1Review For Exam 2School of BusinessEastern Illinois University © Abdou Illia, Fall 2004Wednesday 10/6/2004)InternetworkingSchool of BusinessEastern Illinois University 3Summary Questions1. 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 formats24Medium Access Control Protocols used in LANs 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.5Ethernet and Token ring 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.6Internetworking ? 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 WANs3Internetworking (Part II)School of BusinessEastern Illinois University 8Summary Questions1. 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 LAN2. 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. ………………………9Summary Questions6. 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 3:410Summary Questions 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 bridgeb) Use a Transparent bridgec) Use a Transparent bridge, but check the features to make sure that it has the appropriate conversion function.d) Use a Remote bridge.11Routers Device that connect a LAN to a WAN. Functions:– Conversion between frame formats– Forwarding frames– Making routing decisions– Often firewall functions (protection)Fundamentals of Data & SignalsSchool of BusinessEastern Illinois University513Summary Questions1. Distinguish between digital and analog signals2. Distinguish between digital and binary transmission3. What is the difference between the bit rate and the baud rate? 9-101216in Fundamentals of Data & Signals14Bits and Baud 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 cycle000110011 SecondPossible Change Not Made15Equations # of states– 2Bits 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)616ExerciseA) 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?17Translation Devices Source of Data versus LineAnalog Line Digital LineAnalog Device (e.g. Tel)CodecDigital Device (e.g. Computer)Modem DSUTranslatorTransmission LineSource of DataFundamentals of Data & Signals (Part 2)School of BusinessEastern Illinois University719AttenuationOverall gain or loss = -10 dB + 20dB - 15dB = -5dB 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 log10(P2 / P1), Where P2 & P1 are ending and beginning power levels (in watt)(Figure 2-10 in textbook)20Attenuation 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 log10(P2 / P1) 2. dB = 10 log10(5/10)3. dB = 10 log10(0.5)4. dB = 10 (-0.3)5. dB = -3Q: 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 ?21Summary Questions1. What is the main