03) 30 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. What categories of twisted pair are usually used in LANs? Categories 3, 4, 5 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 interference, Long distance Can you transmit video signal over twisted pair wire? Explain You can, but noise is going to be a serious factor.

11 School of Business Conducted and Wireless Media (Part 2) (Week 6, Friday 2/21/03) 32 a) Wireless transmission can experience propagation problems due to shadow zones and multipath interference. Explain. b) Describe the elements in a typical Wireless LAN. See other questions in PPT notes titled Additional questions about Conducted and Wireless Media Wireless LAN ( standard) 33 Switch UTP Access Point A CSMA/CA+ACK Radio Link Laptop Client PC Wired LAN Server Access Point B Handoff If mobile computer moves to another access point, it switches service to that access point

2. What is the maximum value of each octet in an IP address? A. 128 B. 255 C. 256 D. None of the above

1. How many bits are in an IP address? A. 16 B. 32 C. 64 2. What is the maximum value of each octet in an IP address? A. 128 B. 255 C. 256 3. The network number plays what part in an IP address? A. It