网络技术基础系统方法课件chap

1、IP Network Technology Meng TianTian207 NJUPTMeng TianTian207 NJUPT2GoalsLearn how the Internet works under the covers!How do packets get routed across the Internet?How are packets sent reliably?How does the Internet respond to congestion?How does email and the Web work?Meng TianTian207 NJUPT3Goals (

2、2)Learn about other computer networking principlesWhat is Ethernet and how does an Ethernet LAN work?How do LANs integrate with WANs (Internet)?Obtain practical experience in network experimentMeng TianTian207 NJUPT4Networks What is a network?- A system of lines/channels that interconnect- E.g., rai

3、lroad, highway, telephone, computer What is a computer network?- A form of communication networkmoves information- Links may be wires, optics, EM spectrum, or composite.- Nodes are general-computers (or close to it). Why study computer networks?- You can program the nodes- Very easy to innovate and

4、develop new uses of network- Contrast: Telephone (POTS or cell) networkMeng TianTian207 NJUPT5Building Blocks Nodes: PC, special-purpose hardware hosts switches Links: coax cable, optical fiber point-to-point multiple accessTopologiesMeng TianTian207 NJUPT6Topologies Common Bus Topology Star Topolog

5、y Ring Topology Combined Topology Fully Connected TopologiesMeng TianTian207 NJUPT7LAN TopologiesMeng TianTian207 NJUPT8Common Bus Topology Multipoint medium: contention Transmission propagates throughout medium Heard by all stations Need to identify target station Each station has unique address Ne

6、ed to regulate transmission To avoid collisions Terminator absorbs frames at end of mediumMeng TianTian207 NJUPT9Frame Transmissionon Bus LANMeng TianTian207 NJUPT10Star Topology Each station connected directly to central node Usually via two point to point links Central node can broadcast Physical

7、star, logical bus Only one station can transmit at a time Central node can act as frame switchMeng TianTian207 NJUPT11Ring TopologyRepeaters joined by point to point links in closed loop Receive data on one link and retransmit on another Links unidirectional or bidirectional Stations attach to repea

8、tersData in frames Circulate past all stations Destination recognizes address and copies frame Frame circulates back to source where it is removedMedia access control determines when station can insert frame( token passing for example)Meng TianTian207 NJUPT12Frame TransmissionRing LANMeng TianTian20

9、7 NJUPT13Ring and Star Usage Ring Very high speed links over long distances Single link or repeater failure disables network Star Best for short distances High data rates for small number of devicesMeng TianTian207 NJUPT14 Combined Topology Fully Connected TopologyMeng TianTian207 NJUPT15Switched Ne

10、tworks two or more nodes connected by a link, or two or more networks connected by a node A network can be defined recursively as.Meng TianTian207 NJUPT16Why is switching interesting? As networks grow, switching decisions become difficult. How can a node know which way to forward data?- How much of

11、the network can each node know?- How can they be kept up to date?Meng TianTian207 NJUPT17Strategies Circuit switching: carry bit streams original telephone network Packet switching: store-and-forward messages Datagram: Internet Virtual circuit: ATM networksMeng TianTian207 NJUPT18Addressing and Rout

12、ing Address: byte-string that identifies a node usually unique Routing: process of forwarding messages to the destination node based on its address For packet switched networks, each packet must have destination address. For circuit switched, use address to set up circuit. Types of addresses unicast

13、: node-specific broadcast: all nodes on the network multicast: some subset of nodes on the networkMeng TianTian207 NJUPT19Introduction Under the simplest conditions, a medium can carry only one signal at any moment in time For multiple signals to share a medium, the medium must somehow be divided, g

14、iving each signal a portion of the total bandwidth The current techniques include frequency division multiplexing, time division multiplexing, and wave division multiplexingMultiplexingMeng TianTian207 NJUPT20Frequency Division Multiplexing FDM Useful bandwidth of medium exceeds required bandwidth o

15、f channel Each signal is modulated to a different carrier frequency Carrier frequencies separated so signals do not overlap (guard bands) e.g. broadcast radio Channel allocated even if no dataMeng TianTian207 NJUPT21Frequency Division MultiplexingDiagramMeng TianTian207 NJUPT22FDM SystemMeng TianTia

16、n207 NJUPT23Synchronous Time Division Multiplexing Data rate of medium exceeds data rate of digital signal to be transmitted Multiple digital signals interleaved in time May be at bit level of blocks Time slots preassigned to sources and fixed Time slots allocated even if no data Time slots do not h

17、ave to be evenly distributed amongst sources T-1 and ISDN telephone lines are common examples of synchronous time division multiplexingMeng TianTian207 NJUPT24Time Division MultiplexingMeng TianTian207 NJUPT25TDM SystemMeng TianTian207 NJUPT26Statistical TDMMeng TianTian207 NJUPT27Statistical TDM In

18、 Synchronous TDM many slots are wasted On-demand time-division Multiplexer scans input lines and collects data until frame full. Buffer (queue) overflow is called congestion Schedule link on a per-packet basis Packets from different sources interleaved on link Buffer packets that are contending for

19、the linkMeng TianTian207 NJUPT29Wavelength Division Multiplexing 1997 Bell Labs 100 beams Each at 10 Gbps Giving 1 terabit per second (Tbps) Multiple beams of light at different frequency A form of FDM Carried by optical fiber Each color of light (wavelength) carries separate data channelMeng TianTi

20、an207 NJUPT30Meng TianTian207 NJUPT31Inter-Process Communication Turn host-to-host connectivity into process-to-process communication. Fill gap between what applications expect and what the underlying technology provides. HostHostApplicationHostApplicationHostHostChannelMeng TianTian207 NJUPT32What

21、Goes Wrong in the Network? Bit-level errors (electrical interference) Packet-level errors (congestion) Link and node failures Packets are delayed Packets are deliver out-of-order Third parties eavesdropMeng TianTian207 NJUPT33Layering Use abstractions to hide complexity Modularization eases maintena

22、nce, updating of systemRequest/replychannelMessage streamchannelApplication programsHardwareHost-to-host connectivityProcess-to-process channels34Common Communication Patterns File access program (FTP, NFS), digital library Request/reply channels Message stream channels Request/replychannelMessage s

23、treamchannelApplication programsHardwareHost-to-host connectivityRequest/reply channelsMessage stream channelsProtocols Building blocks of a network architecture Each protocol object has two different interfaces service interface: operations on this protocol peer-to-peer interface: messages exchange

24、d with peer Host 1ProtocolHost 2ProtocolHigh-levelobjectHigh-levelobjectServiceinterfacePeer-to-peerinterfaceMeng TianTian207 NJUPT36Key Elements of a Protocol Syntax Data formats Signal levels Semantics Control information Error handling Timing Speed matchingProtocol Machinery Protocol Graph most p

25、eer-to-peer communication is indirect peer-to-peer is direct only at hardware levelFileapplicationDigitallibraryapplicationVideoapplicationRRPMSPHHPHost 1FileapplicationDigitallibraryapplicationVideoapplicationRRPMSPHHPHost 2RRP:Request/Reply ProtocolMSP:Message Stream ProtocolHHP:Host-to-Host Proto

26、colMeng TianTian207 NJUPT38Machinery (cont) Encapsulation (header/body) Multiplexing and Demultiplexing (demux key)RRP DataHHPApplicationprogramApplicationprogramHost 1Host 2DataRRPRRPDataHHPDataRRPRRPDataHHPMeng TianTian207 NJUPT39Internet Architecture Defined by Internet Engineering Task Force (IE

27、TF) Application vs Application Protocol (FTP, HTTP)FTPHTTPNVTFTPTCPUDPIPNET1NET2NETnMeng TianTian207 NJUPT40ISO ArchitectureApplicationPresentationSessionTransportEnd hostOne or more nodeswithin the networkNetworkData linkPhysicalNetworkData linkPhysicalNetworkData linkPhysicalApplicationPresentatio

28、nSessionTransportEnd hostNetworkData linkPhysicalMeng TianTian207 NJUPT41OSI layers1. Physical sends individual bits2. Data link sends frames; media access control (MAC)3. Network delivers packets to hosts using routing4. Transport delivers data to apps; reliability & flow control5. Session can

29、tie together multiple streams (e.g., audio & video)6. Presentation crypto, representation conversion7. Application what end user gets, e.g., HTTP (web)Layers 1-3 areLayers 4-7 areMeng TianTian207 NJUPT42OSI Layers (1) Physical Layer Physical interface between devices Mechanical Electrical Functi

30、onal ProceduralMeng TianTian207 NJUPT43OSI Layers (2) Data Link Layer Error detection and correction Parity Bit (even/odd) Media Access Control CSMA/CD Token Passing Token Ring Token Bus Flow ControlMeng TianTian207 NJUPT44OSI Layers (3) Network Layer Transport Layer Follow Control Connection Manage

31、ment Exchange of data between end systems Session Control of dialogues between applications Difference from the transport layer connectionMeng TianTian207 NJUPT45OSI Layers (4) Presentation Layer Code Conversion Data Compression Encryption Application Layer File Transfer Protocol Web Browsing E-mail Meng TianTian207 NJUPT46Meng TianTian207 NJUPT47The OSI EnvironmentMeng TianTian207 NJUPT48Logical and physical connectionsMeng TianTian207 NJUPT49Performance Metrics Bandwidth (throughput) d