dcc04-14.ppt

1、计算机网络 Computer Networks,南京大学计算机科学与技术系 杨献春 ,课程编号：160027 授课对象：本科三年级,数据通信与网络（下）,第14单元 局域网系统 （第1讲）,SLIDE 2,IEEE 802 Protocols,(Bluetooth),(100 base VG 100VG AnyLAN),(100 base X ),(no success ),18. IEEE 802.18 RRTAG Radio Regulatory Technical Advisory Group,SLIDE 3,IEEE 802 Protocols Architecture,SLIDE 4

2、,- 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

3、 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 Cla

4、ssification by Protocol and Port - 802.1w: Rapid Reconfiguration Spanning Trees (RSTP) - 802.1x: Port Based Network Access Control,IEEE 802.1 Standards,Ethernet,SLIDE 6,IEEE 802.3 Standards,IEEE 802.3 10Base5 Thick Coax 10Mbps Baseband 500m IEEE 802.3a 1988 10Base2 Thin Coax 10Mbps Baseband 185m IEE

5、E 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

6、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,SLIDE 7,LAN Systems 局域网系统,Et

7、hernet (CSMA/CD) Token Ring / FDDI (Token Passing) Token Bus (Token passing) ATM LANs Fiber Channel Wireless LANs,SLIDE 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 -

8、Ethernet Xerox/DEC/Intel 3com Broadband version - MITREnet MITRE IEEE 802.3 CSMA/CD standard Based on Ethernet,SLIDE 9,SLIDE 10,SLIDE 11,SLIDE 12,SLIDE 13,SLIDE 14,14.1.1 MAC protocolCSMA/CD,IEEE 802.3 Random Access Stations access medium randomly Contention Stations content for time on medium Precu

9、rsors ALOHA Additive Link On-line HAwaii system developed for packet radio networks by Hawaii University Slotted ALOHA CSMA,SLIDE 15,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 transmis

10、sions, 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%,SLIDE 16,Station 1,Station 2,Station N-1,Statio

11、n N,Frames arrive,1,2,3,4,Transmit OK,Transmit OK,5,6,7,Transmit OK,t,t,t,t,t,Collide, retransmit,Collide, retransmit,Collide, retransmit,T0,T0,1 2 3 4 5 6 7,T0,T0,T0,Collide, retransmit again,Operation Principle of ALOHA,SLIDE 17,Slotted ALOHA,Time in uniform slots equal to frame transmission time

12、Need central clock (or other sync mechanism) Transmission begins at slot boundary Frames either miss or overlap totally Max utilization 37%,SLIDE 18,Station 1,Station 2,1,2,Transmit OK,4,3,t,t,Collide, retransmit,T0,Collide, retransmit,4,3,T0,Tx,Frame arrives,Operation Principle of Slotted ALOHA,SLI

13、DE 19,ALOHA v Slotted ALOHA,Throughput efficiency increases dramatically for Slotted ALOHA,SLIDE 20,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

14、 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,SLIDE 21,Strategies of Carriers S

15、ense,ALOHA Non-persistent CSMA p-persistent CSMA 1-persistent CSMA,SLIDE 22,If Busy? (1-persistent CSMA),If medium is idle, transmit If busy, listen for idle then transmit immediately If two stations are waiting, collision,SLIDE 23,CSMA/CD,With CSMA, collision occupies medium for duration of transmi

16、ssion 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,SLIDE 24,SLIDE 25,IEEE 802.3 Transmission Algorithm,SLIDE 26,CSMA/CDO

17、peration,SLIDE 27,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) a

18、ctivity on more than one port is collision Special collision presence signal - jam,SLIDE 28,SLIDE 29,IEEE 802.3 Frame Format,SLIDE 30,14.1.2 Ethernet Specifications,10Mbps specification (IEEE 802.3) 100Mbps specification 100Mbps Ethernet (IEEE802.3u) 100VG-AnyLAN (IEEE802.12 - 802.3/802.5) Demand Pr

19、iority MAC protocol 1Gbps specification(IEEE802.3z / 802.3ab) 10Gbps specification (IEEE802.3ae),SLIDE 31,SLIDE 32,10Mbps Specification (Ethernet), 10Base510Base210Base-T 10Base-FP MediumCoaxialCoaxialUTP 850nm fiber SignalingBasebandBasebandBaseband Manchester ManchesterManchesterManchester On/Off

20、TopologyBusBusStar Star Nodes10030- 33,SLIDE 33,10BASE-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 re

21、peaters,SLIDE 34,Simple 10BASE-T Configuration,SLIDE 35,Multi-level Connection of Repeaters,SLIDE 36,Mixed 10BASE-T and 10BASE5 Configuration,SLIDE 37,SLIDE 38,SLIDE 39,14.1.3 100Mbps Specification,u (100Mbps),SLIDE 40,SLIDE 41,100BASE-T Medium Alternatives,100Base-TX 100Base-FX 100Base-T4 2 pair, S

22、TP 2 pair, Cat 5UTP 2 optical fiber 4 pair, cat 3,4,5 MLT-3 MLT-3 4B5B,NRZI 8B6T,NRZ,SLIDE 42,100BASE-X Configuration,DTE HUB,Transmit D1 Receive D2,Transmit D1 Receive D2,SLIDE 43,100BASE-T4 Configuration,DTE HUB,Transmit D1 Receive D2 Collision detection,Bidirectional D3 Bidirectional D4,Transmit

23、D1 Receive D2 Collision detection,Bidirectional D3 Bidirectional D4,SLIDE 44,SLIDE 45,SLIDE 46,SLIDE 47,SLIDE 48,SLIDE 49,SLIDE 50,SLIDE 51,100BASE-T Collision Domains,SLIDE 52,Two Classes of Repeater,SLIDE 53,SLIDE 54,Example 100Mbps Ethernet Backbone Strategy,SLIDE 55,Interconnection of 100VG-AnyL

24、AN and 100M Ethernet,SLIDE 56,14.1.4 Gigabit Ethernet,Configuration,SLIDE 57,SLIDE 58,SLIDE 59,SLIDE 60,SLIDE 61,Gigabit Ethernet Layers,SLIDE 62,SLIDE 63,Gigabit Ethernet - Physical,1000Base-X (802.3z) FC-0 and FC-1 Fiber channels, 3 Types of Media 1000Base-SX Short wavelength, multimode fiber 1000

25、Base-LX Long wavelength, Multi or single mode fiber 1000Base-CX Copper jumpers 25m, shielded twisted pair 1000Base-T (802.3ab) 4 pairs, cat 5 UTP Signaling - 8B/10B,SLIDE 64,Gigabit Ethernet Media Options (log scale),SLIDE 65,SLIDE 66,SLIDE 67,SLIDE 68,SLIDE 69,Gigabit Ethernet - Differences,Carrier

26、 extension At least 4096 bit-times long (512 for 10/100) Frame bursting,计算机网络 Computer Networks,南京大学计算机科学与技术系 杨献春 ,课程编号：160027 授课对象：本科三年级,数据通信与网络（下）,第14单元 局域网系统 （第2讲）,SLIDE 71,14.2 Token Ring and FDDI,SLIDE 72,14.2.1 Token Ring (802.5) 令牌环,MAC protocol Small frame (token) circulates when idle Statio

27、n waits for token Changes one bit in token to make it SOF for data frame Append rest of data frame Frame makes round trip and is absorbed by transmitting station Station then inserts new token when transmission has finished and leading edge of returning frame arrives Under light loads, some ineffici

28、ency Under heavy loads, round robin,SLIDE 73,Token RingOperation,SLIDE 74,Token Ring MAC Frame,SLIDE 75,Frame Status Field (FS),Destination station nonexistent or not active A=0, C=0 Destination station exists but frame not copied A=1, C=0 Frame received A=1, C=1,SLIDE 76,Token Ring Priority (1),Def

29、ine following variables Pf = priority of frame to be transmitted by station Ps = service priority: priority of current token Pr = value of Ps as contained in last token received by this station Rs = reservation value in current token Rr = highest reservation value in frames received by this station

30、during last token rotation,SLIDE 77,Token Ring Priority (2),Station works as follows Must wait for a token with Ps Pf before transmitting While waiting, may reserve a future token at Pf. If a frame goes by, and if Rs Pf , then Rs Pf . If a token goes by, and if Rs Pf AND Pf Ps , then Rs Pf . When it

31、 seizes a token it sets T bit to 1 to start a frame sets RRR of frame to 0 leaves PPP unchanged Following transmission of one or more frames, it issues a new token with the priority and reservation fields set appropriately,SLIDE 78,Token Ring Priority (3),Each station maintains two stacks Sx = store

32、 new values of token priority Sr = store old values of token priority,SLIDE 79,Priority Scheme,SLIDE 80,Early Token Release (ETR),ETR allows a transmitting station to release a token as soon as it completes frame transmission, whether or not the frame header has returned to the station One effect of

33、 ETR is that access delay for priority traffic may increase when the ring is heavily loaded with short frames Stations that implement ETR are compatible and interoperable with those that do not,SLIDE 81,Dedicated Token Ring (DTR),Central hub Acts as switch Full duplex point to point link Concentrato

34、r acts as frame level repeater No token passing,SLIDE 82,Example Dedicated Token Ring Configuration,SLIDE 83,14.2.2 802.5 Physical Layer,Data Rate4Mbps 16Mbps 100Mbps Medium UTP,STP,Fiber Signaling Differential Manchester Max Frame4550 18200 18200 Access ControlTP or DTR TP or DTR DTR Note: 1Gbps To

35、ken Ring is in development,SLIDE 84,14.2.3 FDDI,100Mbps LAN and MAN applications Token Ring,SLIDE 85,FDDI MAC Frame Format,CLFFZZZZ,the same as 802.5,SLIDE 86,FDDI MAC Protocol,As for 802.5 except: Station seizes token by aborting token transmission Once token captured, one or more data frames trans

36、mitted New token released as soon as transmission finished (ETR in 802.5),SLIDE 87,FDDI Operation,SLIDE 88,Capacity Allocation,Not use the priority scheme used in 802.5 FDDI provides greater control over capacity to meet requirements for high-speed LAN Allocation scheme seeks to accommodate a mixtur

37、e of stream and bursty traffic FDDI defines two types of traffic Synchronous and asynchronous Allocations must be such that TTRT - target token rotation time,SLIDE 89,Capacity Allocation Algorithm,Variables required for operation of the algorithm are maintained at each station token rotation timer (

38、TRT) token holding timer (THT) late counter (LC) Algorithm TRTTTRT and LC0* TRT begins to count down if a token is received before TRT expires, then TRTTTRT else LC+ and TRTTTRT if LC=2 then token is considered lost if LC=0 then THTTRT; TRTTTRT; enable TRT transmit syn-frames; if THT0 then transmit

39、asyn-frames if LC=1 then transmit syn-frames and LC0; TRT continue,SLIDE 90,Operation of FDDI Capacity Allocation Scheme,SLIDE 91,HSTR,High-Speed Token Ring 100Mbps 802.5 specification Why there is both FDDI and HSTR? FDDI was developed long before HSTR HSTR is compatible and interoperable with TR C

40、haracteristics of HSTR frame format and source routing bridge algorithm is the same as TR operates only in switched access mode (DTR) No have to address token-passing and capacity allocation problems that FDDI deals with,SLIDE 92,14.2.4 FDDI Physical Layer,MediumOptical FiberTwisted Pair Data rate10

41、0100 Signaling4B/5B/NRZIMLT-3 Max repeaters100100 Between repeaters2km100m,SLIDE 93,14.3 ATM LANs,LAN Generations First CSMA/CD and token ring Terminal to host and client server Moderate data rates Second FDDI Backbone High performance workstations Third ATM Aggregate throughput and real time suppor

42、t for multimedia applications,SLIDE 94,Third Generation LANs,Support for multiple guaranteed classes of service Live video may need 2Mbps File transfer can use background class Scalable throughput Both aggregate and per host Facilitate LAN/WAN internetworking,SLIDE 95,Possible Types of ATM LANs,Asyn

43、chronous Transfer Mode Virtual paths and virtual channels Preconfigured or switched Gateway to ATM WAN Backbone ATM switch Single ATM switch or local network of ATM switches Workgroup ATM End systems connected directly to ATM switch Mixed system,SLIDE 96,Example - ATM LAN as High-speed Backbone,SLID

44、E 97,Example - ATM LAN HUB,SLIDE 98,Compatibility,Interaction between end system on ATM and end system on legacy LAN Interaction between stations on legacy LANs of the same type Interaction between stations on legacy LANs of different types,计算机网络 Computer Networks,南京大学计算机科学与技术系 杨献春 ,课程编号：160027 授课对象

45、：本科三年级,数据通信与网络（下）,第14单元 局域网系统 （第3讲）,SLIDE 100,14.4 Fiber Channel,Background I/O channel Direct point to point or multipoint comms link Hardware based High Speed Very short distance User data moved from source buffer to destiation buffer Network connection Interconnected access points Software based

46、protocol Flow control, error detection HyperLAN; HyperLAN2 ISM band Industrial, Scientific, Medical band,SLIDE 122,5.725-5.85GHz 125MHz,SLIDE 123,Wireless LAN Technology,802.11a 802.11b 802.11g Frequency Band 5GHz 2.4GHz 2.4GHz Availability US/AP Worldwide Worldwide Max. Data Rate 54Mbps 11Mbps 54Mb

47、ps The Laws of Radio Dynamics: Higher data rates = shorter transmission range Higher power output = increased range, but lower battery life Higher frequency radios = higher data rates Higher data rates = shorter ranges,SLIDE 124,Power and Range,2 Mbps DSSS 250-350 feet radius100mW,5.5 Mbps DSSS 130-

48、150 feet radius 100mW,11 Mbps DSSS 100-130 feet radius 100mW,SLIDE 125,14.5.2 Medium Access Control,Distributed Foundation Wireless MAC (DFWMAC) Distributed Coordination Function (DCF) CSMA No collision detection Point Coordination Function (PCF) Polling of central master,SLIDE 126,SLIDE 127,Distrib

49、uted Coordination Function,DCF uses a simple CSMA algorithm If a station has a MAC frame to transmit, then listen to medium If the medium is idle, then transmit else wait until the current transmission is complete DCF does not include a collision detection function not practical on a wireless networ

50、k the dynamic range of signals on medium is very large, a transmitting station cannot effectively distinguish incoming weak signals from noise and the effects of its own transmission DCF includes a set delays to ensure the smooth and fair functioning of this algorithm,SLIDE 128,CSMA Access Algorithm

51、 Using Delays,The set of Delays mounts to a priority scheme Use a kind of IFS (InterFrame Space) CSMA access rules if medium is idle then waits to see if medium remains idle for a time equal to IFS if idle then transmit immediately if medium is busy then defers transmission and uses 1-persistence if current transmission is over then delays another IFS if medium remains idle for this period then uses a binary exponential backoff scheme senses the medium again if medium is still idl