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Data Link Layer Lecture 17 Imran Ahmed University of Management & Technology

Data Link Layer Lecture 17 Imran Ahmed University of Management & Technology. Agenda. Introduction & services Error detection and correction Multiple access protocols LAN addresses and ARP Ethernet Hubs, bridges and switches. Multiple Access Links & Protocols. Two types of “links”:

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Data Link Layer Lecture 17 Imran Ahmed University of Management & Technology

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  1. Data Link Layer Lecture 17 Imran Ahmed University of Management & Technology

  2. Agenda • Introduction & services • Error detection and correction • Multiple access protocols • LAN addresses and ARP • Ethernet • Hubs, bridges and switches

  3. Multiple Access Links & Protocols Two types of “links”: • Point-to-point:- • PPP for dial-up access • Point-to-point link between Ethernet switch and host • Broadcast:- • Traditional Ethernet • 802.11 wireless LAN

  4. Multiple Access Links & Protocols • MAC protocols: • Channel partitioning • Time division, Code division, Frequency division • Random partitioning • ALOHA, S-ALOHA, CSMA, CSMA/CD • Taking turns • Token passing

  5. Agenda • Introduction & services • Error detection and correction • Multiple access protocols • LAN addresses and ARP • Ethernet • Hubs, bridges and switches

  6. LAN Addresses & ARP • LAN (or MAC or physical or Ethernet) address: • It is used to get datagram from one interface to another physically-connected interface (same network). • 48 – bit MAC address; burned in the adapter ROM.

  7. LAN Addresses & ARP

  8. 223.1.1.2 223.1.2.2 223.1.2.1 223.1.3.2 223.1.3.1 223.1.3.27 IP Addressing • Starting at A, given IP datagram addressed to B: • Look up net. address of B, find B on same net. as A. • Link layer send datagram to B inside link-layer frame. 223.1.1.1 223.1.2.9 223.1.1.4 223.1.1.3

  9. Address Resolution Protocol • Each IP node on LAN has ARP table. • ARP Table: IP/MAC address mappings for some LAN nodes. <IP address; MAC address; TTL> • TTL: time after which address mapping will be forgotten (typically 20 min.)

  10. Agenda • Introduction & services • Error detection and correction • Multiple access protocols • LAN addresses and ARP • Ethernet • Hubs, bridges and switches

  11. Project 802 • In 1985, the Computer Society of the IEEE started a project, called Project 802, to set standards to enable intercommunication between equipment from a variety of manufacturers. • Project 802 uses the first two layers and, to a lesser extent, the network layer.

  12. OSI Model and Project 802

  13. Project 802 • The IEEE has subdivided the data link layer into two sub-layers: • Logical Link Control (LLC) • Medium Access Control (MAC)

  14. IEEE Project 802 • Each subdivision is identified by a number: • IEEE 802.1 (internetworking) • IEEE 802.2 (LLC) • IEEE 802.3 (CSMA/CD or Ethernet) • IEEE 802.4 (Token Bus) • IEEE 802.5 (Token Ring)

  15. Project 802

  16. IEEE Project 802 • IEEE 802.1: This section is devoted to internetworking issues in LANs and MANs. • Logical Link Control: IEEE 802.2 LLC is the upper sub-layer of the data link layer. It contains logical addresses, control information and data unit. • Media Access Control: MAC is the lower sub-layer of the data link layer. It contains the flag, flow and error control specification necessary to move information from one place to another.

  17. IEEE Project 802 Ethernet • IEEE 802.3 supports a LAN standard originally developed by Xerox and later extended by a joint venture between Digital Equipment Corporation, Intel Corporation and Xerox. This was called Ethernet. • IEEE 802.3 defines two categories: • Baseband • Broadband

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