School of Business Review For Exam 2 Wednesday 10/6/2004) Abdou Illia, Fall 2004 School of Business Internetworking 3 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
Medium Access Control Protocols used in LANs 4 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 5 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. Internetworking? 6 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
School of Business Internetworking (Part II) 8 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 #8 in Internetworking 2) 5. 9 6. The local area network shown in Figure 8-21 (p. 268) 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:
10 Your supervisor at Network Inc. wants you to provide your expertise to help a client decide what kind of bridge to interconnect two LANs located in two separate buildings in town. One of the LANs uses CSMA/CD and the other one is a Token Ring LAN. What will be your recommendation? a) Use a Source-Routing bridge b) Use a Transparent bridge c) Use a Transparent bridge, but check the features to make sure that it has the appropriate conversion function. d) Use a Remote bridge. Routers 11 Device that connect a LAN to a WAN. Functions: Conversion between frame formats Forwarding frames Making routing decisions Often firewall functions (protection) School of Business Fundamentals of Data & Signals
1. Distinguish between digital and analog signals 9-10 13 in Fundamentals of Data & Signals 2. Distinguish between digital and binary transmission 12 3. What is the difference between the bit rate and the baud rate? 16 Bits and Baud 14 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 01 01 00 Equations 15 # 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 16 A) If a transmission line has a Baud rate of 10 000 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? Translation Devices 17 Source of Data versus Line Translator Transmission Line Source of Data Analog Line Analog Device (e.g. Tel) Digital Line Codec Digital Device (e.g. Computer) Modem DSU School of Business Fundamentals of Data & Signals (Part 2)
Attenuation Attenuation = Loss of Signal Strength Function of Distance and Friction within the Medium If high signals get too weak, the receiver will not be able to detected it. Decibel (db) is a relative measure of signal loss or gain of strength. db = 10 log 10 (P2 / P1), Where P2 & P1 are ending and beginning power levels (in watt) 19 (Figure 2-10 in textbook) Overall gain or loss = -10 db + 20dB - 15dB = -5dB Attenuation 20 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 log 10 (P2 / P1) 2. db = 10 log 10 (5/10) 3. db = 10 log 10 (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? 21 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
22 Check additional questions about data & signals on the course website at http://www.eiu.edu/~a_illia/cis3200/notes/additio nalquestions1.ppt Check Quiz 1 School of Business Conducted and Wireless Media (Part 1) 24 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, 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 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.
Case study 25 The following figure shows a common situation in LANs. Remember : Using Category 5 UTP, the maximum segment length is 100 meters. A wall jack is a passive device and does not regenerate a signal Cat 5-UTP Optical Fiber Case study 26 Cat 5-UTP Optical Fiber If the distance between the Workstation and the Hub is more than 100 meters, what will be the problem? What solution can be used? If the cable that connect the Workstation and the Hub pass through a noisy environment (Heating or cooling mechanical room), what solution can be used? Case study 27 Cat 5-UTP Optical Fiber If the needed data rate is higher than 100 Mbps, what are the possible solutions?
School of Business Conducted and Wireless Media (Part 2) 29 a) Wireless transmission can experience propagation problems due to shadow zones and multipath interference. Explain. b) Describe the elements in a typical 802.11 Wireless LAN. See other questions in PPT notes titled Additional questions about Conducted and Wireless Media Wireless LAN (802.11 standard) 30 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