CS536-2009-01-15

CS536-2009-01-15 - CS536: Intro, day 2 Charles Killian...

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Unformatted text preview: CS536: Intro, day 2 Charles Killian Slides used from Kurose-Ross, Computer Networking, a Top Down Approach Introduction 1-1 Announcements   Note the correct PSO times (correction from Tuesday)   Monday: 3:30p-5:20p (TA: Camille Gaspard)   Wednesday: 11:30a-1:20p (TA: Zhen Zhu)   Link updated on course webpage to the 4th edition of Kurose-Ross Introduction 1-2 Last Time   Internet => Network of Networks   Edge devices use Access networks to connect to higher level ISPs   Devices communicate using Protocols   Specified in RFCs (Requests for Comments)   Standardized through the IETF (Internet Engineering Task Force)   Bits travel on physical medium   Twisted pair (Cat 3/5/6), Coaxial, Optical Fiber, Satellite, 802.11a/b/g, HSDPA, … Introduction 1-3 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core   circuit switching, packet switching, network structure   end systems, access networks, links 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 Introduction 1-4 The Network Core   mesh of interconnected routers   the fundamental question: how is data transferred through net?   circuit switching: dedicated circuit per call: telephone net   packet-switching: data sent thru net in discrete “chunks” Introduction 1-5 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 Introduction 1-6 Network Core: Circuit Switching network resources (e.g., bandwidth) divided into “pieces”   pieces allocated to calls   resource piece   dividing link bandwidth idle if not used by owning call (no sharing) into “pieces”   frequency division   time division Introduction 1-7 Circuit Switching: FDM and TDM FDM frequency time TDM Example: 4 users frequency time Introduction 1-8 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! Introduction 1-9 Network Core: Packet Switching each end-end data stream divided into packets   user A, B packets share network resources   each packet uses full link bandwidth   resources used as needed Bandwidth division into “pieces” Dedicated allocation Resource reservation resource contention:   aggregate resource demand can exceed amount available   congestion: packets queue, wait for link use   store and forward: packets move one hop at a time   Node receives complete packet before forwarding Introduction 1-10 Packet Switching: Statistical Multiplexing A B 100 Mb/s Ethernet statistical multiplexing 1.5 Mb/s C queue of packets waiting for output link D E Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand statistical multiplexing. TDM: each host gets same slot in revolving TDM frame. Introduction 1-11 Packet-switching: store-and-forward L R R R   takes L/R seconds to transmit (push out) packet of L bits on to link at R bps   store and forward: entire packet must arrive at router before it can be transmitted on next link   delay = 3L/R (assuming zero propagation delay) Example:   L = 7.5 Mbits   R = 1.5 Mbps   transmission delay = 15 sec more on delay shortly … Introduction 1-12 Packet switching versus circuit switching Packet switching allows more users to use network!   1 Mb/s link   each user:   100 kb/s when “active”   active 10% of time   circuit-switching:   10 users   packet switching:   with 35 users, probability > 10 active at same time is less than .0004 N users 1 Mbps link Q: how did we get value 0.0004? Introduction 1-13 Packet switching versus circuit switching Is packet switching a “slam dunk winner?”   great for bursty data sharing   simpler, no call setup   excessive congestion: packet delay and loss   protocols needed for reliable data transfer, congestion control   Q: How to provide circuit-like behavior?   bandwidth guarantees needed for audio/video apps   still an unsolved problem (chapter 7) Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)? Introduction 1-14   resource Internet structure: network of networks   roughly hierarchical   at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable and Wireless), national/international coverage   treat each other as equals Tier-1 providers interconnect (peer) privately Tier 1 ISP Tier 1 ISP Tier 1 ISP Introduction 1-15 Tier-1 ISP: e.g., Sprint POP: point-of-presence to/from backbone … … … peering … . to/from customers … Introduction 1-16 Internet structure: network of networks   “Tier-2” ISPs: smaller (often regional) ISPs   Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet   tier-2 ISP is customer of tier-1 provider Tier-2 ISP Tier-2 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISPs also peer privately with each other. Tier 1 ISP Tier-2 ISP Tier-2 ISP Introduction 1-17 Internet structure: network of networks   “Tier-3” ISPs and local ISPs   last hop (“access”) network (closest to end systems) local ISP Local and tier3 ISPs are customers of higher tier ISPs connecting them to rest of Internet Tier 3 ISP Tier-2 ISP local ISP Tier-2 ISP local ISP local ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP local ISP Tier 1 ISP Tier-2 ISP local ISP Introduction 1-18 Tier-2 ISP local local ISP ISP Internet structure: network of networks   a packet passes through many networks! local ISP Tier 3 ISP Tier-2 ISP local ISP local ISP Tier-2 ISP local ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP local ISP Tier 1 ISP Tier-2 ISP local local ISP ISP Tier-2 ISP local ISP Introduction 1-19 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core   circuit switching, packet switching, network structure   end systems, access networks, links 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 Introduction 1-20 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 Introduction 1-21 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 A B transmission propagation nodal processing queueing Introduction 1-22 Delay in packet-switched networks 3. Transmission delay:   R=link bandwidth (bps)   L=packet length (bits)   time to send bits into link = L/R 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 A B transmission nodal processing queueing Introduction 1-23 Caravan analogy 100 km ten-car caravan toll booth toll booth 100 km   cars “propagate” at 100 km/hr   toll booth takes 12 sec to service car (transmission time)   car~bit; caravan ~ packet   Q: How long until caravan is lined up before 2nd toll booth?   Time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec   Time for last car to propagate from 1st to 2nd toll both: 100km/ (100km/hr)= 1 hr   A: 62 minutes Introduction 1-24 Caravan analogy (more) 100 km ten-car caravan toll booth toll booth 100 km   Cars now “propagate” at   Yes! After 7 min, 1st car 1000 km/hr   Toll booth now takes 1 min to service a car   Q: Will cars arrive to 2nd booth before all cars serviced at 1st booth? at 2nd booth and 3 cars still at 1st booth.   1st bit of packet can arrive at 2nd router before packet is fully transmitted at 1st router!   See Ethernet applet at AWL Web site Introduction 1-25 Nodal delay   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 Introduction 1-26 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! Introduction 1-27 “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 Introduction 1-28 “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 Introduction 1-29 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 A B buffer (waiting area) packet being transmitted packet arriving to full buffer is lost Introduction 1-30 Throughput   throughput: rate (bits/time unit) at which   instantaneous: bits transferred between sender/receiver rate at given point in time   average: rate over longer period of time link capacity server, with server sends bits pipe that can carry Rs b at rate fluidits/sec file into bits (fluid) of F pipe Rs bits/sec) to send to client ink capacity plipe that can carry Rfluid at rate c bits/sec Rc bits/sec) Introduction 1-31 Throughput (more)   R s < Rc What is average end-end throughput? Rs bits/sec Rc bits/sec   R s > 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 Introduction 1-32 Throughput: Internet scenario   per-connection Rs Rs R Rc Rc Rc Rs end-end throughput: min(Rc,Rs,R/10)   in practice: Rc or Rs is often bottleneck 10 connections (fairly) share backbone bottleneck link R bits/sec Introduction 1-33 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core   circuit switching, packet switching, network structure   end systems, access networks, links 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 Introduction 1-34 Protocol “Layers” Networks are complex!   many “pieces”:   hosts   routers   links of various media   applications   protocols   hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks? Introduction 1-35 Organization of air travel ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing   a series of steps Introduction 1-36 Layering of airline functionality ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport ticket (complain) baggage (claim gates (unload) runway (land) airplane routing airplane routing airplane routing arrival airport ticket baggage gate takeoff/landing airplane routing intermediate air-traffic control centers Layers: each layer implements a service   via its own internal-layer actions   relying on services provided by layer below Introduction 1-37 Why layering? Dealing with complex systems:   explicit structure allows identification, relationship of complex system’s pieces   layered reference model for discussion   modularization eases maintenance, updating of system   change of implementation of layer’s service transparent to rest of system   e.g., change in gate procedure doesn’t affect rest of system   layering considered harmful? Introduction 1-38 Internet protocol stack   application: supporting network applications   FTP, SMTP, HTTP application transport network link physical   transport: process-process data transfer   TCP, UDP   network: routing of datagrams from source to destination   IP, routing protocols   link: data transfer between   neighboring network elements PPP, Ethernet Introduction 1-39   physical: bits “on the wire” ISO/OSI reference model   presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machinespecific conventions   session: synchronization, checkpointing, recovery of data exchange   Internet stack “missing” these layers!   these services, if needed, must be implemented in application   needed? application presentation session transport network link physical Introduction 1-40 source message segment Ht M M M M frame Hl Hn Ht datagram Hn Ht application transport network link physical Encapsulation link physical switch destination M Ht Hn Ht Hl Hn Ht M M M application transport network link physical Hn Ht Hl Hn Ht M M network link physical Hn Ht M router Introduction 1-41 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core   circuit switching, packet switching, network structure   end systems, access networks, links 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 Introduction 1-42 Network Security   The field of network security is about:   how bad guys can attack computer networks   how we can defend networks against attacks   how to design architectures that are immune to attacks   Internet not originally designed with (much) security in mind   original vision: “a group of mutually trusting users attached to a transparent network”   Internet protocol designers playing “catch-up”   Security considerations in all layers! Introduction 1-43 Bad guys can put malware into hosts via Internet   Malware can get in host from a virus, worm, or trojan horse.   Spyware malware can record keystrokes, web sites visited, upload info to collection site. for spam and DDoS attacks.   Infected host can be enrolled in a botnet, used   Malware is often self-replicating: from an infected host, seeks entry into other hosts Introduction 1-44 Bad guys can put malware into hosts via Internet   Trojan horse   Hidden part of some otherwise useful software   Today often on a Web page (Active-X, plugin)   Virus   infection by receiving object (e.g., e-mail attachment), actively executing   self-replicating: propagate itself to other hosts, users   Worm:   infection by passively receiving object that gets itself executed   self- replicating: propagates to other hosts, users Sapphire Worm: aggregate scans/sec in first 5 minutes of outbreak (CAIDA, UWisc data) Introduction 1-45 Bad guys can attack servers and network infrastructure   Denial of service (DoS): attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic 1.  select target 2.  break into hosts around the network (see botnet) 3.  send packets toward target from compromised hosts target Introduction 1-46 The bad guys can sniff packets Packet sniffing:   broadcast media (shared Ethernet, wireless)   promiscuous network interface reads/records all packets (e.g., including passwords!) passing by A C src:B dest:A payload B   Wireshark software used for end-of-chapter labs is a (free) packet-sniffer Introduction 1-47 The bad guys can use false source addresses   IP spoofing: send packet with false source address A src:B dest:A payload C B Introduction 1-48 The bad guys can record and playback   record-and-playback: sniff sensitive info (e.g., password), and use later   password holder is that user from system point of view A C src:B dest:A user: B; password: foo B Introduction 1-49 Network Security   more throughout this course   chapter 8: focus on security   crypographic techniques: obvious uses and not so obvious uses Introduction 1-50 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core   circuit switching, packet switching, network structure   end systems, access networks, links 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 Introduction 1-51 Internet History 1961-1972: Early packet-switching principles   1961: Kleinrock - queueing theory shows effectiveness of packetswitching   1964: Baran - packetswitching in military nets   1967: ARPAnet conceived by Advanced Research Projects Agency   1969: first ARPAnet node operational   1972:         ARPAnet public demonstration NCP (Network Control Protocol) first host-host protocol first e-mail program ARPAnet has 15 nodes Introduction 1-52 Internet History 1972-1980: Internetworking, new and proprietary nets   1970: ALOHAnet satellite           network in Hawaii 1974: Cerf and Kahn architecture for interconnecting networks 1976: Ethernet at Xerox PARC ate70’s: proprietary architectures: DECnet, SNA, XNA late 70’s: switching fixed length packets (ATM precursor) 1979: ARPAnet has 200 nodes Cerf and Kahn’s internetworking principles:   minimalism, autonomy - no internal changes required to interconnect networks   best effort service model   stateless routers   decentralized control define today’s Internet architecture Introduction 1-53 Internet History 1980-1990: new protocols, a proliferation of networks   1983: deployment of   new national networks: TCP/IP   1982: smtp e-mail protocol defined   1983: DNS defined for name-to-IP-address translation   1985: ftp protocol defined   1988: TCP congestion control Csnet, BITnet, NSFnet, Minitel   100,000 hosts connected to confederation of networks Introduction 1-54 Internet History 1990, 2000’s: commercialization, the Web, new apps   Early 1990’s: ARPAnet decommissioned   1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)   early 1990s: Web   hypertext [Bush 1945, Nelson 1960’s]   HTML, HTTP: Berners-Lee   1994: Mosaic, later Netscape   late 1990’s: commercialization of the Web Late 1990’s – 2000’s:   more killer apps: instant messaging, P2P file sharing   network security to forefront   est. 50 million host, 100 million+ users   backbone links running at Gbps Introduction 1-55 Internet History 2007:   ~500 million hosts   Voice, Video over IP   P2P applications: BitTorrent (file sharing) Skype (VoIP), PPLive (video)   more applications: YouTube, gaming   wireless, mobility Introduction 1-56 Introduction: Summary Covered a “ton” of material!   Internet overview   what’s a protocol?   network edge, core, access network   packet-switching versus circuit-switching   Internet structure   performance: loss, delay, throughput   layering, service models   security   history You now have:   context, overview, “feel” of networking   more depth, detail to follow! Introduction 1-57 ...
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