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Any Questions?. Chapter 3- Fundamentals of LANs . An Overview of Modern Ethernet LANs A Brief History of Ethernet Ethernet UTP Cabling Improving Performance by Using Switches Instead of Hubs Ethernet Data-Link Protocols. Pg 41. Do I know this?. Go through the Quiz- 5 minutes.

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Any questions l.jpg

Any Questions?


Chapter 3 fundamentals of lans l.jpg

Chapter 3-Fundamentals of LANs

  • An Overview of Modern Ethernet LANs

  • A Brief History of Ethernet

  • Ethernet UTP Cabling

  • Improving Performance by Using Switches Instead of Hubs

  • Ethernet Data-Link Protocols

Pg 41


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Do I know this?

Go through the Quiz-

5 minutes


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1. Which of the following is true about the cabling of a typical modern Ethernet LAN?

a. Connect each device in series using coaxial cabling

b. Connect each device in series using UTP cabling

c. Connect each device to a centralized LAN hub using UTP cabling

d. Connect each device to a centralized LAN switch using UTP cabling


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1. Which of the following is true about the cabling of a typical modern Ethernet LAN?

a. Connect each device in series using coaxial cabling

b. Connect each device in series using UTP cabling

c. Connect each device to a centralized LAN hub using UTP cabling

d. Connect each device to a centralized LAN switch using UTP cabling

Answer: D


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2. Which of the following is true about the cabling of a 10BASE2 Ethernet LAN?

a. Connect each device in series using coaxial cabling

b. Connect each device in series using UTP cabling

c. Connect each device to a centralized LAN hub using UTP cabling

d. Connect each device to a centralized LAN switch using UTP cabling


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2. Which of the following is true about the cabling of a 10BASE2 Ethernet LAN?

a. Connect each device in series using coaxial cabling

b. Connect each device in series using UTP cabling

c. Connect each device to a centralized LAN hub using UTP cabling

d. Connect each device to a centralized LAN switch using UTP cabling

Answer: A


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3. Which of the following is true about Ethernet crossover cables?

a. Pins 1 and 2 are reversed on the other end of the cable.

b. Pins 1 and 2 on one end of the cable connect to pins 3 and 6 on the other end of the cable.

c. Pins 1 and 2 on one end of the cable connect to pins 3 and 4 on the other end of the cable.

d. The cable can be up to 1000 meters long to cross over between buildings.

e. None of the other answers is correct.


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3. Which of the following is true about Ethernet crossover cables?

a. Pins 1 and 2 are reversed on the other end of the cable.

b. Pins 1 and 2 on one end of the cable connect to pins 3 and 6 on the other end of the cable.

c. Pins 1 and 2 on one end of the cable connect to pins 3 and 4 on the other end of the cable.

d. The cable can be up to 1000 meters long to cross over between buildings.

e. None of the other answers is correct.

Answer: B


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4. Each answer lists two types of devices used in a 100BASE-TX network. If these devices were connected with UTP Ethernet cables, which pairs of devices would require a straight-through cable?

a. PC and router

b. PC and switch

c. Hub and switch

d. Router and hub

e. Wireless access point (Ethernet port) and switch


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4. Each answer lists two types of devices used in a 100BASE-TX network. If these devices were connected with UTP Ethernet cables, which pairs of devices would require a straight-through cable?

a. PC and router

b. PC and switch

c. Hub and switch

d. Router and hub

e. Wireless access point (Ethernet port) and switch

Answer: B, D & E


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5. Which of the following is true about the CSMA/CD algorithm?

a. The algorithm never allows collisions to occur.

b. Collisions can happen, but the algorithm defines how the computers should notice a collision and how to recover.

c. The algorithm works with only two devices on the same Ethernet.

d. None of the other answers is correct.


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5. Which of the following is true about the CSMA/CD algorithm?

a. The algorithm never allows collisions to occur.

b. Collisions can happen, but the algorithm defines how the computers should notice a collision and how to recover.

c. The algorithm works with only two devices on the same Ethernet.

d. None of the other answers is correct.

Answer: B


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6. Which of the following is a collision domain?

a. All devices connected to an Ethernet hub

b. All devices connected to an Ethernet switch

c. Two PCs, with one cabled to a router Ethernet port with a crossover cable and the other PC cabled to another router Ethernet port with a crossover cable

d. None of the other answers is correct.


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6. Which of the following is a collision domain?

a. All devices connected to an Ethernet hub

b. All devices connected to an Ethernet switch

c. Two PCs, with one cabled to a router Ethernet port with a crossover cable and the other PC cabled to another router Ethernet port with a crossover cable

d. None of the other answers is correct.

Answer: A


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7. Which of the following describe a shortcoming of using hubs that is improved by instead using switches?

a. Hubs create a single electrical bus to which all devices connect, causing the devices to share the bandwidth.

b. Hubs limit the maximum cable length of individual cables (relative to switches)

c. Hubs allow collisions to occur when two attached devices send data at the same time.

d. Hubs restrict the number of physical ports to at most eight.


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7. Which of the following describe a shortcoming of using hubs that is improved by instead using switches?

a. Hubs create a single electrical bus to which all devices connect, causing the devices to share the bandwidth.

b. Hubs limit the maximum cable length of individual cables (relative to switches)

c. Hubs allow collisions to occur when two attached devices send data at the same time.

d. Hubs restrict the number of physical ports to at most eight.

Answer: A & C


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8. Which of the following terms describe Ethernet addresses that can be used to communicate with more than one device at a time?

a. Burned-in address

b. Unicast address

c. Broadcast address

d. Multicast address


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8. Which of the following terms describe Ethernet addresses that can be used to communicate with more than one device at a time?

a. Burned-in address

b. Unicast address

c. Broadcast address

d. Multicast address

Answer: C & D


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9. Which of the following is one of the functions of OSI Layer 2 protocols?

a. Framing

b. Delivery of bits from one device to another

c. Error recovery

d. Defining the size and shape of Ethernet cards


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9. Which of the following is one of the functions of OSI Layer 2 protocols?

a. Framing

b. Delivery of bits from one device to another

c. Error recovery

d. Defining the size and shape of Ethernet cards

Answer: A


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10. Which of the following are true about the format of Ethernet addresses?

a. Each manufacturer puts a unique code into the first 2 bytes of the address.

b. Each manufacturer puts a unique code into the first 3 bytes of the address.

c. Each manufacturer puts a unique code into the first half of the address.

d. The part of the address that holds this manufacturer’s code is called the MAC.

e. The part of the address that holds this manufacturer’s code is called the OUI.

f. The part of the address that holds this manufacturer’s code has no specific name.


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10. Which of the following are true about the format of Ethernet addresses?

a. Each manufacturer puts a unique code into the first 2 bytes of the address.

b. Each manufacturer puts a unique code into the first 3 bytes of the address.

c. Each manufacturer puts a unique code into the first half of the address.

d. The part of the address that holds this manufacturer’s code is called the MAC.

e. The part of the address that holds this manufacturer’s code is called the OUI.

f. The part of the address that holds this manufacturer’s code has no specific name.

Answer: B, C, & E


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11. Which of the following is true about the Ethernet FCS field?

a. It is used for error recovery.

b. It is 2 bytes long.

c. It resides in the Ethernet trailer, not the Ethernet header.

d. It is used for encryption.

e. None of the other answers is correct.


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11. Which of the following is true about the Ethernet FCS field?

a. It is used for error recovery.

b. It is 2 bytes long.

c. It resides in the Ethernet trailer, not the Ethernet header.

d. It is used for encryption.

e. None of the other answers is correct.

Answer: C


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Any Questions?


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An Overview of Modern Ethernet LANs

  • Ethernet is a family standards for physical and data-link layers

  • Different Speeds

    • 10, 100, 1000 Mbps

  • Different Cabling

    • UTP-Most common

    • Fiber-most secure

Pg 45


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An Overview of Modern Ethernet LANs

  • IEEE Standard

    • 802.3 Media Access Control sublayer

    • 802.2 Logical Link Control sublayer

Pg 46


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To Build a LAN

  • Computers with Ethernet NIC

  • Ethernet Hub or Switch

  • UTP cables to connecct PC to hub/switch

Pg 46


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LANS can be used without WAN

  • File sharing: Each computer can be configured to share all or parts of its file system so that the other computers can read, or possibly read and write, the files on another computer. This function typically is simply part of the PC operating system.

  • Printer sharing: Computers can share their printers as well. For example, PCs A, B, and C in Figure 3-1 could print documents on PC D’s printer. This function is also typically part of the PC’s operating system.

  • File transfers: A computer could install a file transfer server, thereby allowing other computers to send and receive files to and from that computer. For example, PC C could install File Transfer Protocol (FTP) server software, allowing the other PCs to use FTP client software to connect to PC C and transfer files.

  • Gaming: The PCs could install gaming software that allows multiple players to play in the same game. The gaming software would then communicate using the Ethernet.

Pg 46


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A Brief History of Ethernet

  • Developed by Xerox

    • Then by Intel and DEC

    • DIX Ethernet

  • Gave standard to IEEE

    • 802.2 group-LLC

      • Ethernet, Token Ring, etc.

    • 802.3 group-MAC

      • MAC Addresses

Pg 48


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10BASE2 AND 10BASE5

  • Original Ethernet standards used coaxial cable on a bus network

    • 10BASE2-10 Mbps, Baseband, 200 meter length

    • 10BASE5-10Mbps, Baseband, 500 meter length

  • On a bus, if two or more hosts send-COLLISION


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10BASE2 AND 10BASE5

  • Carrier Sense Multiple Access/Collision Detection-CSMA/CD

    • A device that wants to send a frame waits until the LAN is silent—in other words, no frames are currently being sent—before attempting to send an electrical signal.

    • If a collision still occurs, the devices that caused the collision wait a random amount of time and then try again.


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Repeaters

  • Maximum cable lengths were limitations

    • Attenuation if cable ran to long-reduced signal strength

  • Added repeaters to extend cable runs

    • Connect multiple segments

    • Receive bits, send out new, clean signal on other side

  • The original Ethernet LANs created an electrical bus to which all devices connected.

  • Because collisions could occur on this bus, Ethernet defined the CSMA/CD algorithm, which defined a way to both avoid collisions and take action when collisions occurred.

  • Repeaters extended the length of LANs by cleaning up the electrical signal and repeating it—a Layer 1 function—but without interpreting the meaning of theelectrical signal.


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Building 10BASE-T Networks with Hubs

  • Updates to Ethernet (Twisted pair based networks)

    • 10BASE-T-1990

    • 100BASE-T-1995

    • 1000BASE-T-1999

  • Allowed use of UTP telephone cabling that was often in place

  • UTP cheaper and easier to install thatn Coax

Pg 51


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Building 10BASE-T Networks with Hubs

  • Updates to Ethernet (Twisted pair based networks)

    • 10BASE-T-1990

    • 100BASE-T-1995

    • 1000BASE-T-1999

  • Allowed use of UTP telephone cabling that was often in place

  • UTP cheaper and easier to install than Coax

  • Centralized connection point

    • Hubs/Switches

    • Start wired networks

Pg 51


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Hubs

  • Basically Multi-port repeaters

  • LANS using hubs create an electrical bus

    • Inside the hub

    • Collisions still occur

  • Limited problems to singe host rather than bringing the whole network down

Pg 51


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Basic Ethernet Summary

  • The original Ethernet LANs created an electrical bus to which all devices connected.

  • 10BASE2 and 10BASE5 repeaters extended the length of LANs by cleaning up theelectrical signal and repeating it—a Layer 1 function—but without interpreting the meaning of the electrical signal.

  • Hubs are repeaters that provide a centralized connection point for UTP cabling—but they still create a single electrical bus, shared by the various devices, just like 10BASE5 and 10BASE2.

  • Because collisions could occur in any of these cases, Ethernet defines the CSMA/CD algorithm, which tells devices how to both avoid collisions and take action when collisions do occur.

Pg 51


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Ethernet UTP Cabling

  • UTP Ethernet standards use wither 2 or 4 pairs of the cable

  • Individual wires wrapped in plastic and all wires wrapped in outer jacket

  • Wires are different colors

Pg 52


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RJ-45 Connectors

  • Eight physical locations in which the wires are inserted

    • Pins

  • Cables with RJ-45 connectors are inserted into RJ-45 ports

    • On NIC Card

    • On Switch

    • Patch Panel

Pg 53


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Switch Connections

  • Some Switches are modular and support pluggable slots for different types of connectors

Pg 54


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Transmitting Data with Twisted Pairs

  • Wires are twisted in an attempt to cancel out interferance

  • Signal is encoded

    • Defines how signal should vary over time to show 1 or 0

Pg 54


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10 and 100 BASE t Wiring

Pg 55


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10 and 100 BASE t Wiring

  • Pins must be properly arranged

  • NICS use pin 1 and 2 to transmit

  • NICS use 2 and 6 to receive

Pg 56


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Crossover

  • When you connect like to like

  • Cross pin 1-2 and 3-6

  • Many systems can auto cross

Pg 56


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Crossover

Pg 58


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1000BASE-t Cabling

  • Uses all 4 pairs

  • Need to cross other pairs

    • 4-5 and 7-8

Pg 58


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Improving Performance by Using Switches Instead of Hubs

  • With Hubs-it is like a bus-Any incoming signal is sent out to all ports

  • Step 1 The network interface card (NIC) sends a frame.

  • Step 2 The NIC loops the sent frame onto its receive pair internally on the card.

  • Step 3 The hub receives the electrical signal, interpreting the signal as bits so that it can clean up and repeat the signal.

  • Step 4 The hub’s internal wiring repeats the signal out all other ports, but not back to the port from which the signal was received.

  • Step 5 The hub repeats the signal to each receive pair on all other devices.

Pg 59


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Improving Performance by Using Switches Instead of Hubs

  • CSMA/CD does not prevent collisions

  • Means the connection is half-duplex

  • Too many collisions causes the system to slow down

    • More than 30% utilization

  • Shared network-shared bandwidth

Pg 60


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CSMA/CD

Step 1 A device with a frame to send listens until the Ethernet is not busy.

Step 2 When the Ethernet is not busy, the sender(s) begin(s) sending the frame.

Step 3 The sender(s) listen(s) to make sure that no collision occurred.

Step 4 If a collision occurs, the devices that had been sending a frame each sends a jamming signal to ensure that all stations recognize the collision.

Step 5 After the jamming is complete, each sender randomizes a timer and waits that long before trying to resend the collided frame.

Step 6 When each random timer expires, the process starts over with Step 1.


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Increasing Bandwidth Using Switches

  • Collision Domain

    • Set of devices whose frames can collide

    • All devices on 10BASE2 or 10BASE5

    • All devices on a hub

  • Switches reduce or eliminate collisions

    • Not a shared bus

    • Switches only send traffic to port where host is connected

    • Switches can buffer traffic for a port

    • Switches use Layer 2 addresses-hence they are layer 2 devices

Pg 61


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Increasing Bandwidth Using Switches

  • If only one device is cabled to each port of a switch, no collisions can occur.

  • Devices connected to one switch port do not share their bandwidth with devices connected to another switch port. Each has its own separate bandwidth, meaning that a switch with 100-Mbps ports has 100 Mbps of bandwidth per port.

    • Switched Ethernet

Pg 61


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How Many Collision Domains


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Doubling performance using full duplex Ethernet

  • CSMA/CD forces half-duplex functionality

    • You can send or receive, but not at the same time

  • Switches can completely eliminate collisions

    • On switch ports that have a SINGLE device

Pg 62


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Ethernet Data-Link Protocols

  • Ethernet family all use same data link protocols

  • Addressing, Framing, error detection and identifying the type of data

Pg 63


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Ethernet Addressing

  • Identifies devices on the network

  • 6 bytes long (48 bits)

  • Usually shown in hexadecimal

  • Cisco writes it 0000.0C12.3456

Pg 36


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Ethernet Addressing

  • Unicast

    • For a single (uni) computer

  • Broadcast

    • For all computers on network

  • Multicast

    • For subset of computers

  • Group Addresses

    • For defined group

Pg 36


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Ethernet Addressing

  • Unicast traffic

    • Sender and receiver are defined in frame

  • Receiver know to look at data

    • Because their address is destination

Pg 36


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MAC Address Structure

  • Organizationally Unique Identifier

    • Manufacturer code

  • Vendor Code

    • Serial number

Pg 64


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Ethernet Addresses

  • Broadcast addresses: The most often used of the IEEE group MAC addresses, the broadcast address, has a value of FFFF.FFFF.FFFF (hexadecimal notation). The broadcast address implies that all devices on the LAN should process the frame.

  • Multicast addresses: Multicast addresses are used to allow a subset of devices on a LAN to communicate. When IP multicasts over an Ethernet, the multicast MAC addresses used by IP follow this format: 0100.5exx.xxxx, where any value can be used in the last half of the address.

Pg 65


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Terminology

Pg 65


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Ethernet Framing

  • Give format to what bits mean

  • Multiple Formats-Key ideas

    • Older formats didn’t have length and type. One or other

    • Maximum length of packet-MTU-1500 bytes

    • 802.2 SNAP header

      • Allows for length and type

Pg 65-66


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Original 802.3 & revised

Pg 66


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SNAP header

Pg 68


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Identifying Data in Ehternet

  • What type of Packet is in the frame?

    • IP

    • SNA

    • Etc

  • 802.3 original had no type

    • Revised has type/length

  • If type/length is used for length, still need type

    • SNAP headers


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Error Detection

  • Done through FCS-Frame Check Sequence

  • If FCS doesn’t match, Frame is discarded

  • Not Error recovery-that is TCP

Pg 69


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Any Questions?


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