mạng máy tính nâng cao nguyễn đức thái chương 5 link layer and lan sinhvienzone com

om Zo ne C Chapter Link Layer and LANs nh Vi en A note on the use of these ppt slides: Si We’re making these slides freely available to all (faculty, students, readers) They’re in PowerPoint form so you 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) in substantially unaltered form, that you mention their source (after all, we’d like people to use our book!)  If you post any slides in substantially unaltered form 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 Top Down Approach 4th edition Jim Kurose, Keith Ross Addison-Wesley, July 2007 Thanks and enjoy! JFK/KWR All material copyright 1996-2007 J.F Kurose and K.W Ross, All Rights Reserved SinhVienZone.com 5: DataLink Layer https://fb.com/sinhvienzonevn 5-1 Chapter 5: The Data Link Layer om Our goals: C  understand principles behind data link layer   Zo  error detection, correction sharing a broadcast channel: multiple access link layer addressing reliable data transfer, flow control: done! nh Vi en  ne services:  instantiation and implementation of various link Si layer technologies SinhVienZone.com 5: DataLink Layer https://fb.com/sinhvienzonevn 5-2 om Link Layer  5.1 Introduction and   C Zo ne  5.8 Link virtualization: ATM, MPLS nh Vi en   5.7 PPP Si  services 5.2 Error detection and correction 5.3Multiple access protocols 5.4 Link-layer Addressing 5.5 Ethernet  5.6 Link-layer switches SinhVienZone.com 5: DataLink Layer https://fb.com/sinhvienzonevn 5-3 Link Layer: Introduction om Some terminology:  hosts and routers are nodes   ne wired links wireless links LANs nh Vi en  Zo connect adjacent nodes along communication path are links C  communication channels that  layer-2 packet is a frame, Si encapsulates datagram data-link layer has responsibility of transferring datagram from one node to adjacent node over a link SinhVienZone.com 5: DataLink Layer https://fb.com/sinhvienzonevn 5-4 Link layer: context e.g., Ethernet on first link, frame relay on intermediate links, 802.11 on last link nh Vi en om Zo   trip from Princeton to  each link protocol provides different services e.g., may or may not provide rdt over link Si  SinhVienZone.com Lausanne  limo: Princeton to JFK  plane: JFK to Geneva  train: Geneva to Lausanne C different link protocols over different links: transportation analogy ne  datagram transferred by  tourist = datagram  transport segment = communication link  transportation mode = link layer protocol  travel agent = routing algorithm 5: DataLink Layer https://fb.com/sinhvienzonevn 5-5 Link Layer Services  reliable delivery between adjacent nodes    we learned how to this already (chapter 3)! seldom used on low bit-error link (fiber, some twisted pair) wireless links: high error rates • Q: why both link-level and end-end reliability? Si  nh Vi en Zo  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! C  om framing, link access: ne  SinhVienZone.com 5: DataLink Layer https://fb.com/sinhvienzonevn 5-6 flow control:   ne error detection: errors caused by signal attenuation, noise receiver detects presence of errors: • signals sender for retransmission or drops frame Zo  pacing between adjacent sending and receiving nodes C  nh Vi en  om Link Layer Services (more)  error correction:  receiver identifies and corrects bit error(s) without resorting to retransmission Si  half-duplex and full-duplex  with half duplex, nodes at both ends of link can transmit, but not at same time SinhVienZone.com 5: DataLink Layer https://fb.com/sinhvienzonevn 5-7 Where is the link layer implemented? om  in each and every host  Ethernet card, PCMCI card, 802.11 card implements link, physical layer nh Vi en   attaches into host’s application transport network link cpu memory controller link physical host bus (e.g., PCI) physical transmission Si system buses  combination of hardware, software, firmware host schematic ne Zo “adaptor” (aka network interface card NIC) C  link layer implemented in SinhVienZone.com network adapter card 5: DataLink Layer https://fb.com/sinhvienzonevn 5-8 om Adaptors Communicating datagram C datagram Zo nh Vi en sending host ne controller controller receiving host datagram frame Si  sending side:  encapsulates datagram in frame  adds error checking bits, rdt, flow control, etc SinhVienZone.com  receiving side  looks for errors, rdt, flow control, etc  extracts datagram, passes to upper layer at receiving side 5: DataLink Layer https://fb.com/sinhvienzonevn 5-9 om Link Layer  5.1 Introduction and   C Zo ne  5.8 Link Virtualization: ATM MPLS nh Vi en   5.7 PPP Si  services 5.2 Error detection and correction 5.3Multiple access protocols 5.4 Link-layer Addressing 5.5 Ethernet  5.6 Link-layer switches SinhVienZone.com 5: DataLink Layer https://fb.com/sinhvienzonevn 5-10 ATM Layer: Virtual Circuits nh Vi en Zo ne C om  VC transport: cells carried on VC from source to dest  call setup, teardown for each call before data can flow  each packet carries VC identifier (not destination ID)  every switch on source-dest path maintain “state” for each passing connection  link,switch resources (bandwidth, buffers) may be allocated to VC: to get circuit-like perf  Permanent VCs (PVCs) long lasting connections  typically: “permanent” route between to IP routers  Switched VCs (SVC):  dynamically set up on per-call basis Si  SinhVienZone.com 5: DataLink Layer https://fb.com/sinhvienzonevn 5-89 om ATM VCs  Advantages of ATM VC approach: QoS performance guarantee for connection mapped to VC (bandwidth, delay, delay jitter)  Drawbacks of ATM VC approach:  Inefficient support of datagram traffic  one PVC between each source/dest pair) does not scale (N*2 connections needed)  SVC introduces call setup latency, processing overhead for short lived connections Si nh Vi en Zo ne C  SinhVienZone.com 5: DataLink Layer https://fb.com/sinhvienzonevn 5-90 ATM Layer: ATM cell om  5-byte ATM cell header C  48-byte payload Why?: small payload -> short cell-creation delay for digitized voice  halfway between 32 and 64 (compromise!) nh Vi en Zo ne  Cell format Si Cell header SinhVienZone.com 5: DataLink Layer https://fb.com/sinhvienzonevn 5-91 om ATM cell header  VCI: virtual channel ID will change from link to link thru net  PT: Payload type (e.g RM cell versus data cell)  CLP: Cell Loss Priority bit  CLP = implies low priority cell, can be discarded if congestion  HEC: Header Error Checksum  cyclic redundancy check Si nh Vi en Zo ne C  SinhVienZone.com 5: DataLink Layer https://fb.com/sinhvienzonevn 5-92 om ATM Physical Layer (more) Two pieces (sublayers) of physical layer: C  Transmission Convergence Sublayer (TCS): adapts nh Vi en Zo ne ATM layer above to PMD sublayer below  Physical Medium Dependent: depends on physical medium being used Si TCS Functions:  Header checksum generation: bits CRC  Cell delineation  With “unstructured” PMD sublayer, transmission of idle cells when no data cells to send SinhVienZone.com 5: DataLink Layer https://fb.com/sinhvienzonevn 5-93 om ATM Physical Layer Physical Medium Dependent (PMD) sublayer C  SONET/SDH: transmission frame structure (like a nh Vi en Zo ne container carrying bits);  bit synchronization;  bandwidth partitions (TDM);  several speeds: OC3 = 155.52 Mbps; OC12 = 622.08 Mbps; OC48 = 2.45 Gbps, OC192 = 9.6 Gbps  TI/T3: transmission frame structure (old Si telephone hierarchy): 1.5 Mbps/ 45 Mbps  unstructured: just cells (busy/idle) SinhVienZone.com 5: DataLink Layer https://fb.com/sinhvienzonevn 5-94 .C ne Zo ATM network Si nh Vi en Classic IP only  “networks” (e.g., LAN segments)  MAC (802.3) and IP addresses IP over ATM  replace “network” (e.g., LAN segment) with ATM network  ATM addresses, IP addresses om IP-Over-ATM Ethernet LANs Ethernet LANs SinhVienZone.com 5: DataLink Layer https://fb.com/sinhvienzonevn 5-95 .C ne Zo IP AAL Eth ATM phy phy ATM phy ATM phy app transport IP AAL ATM phy Si nh Vi en app transport IP Eth phy om IP-Over-ATM SinhVienZone.com 5: DataLink Layer https://fb.com/sinhvienzonevn 5-96 Datagram Journey in IP-over-ATM Network ne C om  at Source Host:  IP layer maps between IP, ATM dest address (using ARP)  passes datagram to AAL5  AAL5 encapsulates data, segments cells, passes to ATM layer nh Vi en  at Destination Host: Zo  ATM network: moves cell along VC to destination AAL5 reassembles cells into original datagram  if CRC OK, datagram is passed to IP Si  SinhVienZone.com 5: DataLink Layer https://fb.com/sinhvienzonevn 5-97 Si SinhVienZone.com ne C ATM network Zo nh Vi en Issues:  IP datagrams into ATM AAL5 PDUs  from IP addresses to ATM addresses  just like IP addresses to 802.3 MAC addresses! om IP-Over-ATM Ethernet LANs 5: DataLink Layer https://fb.com/sinhvienzonevn 5-98 om Multiprotocol label switching (MPLS)  initial goal: speed up IP forwarding by using fixed Zo  borrowing ideas from Virtual Circuit (VC) approach but IP datagram still keeps IP address! MPLS header IP header remainder of link-layer frame Si PPP or Ethernet header nh Vi en  ne C length label (instead of IP address) to forwarding label 20 SinhVienZone.com Exp S TTL 5: DataLink Layer https://fb.com/sinhvienzonevn 5-99 om MPLS capable routers  a.k.a label-switched router C  forwards packets to outgoing interface based Zo MPLS forwarding table distinct from IP forwarding tables nh Vi en  ne only on label value (don’t inspect IP address) Si  signaling protocol needed to set up forwarding  RSVP-TE  forwarding possible along paths that IP alone would not allow (e.g., source-specific routing) !!  use MPLS for traffic engineering  must co-exist with IP-only routers SinhVienZone.com 5: DataLink Layer 5-100 https://fb.com/sinhvienzonevn A D A 0 C 10 12 out interface in label ne out label dest out label dest 10 Zo in label om MPLS forwarding tables nh Vi en 12 R6 R4 Si R5 SinhVienZone.com out label dest 6 A D 0 D R3 0 R2 in label out interface A out interface in label outR1 label dest - A A out interface 0 5: DataLink Layer 5-101 https://fb.com/sinhvienzonevn Chapter 5: Summary ne C om  principles behind data link layer services:  error detection, correction  sharing a broadcast channel: multiple access  link layer addressing Zo  instantiation and implementation of various link Si nh Vi en layer technologies  Ethernet  switched LANS  PPP  virtualized networks as a link layer: ATM, MPLS SinhVienZone.com 5: DataLink Layer 5-102 https://fb.com/sinhvienzonevn Chapter 5: let’s take a breath complete om  journey down protocol stack nh Vi en Zo ne C (except PHY)  solid understanding of networking principles, practice  … could stop here … but lots of interesting topics! wireless  multimedia  security  network management Si  SinhVienZone.com 5: DataLink Layer 5-103 https://fb.com/sinhvienzonevn ... en   5. 7 PPP Si  services 5. 2 Error detection and correction 5. 3Multiple access protocols 5. 4 Link- layer Addressing 5. 5 Ethernet  5. 6 Link- layer switches SinhVienZone.com 5: DataLink Layer. .. PPP Si  services 5. 2 Error detection and correction 5. 3Multiple access protocols 5. 4 Link- layer Addressing 5. 5 Ethernet  5. 6 Link- layer switches SinhVienZone.com 5: DataLink Layer https://fb.com/sinhvienzonevn... detection and correction 5. 3Multiple access protocols 5. 4 Link- layer Addressing 5. 5 Ethernet  5. 6 Link- layer switches SinhVienZone.com 5: DataLink Layer https://fb.com/sinhvienzonevn 5- 16 Multiple