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Data Link LayerData Link LayerLecture 17Lecture 17
Imran AhmedImran AhmedUniversity of Management & TechnologyUniversity of Management & Technology
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Agenda
• Introduction & services
• Error detection and correction
• Multiple access protocols
• LAN addresses and ARP
• Ethernet
• Hubs, bridges and switches
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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
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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
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Agenda
• Introduction & services
• Error detection and correction
• Multiple access protocols
• LAN addresses and ARP
• Ethernet
• Hubs, bridges and switches
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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.
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LAN Addresses & ARP
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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
223.1.1.2
223.1.1.3
223.1.1.4 223.1.2.9
223.1.2.2
223.1.2.1
223.1.3.2223.1.3.1
223.1.3.27
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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.)
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Agenda
• Introduction & services
• Error detection and correction
• Multiple access protocols
• LAN addresses and ARP
• Ethernet
• Hubs, bridges and switches
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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.
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OSI Model and Project 802
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Project 802• The IEEE has subdivided the data link layer into
two sub-layers:– Logical Link Control (LLC)
– Medium Access Control (MAC)
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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)
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Project 802
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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.
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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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