Review For Exam 2

School of BusinessEastern Illinois University

© Abdou Illia, Spring 2005

Tuesday 2/22/2005)

Internetworking

School of BusinessEastern Illinois University

3Summary 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

4Medium 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 WANs

Internetworking (Part II)

School of BusinessEastern Illinois University

8Summary 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 #8 in Internetworking 2)

5. ………………………

9Summary Questions

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:

10Summary 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 & Signals

School of BusinessEastern Illinois University

13Summary 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?

9-10

12

16

in Fundamentals of Data & Signals

14Bits 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 cycle

0001

1001

1 Second

Possible Change Not Made

15Equations

# 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)

16Exercise

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?

17Translation Devices

Source of Data versus Line

Analog Line Digital Line

Analog Device (e.g. Tel) Codec

Digital Device (e.g. Computer) Modem DSU

Translator Transmission Line

Source of Data

Fundamentals of Data & Signals (Part 2)

School of BusinessEastern Illinois University

19Attenuation

Overall 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 = -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 ?

21Summary 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 three 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/AdditionalQuestions(Cond-Wireless).ppt

Check Quiz 1

Conducted and Wireless Media (Part 1)

School of BusinessEastern Illinois University

24Summary Questions

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.

25Case study

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

26Case study

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 ?

27Case study

Cat 5-UTP

Optical Fiber

If the needed data rate is higher than 100 Mbps, what are the possible solutions?

Conducted and Wireless Media (Part 2)

School of BusinessEastern Illinois University

29Summary Questions

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” in Review section

30Wireless LAN (802.11 standard)

Switch

Client PCServer

Wired LAN

AccessPoint A

AccessPoint B

UTP Radio Link

HandoffIf mobile computermoves to another

access point,it switches serviceto that access point

Laptop

CSMA/CA+ACK