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Data and Computer Communications

Data and Computer Communications. Chapter 16 – High Speed LAN s. Ninth Edition by William Stallings. Introduction. rapid changes in technology designs broader use of LANs new schemes for high-speed LANs high-speed technologies: Fast and Gigabit Ethernet Fibre Channel

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Data and Computer Communications

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  1. Data and Computer Communications Chapter 16 – High Speed LANs Ninth Edition by William Stallings Data and Computer Communications, Ninth Edition by William Stallings, (c) Pearson Education - Prentice Hall, 2011

  2. Introduction • rapid changes in technology designs • broader use of LANs • new schemes for high-speed LANs • high-speed technologies: • Fast and Gigabit Ethernet • Fibre Channel • High Speed Wireless LANs

  3. Characteristics of Some High-Speed LANs

  4. CSMA/CD Precursors

  5. Pure (unslotted) ALOHA • unslotted Aloha: simpler, no synchronization • when frame first arrives • transmit immediately • collision probability increases: • frame sent at t0 collides with other frames sent in [t0-1,t0+1] Lappeenranta University of Technology / JP, PH, AH

  6. Assumptions: all frames same size time divided into equal size slots (time to transmit 1 frame) nodes start to transmit only slot beginning nodes are synchronized if 2 or more nodes transmit in slot, all nodes detect collision Operation: when node obtains fresh frame, transmits in next slot if no collision: node can send new frame in next slot if collision: node retransmits frame in each subsequent slot with prob. p until success Slotted ALOHA Lappeenranta University of Technology / JP, PH, AH

  7. Pros single active node can continuously transmit at full rate of channel highly decentralized: only slots in nodes need to be in sync simple Cons collisions, wasting slots idle slots nodes may be able to detect collision in less than time to transmit packet clock synchronization Slotted ALOHA Lappeenranta University of Technology / JP, PH, AH

  8. CSMA/CD Precursors • Carrier Sense Multiple Access (CSMA) • station listens to determine in there is another transmission in progress • if idle, station transmits • waits for acknowledgment • if no acknowledgment, collision is assumed and station retransmits • utilization far exceeds ALOHA

  9. CSMA collisions spatial layout of nodes collisions can still occur: propagation delay means two nodes may not hear each other’s transmission collision: entire packet transmission time wasted note: role of distance & propagation delay in determining collision probability Lappeenranta University of Technology / JP, PH, AH

  10. Nonpersistent CSMA

  11. 1-persistent CSMA • 1-persistent CSMA avoids idle channel time • 1-persistent CSMA rules: • if medium idle, transmit; • if medium busy, listen until idle; then transmit immediately • 1-persistent stations are selfish • if two or more stations waiting, a collision is guaranteed

  12. P-persistent CSMA • a compromise to try and reduce collisions and idle time • p-persistent CSMA rules: • if medium idle, transmit with probability p, and delay one time unit with probability (1–p) • if medium busy, listen until idle and repeat step 1 • if transmission is delayed one time unit, repeat step 1 • issue of choosing effective value of p to avoid instability under heavy load

  13. Value of p? • have n stations waiting to send • at end of tx, expected number of stations is np • if np>1 on average there will be a collision • repeated tx attempts mean collisions likely • eventually when all stations trying to send have continuous collisions hence zero throughput • thus want np<1 for expected peaks of n • if heavy load expected, p small • but smaller p means stations wait longer

  14. CSMA/CD (Collision Detection) CSMA/CD: carrier sensing, deferral as in CSMA • collisions detected within short time • colliding transmissions aborted, reducing channel wastage • collision detection: • easy in wired LANs: measure signal strengths, compare transmitted, received signals • difficult in wireless LANs: received signal strength overwhelmed by local transmission strength • human analogy: the polite conversationalist Lappeenranta University of Technology / JP, PH, AH

  15. CSMA/CD collision detection Lappeenranta University of Technology / JP, PH, AH

  16. Description of CSMA/CD

  17. CSMA/CDOperation

  18. Which Persistence Algorithm? • IEEE 802.3 uses 1-persistent • both nonpersistent and p-persistent have performance problems

  19. Binary Exponential Backoff • for backoff stability, IEEE 802.3 and Ethernet both use binary exponential backoff • stations repeatedly resend when collide • on first 10 attempts, mean random delay doubled • value then remains same for 6 further attempts • after 16 unsuccessful attempts, station gives up and reports error • 1-persistent algorithm with binary exponential backoff efficient over wide range of loads • backoff algorithm has last-in, first-out effect

  20. Collision Detection

  21. Ethernet “dominant” wired LAN technology: • cheap $20 for NIC • first widely used LAN technology • simpler, cheaper than token LANs and ATM • kept up with speed race: 10 Mbps – 10 Gbps Metcalfe’s Ethernet sketch Lappeenranta University of Technology / JP, PH, AH

  22. IEEE 802.3 MAC Frame Format

  23. 10Mbps Specification (Ethernet)

  24. IEEE 802.3 10-Mbps Physical Layer Medium Alternatives

  25. Fast Ethernet • Termi viittaa IEEE:n määrittelemiin 100 MbpsEthernet-yhteensopiviin lähiverkkotekniikoihin • Käsitellään yhdessä otsikolla 100BASE-T • Erilaisia siirtoteitä käyttäville eri nimet • 100BASE-TX käyttää 2 paria johtimia, joko STP tai Cat5 UTP • 100BASE-FX käyttää 2 optista kuitua • 2 ylempää luokituksen 100BASE-X alla • 100BASE-T4 käyttää 4 paria Cat3/4/5 UTP • yhteensopivuus vanhojen kaapelointien kanssa Lappeenranta University of Technology / JP, PH, AH

  26. 100Mbps Fast Ethernet

  27. Fast ethernet, 100BASE-X • 100BASE-X viittaa tekniikoihin, joissa saadaan yhdellä linkillä (esim. yksittäinen kierretty pari) 100 Mbps yksisuuntainen nopeus • 100BASE-TX (parikaapeli) • 100BASE-FX (optinen kuitu) • Mainitut 2 tekniikkaa eroavat paitsi siirtotieltään, myös signaloinniltaan T = Twisted pair (kierretty pari), F = fibre (kuitu) Lappeenranta University of Technology / JP, PH, AH

  28. 100BASE-X • uses a unidirectional data rate 100 Mbps over single twisted pair or optical fiber link • encoding scheme same as FDDI • 4B/5B-NRZI

  29. Fast Ethernet, 100BASE-T4 • 100BASE-T4:ssä mahdollisuus käyttää Cat3- kaapeleita, joten määrittely ei vaadi100 Mbps datanopeutta yhdeltä linkiltä • 33 1/3 Mbps yhdessä linkissä • 100 Mbps kaksisuuntaisena vaatii 3 datavirtaa molempiin suuntiin = 6 linkkiä • johtimina 4 kierrettyä paria, joista kahden täytyy olla 2-suuntaisia Lappeenranta University of Technology / JP, PH, AH

  30. 100BASE-T4 • 100-Mbps over lower-quality Cat 3 UTP • takes advantage of large installed base • does not transmit continuous signal between packets • useful in battery-powered applications • can not get 100 Mbps on single twisted pair • so data stream split into three separate streams • four twisted pairs used • data transmitted and received using three pairs • two pairs configured for bidirectional transmission • use ternary signaling scheme (8B6T)

  31. Full Duplex Operation • traditional Ethernet half duplex • using full-duplex, station can transmit and receive simultaneously • 100-Mbps Ethernet in full-duplex mode, giving a theoretical transfer rate of 200 Mbps • stations must have full-duplex adapter cards • and must use switching hub • each station constitutes separate collision domain • CSMA/CD algorithm no longer needed • 802.3 MAC frame format used

  32. Mixed Configurations • Fast Ethernet supports mixture of existing 10-Mbps LANs and newer 100-Mbps LANs • supporting older and newer technologies • stationsattach to 10-Mbps hubs using 10BASE-T • hubs connected to switching hubs using 100BASE-T • high-capacity workstations and servers attach directly to 10/100 switches • switches connected to 100-Mbps hubs use 100-Mbps links • 100-Mbps hubs provide building backbone • connected torouter providing connection to WAN

  33. Gigabit Ethernet Configuration

  34. Gigabit Ethernet • Gigabit Ethernetissä käytössä sama MAC-protokolla (CSMA/CD) ja Ethernet-formaatti kuin 10BASE-T ja 100BASE-T –tekniikoissakin • Gigabit Ethernetiä käytetään yleensä 100 ja 10 Mbps nopeudella toimivien lähiverkkojen runkoverkkoina • lisäksi suuria nopeuksia vaativia palvelimia yms. liitetään suoraan GE-kytkimiin Lappeenranta University of Technology / JP, PH, AH

  35. Gigabit Ethernet - Differences • carrier extension • at least 4096 bit-times long (512 for 10/100) • frame bursting • not needed if using a switched hub to provide dedicated media access

  36. Gigabit Ethernet, fyysinen kerros • GigabitEthernetissä on määritelty 4 erilaista fyysistä kerrosta • 1000BASE-SX (optinen, pieni aallonpituus) • 1000BASE-LX (optinen, suuri aallonpituus) • 1000BASE-CX (erityissuojattu kierretty pari, max 25 metriä) • 1000BASE-T (4 paria CAT5 UTP) • 3 ensimmäistä käyttää samaa signaalin koodaustapaa, viimeinen monimutkaisempaa • (taulukko toimintaetäisyyksistä seuraavalla kalvolla) Lappeenranta University of Technology / JP, PH, AH

  37. Gigabit Ethernet – Physical

  38. 10 Gbps Ethernet • Vaikka Gigabitethernet –tekniikat ovat vielä varsin uusia, 10 GbpsEthernet –tekniikat ovat saaneet jo paljon huomiota • Laajentuva Internet ja intranet –liikenne vaatii aina vaan nopeampia yhteyksiä • verkkoon liitettävien laitteiden määrät kasvavat • verkkoliittymät nopeutuvat (esim. 10 Mbps -> 100 Mbps; 56 kbps modeemi -> xDSL) • kaistaa vaativia sovelluksia (korkealaatuiset videot yms.) • webhosting - ja applicationhosting -liikenne Lappeenranta University of Technology / JP, PH, AH

  39. 10 Gigabit Ethernet • Aluksi 10 Gigabit Ethernetiä käytetään paikallisissa runkoverkkoyhteyksissä • Myöhemmin käytettäneen laajemmin, esim. ”palvelinfarmeissa”, kampusverkoissa, ja myös ISP-käytössä (internet service provider) • Ethernet alkaa kilpailla vanhojen WAN-tekniikoiden kanssa Lappeenranta University of Technology / JP, PH, AH

  40. 10Gbps Ethernet Configurations

  41. 10 Gigabit Ethernet • IEEE 802.3ae, ak, an, ap, aq • Kuitu (10GBase-R) • SR, LR, LRM (multimode), ER, ZR (80 km), LX4 • Kupari (10GBase-X/10GBase-T) • CX4, KX4, Base-T • WAN (10GBase-W) Lappeenranta University of Technology / JP, PH, AH

  42. 10 Gigabit Ethernet, fyysinen kerros • Neljä (optista kuitua käyttävää) määritystä: • 10GBASE-S (short) – 850 nanometrin aallonpituus, multi-mode, max 300 m • 10GBASE-L (long) – 1310 nm, single-mode, max 10 km • 10GBASE-E (extended) – 1550 nm, single-mode, jopa 40 km • 10GBASE-LX4 1310 nm, single- tai multi-mode, käyttää aallonpituusjakokanavointia (WDM), 4 eri valoa käytössä Lappeenranta University of Technology / JP, PH, AH

  43. 10 Gigabit Ethernet, fyysinen kerros • 10GBase - CX4 • 4 paria • Max 15 metriä • 10GBase – KX4 ja KR • 1 metri • 10GBase – T • UTP, STP • 10GBASE-W • Yhteensopivuus OC-192/STM-64 SDH/SONET Lappeenranta University of Technology / JP, PH, AH

  44. 10Gbps Ethernet Options

  45. 100-Gbps Ethernet • preferred technology for wired LAN • preferred carrier for bridging wireless technologies into local Ethernet networks • cost-effective, reliable and interoperable • popularity of Ethernet technology: • availability of cost-effective products • reliable and interoperable network products • variety of vendors

  46. 100Gbps Ethernet

  47. Multilane Distribution used to achieve the required data rates • multilane distribution: • switches implemented as multiple parallel channels • separate physical wires • virtual lanes: • if a different number of lanes are actually in use, virtual lanes are distributed into physical lanes in the PMD sublaver • form of inverse multiplexing

  48. Multiline Distribution for 100Gbps Ethernet

  49. Media Options for 40-Gbps and 100-Gbps Ethernet

  50. Multilane Distribution for 100 Gbps Ethernet

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