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计算机网络 Computer Networks

数据通信与网络（下）. 计算机网络 Computer Networks. 课程编号：160027 授课对象：本科三年级. 第14单元 局域网系统 （ 第1讲）. 南京大学计算机科学与技术系 杨献春 xcy@nju.edu.cn http://cs.nju.edu.cn/yangxc. IEEE 802 Protocols. (100 base VG ——100VG AnyLAN). (no success ). (100 base X ). (Bluetooth).

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计算机网络 Computer Networks

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  1. 数据通信与网络（下） 计算机网络 Computer Networks 课程编号：160027 授课对象：本科三年级 第14单元 局域网系统（第1讲） 南京大学计算机科学与技术系杨献春 xcy@nju.edu.cn http://cs.nju.edu.cn/yangxc

  2. IEEE 802 Protocols (100 base VG ——100VG AnyLAN) (no success ) (100 base X ) (Bluetooth) 18. IEEE 802.18 RRTAG Radio Regulatory Technical Advisory Group

  3. IEEE 802 Protocols Architecture

  4. IEEE 802.1 Standards • - 802.1a-1990: Overview and Architecture • - 802.1b-1992: LAN / MAN Management • - 802.1d-1990: MAC Bridges, GARP- und GMRP-Protokoll • - 802.1e-1990: System Load Control • - 802.1g: Remote Bridging • - 802.1i-1992: Supplement to MAC Bridges: FDDI • - 802.1j: Managed Objects for MAC Bridges • - 802.1p: Expedited Traffic and Multicast Filtering • 802.1q: Virtual LANs, VLAN Architecture and Bridging • - 802.1r: GARP Proprietary Attribute Registration Protocol for 802.1d Bridges • - 802.1s: Supplement to 802.1q: Support for Multiple Spanning Trees • - 802.1t: 1d Maintenance • - 802.1u: 1q Maintenance • - 802.1v: VLAN Classification by Protocol and Port • - 802.1w: Rapid Reconfiguration Spanning Trees (RSTP) • - 802.1x: Port Based Network Access Control

  5. Ethernet

  6. IEEE 802.3 Standards • IEEE 802.3 10Base5 Thick Coax 10Mbps Baseband 500m • IEEE 802.3a 1988 10Base2 Thin Coax 10Mbps Baseband 185m • IEEE 802.3b 1985 10Broad36 Broadband 10 Mbps Broadband 3600m • IEEE 802.3e 1987 1Base5 StarLAN 1 Mbps Baseband 500m • IEEE 802.3i 1990 10BaseT Twisted Pair 10Mps Baseband 100m • IEEE 802.3u 1995 Fast Ethernet • IEEE 802.3z 1998 Gigabit Ethernet • IEEE 802.3ab 1999 1000BASE-T. • IEEE 802.3ac 1998 VLAN • IEEE 802.3ad 2000, Link Aggregation • IEEE 802.3ae 2002 10Gb/s Ethernet • IEEE 802.3af 2003 DTE Power via MDI. • IEEE 802.3ag 2002 Maintenance Revisions #6. • IEEE P802.3ah, Ethernet in the First Mile Task Force. • IEEE P802.3aj, Maintenance #7 Task Force. • IEEE P802.3ak, 10GBASE-CX4 Task Force

  7. LAN Systems 局域网系统 • Ethernet (CSMA/CD) • Token Ring / FDDI (Token Passing) • Token Bus (Token passing) • ATM LANs • Fiber Channel • Wireless LANs

  8. 14.1 Ethernet 以太网 • CSAM/CD Carriers Sense Multiple Access with Collision Detection • The most commonly used MAC technique • A random access or contention technique • Baseband version - Ethernet • Xerox/DEC/Intel 3com • Broadband version - MITREnet • MITRE • IEEE 802.3 • CSMA/CD standard • Based on Ethernet

  9. 14.1.1 MAC protocol—CSMA/CD • IEEE 802.3 • Random Access • Stations access medium randomly • Contention • Stations content for time on medium • Precursors • ALOHA Additive Link On-line HAwaii system • developed for packet radio networks • by Hawaii University • Slotted ALOHA • CSMA

  10. ALOHA • When station has frame, it sends • Station listens (for max round trip time)plus small increment • If ACK, fine. If not, retransmit • If no ACK after repeated transmissions, give up • Frame check sequence (as in HDLC) • If frame OK and address matches receiver, send ACK • Frame may be damaged by noise or by another station transmitting at the same time (collision) • Any overlap of frames causes collision • Max utilization 18%

  11. Transmit OK Collide, retransmit 1 6 Station 1 t T0 Collide, retransmit Collide, retransmit again 2 5 Station 2 t Collide, retransmit Transmit OK 3 7 Station N-1 t Transmit OK 4 Station N t 1 2 3 4 5 6 7 Frames arrive t T0 T0 T0 T0 Operation Principle of ALOHA

  12. Slotted ALOHA • Time in uniform slots equal to frame transmission time • Need central clock (or other sync mechanism) • Transmission begins at slot boundary • Frames either miss or overlap totally • Max utilization 37%

  13. Transmit OK Collide, retransmit 1 3 3’ Station 1 t T0 Collide, retransmit t 2 4 4’ Station 2 Tx T0 Frame arrives Operation Principle of Slotted ALOHA

  14. ALOHA v Slotted ALOHA • Throughput efficiency increases dramatically for Slotted ALOHA

  15. CSMA • Propagation time is much less than transmission time • All stations know that a transmission has started almost immediately • First listen for clear medium (carrier sense) • If medium idle, transmit • If two stations start at the same instant, collision • Wait reasonable time (round trip plus ACK contention) • No ACK then retransmit • Max utilization depends on propagation time (medium length) and frame length • Longer frame and shorter propagation gives better utilization

  16. Strategies of Carriers Sense • ALOHA • Non-persistent CSMA • p-persistent CSMA • 1-persistent CSMA

  17. If Busy? (1-persistent CSMA) • If medium is idle, transmit • If busy, listen for idle then transmit immediately • If two stations are waiting, collision

  18. CSMA/CD • With CSMA, collision occupies medium for duration of transmission • Stations listen whilst transmitting • If medium idle, transmit • If busy, listen for idle, then transmit • If collision detected, jam then cease transmission • After jam, wait random time then start again • Binary exponential back off

  19. IEEE 802.3 Transmission Algorithm

  20. CSMA/CDOperation

  21. Collision Detection • On baseband bus, collision produces much higher signal voltage than signal • Collision detected if cable signal greater than single station signal • Signal attenuated over distance • Limit distance to 500m (10Base5) or 200m (10Base2) • For twisted pair (star-topology) activity on more than one port is collision • Special collision presence signal - jam

  22. IEEE 802.3 Frame Format

  23. 14.1.2 Ethernet Specifications • 10Mbps specification (IEEE 802.3) • 100Mbps specification • 100Mbps Ethernet (IEEE802.3u) • 100VG-AnyLAN (IEEE802.12 - 802.3/802.5) • Demand Priority MAC protocol • 1Gbps specification(IEEE802.3z / 802.3ab) • 10Gbps specification (IEEE802.3ae)

  24. 10Mbps Specification (Ethernet) • <data rate><Signaling method><Max segment length> • 10Base5 10Base2 10Base-T 10Base-FP • Medium Coaxial Coaxial UTP 850nm fiber • Signaling Baseband Baseband Baseband Manchester • Manchester Manchester Manchester On/Off • Topology Bus Bus Star Star • Nodes 100 30 - 33

  25. 10BASE-F Medium Specifications • 10BASE-FT Passive <1000m • Star topology for interconnecting stations and repeaters • 10BASE-FL Link <2000m • Point-to-point link for connecting stations or repeaters • 10BASE-FB Backbone <2000m • Point-to-point link for connecting repeaters

  26. Simple 10BASE-T Configuration

  27. Multi-level Connection of Repeaters

  28. Mixed 10BASE-T and 10BASE5 Configuration

  29. 14.1.3 100Mbps Specification u (100Mbps)

  30. 100BASE-T Medium Alternatives • 100Base-TX 100Base-FX 100Base-T4 • 2 pair, STP 2 pair, Cat 5UTP 2 optical fiber 4 pair, cat 3,4,5 • MLT-3 MLT-3 4B5B,NRZI 8B6T,NRZ

  31. 100BASE-X Configuration DTE HUB Transmit D1 Receive D2 Transmit D1 Receive D2

  32. 100BASE-T4 Configuration DTE HUB Transmit D1 Receive D2 Collision detection Transmit D1 Receive D2 Collision detection Bidirectional D3 Bidirectional D4 Bidirectional D3 Bidirectional D4

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