《计算机网络 Computer Networking》课程PPT教学课件（A Top Down Approach，8th edition）Chapter 6 Link Layer and LANs

Chapter 6 James F.Kurose Keith W.Ross The Link Layer and LANs A note on the use of these PowerPoint slides: We're making these slides freely available to all(faculty,students, readers).They're in PowerPoint form so you see the animations;and can add,modify,and delete slides (including this one)and slide content to suit your needs.They obviously represent a lot of work on our part. COMPUTER In return for use,we only ask the following: NETWORKING If you use these slides(e.g.,in a class)that you mention their A TOP-DOWN APPROACH source(after all,we'd like people to use our book!) ththtdtion If you postany slides on a www site,that you note that they are adapted from (or perhaps identical to)our slides,and note our copyright of this material. Computer Networking:A For a revision history,see the slide note for this page. Top-Down Approach Thanks and enjoy!JFK/KWR 8th edition All material copyright 1996-2020 Jim Kurose,Keith Ross J.F Kurose and K.W.Ross,All Rights Reserved Pearson,2020

Computer Networking: A Top-Down Approach 8 th edition Jim Kurose, Keith Ross Pearson, 2020 Chapter 6 The Link Layer and LANs A note on the use of these PowerPoint slides: We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: ▪ If you use these slides (e.g., in a class) that you mention their source (after all, we’d like people to use our book!) ▪ If you post any slides on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. For a revision history, see the slide note for this page. Thanks and enjoy! JFK/KWR All material copyright 1996-2020 J.F Kurose and K.W. Ross, All Rights Reserved

Link layer and LANs:our goals -understand principles instantiation,implementation behind link layer services: of various link layer error detection,correction technologies sharing a broadcast channel: multiple access link layer addressing ·local area networks: Ethernet,VLANs ■datacenter networks LinkLayer:6-2

Link layer and LANs: our goals ▪understand principles behind link layer services: • error detection, correction • sharing a broadcast channel: multiple access • link layer addressing • local area networks: Ethernet, VLANs ▪datacenter networks ▪ instantiation, implementation of various link layer technologies Link Layer: 6-2

Link layer,LANs:roadmap -introduction error detection,correction multiple access protocols ■LANs ·addressing,.ARP ·Ethernet ·switches ·VLANs a day in the life of a web link virtualization:MPLS request data center networking LinkLayer:6-3

Link layer, LANs: roadmap ▪ a day in the life of a web request ▪ introduction ▪ error detection, correction ▪ multiple access protocols ▪ LANs • addressing, ARP • Ethernet • switches • VLANs ▪ link virtualization: MPLS ▪ data center networking Link Layer: 6-3

Link layer:introduction terminology: mobile network hosts and routers:nodes national or global ISP communication channels that connect adjacent nodes along communication path:links ·wired ·wireless ·LANS layer-2 packet:frame, datacente encapsulates datagram link layer has responsibility of transferring datagram from one node enterprise to physically adjacent node over a link network LinkLayer:6-4

Link layer: introduction terminology: ▪ hosts and routers: nodes ▪ communication channels that connect adjacent nodes along communication path: links • wired • wireless • LANs ▪ layer-2 packet: frame, encapsulates datagram mobile network enterprise network national or global ISP datacenter network link layer has responsibility of transferring datagram from one node to physically adjacent node over a link Link Layer: 6-4

Link layer:context datagram transferred by transportation analogy: different link protocols over trip from Princeton to Lausanne different links: limo:Princeton to JFK e.g.,WiFi on first link,Ethernet ·plane:JFK to Geneva on next link train:Geneva to Lausanne each link protocol provides ■tourist=datagram different services transport segment= e.g.,may or may not provide communication link reliable data transfer over link "transportation mode link-layer protocol travel agent routing algorithm LinkLayer:6-5

Link layer: context ▪ datagram transferred by different link protocols over different links: • e.g., WiFi on first link, Ethernet on next link ▪ each link protocol provides different services • e.g., may or may not provide reliable data transfer over link transportation analogy: ▪ trip from Princeton to Lausanne • limo: Princeton to JFK • plane: JFK to Geneva • train: Geneva to Lausanne ▪ tourist = datagram ▪ transport segment = communication link ▪ transportation mode = link-layer protocol ▪ travel agent = routing algorithm Link Layer: 6-5

Link layer:services framing,link access: encapsulate datagram into frame,adding header,trailer channel access if shared medium "MAC"addresses in frame headers identify source,destination(different from IP address!) reliable delivery between adjacent nodes we already know how to do this! seldom used on low bit-error links wireless links:high error rates Q:why both link-level and end-end reliability? LinkLayer:6-6

Link layer: services ▪ framing, link access: • encapsulate datagram into frame, adding header, trailer • channel access if shared medium • “MAC” addresses in frame headers identify source, destination (different from IP address!) ▪ reliable delivery between adjacent nodes • we already know how to do this! • seldom used on low bit-error links • wireless links: high error rates • Q: why both link-level and end-end reliability? … … Link Layer: 6-6

Link layer:services(more) ■flow control:: pacing between adjacent sending and receiving nodes error detection: errors caused by signal attenuation,noise. receiver detects errors,signals retransmission,or drops frame error correction: receiver identifies and corrects bit error(s) without retransmission half-duplex and full-duplex: with half duplex,nodes at both ends of link can transmit,but not at same time LinkLayer:6-7

Link layer: services (more) ▪ flow control: • pacing between adjacent sending and receiving nodes ▪ error detection: • errors caused by signal attenuation, noise. • receiver detects errors, signals retransmission, or drops frame ▪ error correction: • receiver identifies and corrects bit error(s) without retransmission ▪ half-duplex and full-duplex: • with half duplex, nodes at both ends of link can transmit, but not at same time … … Link Layer: 6-7

Where is the link layer implemented? in each-and-every host -link layer implemented in network interface card (NIC)or on a chip application transport Ethernet,WiFi card or chip network cpu emory link implements link,physical layer host bus (e.g.,PCI) attaches into host's system link physical buses combination of hardware, network interface software,firmware LinkLayer:6-8

Where is the link layer implemented? ▪ in each-and-every host ▪ link layer implemented in network interface card (NIC) or on a chip • Ethernet, WiFi card or chip • implements link, physical layer ▪ attaches into host’s system buses ▪ combination of hardware, software, firmware controller physical cpu memory host bus (e.g., PCI) network interface application transport network link link physical Link Layer: 6-8

Interfaces communicating application application transport transport datagram hetwork cpu memory network link link linkhdatagram link datagram link physical physical physica sending side: receiving side: encapsulates datagram in frame looks for errors,reliable data adds error checking bits,reliable data transfer,flow control,etc. transfer,flow control,etc. extracts datagram,passes to upper layer at receiving side LinkLayer:6-9

controller physical memory CPU Interfaces communicating controller physical cpu memory application transport network link link physical application transport network link link physical sending side: ▪ encapsulates datagram in frame ▪ adds error checking bits, reliable data transfer, flow control, etc. receiving side: ▪ looks for errors, reliable data transfer, flow control, etc. ▪ extracts datagram, passes to upper layer at receiving side linkh link datagram datagram datagram Link Layer: 6-9

Link layer,LANs:roadmap ■introduction -error detection,correction multiple access protocols ■LANS ·addressing,ARP ·Ethernet 。switches ·VLANs a day in the life of a web link virtualization:MPLS request data center networking Link Layer:6-10

Link layer, LANs: roadmap ▪ a day in the life of a web request ▪ introduction ▪ error detection, correction ▪ multiple access protocols ▪ LANs • addressing, ARP • Ethernet • switches • VLANs ▪ link virtualization: MPLS ▪ data center networking Link Layer: 6-10