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1 Chapter 1: Introduction Chapter 1 Introduction Our goal: Overview: note on the use of these ppt slides: We re making these slides freely available to all (faculty, students, readers). They re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: If you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source (after all, we d like people to use our book!) If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. Computer Networking: Top Down pproach, 5th edition. Jim Kurose, Keith Ross ddison-wesley, pril get feel and terminology more depth, detail later in course approach: use Internet as example Thanks and enjoy! JFK/KWR ll material copyright J.F Kurose and K.W. Ross, ll Rights Reserved what s the Internet? what s a protocol? edge; hosts, access net, physical media core: packet/circuit switching, Internet structure performance: loss, delay, throughput security protocol layers, service models history Introduction 1-1 Introduction 1-2 What s the Internet: nuts and bolts view Chapter 1: roadmap millions PC server wireless laptop cellular handheld end systems, access s, s circuit switching, packet switching, structure s access points wired s router of connected computing devices: hosts = end systems running apps communication s fiber, copper, radio, satellite transmission rate = bandwidth routers: forward packets (chunks of data) obile Global Home Regional Institutional Introduction 1-3 What s the Internet: nuts and bolts view protocols control sending, receiving of msgs Internet: of s loosely hierarchical public Internet versus private intranet What s the Internet: a service view obile Global e.g., TCP, IP, HTTP, Skype, Ethernet Introduction 1-4 Home Regional Institutional Internet standards RFC: Request for comments IETF: Internet Engineering Task Force Introduction 1-5 communication infrastructure enables distributed applications: Web, VoIP, , games, e-commerce, file sharing communication services provided to apps: reliable data delivery from source to destination best effort (unreliable) data delivery Introduction 1-6 1
2 What s a protocol? What s a protocol? human protocols: v what s the time? v I have a question v introductions specific msgs sent specific actions taken when msgs received, or other events protocols: v machines rather than humans v all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among entities, and actions taken on msg transmission, receipt Introduction 1-7 a human protocol and a computer protocol: Hi Hi Got the time? 2:00 time Q: Other human protocols? TCP connection request TCP connection response Get <file> Introduction 1-8 Chapter 1: roadmap v end systems, access s, s v circuit switching, packet switching, structure s Introduction 1-9 closer look at structure: v edge: applications and hosts v access s, physical media: wired, wireless communication s v core: interconnected routers of s Introduction 1-10 The edge: v end systems (hosts): run application programs e.g. Web, at edge of v client/server model client host requests, receives peer-peer service from always-on server e.g. Web browser/server; client/server client/server v peer-peer model: minimal (or no) use of dedicated servers e.g. Skype, ittorrent Introduction 1-11 ccess s and physical media Q: How to connect end systems to edge router? v residential access nets v institutional access s (school, company) v mobile access s Keep in mind: v bandwidth (bits per second) of access? v shared or dedicated? Introduction
3 Dial-up odem Digital Subscriber Line (DSL) central office telephone Internet phone Existing phone line: 0-4KHz phone; 4-50KHz upstream data; 50KHz-1Hz downstream data Internet PC dial-up modem modem (e.g., OL) v uses existing telephony infrastructure directly-connected to central office v up to 56Kbps direct access to router (often less) v can t surf, phone at same time: not always on Introduction 1-13 PC DSL modem splitter DSL central office telephone v uses existing telephone infrastructure v up to 1 bps upstream (today typically < 256 kbps) v up to 8 bps downstream (today typically < 1 bps) v dedicated physical line to telephone central office Introduction 1-14 Residential access: cable modems Residential access: cable modems v uses cable TV infrastructure, rather than telephone infrastructure v HFC: hybrid fiber coax asymmetric: up to 30bps downstream, 2 bps upstream v of cable, fiber attaches s to router s share access to router unlike DSL, which has dedicated access Introduction 1-15 Diagram: Introduction 1-16 Cable Network rchitecture: Overview Cable Network rchitecture: Overview server(s) Typically 500 to 5,000 s cable headend cable headend cable distribution (simplified) cable distribution Introduction 1-17 Introduction
4 Cable Network rchitecture: Overview Cable Network rchitecture: Overview FD (more shortly): V I D E O V I D E O V I D E O V I D E O V I D E O C O V N I D D T D R E T T O O L Channels cable headend cable headend cable distribution (simplified) cable distribution Introduction 1-19 Introduction 1-20 Fiber to the Home Ethernet Internet access Internet OLT central office optical fiber optical splitter optical fibers v optical s from central office to the v two competing optical technologies: Passive Optical (PON) ctive Optical Network (PN) v much higher Internet rates; fiber also carries television and phone services ONT ONT ONT Introduction bps 100 bps 100 bps Ethernet switch 1 Gbps server institutional router to institution s v typically used in companies, universities, etc v 10 bps, 100bps, 1Gbps, 10Gbps Ethernet v today, end systems typically connect into Ethernet switch Introduction 1-22 Wireless access s Home s v shared wireless access connects end system to router router via base station aka access point base v wireless LNs: station b/g (WiFi): 11 or 54 bps v wider-area wireless access provided by telco operator ~1bps over cellular system (EVDO, HSDP) next up (?): WiX (10 s bps) over wide area mobile hosts Typical components: v DSL or cable modem v router/firewall/nt v Ethernet v wireless access point to/from cable headend cable modem router/ firewall Ethernet wireless access point wireless laptops Introduction 1-23 Introduction
5 Physical edia v bit: propagates between transmitter/rcvr pairs v physical : what lies between transmitter & receiver v guided media: signals propagate in solid media: copper, fiber, coax v unguided media: signals propagate freely, e.g., radio Twisted Pair (TP) v two insulated copper wires Category 3: traditional phone wires, 10 bps Ethernet Category 5: 100bps Ethernet Physical edia: coax, fiber Coaxial cable: v two concentric copper conductors v bidirectional v baseband: single channel on cable legacy Ethernet v broadband: multiple channels on cable HFC Fiber optic cable: v glass fiber carrying light pulses, each pulse a bit v high-speed operation: high-speed point-to-point transmission (e.g., 10 s-100 s Gpbs) v low error rate: repeaters spaced far apart ; immune to electromagnetic noise Introduction 1-25 Introduction 1-26 Physical media: radio v signal carried in electromagnetic spectrum v no physical wire v bidirectional v propagation environment effects: reflection obstruction by objects interference Radio types: v terrestrial microwave e.g. up to 45 bps channels v LN (e.g., WiFi) 11bps, 54 bps v wide-area (e.g., cellular) 3G cellular: ~ 1 bps v satellite Kbps to 45bps channel (or multiple smaller channels) 270 msec end-end delay geosynchronous versus low altitude Chapter 1: roadmap v end systems, access s, s v circuit switching, packet switching, structure s Introduction 1-27 Introduction 1-28 The Network Core x v mesh of interconnected routers v 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 Network Core: Circuit Switching end-end resources reserved for call v bandwidth, switch capacity v dedicated resources: no sharing v circuit-like (guaranteed) performance v call setup required Introduction 1-29 Introduction
6 Network Core: Circuit Switching Circuit Switching: FD and TD resources (e.g., bandwidth) divided into pieces v pieces allocated to calls v resource piece idle if not used by owning call (no sharing) v dividing bandwidth into pieces frequency division time division FD TD frequency time Example: 4 users frequency Introduction 1-31 time Introduction 1-32 Numerical example Network Core: Packet Switching v How long does it take to send a file of 640,000 bits from host to host over a circuit-switched? all speeds: bps each uses TD with 24 slots/sec 500 msec to establish end-to-end circuit Let s work it out! each end-end data stream divided into packets v user, packets share resources v each packet uses full bandwidth v resources used as needed andwidth division into pieces Dedicated allocation Resource reservation resource contention: v aggregate resource demand can exceed amount available v congestion: packets queue, wait for use v store and forward: packets move one hop at a time node receives complete packet before forwarding Introduction 1-33 Introduction 1-34 Packet Switching: Statistical ultiplexing Packet-switching: store-and-forward 100 b/s Ethernet statistical multiplexing C L R R R queue of packets waiting for output 1.5 b/s D v sequence of & packets has no fixed timing pattern bandwidth shared on demand: statistical multiplexing. v TD: each host gets same slot in revolving TD frame. E Introduction 1-35 v takes L/R seconds to transmit (push out) packet of L bits on to at R bps v store and forward: entire packet must arrive at router before it can be transmitted on next v delay = 3L/R (assuming zero propagation delay) Example: L = 7.5 bits R = 1.5 bps transmission delay = 15 sec more on delay shortly Introduction
7 .. Packet switching versus circuit switching Packet switching allows more users to use! Example: 1 b/s each user: 100 kb/s when active active 10% of time v circuit-switching: 10 users v packet switching: with 35 users, probability > 10 active at same time is less than.0004 N users 1 bps Q: how did we get value ? Q: what happens if > 35 users? Introduction 1-37 Packet switching versus circuit switching Is packet switching a slam dunk winner? v great for bursty data resource sharing simpler, no call setup v excessive congestion: packet delay and loss protocols needed for reliable data transfer, congestion control v 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 1-38 Internet structure: of s v roughly hierarchical v at center: small # of well-connected large s tier-1 commercial s (e.g., Verizon, Sprint, T&T, Qwest, Level3), national & international coverage large content distributors (Google, kamai, icrosoft) treat each other as equals (no charges) Tier-1 s & Content s, interconnect (peer) privately or at Internet Exchange Points s (e.g., kamai) Tier 1 Tier 1 Tier 1 (e.g., Google) Introduction 1-39 Internet structure: of s tier-2 s: smaller (often regional) s v connect to one or more tier-1 (provider) s each tier-1 has many tier-2 customer nets tier 2 pays tier 1 provider v tier-2 nets sometimes peer directly with each other (bypassing tier 1), or at (e.g., kamai) Tier 1 Tier 1 Tier 1 (e.g., Google) Introduction 1-40 Internet structure: of s v Tier-3 s, local s v customer of tier 1 or tier 2 last hop ( access ) (closest to end systems) Internet structure: of s v a packet passes through many s from source host to destination host (e.g., kamai) Tier 1 (e.g., Google) (e.g., kamai) Tier 1 (e.g., Google) Tier 1 Tier 1 Tier 1 Tier 1 Introduction 1-41 Introduction
8 Chapter 1: roadmap v end systems, access s, s v circuit switching, packet switching, structure s How do loss and delay occur? packets queue in router buffers v packet arrival rate to exceeds output capacity v packets queue, wait for turn packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction 1-43 Introduction 1-44 Four sources of packet delay Four sources of packet delay transmission propagation transmission propagation nodal processing queueing nodal processing queueing d nodal = d proc + d queue + d trans + d prop d nodal = d proc + d queue + d trans + d prop d proc : nodal processing check bit errors determine output typically < msec d queue : queueing delay time waiting at output for transmission depends on congestion level of router d trans : transmission delay: L: packet length (bits) R: bandwidth (bps) d trans = L/R d trans and d prop very different d prop : propagation delay: d: length of physical s: propagation speed in medium (~2x10 8 m/sec) d prop = d/s Introduction 1-45 Introduction 1-46 Caravan analogy Caravan analogy (more) 100 km 100 km 100 km 100 km ten-car caravan toll booth toll booth ten-car caravan toll booth toll booth v cars propagate at 100 km/hr v toll booth takes 12 sec to service car (transmission time) v car~bit; caravan ~ packet v 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 : 62 minutes Introduction 1-47 v cars now propagate at 1000 km/hr v toll booth now takes 1 min to service a car v Q: Will cars arrive to 2nd booth before all cars serviced at 1st booth? : Yes! fter 7 min, 1st car arrives at second booth; three 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 WL Web site Introduction
9 Queueing delay (revisited) v R: bandwidth (bps) v L: packet length (bits) v a: average packet arrival rate average queueing delay traffic intensity = La/R v La/R ~ 0: avg. queueing delay small v La/R -> 1: avg. queueing delay large v La/R > 1: more work arriving than can be serviced, average delay infinite! La/R ~ 0 La/R -> 1 Introduction 1-49 Real Internet delays and routes v What do real Internet delay & loss look like? v 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 1-50 Real Internet delays and routes traceroute: gaia.cs.umass.edu to Three delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu 1 cs-gw ( ) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu ( ) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu ( ) 6 ms 5 ms 5 ms 4 jn1-at wor.vbns.net ( ) 16 ms 11 ms 13 ms 5 jn1-so wae.vbns.net ( ) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu ( ) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu ( ) 22 ms 22 ms 22 ms ( ) 104 ms 109 ms 106 ms 9 de2-1.de1.de.geant.net ( ) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net ( ) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant.net ( ) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr ( ) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr ( ) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr ( ) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net ( ) 135 ms 128 ms 133 ms ( ) 126 ms 128 ms 126 ms 17 * * * 18 * * * 19 fantasia.eurecom.fr ( ) 132 ms 128 ms 136 ms trans-oceanic * means no response (probe lost, router not replying) Packet loss v queue (aka buffer) preceding in buffer has finite capacity v packet arriving to full queue dropped (aka lost) v lost packet may be retransmitted by previous node, by source end system, or not at all buffer (waiting area) packet arriving to full buffer is lost packet being transmitted Introduction 1-51 Introduction 1-52 Throughput v 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 Throughput (more) v R s < R c What is average end-end throughput? R s bits/sec R c bits/sec v R s > R c What is average end-end throughput? R s bits/sec R c bits/sec server server, sends with bits (fluid) file of into F pipe bits to send to client pipe that capacity can carry fluid R s bits/sec at rate R s bits/sec) pipe that capacity can carry Rfluid c bits/sec at rate R c bits/sec) bottleneck on end-end path that constrains end-end throughput Introduction 1-53 Introduction
10 Throughput: Internet scenario Chapter 1: roadmap v per-connection end-end throughput: mi n(r c,r s,r/10) v in practice: R c or R s is often bottleneck R s R s R s R c R c R c 10 connections (fairly) share backbone bottleneck R bits /sec R Introduction 1-55 v end systems, access s, s v circuit switching, packet switching, structure s Introduction 1-56 Protocol Layers Organization of air travel Networks are complex, with many pieces : v hosts v routers v s of various media v applications v protocols v hardware, software Question: Is there any hope of organizing structure of? Or at least our discussion of s? ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing v a series of steps Introduction 1-57 Introduction 1-58 Layering of airline functionality ticket (purchase) baggage (check) gates (load) runway (takeoff) departure airport intermediate air-traffic control centers Layers: each layer implements a service v via its own internal-layer actions ticket (complain) baggage (claim gates (unload) runway (land) arrival airport v relying on services provided by layer below ticket baggage gate takeoff/landing Why layering? Dealing with complex systems: v explicit structure allows identification, relationship of complex system s pieces layered reference model for discussion v 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 v layering considered harmful? Introduction 1-59 Introduction
11 Internet protocol stack ISO/OSI reference model v application: supporting applications FTP, STP, HTTP v transport: process-process data transfer TCP, UDP v : routing of datagrams from source to destination IP, routing protocols v : data transfer between neighboring elements Ethernet, (WiFi), PPP v physical: bits on the wire application transport physical v presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine -specific conventions v session: synchronization, checkpointing, recovery of data exchange v Internet stack missing these layers! these services, if needed, must be implemented in application needed? application presentation session transport physical Introduction 1-61 Introduction 1-62 message segment H t datagram H n H t frame H l H n H t H t H t H n H t H n H l destination application transport physical source application transport physical H t H n H t H n H l Encapsulation physical physical H t H n switch router Chapter 1: roadmap v end systems, access s, s v circuit switching, packet switching, structure s Introduction 1-63 Introduction 1-64 Network Security v field of security: how bad guys can attack computer s how we can defend s against attacks how to design architectures that are immune to attacks v Internet not originally designed with (much) security in mind original vision: a group of mutually trusting users attached to a transparent J Internet protocol designers playing catch -up security considerations in all layers! Introduction 1-65 ad guys: put malware into hosts via Internet v malware can get in host from a virus, worm, or Trojan horse. v spyware malware can record keystrokes, web sites visited, upload info to collection site. v infected host can be enrolled in botnet, used for spam and DDoS attacks. v malware often self-replicating: from one infected host, seeks entry into other hosts Introduction
12 ad guys: put malware into hosts via Internet Trojan horse v hidden part of some otherwise useful software v today often in Web page (ctive-x, plugin) virus v infection by receiving object (e.g., attachment), actively executing v self-replicating: propagate itself to other hosts, users worm: v infection by passively receiving object that gets itself executed v self- replicating: propagates to other hosts, users Sapphire Worm: aggregate scans/sec in first 5 minutes of outbreak (CID, UWisc data) ad guys: attack server, 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 (see botnet) 3. send packets to target from compromised hosts target Introduction 1-67 Introduction 1-68 The bad guys can sniff packets Packet sniffing: v broadcast media (shared Ethernet, wireless) v promiscuous interface reads/records all packets (e.g., including passwords!) passing by The bad guys can use false source addresses IP spoofing: send packet with false source address C C src: dest: payload src: dest: payload v Wireshark software used for end-of-chapter labs is a (free) packet-sniffer Introduction 1-69 Introduction 1-70 The bad guys can record and playback record-and-playback: sniff sensitive info (e.g., password), and use later v password holder is that user from system point of view C src: dest: user: ; password: foo lots more on security (throughout, Chapter 8) Introduction 1-71 Chapter 1: roadmap v end systems, access s, s v circuit switching, packet switching, structure s Introduction
13 Internet History : Early packet-switching principles v v v v 1961: Kleinrock - queueing theory shows effectiveness of packet -switching 1964: aran - packet -switching in military nets 1967: RPnet conceived by dvanced Research Projects gency 1969: first RPnet node operational v 1972: RPnet public demonstration NCP (Network Control Protocol) first host-host protocol first program RPnet has 15 nodes Internet History : Intering, new and proprietary nets v 1970: LOHnet satellite in Hawaii v 1974: Cerf and Kahn - architecture for interconnecting s v 1976: Ethernet at Xerox PRC v late70 s: proprietary architectures: DECnet, SN, XN v late 70 s: switching fixed length packets (T precursor) v 1979: RPnet has 200 nodes Cerf and Kahn s intering principles: minimalism, autonomy - no internal changes required to interconnect s best effort service model stateless routers decentralized control define today s Internet architecture Introduction 1-73 Introduction 1-74 Internet History : new protocols, a proliferation of s Internet History 1990, 2000 s: commercialization, the Web, new apps v 1983: deployment of TCP/IP v 1982: smtp protocol defined v 1983: DNS defined for name-to-ip-address translation v 1985: ftp protocol defined v 1988: TCP congestion control v new national s: Csnet, ITnet, NSFnet, initel v 100,000 hosts connected to confederation of s v early 1990 s: RPnet decommissioned v 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) v early 1990s: Web hypertext [ush 1945, Nelson 1960 s] HTL, HTTP: erners-lee 1994: osaic, later Netscape late 1990 s: commercialization of the Web late 1990 s 2000 s: v more killer apps: instant messaging, P2P file sharing v security to forefront v est. 50 million host, 100 million+ users v backbone s running at Gbps Introduction 1-75 Introduction 1-76 Internet History Introduction: Summary 2010: v ~750 million hosts v voice, video over IP v P2P applications: ittorrent (file sharing) Skype (VoIP), PPLive (video) v more applications: YouTube, gaming, Twitter v wireless, mobility Introduction 1-77 Covered a ton of material! v Internet overview v what s a protocol? v edge, core, access packet-switching versus circuit-switching Internet structure v performance: loss, delay, throughput v layering, service models v security v history You now have: v context, overview, feel of ing v more depth, detail to follow! Introduction
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