Ch 9 -  Chapter 9 Ethernet
Objectives <ul><li>Describe the evolution of Ethernet  </li></ul><ul><li>Explain the  field  of the Ethernet frame  </li><...
Ethernet Overview <ul><li>Ethernet is the predominant LAN technology  </li></ul><ul><li>The OSI model separates the Data L...
IEEE Standard for Ethernet <ul><li>The first Ethernet standard was published in 1980 by a consortium of Digital Equipment ...
Ethernet – Layer 1 and Layer 2 <ul><li>Layer 1 performs a key role in the communication that takes place between devices, ...
IEEE 802 Ch 9 -
Logical Link Control (LLC) <ul><li>The IEEE 802.2 standard describes the LLC sub-layer functions </li></ul><ul><ul><li>LLC...
Media Access Control (MAC) <ul><li>The MAC is the lower sub-layer of the Data Link layer  </li></ul><ul><li>The two primar...
Success of Ethernet <ul><li>Simplicity and ease of maintenance  </li></ul><ul><li>Ability to incorporate new technologies ...
Historic Ethernet <ul><li>The foundation for Ethernet technology was first established in 1970 with a program called Aloha...
Early Ethernet <ul><li>The first versions of Ethernet used coaxial cable to connect computers in a bus topology  </li></ul...
Early Ethernet Implementations <ul><li>The early Ethernet was a logical bus topology at the Data Link layer and also used ...
Collision Management <ul><li>Legacy  Ethernet  </li></ul><ul><ul><li>the central point of the network segment was a  hub  ...
Gigabit Ethernet <ul><li>Gigabit Ethernet is used to describe Ethernet implementations that provide bandwidth of 1,000 Mbp...
Ethernet Beyond the LAN <ul><li>The increase cabling distance enabled by the use of fiber-optic cable in Ethernet-based ne...
Ethernet Frame <ul><li>The most significant difference between the original IEEE 802.3 and the revised IEEE 802.3 is the a...
Ethernet Frame Size <ul><li>An Ethernet frame size includes the Destination MAC Address, Source MAC Address, Length/Type, ...
Ethernet Frame Fields <ul><li>Preamble and Start of Frame Delimiter (SFD) </li></ul><ul><ul><li>used for  synchronization ...
Ethernet Frame Fields (cont’d) <ul><li>Length/Type  </li></ul><ul><ul><li>if the two-octet field is equal to or greater th...
Frame Check Sequence (FCS) <ul><li>The  FCS  field is used to  detect errors  in a frame  </li></ul><ul><li>Contains a cyc...
Ethernet MAC Address <ul><li>A unique identifier called a Media Access Control ( MAC ) address is used to  identify each d...
MAC Address Structure <ul><li>All MAC addresses contain the vendor’s assigned OUI in the first 3 bytes  </li></ul><ul><li>...
Hexadecimal Numbering System <ul><li>Hexadecimal is a base sixteen system </li></ul><ul><ul><li>uses the numbers 0 to 9 an...
Viewing The MAC Address <ul><li>The  ipconfig /all  command can be used to display the NIC physical address  </li></ul><ul...
Physical and Logical Addressing <ul><li>Layer 2 physical addressing is used to transport frames across the local media  </...
*Unicast MAC Address <ul><li>A unicast MAC address is the unique address used when a frame is sent from a single transmitt...
*Broadcast MAC Address <ul><li>The frame contains a destination MAC address with 48 ones (1s) </li></ul><ul><ul><li>FF-FF-...
*Multicast MAC Address <ul><li>The multicast MAC address is a special value that begins with 01-00-5E in hexadecimal  </li...
Shared-Media Access <ul><li>If more than one device transmits simultaneously, the physical signals collide  </li></ul><ul>...
CSMA/CD <ul><li>Carrier sense </li></ul><ul><ul><li>all devices must  listen before transmitting   </li></ul></ul><ul><ul>...
CSMA/CD (cont’d) <ul><li>Collision detection </li></ul><ul><ul><li>once a collision occurs, all devices will detect an inc...
Hubs and Collision Domains  <ul><li>Hubs retransmit received signals to all connected devices  </li></ul><ul><li>Hubs do n...
Hubs and Collision Domains (cont’d) <ul><li>The interconnection of hubs form a physical topology called an extended star  ...
Latency <ul><li>The electrical signal that is transmitted takes a certain amount of time (latency or delay) to propagate (...
Timing and Synchronization <ul><li>In a half-duplex mode, a sending device transmits 64 bits of timing and synchronization...
Bit Time <ul><li>The period of time required for a bit to be placed and sensed on the media is known as the bit time  </li...
Slot Time <ul><li>Ensures that if a collision is going to occur, it will be detected within the first 512 bits (or the min...
Interframe Spacing <ul><li>The minimum spacing between two non-colliding frames  </li></ul><ul><ul><li>the time is measure...
Jam Signal <ul><li>As soon as a collision is detected, the sending devices transmit a 32-bit jam signal  </li></ul><ul><ul...
Backoff Timing <ul><li>Each device waits for a random period of time before retransmitting  </li></ul><ul><ul><li>prevents...
IEEE 802.3 Standards <ul><li>Four data rates are currently defined for operation over optical fiber and twisted-pair cable...
*Types of Ethernet Ch 9 -  Ethernet Type Bandwidth Cable Type Duplex Maximum Distance 10Base5 10 Mbps Thicknet  Coaxial Ha...
10 Mbps Ethernet <ul><li>10Base-T uses Manchester encoding over two pairs of UTP wires </li></ul><ul><li>The early impleme...
RJ-45 Pin Assignments Ch 9 -
100 Mbps Ethernet <ul><li>100 Mbps Ethernet (IEEE 802.3u) or Fast Ethernet can be implemented using  twisted-pair  copper ...
100Base-TX <ul><li>Supports transmission over two pairs of Cat 5 UTP copper wires  </li></ul><ul><li>Uses the same two pai...
100Base-FX <ul><li>Uses a pair of optic fiber media  </li></ul><ul><ul><li>most suitable for connections between floors an...
1000 Mbps Ethernet <ul><li>1000 Mbps Ethernet is also known as  Gigabit Ethernet  </li></ul><ul><li>Gigabit Ethernet frame...
Hubs <ul><li>Legacy Ethernet  uses  hubs  to interconnect nodes on the LAN segment  </li></ul><ul><li>In a hub network the...
*Switches <ul><li>Switches allow the segmentation of the LAN into  separate collision domains (CD) </li></ul><ul><li>Each ...
Benefits of Switch-based LANs <ul><li>Dedicated bandwidth  to each port </li></ul><ul><ul><li>each device effectively has ...
Selective Forwarding <ul><li>Establishing a momentary  point-to-point  connection between each transmitting and receiving ...
Selective Forwarding (cont’d) <ul><li>The switch maintains a table called a  MAC table  or switch table </li></ul><ul><ul>...
Store and Forward <ul><li>Switch will  buffer  an incoming frame and then forward it to the proper port when that port is ...
Switch Operation – Learning and Aging <ul><li>The learning process maps the MAC address with the corresponding ports dynam...
Switch Operation – Flooding <ul><li>The switch sends the frame to  all ports  except the port on which the frame arrived i...
Switch Operation – Forwarding <ul><li>The switch sends the frame to the destination node  </li></ul><ul><ul><li>examines t...
Switch Operation – Filtering  <ul><li>The frame is not forwarded  </li></ul><ul><li>A switch does not forward a frame to t...
Address Resolution Protocol (ARP) <ul><li>The ARP protocol provides two basic functions </li></ul><ul><ul><li>resolving IP...
ARP (cont’d) <ul><li>The  ARP table  or  cache  is maintained dynamically </li></ul><ul><ul><li>record the  source IP addr...
*ARP Process Ch 9 -
Destinations Outside the Local Network <ul><li>The source node will use the MAC address of the gateway as the destination ...
Segmentation with Switch  Ch 9 -  How many collision domain?
Segmentation with Switch  Ch 9 -  How many collision domain?
Pls Copy this Table to your Notebook Ch 9 -
Destinations Outside the Local Network (cont’d) <ul><li>The gateway responds with an ARP reply telling the source node its...
Proxy ARP <ul><li>Proxy ARP is a technique by which a network device answers to ARP requests for an IP address that it doe...
Removing Address Mappings <ul><li>An ARP cache timer removes ARP entries that have not been used for a specified period of...
ARP Broadcast <ul><li>Overhead on the media  </li></ul><ul><ul><li>a broadcast ARP request is received and processed by ev...
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  • This chapter examines the characteristics and operation of Ethernet as it has evolved from a shared media, contention-based data communications technology to today&apos;s high bandwidth, full-duplex technology.
  • Alohanet was a digital radio network designed to transmit information over a shared radio frequency between the Hawaiian Islands. Alohanet required all stations to follow a protocol in which an unacknowledged transmission required re-transmitting after a short period of waiting.
  • All Ethernet nodes share the media. To receive the data send to it, each node needs a unique address.
  • It is usually easier to convert the decimal or hexadecimal value to binary, and then to convert the binary value to either hexadecimal or decimal as appropriate.
  • The lower 23 bits of the IP multicast address is 0000000 00000000 00001010. Add a 0 on the left-hand side of the bit stream: 00000000 00000000 00001010. Convert it to hexadecimal: 00-00-0A. The multicast MAC address is 01-00-5E-00-00-0A.
  • For CSMA/CD Ethernet to operate, the sending device must become aware of a collision before it has completed transmission of a minimum-sized frame. At 100 Mbps, the device timing is barely able to accommodate 100 meter cables. At 1000 Mbps, special adjustments are required because nearly an entire minimum-sized frame would be transmitted before the first bit reached the end of the first 100 meters of UTP cable. For this reason, half-duplex mode is not permitted in 10-Gigabit Ethernet.
  • Ethernet standard require a 96 bit time for the interframe spacing.
  • If the destination IPv4 host is not on the local network, the source node needs to deliver the frame to the router interface that is the gateway or next hop used to reach that destination.
  • Chapter9

    1. 1. Ch 9 - Chapter 9 Ethernet
    2. 2. Objectives <ul><li>Describe the evolution of Ethernet </li></ul><ul><li>Explain the field of the Ethernet frame </li></ul><ul><li>Describe the function and characteristics of the media access control method used by Ethernet protocol </li></ul><ul><li>Describe the Physical and Data Link features of Ethernet </li></ul><ul><li>Compare and contrast Ethernet hubs and switches </li></ul><ul><li>Explain the Address Resolution Protocol (ARP) </li></ul>Ch 9 -
    3. 3. Ethernet Overview <ul><li>Ethernet is the predominant LAN technology </li></ul><ul><li>The OSI model separates the Data Link functionalities of addressing, framing and accessing the media from the Physical layer standards of the media </li></ul>Ch 9 - <ul><li>Ethernet standards define both the Layer 2 protocols and Layer 1 technologies </li></ul><ul><ul><li>basic frame format and address scheme are the same for all varieties of Ethernet </li></ul></ul>
    4. 4. IEEE Standard for Ethernet <ul><li>The first Ethernet standard was published in 1980 by a consortium of Digital Equipment Corporation (DEC), Intel and Xerox (DIX) </li></ul><ul><li>The standard for Ethernet is the IEEE 802.3 </li></ul><ul><ul><li>the IEEE 802.3 standard describes the Physical layer functions and the lower sub-layer of the Data Link layer </li></ul></ul><ul><li>Ethernet operates in the lower two layers of the OSI model </li></ul>Ch 9 -
    5. 5. Ethernet – Layer 1 and Layer 2 <ul><li>Layer 1 performs a key role in the communication that takes place between devices, but each of its functions has limitations </li></ul><ul><li>Layer 2 addresses these limitations </li></ul>Ch 9 - <ul><ul><li>the MAC sub-layer is concerned with the physical components that will be used to communicate the information and prepares the data over the media </li></ul></ul><ul><ul><li>the LLC sub-layer remains independent of the physical equipment used </li></ul></ul>
    6. 6. IEEE 802 Ch 9 -
    7. 7. Logical Link Control (LLC) <ul><li>The IEEE 802.2 standard describes the LLC sub-layer functions </li></ul><ul><ul><li>LLC handles the communication between the upper layers and the networking software </li></ul></ul><ul><ul><li>takes the network protocol data, typically an IPv4 packet, and adds control information to help deliver the packet to the destination </li></ul></ul><ul><li>Layer 2 communicates with the upper layers through LLC </li></ul><ul><li>LLC is implemented in software </li></ul><ul><ul><li>implementation is independent of the physical equipment </li></ul></ul><ul><ul><li>the LLC can be considered the driver software for the NIC </li></ul></ul>Ch 9 -
    8. 8. Media Access Control (MAC) <ul><li>The MAC is the lower sub-layer of the Data Link layer </li></ul><ul><li>The two primary responsibilities of the MAC sub-layer are data encapsulation and media access control </li></ul><ul><li>The data encapsulation functions provide frame delimiting , addressing and error detection </li></ul><ul><li>The media access control manages the placement and removal of frames on the media, which includes the initiation of frame transmission and recovery from transmission failure due to collisions </li></ul>Ch 9 -
    9. 9. Success of Ethernet <ul><li>Simplicity and ease of maintenance </li></ul><ul><li>Ability to incorporate new technologies </li></ul><ul><ul><li>the same protocol that transported data at 3 Mbps can carry data at 10 Gbps </li></ul></ul><ul><li>Reliability </li></ul><ul><li>Low cost of installation and upgrade </li></ul><ul><ul><li>uses UTP copper wires and optical fiber </li></ul></ul>Ch 9 -
    10. 10. Historic Ethernet <ul><li>The foundation for Ethernet technology was first established in 1970 with a program called Alohanet </li></ul><ul><li>The first version of Ethernet incorporated a shared media access method known as Carrier Sense Multiple Access with Collision Detection (CSMA/CD) </li></ul>Ch 9 -
    11. 11. Early Ethernet <ul><li>The first versions of Ethernet used coaxial cable to connect computers in a bus topology </li></ul><ul><ul><li>each computer was connected to the backbone </li></ul></ul><ul><ul><li>early versions of Ethernet were known as Thicknet (10Base5) and Thinnet (10Base2) </li></ul></ul><ul><li>10Base5 used a thick coaxial cable that allowed distances of up to 500 meters before the signal required a repeater </li></ul><ul><li>10Base2 used a thin coaxial cable that has a smaller diameter and more flexible cable than Thicknet and allowed for cabling distances of 185 meters </li></ul><ul><li>The original thick and thin coaxial cables were replaced by early categories of UTP cables </li></ul><ul><ul><li>UTP cables are easier to work with, lightweight and less expensive </li></ul></ul>Ch 9 -
    12. 12. Early Ethernet Implementations <ul><li>The early Ethernet was a logical bus topology at the Data Link layer and also used a physical bus topology </li></ul><ul><li>The physical bus topology was changed to a star topology </li></ul><ul><ul><li>coaxial cables were replaced by early UTP copper cables </li></ul></ul><ul><ul><li>a hub is used as a central point for all connections </li></ul></ul><ul><ul><li>still half-duplex communication </li></ul></ul>Ch 9 - UTP cable coaxial cable
    13. 13. Collision Management <ul><li>Legacy Ethernet </li></ul><ul><ul><li>the central point of the network segment was a hub </li></ul></ul><ul><ul><li>frame is broadcast to all devices </li></ul></ul><ul><ul><li>uses half-duplex communication </li></ul></ul><ul><ul><li>frame collisions increased significantly as more devices are added </li></ul></ul><ul><li>Current Ethernet </li></ul><ul><ul><li>hub was replaced by a switch </li></ul></ul><ul><ul><li>switch can control the flow of data by isolating each port by sending a frame to its proper destination only </li></ul></ul><ul><ul><li>reduces collision </li></ul></ul><ul><ul><li>full-duplex communication was later introduced </li></ul></ul>Ch 9 -
    14. 14. Gigabit Ethernet <ul><li>Gigabit Ethernet is used to describe Ethernet implementations that provide bandwidth of 1,000 Mbps ( 1 Gbps ) or greater </li></ul><ul><li>Existing network infrastructure of cables and switches does not necessary has to be completely replaced </li></ul>Ch 9 - <ul><ul><li>some of the equipment and cabling in modern, well-designed and installed networks may be capable of working at higher speeds with only minimal upgrading </li></ul></ul><ul><ul><li>reduces the total cost of ownership of the network </li></ul></ul>
    15. 15. Ethernet Beyond the LAN <ul><li>The increase cabling distance enabled by the use of fiber-optic cable in Ethernet-based networks has resulted in a larger geographic area coverage </li></ul><ul><li>Ethernet was initially limited to LAN systems within single buildings, and then extended to between buildings </li></ul><ul><li>It can now apply across a city and is called Metropolitan Area Network (MAN) </li></ul>Ch 9 -
    16. 16. Ethernet Frame <ul><li>The most significant difference between the original IEEE 802.3 and the revised IEEE 802.3 is the addition of a Start of Frame Delimiter (SFD) field </li></ul><ul><li>A small change to the Type field to include the Length </li></ul>Ch 9 - revised original
    17. 17. Ethernet Frame Size <ul><li>An Ethernet frame size includes the Destination MAC Address, Source MAC Address, Length/Type, Data and FCS fields </li></ul><ul><ul><li>the Preamble and Start of Frame delimiter fields are not included when describing the frame size </li></ul></ul><ul><li>The minimum frame size is 64 bytes (or octets)  6+6+2+46+4 </li></ul><ul><li>The maximum frame size is 1518 bytes  6+6+2+1500+4 </li></ul><ul><li>The receiving device drops the frame if frame size is less than 64 bytes or more than 1518 bytes </li></ul><ul><li>The IEEE 802.3ac standard, released in 1998, extended the maximum frame size to 1522 bytes </li></ul><ul><ul><li>increased to accommodate a technology called virtual LAN (VLAN) </li></ul></ul><ul><ul><li>VLAN tagging </li></ul></ul>Ch 9 -
    18. 18. Ethernet Frame Fields <ul><li>Preamble and Start of Frame Delimiter (SFD) </li></ul><ul><ul><li>used for synchronization between the sending and receiving devices </li></ul></ul><ul><ul><li>the Preamble (10101010) is used to get the attention of the receiving node </li></ul></ul><ul><ul><li>the SFD (10101011) marks the end of the timing information and announces that the MAC frame follows immediately </li></ul></ul><ul><li>Destination MAC Address </li></ul><ul><ul><li>identifies the intended recipient </li></ul></ul><ul><ul><li>48-bit Layer 2 address </li></ul></ul><ul><li>Source MAC Address </li></ul><ul><ul><li>identifies the frame’s originating NIC or interface </li></ul></ul><ul><ul><li>48-bit Layer 2 address </li></ul></ul><ul><ul><li>switches use this address to build the lookup tables (or MAC tables) </li></ul></ul>Ch 9 -
    19. 19. Ethernet Frame Fields (cont’d) <ul><li>Length/Type </li></ul><ul><ul><li>if the two-octet field is equal to or greater than 0x0600 hexadecimal (1536 decimal), it is a Type field specifying the upper-layer protocol to receive the data </li></ul></ul><ul><ul><li>if the two-octet field is less than 0x0600, the Length field indicates the number of bytes of data that follows </li></ul></ul><ul><li>Data and Pad </li></ul><ul><ul><li>carries the payload for the Layer 3 packet </li></ul></ul><ul><ul><li>minimum size of 46 bytes </li></ul></ul><ul><ul><li>a PAD (or filler) is added if the payload is less than 46 bytes to maintain a minimum frame size of 64 bytes </li></ul></ul>Ch 9 -
    20. 20. Frame Check Sequence (FCS) <ul><li>The FCS field is used to detect errors in a frame </li></ul><ul><li>Contains a cyclic redundancy check (CRC) which is generated by the source device </li></ul><ul><li>The CRC is based on the destination address, source address, length/type and data fields </li></ul><ul><li>The receiving device recalculates the CRC based on the contents of the received frame </li></ul><ul><ul><li>no error if the CRCs match </li></ul></ul>Ch 9 -
    21. 21. Ethernet MAC Address <ul><li>A unique identifier called a Media Access Control ( MAC ) address is used to identify each device on a shared-media network </li></ul><ul><ul><li>MAC addressing is added as part of a Layer 2 PDU </li></ul></ul><ul><ul><li>the Ethernet MAC address is a 48-bit value expressed as 12 hexadecimal digit format, e.g. 00-60-2F-3A-07-BC, 00:60:2F:3A:07:BC or 0060:2F3A:07BC </li></ul></ul><ul><ul><li>MAC address is burned into ROM </li></ul></ul>Ch 9 -
    22. 22. MAC Address Structure <ul><li>All MAC addresses contain the vendor’s assigned OUI in the first 3 bytes </li></ul><ul><li>All MAC addresses with the same OUI must be assigned a unique number, such as a code or serial number, in the last 3 bytes </li></ul>Ch 9 -
    23. 23. Hexadecimal Numbering System <ul><li>Hexadecimal is a base sixteen system </li></ul><ul><ul><li>uses the numbers 0 to 9 and the letters A to F </li></ul></ul><ul><li>Each hexadecimal digit is made up of 4 bits </li></ul><ul><ul><li>8421 binary code </li></ul></ul>Ch 9 - <ul><li>Easier to convert the decimal value to binary and then convert the binary value to hexadecimal </li></ul>
    24. 24. Viewing The MAC Address <ul><li>The ipconfig /all command can be used to display the NIC physical address </li></ul><ul><ul><li>the physical address is also known as the hardware address or MAC address </li></ul></ul><ul><ul><li>the physical address is non-hierarchical </li></ul></ul>Ch 9 -
    25. 25. Physical and Logical Addressing <ul><li>Layer 2 physical addressing is used to transport frames across the local media </li></ul><ul><li>Layer 3 addresses provide the logical addressing that is used to communicate between networks </li></ul>Ch 9 -
    26. 26. *Unicast MAC Address <ul><li>A unicast MAC address is the unique address used when a frame is sent from a single transmitting device to a single destination device </li></ul>Ch 9 -
    27. 27. *Broadcast MAC Address <ul><li>The frame contains a destination MAC address with 48 ones (1s) </li></ul><ul><ul><li>FF-FF-FF-FF-FF-FF </li></ul></ul><ul><li>The packet contains a destination IP address that has all 1s in the host portion </li></ul>Ch 9 -
    28. 28. *Multicast MAC Address <ul><li>The multicast MAC address is a special value that begins with 01-00-5E in hexadecimal </li></ul><ul><li>The value ends by converting the lower 23 bit of the IP multicast group address into the remaining 6 hexadecimal characters </li></ul><ul><ul><li>the remaining bit in the MAC address is always a 0 </li></ul></ul>Ch 9 -
    29. 29. Shared-Media Access <ul><li>If more than one device transmits simultaneously, the physical signals collide </li></ul><ul><li>Ethernet uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD) to detect and handle collisions and manage the resumption of communications </li></ul><ul><ul><li>detect the electrical activity on the cable </li></ul></ul><ul><ul><li>when a device detects that no other computer is sending a frame, it will transmit if it has something to send </li></ul></ul><ul><ul><li>if there is a collision, it is detected and frames are retransmitted </li></ul></ul>Ch 9 -
    30. 30. CSMA/CD <ul><li>Carrier sense </li></ul><ul><ul><li>all devices must listen before transmitting </li></ul></ul><ul><ul><li>if a device detects a signal, it will wait for a specified amount of time before attempting to transmit </li></ul></ul><ul><ul><li>when there is no traffic detected, the device will transmit is message </li></ul></ul><ul><ul><li>the transmitting device continues to listen for any collision </li></ul></ul><ul><li>Multiple access </li></ul><ul><ul><li>more than one device can be listening and waiting to transmit at a time </li></ul></ul><ul><ul><li>a device’s signals may not be detected by another device due to latency , and a second device may start to transmit </li></ul></ul><ul><ul><li>the media has two devices transmitting their signals at the same time </li></ul></ul>Ch 9 -
    31. 31. CSMA/CD (cont’d) <ul><li>Collision detection </li></ul><ul><ul><li>once a collision occurs, all devices will detect an increase in the signal amplitude above the normal level </li></ul></ul><ul><ul><li>once a collision is detected , the device transmitting will continue to transmit to ensure all the devices on the network detect the collision </li></ul></ul><ul><li>Jam signal and random backoff </li></ul><ul><ul><li>after detecting a collision, the transmitting devices will send out a 32-bit jam signal to notify all devices of a collision </li></ul></ul><ul><ul><li>all the devices will invoke a backoff algorithm to stop transmitting for a random amount of time </li></ul></ul>Ch 9 -
    32. 32. Hubs and Collision Domains <ul><li>Hubs retransmit received signals to all connected devices </li></ul><ul><li>Hubs do not direct data traffic based on addresses </li></ul><ul><li>Hubs extend the distance that Ethernet cables can reach </li></ul><ul><li>Hubs operate at the Physical layer, dealing with signals on the media </li></ul><ul><li>Using hubs to provide network access to more users reduces the performance for each user </li></ul><ul><ul><li>fixed capacity of the cable is now shared between more devices </li></ul></ul><ul><ul><li>only one device can send data at any one time </li></ul></ul><ul><ul><li>the probability of a collision now increases </li></ul></ul><ul><li>The connected devices that access a common media, via a hub or a series of connected hub, make up a collision domain </li></ul>Ch 9 -
    33. 33. Hubs and Collision Domains (cont’d) <ul><li>The interconnection of hubs form a physical topology called an extended star </li></ul><ul><li>The extended star creates a greatly expanded collision domain </li></ul>Ch 9 -
    34. 34. Latency <ul><li>The electrical signal that is transmitted takes a certain amount of time (latency or delay) to propagate (travel) down the cable </li></ul><ul><li>Each hub or repeater in the signal’s path adds latency </li></ul><ul><ul><li>this accumulated delay increases the probability of collisions </li></ul></ul><ul><ul><li>a listening node may start transmitting signals because another signal has not reached this node while it was listening </li></ul></ul>Ch 9 -
    35. 35. Timing and Synchronization <ul><li>In a half-duplex mode, a sending device transmits 64 bits of timing and synchronization information </li></ul><ul><li>Ethernet with throughput speeds of 10 Mbps and slower are asynchronous </li></ul><ul><ul><li>asynchronous communication in this context means that the receiving device will use the 8 bytes of timing information for synchronization </li></ul></ul><ul><li>Ethernet implementations with throughput of 100 Mbps and higher are synchronous </li></ul><ul><ul><li>synchronous communications in this context means that timing information is not required </li></ul></ul><ul><ul><li>Preamble and Start of Frame Delimiter fields are present for compatibility reasons </li></ul></ul>Ch 9 -
    36. 36. Bit Time <ul><li>The period of time required for a bit to be placed and sensed on the media is known as the bit time </li></ul><ul><li>The time taken to transmit one bit </li></ul>Ch 9 -
    37. 37. Slot Time <ul><li>Ensures that if a collision is going to occur, it will be detected within the first 512 bits (or the minimum frame size of 64 bytes) </li></ul><ul><li>Establishes a limit on the maximum size of a network’s segment </li></ul>Ch 9 -
    38. 38. Interframe Spacing <ul><li>The minimum spacing between two non-colliding frames </li></ul><ul><ul><li>the time is measured from the last bit of one frame to the first bit of the next frame </li></ul></ul><ul><li>After a frame has been sent, all devices on a 10 Mbps Ethernet are required to wait a minimum of 96 bit times (9.6 microseconds) before any device can transmit its next frame </li></ul>Ch 9 -
    39. 39. Jam Signal <ul><li>As soon as a collision is detected, the sending devices transmit a 32-bit jam signal </li></ul><ul><ul><li>repeating 10101010 pattern similar to the Preamble </li></ul></ul>Ch 9 -
    40. 40. Backoff Timing <ul><li>Each device waits for a random period of time before retransmitting </li></ul><ul><ul><li>prevents two devices to transmit again at the same time </li></ul></ul><ul><ul><li>uses a binary exponential backoff algorithm </li></ul></ul><ul><li>The frame is discarded after 16 unsuccessful attempts to retransmit </li></ul><ul><ul><li>device generates an error message to the Network layer </li></ul></ul>Ch 9 -
    41. 41. IEEE 802.3 Standards <ul><li>Four data rates are currently defined for operation over optical fiber and twisted-pair cables </li></ul><ul><ul><li>10 Mbps – Ethernet </li></ul></ul><ul><ul><li>100 Mbps – Fast Ethernet </li></ul></ul><ul><ul><li>1000 Mbps – Gigabit Ethernet </li></ul></ul><ul><ul><li>10 Gbps – 10 Gigabit Ethernet </li></ul></ul><ul><li>The difference between standard Ethernet, Fast Ethernet, Gigabit Ethernet and 10 Gigabit Ethernet occur at the Physical layer, often referred to as Ethernet PHY </li></ul>Ch 9 -
    42. 42. *Types of Ethernet Ch 9 - Ethernet Type Bandwidth Cable Type Duplex Maximum Distance 10Base5 10 Mbps Thicknet Coaxial Half 500 m 10Base2 10 Mbps Thinnet Coaxial Half 185 m 10Base-T 10 Mbps Cat 3/Cat 5 UTP Half 100 m 100Base-TX 100 Mbps Cat 5 UTP Half 100 m 100Base-TX 200 Mbps Cat 5 UTP Full 100 m 100Base-FX 100 Mbps Multimode Fiber Half 400 m 100Base-FX 200 Mbps Multimode Fiber Full 2 km 1000Base-T 1 Gbps Cat 5e UTP Full 100 m 1000Base-SX 1 Gbps Multimode Fiber Full 550 m 1000Base-LX 1 Gbps Multimode Fiber Full 5 km 1000Base-CX 1 Gbps Shielded Copper Full 25 m 10GBase-T 10 Gbps Cat 6a/Cat 7 UTP Full 100m 10GBase-CX4 10 Gbps Twin-axial Full 15m 10GBase-LX4 10 Gbps Multimode Fiber Full 300 m 10GBase-LX4 10 Gbps Single-mode Fiber Full 10 km
    43. 43. 10 Mbps Ethernet <ul><li>10Base-T uses Manchester encoding over two pairs of UTP wires </li></ul><ul><li>The early implementations of 10Base-T used Cat 3 UTP cables </li></ul><ul><ul><li>Cat 3 cables are no longer used in new installations </li></ul></ul><ul><ul><li>Cat 5 UTP cables or better, such as Cat 5e or 6, are used today </li></ul></ul><ul><li>The maximum cable length of 10Base-T networks is 100 meters before requiring a hub or repeater </li></ul><ul><li>10Base-T uses two pairs of a four-pair cable and is terminated at each end with an 8-pin RJ-45 connector </li></ul><ul><ul><li>pins 1 and 2 are used for transmitting </li></ul></ul><ul><ul><li>pins 3 and 6 are used for receiving </li></ul></ul><ul><li>10Base-T or legacy Ethernet uses a physical star topology </li></ul><ul><ul><li>can support either half-duplex or full-duplex operation when used with a switch </li></ul></ul>Ch 9 -
    44. 44. RJ-45 Pin Assignments Ch 9 -
    45. 45. 100 Mbps Ethernet <ul><li>100 Mbps Ethernet (IEEE 802.3u) or Fast Ethernet can be implemented using twisted-pair copper wire or fiber optic media </li></ul><ul><ul><li>100Base-TX uses Cat 5 or better UTP </li></ul></ul><ul><ul><li>100Base-FX uses fiber-optic cable </li></ul></ul><ul><li>Higher frequency signals used in Fast Ethernet are more susceptible to noise </li></ul><ul><li>Two separate encoding steps are used to enhance signal integrity </li></ul><ul><ul><li>4B/5B binary encoding </li></ul></ul><ul><ul><li>actual line encoding specific to copper or fiber </li></ul></ul>Ch 9 -
    46. 46. 100Base-TX <ul><li>Supports transmission over two pairs of Cat 5 UTP copper wires </li></ul><ul><li>Uses the same two pairs and pinouts of UTP as 10Base-T </li></ul><ul><li>A segment length of up to 100 meters </li></ul><ul><li>Uses 4B/5B binary encoding which is scrambled and converted to MLT-3 line encoding </li></ul><ul><li>100Base-TX uses a physical star topology as 10Base-T </li></ul><ul><ul><li>a switch is used at the center of the star instead of a hub </li></ul></ul>Ch 9 -
    47. 47. 100Base-FX <ul><li>Uses a pair of optic fiber media </li></ul><ul><ul><li>most suitable for connections between floors and buildings, and also in high-noise environment </li></ul></ul><ul><ul><li>uses SC connectors </li></ul></ul><ul><li>Uses 4B/5B binary encoding with NRZI line encoding </li></ul>Ch 9 -
    48. 48. 1000 Mbps Ethernet <ul><li>1000 Mbps Ethernet is also known as Gigabit Ethernet </li></ul><ul><li>Gigabit Ethernet frame has the same format as 10 Mbps and 100 Mbps Ethernet </li></ul><ul><li>1000Base-T standard is specified in IEEE 802.3ab </li></ul><ul><ul><li>uses Cat 5e or better UTP cables </li></ul></ul><ul><li>1000Base-X standard, IEEE802.3z, specifies 1 Gbps full-duplex transmission over optical fiber </li></ul><ul><ul><li>1000Base-SX and 1000Base-LX </li></ul></ul>Ch 9 -
    49. 49. Hubs <ul><li>Legacy Ethernet uses hubs to interconnect nodes on the LAN segment </li></ul><ul><li>In a hub network the bandwidth is shared by the number of devices </li></ul><ul><li>Latency can increase significantly as the number of hubs connected to a segment increases </li></ul><ul><li>If any device connected to the hub generates detrimental traffic, the communication for all devices could be impeded </li></ul>Ch 9 - <ul><li>A network with a large number of nodes on the same segment has a larger collision domain and more traffic </li></ul>
    50. 50. *Switches <ul><li>Switches allow the segmentation of the LAN into separate collision domains (CD) </li></ul><ul><li>Each port represents a separate collision domain and provides the full media bandwidth to the node </li></ul>Ch 9 - 1 CD 1 CD
    51. 51. Benefits of Switch-based LANs <ul><li>Dedicated bandwidth to each port </li></ul><ul><ul><li>each device effectively has a point-to-point connection between the device and the switch </li></ul></ul><ul><li>Collision-free environment </li></ul><ul><ul><li>a dedicated point-to-point connection to a switch also removes any media contention between devices </li></ul></ul><ul><ul><li>overhead devoted to collision recovery is virtually eliminated </li></ul></ul><ul><ul><li>significantly better throughput rates </li></ul></ul><ul><li>Full-duplex operation </li></ul><ul><ul><li>switching allows a network to operate as a full-duplex Ethernet environment </li></ul></ul><ul><ul><li>switch ports can transmit and receive simultaneously at the full media bandwidth </li></ul></ul>Ch 9 -
    52. 52. Selective Forwarding <ul><li>Establishing a momentary point-to-point connection between each transmitting and receiving nodes </li></ul><ul><ul><li>the two nodes have a full bandwidth connection between them </li></ul></ul><ul><ul><li>examines the destination MAC address and forwards the frame out the appropriate port </li></ul></ul>Ch 9 -
    53. 53. Selective Forwarding (cont’d) <ul><li>The switch maintains a table called a MAC table or switch table </li></ul><ul><ul><li>reads the source MAC address of each data frame that is transmitted and noting the port where the frame entered the switch </li></ul></ul><ul><li>The destination MAC address in the frame header is compared to the list of addresses in the table for a match </li></ul>Ch 9 -
    54. 54. Store and Forward <ul><li>Switch will buffer an incoming frame and then forward it to the proper port when that port is idle </li></ul><ul><li>Switch receives the entire frame , checks the FCS for errors and forwards the frame to the appropriate port for the destination node </li></ul><ul><li>The nodes do not have to wait for the media to be idle </li></ul><ul><ul><li>nodes can send and receive at full media speed without losses due to collisions or the overhead associated with managing collisions </li></ul></ul><ul><li>The frame is forwarded based on the destination MAC address in the frame header </li></ul><ul><ul><li>it is compared to the list of addresses in the MAC table </li></ul></ul>Ch 9 -
    55. 55. Switch Operation – Learning and Aging <ul><li>The learning process maps the MAC address with the corresponding ports dynamically acquired during normal operation </li></ul><ul><li>As each frame enters the switch port, it examines the source MAC address </li></ul><ul><li>The learned entries in the MAC table are time-stamped </li></ul><ul><ul><li>removes entries that have not been used for a specified period of time </li></ul></ul>Ch 9 -
    56. 56. Switch Operation – Flooding <ul><li>The switch sends the frame to all ports except the port on which the frame arrived if the destination address is not in the MAC table </li></ul>Ch 9 -
    57. 57. Switch Operation – Forwarding <ul><li>The switch sends the frame to the destination node </li></ul><ul><ul><li>examines the frame’s destination MAC address </li></ul></ul><ul><ul><li>looks for a match in the MAC table </li></ul></ul><ul><ul><li>forwards the frame to corresponding port </li></ul></ul>Ch 9 -
    58. 58. Switch Operation – Filtering <ul><li>The frame is not forwarded </li></ul><ul><li>A switch does not forward a frame to the same port on which it arrived </li></ul><ul><li>The frame is dropped if the FCS is bad </li></ul><ul><li>Security settings for blocking frames to selective MAC addresses or specific ports </li></ul>Ch 9 -
    59. 59. Address Resolution Protocol (ARP) <ul><li>The ARP protocol provides two basic functions </li></ul><ul><ul><li>resolving IPv4 addresses to MAC addresses </li></ul></ul><ul><ul><li>maintaining a cache of mappings </li></ul></ul><ul><li>The node refers to an ARP table in its memory </li></ul><ul><ul><li>finds the Data Link layer address that is mapped to the destination IPv4 address </li></ul></ul>Ch 9 - <ul><ul><li>if this map is cached in the table, the node uses the MAC address </li></ul></ul><ul><ul><li>otherwise the node will send a broadcast ARP request to the other devices </li></ul></ul>
    60. 60. ARP (cont’d) <ul><li>The ARP table or cache is maintained dynamically </li></ul><ul><ul><li>record the source IP address and MAC address as a mapping in the ARP table when the node receives a frame </li></ul></ul><ul><ul><li>broadcast an ARP request </li></ul></ul><ul><li>The dynamic entries in the ARP table are time-stamped </li></ul><ul><li>Static map entries can be entered into the ARP table </li></ul>Ch 9 - <ul><ul><li>rarely done </li></ul></ul><ul><ul><li>static entries do not expire and must be manually removed </li></ul></ul>
    61. 61. *ARP Process Ch 9 -
    62. 62. Destinations Outside the Local Network <ul><li>The source node will use the MAC address of the gateway as the destination MAC address for frames containing an IP address on other networks </li></ul><ul><li>The source uses the ARP process to determine the MAC address for the router interface (or gateway ) </li></ul><ul><ul><li>broadcasts an ARP request to retrieve the gateway MAC address </li></ul></ul>Ch 9 -
    63. 63. Segmentation with Switch Ch 9 - How many collision domain?
    64. 64. Segmentation with Switch Ch 9 - How many collision domain?
    65. 65. Pls Copy this Table to your Notebook Ch 9 -
    66. 66. Destinations Outside the Local Network (cont’d) <ul><li>The gateway responds with an ARP reply telling the source node its MAC address </li></ul><ul><li>The source node creates a map in the ARP table </li></ul>Ch 9 -
    67. 67. Proxy ARP <ul><li>Proxy ARP is a technique by which a network device answers to ARP requests for an IP address that it does not have configured on the receiving interface </li></ul><ul><li>Proxy ARP can help host devices reach remote subnets without the need to configure routing or a default network </li></ul>Ch 9 -
    68. 68. Removing Address Mappings <ul><li>An ARP cache timer removes ARP entries that have not been used for a specified period of time </li></ul><ul><ul><li>if the entry is used again, the ARP timer is refreshed or extended </li></ul></ul><ul><li>The entry can be removed manually </li></ul>Ch 9 -
    69. 69. ARP Broadcast <ul><li>Overhead on the media </li></ul><ul><ul><li>a broadcast ARP request is received and processed by every device on the network </li></ul></ul><ul><ul><li>floods the local media which may cause some reduction in performance </li></ul></ul><ul><li>Security </li></ul><ul><ul><li>can lead to a potential security risk </li></ul></ul><ul><ul><li>ARP spoofing, or ARP poisoning, is a technique used by an attacker to inject a wrong MAC address association into a network by issuing fake ARP requests </li></ul></ul>Ch 9 -

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