Chapter5 - 5: DataLink Layer 5-1 Chapter 5 Link Layer and...

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Unformatted text preview: 5: DataLink Layer 5-1 Chapter 5 Link Layer and LANs This set of slides is extended from the textbook PowerPoint slides by Jim Kurose & Keith Ross. 5: DataLink Layer 5-2 Chapter 5: The Data Link Layer Our goals: understand principles behind data link layer services: error detection, correction sharing a broadcast channel: multiple access link layer addressing reliable data transfer, flow control: done! 5: DataLink Layer 5-3 Link Layer 5.1 Introduction and services 5.2 Error detection and correction 5.3Multiple access protocols 5.4 Link-Layer Addressing 5.5 Ethernet 5.6 Hubs and switches 5.7 PPP 5: DataLink Layer 5-4 Link Layer: Introduction Some terminology: hosts and routers are nodes communication channels that connect adjacent nodes along communication path are links wired links wireless links LANs layer-2 packet is a frame , encapsulates datagram link data-link layer has responsibility of transferring datagram from one node to adjacent node over a link 5: DataLink Layer 5-5 Link layer: context Datagram transferred by different link protocols over different links: e.g., Ethernet on first link, frame relay on intermediate links, 802.11 on last link Each link protocol provides different services e.g., may or may not provide rdt over link 5: DataLink Layer 5-6 Link Layer Services Framing, link access: encapsulate datagram into frame, adding header, trailer channel access if shared medium MAC addresses used in frame headers to identify source, dest different from IP address! Reliable delivery between adjacent nodes we learned how to do this already (chapter 3)! seldom used on low bit error link (fiber, some twisted pair) wireless links: high error rates 5: DataLink Layer 5-7 Link Layer Services (more) Flow Control: pacing between adjacent sending and receiving nodes Error Detection: errors caused by signal attenuation, noise. receiver detects presence of errors: signals sender for retransmission or drops frame Error Correction: receiver identifies and corrects bit error(s) without resorting to retransmission Half-duplex and full-duplex with half duplex, nodes at both ends of link can transmit, but not at same time 5: DataLink Layer 5-8 Adaptors Communicating link layer implemented in adaptor (aka NIC) Ethernet card, PCMCI card, 802.11 card sending side: encapsulates datagram in a frame adds error checking bits, rdt, flow control, etc. receiving side looks for errors, rdt, flow control, etc extracts datagram, passes to rcving node link & physical layers sending node frame rcving node datagram frame adapter adapter link layer protocol 5: DataLink Layer 5-9 Link Layer 5.1 Introduction and services 5.2 Error detection and correction 5.3Multiple access protocols 5.4 Link-Layer Addressing 5.5 Ethernet 5.6 Hubs and switches 5.7 PPP 5: DataLink Layer...
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Chapter5 - 5: DataLink Layer 5-1 Chapter 5 Link Layer and...

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