* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Welcome to COE321: Logic Design
Survey
Document related concepts
Backpressure routing wikipedia , lookup
Multiprotocol Label Switching wikipedia , lookup
Internet protocol suite wikipedia , lookup
Net neutrality law wikipedia , lookup
Zero-configuration networking wikipedia , lookup
Asynchronous Transfer Mode wikipedia , lookup
Distributed firewall wikipedia , lookup
Recursive InterNetwork Architecture (RINA) wikipedia , lookup
Network tap wikipedia , lookup
Airborne Networking wikipedia , lookup
Computer network wikipedia , lookup
Wake-on-LAN wikipedia , lookup
Piggybacking (Internet access) wikipedia , lookup
Deep packet inspection wikipedia , lookup
Cracking of wireless networks wikipedia , lookup
Transcript
What’s the Internet: “nuts and bolts” view PC server wireless laptop cellular handheld Mobile network millions of connected computing devices: hosts Global ISP = end systems communication links access points wired links router running network apps fiber, copper, radio, satellite transmission rate = bandwidth Home network Regional ISP Institutional network routers: forward packets (chunks of data) 1 What’s the Internet: “nuts and bolts” view protocols control sending, receiving of msgs e.g., TCP, IP, HTTP, Skype, Ethernet Internet: “network of networks” loosely hierarchical public Internet versus private intranet Internet standards RFC: Request for comments IETF: Internet Engineering Task Force Mobile network Global ISP Home network Regional ISP Institutional network 2 What’s the Internet: a service view communication infrastructure enables distributed applications: Web, VoIP, email, games, e-commerce, file sharing communication services provided to apps: reliable data delivery from source to destination “best effort” (unreliable) data delivery 3 What’s a protocol? human protocols: “what’s the time?” “I have a question” introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: machines rather than humans all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt 4 What’s a protocol? a human protocol and a computer network protocol: Hi TCP connection request Hi TCP connection response Got the time? Get http://www.awl.com/kurose-ross 2:00 <file> time Q: Other human protocols? 5 Computer networks: overview Two most important aspects of computer networks Hardware And, software Network hardware can be classified by Transmission technology And, scale 6 Classification of hardware by transmission technology Communication is a primary concern in a network => we are dealing with both computers and Communication (transmission) technologies Types of transmission technology Broadcast links A single communication channel is shared by all machines Restricting transmission to a set of machines => multicasting Point-to-point links Many connections between individual pairs of machines 7 Broadcast communication networks Examples: satellite networks multi-access Ethernet. 8 General rule Smaller networks Larger networks Broadcasting Point-to-point An alternative criterion for classifying networks Their scale Personal area networks, and local area networks Metropolitan are networks, and wide are networks 9 Classification of interconnected processor by scale 10 Local area networks LANs are privately owned networks Within a single building or campus of few kilometers in size Various topologies are possible for LANs Bus A single shared cable connect all devices Example: IEEE 802.3 Ethernet Ring All messages travel thru a ring in the same direction Example: FDDI (Fiber Distributed Date Interface) 11 LANs topologies 12 Metropolitan Area Networks A MAN Covers a city The best known example is Cable television network available in many cities 13 Wide area networks WANs Within a country or even whole continent 14 Connectionless WAN packet-switched networks In an IP network, a user can send packets to a destination without having to set up a connection first, i.e., without informing the network prior to transmitting them. This simplifies the network, as there is no need for a special signaling protocol. 15 Routing in IP User A User B IP network The routing of a packet through the network is done on a hop-per-hop basis based on the destination IP address carried in the IP packet’s header. 16 Quality of Service (QoS) in IP Typically, an IP router does not offer QoS. It cannot distinguish packets belonging to different service classes based on their destination address. IP is almost ubiquitous. There is a lot of interest in introducing QoS in the IP network, and MPLS seems to be the architecture for introducing QoS. 17 Internetworks Internetwork or internet A collection of interconnected networks Deals with how to connect different kinds of networks It is formed when distinct networks are interconnected Resulting in the Internet That really covers the whole Planet 18 Network Core: Circuit Switching End-end resources reserved for “call” link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup required 19 Network Core: Circuit Switching network resources (e.g., bandwidth) divided into “pieces” pieces allocated to calls resource piece idle if not used by owning call (no sharing) dividing link bandwidth into “pieces” frequency division time division 20 Circuit Switching: FDM and TDM Example: FDM 4 users frequency time TDM frequency time 21 Numerical example How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network? All links are 1.536 Mbps Each link uses TDM with 24 slots/sec 500 msec to establish end-to-end circuit Let’s work it out! 22 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge end systems, access networks, links 1.3 Network core circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History 23 How do loss and delay occur? packets queue in router buffers packet arrival rate to link exceeds output link capacity packets queue, wait for turn packet being transmitted (delay) A B packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers 24 Four sources of packet delay 1. nodal processing: check bit errors determine output link 2. queueing time waiting at output link for transmission depends on congestion level of router transmission A propagation B nodal processing queueing 25 Delay in packet-switched networks 3. Transmission delay: R=link bandwidth (bps) L=packet length (bits) time to send bits into link = L/R transmission A 4. Propagation delay: d = length of physical link s = propagation speed in medium (~2x108 m/sec) propagation delay = d/s Note: s and R are very different quantities! propagation B nodal processing queueing 26 Transmission vs. propagation applet An applet Illustrating the difference between Transmission delay and propagation delay An interactive animation Speaks a thousand words http://media.pearsoncmg.com/aw/aw_kurose_network_2/apple ts/transmission/delay.html 27 Nodal delay d nodal d proc d queue d trans d prop dproc = processing delay typically a few microsecs or less dqueue = queuing delay depends on congestion dtrans = transmission delay = L/R, significant for low-speed links dprop = propagation delay a few microsecs to hundreds of msecs 28 Queueing delay (revisited) R=link bandwidth (bps) L=packet length (bits) a=average packet arrival rate traffic intensity = La/R La/R ~ 0: average queueing delay small La/R -> 1: delays become large La/R > 1: more “work” arriving than can be serviced, average delay infinite! 29 Queuing delay vs. packet loss Applet can be found at: http://media.pearsoncmg.com/aw/aw_kurose_network_2 /applets/queuing/queuing.html 30 “Real” Internet delays and routes What do “real” Internet delay & loss look like? Traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i: sends three packets that will reach router i on path towards destination router i will return packets to sender sender times interval between transmission and reply. 3 probes 3 probes 3 probes 31 “Real” Internet delays and routes traceroute: gaia.cs.umass.edu to www.eurecom.fr Three delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu 1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms 4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms trans-oceanic 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms link 9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms 17 * * * * means no response (probe lost, router not replying) 18 * * * 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms 32 33 Tracing LAU’s webserver 34 Tracing webserver (cont’d) 35 Packet loss queue (aka buffer) preceding link in buffer has finite capacity packet arriving to full queue dropped (aka lost) lost packet may be retransmitted by previous node, by source end system, or not at all buffer (waiting area) A B packet being transmitted packet arriving to full buffer is lost 36 Throughput throughput: rate (bits/time unit) at which bits transferred between sender/receiver instantaneous: rate at given point in time average: rate over longer period of time link capacity that can carry server, with server sends bits pipe Rs bits/sec fluid at rate file of F bits (fluid) into pipe Rs bits/sec) to send to client link that capacity pipe can carry Rfluid c bits/sec at rate Rc bits/sec) 37 Throughput (more) Rs < Rc What is average end-end throughput? Rs bits/sec Rc bits/sec Rs > Rc What is average end-end throughput? Rs bits/sec Rc bits/sec bottleneck link link on end-end path that constrains end-end throughput 38 Throughput: Internet scenario per-connection endend throughput: min(Rc,Rs,R/10) in practice: Rc or Rs is often bottleneck Rs Rs Rs R Rc Rc Rc 10 connections (fairly) share backbone bottleneck link R bits/sec 39