Chapter 1: Introduction

Transcription

1 Introduction to Computer Networking Guy Leduc Chapter 1: Computer Networks and the Inter Computer Networking: A Top Down Approach, 7 th edition. Jim Kurose, Keith Ross Addison-Wesley, April : Introduction 1-1 Chapter 1: Introduction Our goal:! get feel and terminology! more depth, detail later in course! approach: " use Inter as example Overview:! what s the Inter?! what s a protocol?! work edge: hosts,, physical media! work core: packet/circuit switching, Inter structure! performance: loss, delay, throughput! protocol layers, service models! history From Computer Networking, by Kurose&Ross Introduction 1-2 1

2 Chapter 1: roadmap 1.1 What is the Inter? 1.2 Network edge - end systems, works, links 1.3 Network core - packet switching vs circuit switching, work structure 1.4 Delay, loss and throughput in works 1.5 Protocol layers, service models 1.6 History From Computer Networking, by Kurose&Ross Introduction 1-3 What s the Inter: nuts and bolts view PC server wireless laptop smartphone! millions of connected computing devices: # hosts = end systems # running work apps mobile work global wireless links wired links! communication links # fiber, copper, radio, satellite # transmission rate (bps) # delay # error rate home work regional router! packet switches: forward packets (chunks of data) # routers and switches institutional work From Computer Networking, by Kurose&Ross Introduction 1-4 2

3 Fun inter appliances Web-enabled toaster + weather forecaster IP picture frame Tweet-a-watt: monitor energy use Slingbox: watch, control cable TV remotely Inter refrigerator Inter phones Introduction From Computer Networking, by Kurose&Ross 1-5 What s the Inter: nuts and bolts view! Inter: work of works "! global Interconnected s (Inter Service Providers) protocols control sending, receiving of messages " mobile work home work regional e.g., TCP, IP, HTTP, Skype, WiFi, Ether! Inter standards " RFC: Request for comments " IETF: Inter Engineering Task Force From Computer Networking, by Kurose&Ross institutional work Introduction 1-6 3

4 What s the Inter: a service view! Infrastructure that provides services to applications: " Web, VoIP, , games, e-commerce, social s,! provides programming interface to apps " hooks that allow sending and receiving app programs to connect to Inter " provides service options, analogous to postal service mobile work home work institutional work global regional From Computer Networking, by Kurose&Ross Introduction 1-7 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 work protocols:! machines rather than humans! all communication activity in Inter governed by protocols protocols define format, order of msgs sent and received among work entities, and actions taken on msg transmission, receipt From Computer Networking, by Kurose&Ross Introduction 1-8 4

5 What s a protocol? a human protocol and a computer work protocol: Hi Hi Got the time? 2:00 time TCP connection request TCP connection response Get <file> Q: Other human protocols? From Computer Networking, by Kurose&Ross Introduction 1-9 Chapter 1: roadmap 1.1 What is the Inter? 1.2 Network edge - end systems, works, links 1.3 Network core - packet switching vs circuit switching, work structure 1.4 Delay, loss and throughput in works 1.5 Protocol layers, service models 1.6 History From Computer Networking, by Kurose&Ross Introduction

6 A closer look at work structure: work edge: # hosts: clients and servers # servers often in data centers works, physical media: wired, wireless communication links work core: # interconnected routers # work of works mobile work home work institutional work global regional From Computer Networking, by Kurose&Ross Introduction 1-11 Access works and physical media Q: How to connect end systems to edge router?! residential s! institutional works (school, company)! mobile works keep in mind:! data rate (in bits per second) of work?! shared or dedicated? From Computer Networking, by Kurose&Ross Introduction

7 Historically: Dial-up Modem central office telephone work Inter home PC home dial-up modem modem! Uses existing telephony infrastructure " Home is connected to central office! Up to 56Kbps direct to router (often less)! Can t surf and phone at same time: not always on From Computer Networking, by Kurose&Ross Introduction 1-13 Modems: Types of Modulations A binary signal Amplitude modulation Frequency modulation Phase modulation Phase changes From From Computer Computer Networks, Networking, by Tanenbaum by Kurose&Ross Prentice Hall Introduction

8 Combination of Amplitude and Phase Modulations 1 baud = 1 symbol per second 1 bit per second 1 symbol = 2 bits «2 bits/baud» 1 symbol = 4 bits 1 symbol = 6 bits 1 symbol = (co)sine with some amplitude and phase Consider a 2400 baud-line: Encoding Data rate (bps) Modulation technique 2 bits/baud 4.8 kbps QPSK: Quadrature Phase Shift Keying 4 bits/baud 9.6 kbps QAM-16: Quadrature Amplitude Modulation 6 bits/baud 14.4 kbps QAM-64 Data-rate = baud-rate x (nr. of bits/baud) From From Computer Computer Networks, Networking, by Tanenbaum by Kurose&Ross Prentice Hall Introduction 1-15 Upper bounds on the baud-rate and the data-rate! The baud-rate (expressed in bauds, number of symbols per second) is limited by the frequency bandwidth (H) of the physical channel (H is expressed in Hertz) " Nyquist law: baud-rate 2 H Means that the symbol duration Δ cannot be smaller than 1/2H " This law does not constrain the data-rate E.g. encoding could use an arbitrarily large number of bits per baud! The data-rate (expressed in bps, bits per second) is however limited! " The upper bound is the capacity of the channel " Given by Shannon law: data-rate H log 2 (1 + S/N) S = (Average received) Signal power, N = (Average) Noise power " Depends on frequency bandwidth and Signal-to-Noise (S/N) ratio Dial-up modem example: H = 4 khz and S/N = 1000 give data-rate ~ 40 kbps Note: when H and S are > 0, capacity is always > 0, for all N > 0 From Computer Networking, by Kurose&Ross Introduction

9 Access : digital subscriber line (DSL) central office telephone work DSL modem splitter voice, data transmitted at different frequencies over dedicated line to central office DSLAM DSL multiplexer! use existing telephone line to central office DSLAM # data over DSL phone line goes to Inter # voice over DSL phone line goes to telephone # data and voice sent/received over different frequency bands # data frequency band much larger => capacity much larger! typically a few Mbps upstream transmission rate! typically Mbps downstream transmission rate From Computer Networking, by Kurose&Ross Introduction 1-17 DSL: data rate versus distance Over category 3 copper twisted pairs (used in telephone works) If distance increases, signal attenuates, so S/N decreases From From Computer Computer Networks, Networking, by Tanenbaum by Kurose&Ross Prentice Hall Introduction

10 Access : cable work cable headend cable modem splitter 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 Channels From Computer Networking, by Kurose&Ross Introduction 1-19 V I D E O D A T A D A T A C O N T R O L Frequency Division Multiplexing (FDM): different channels transmitted in different frequency bands (like in DSL) Access : cable work cable headend cable modem splitter data, TV transmitted at different frequencies over shared cable distribution work CMTS cable modem termination system! HFC: hybrid fiber coax # asymmetric: up to 30 Mbps downstream transmission rate, 2 Mbps upstream transmission rate! work of cable, fiber attaches homes to router # homes share work to cable headend # unlike DSL, which has dedicated to central office From Computer Networking, by Kurose&Ross Introduction

11 Access : home work wireless devices often combined in single box to/from headend or central office cable or DSL modem wireless point (54 Mbps) router, firewall, NAT wired Ether (100 Mbps) From Computer Networking, by Kurose&Ross Introduction 1-21 Enterprise works (Ether) institutional link to (Inter) institutional router Ether switch institutional mail, web servers! typically used in companies, universities, etc! 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates! today, end systems typically connect into Ether switch From Computer Networking, by Kurose&Ross Introduction

12 Wireless works Shared wireless work connects end system to router " via base station, aka point wireless LANs: # within building (30m) # b/g/n/ac (WiFi): 11, 54, 200, >1000 Mbps transmission rate wide-area wireless # provided by telco (cellular) operator, 10 s km # up to ± 100 Mbps # 3G, 4G, to Inter to Inter From Computer Networking, by Kurose&Ross Introduction 1-23 Host: sends packets of data host sending function:! takes application message! breaks into smaller chunks, known as packets, of length L bits! transmits packet into work at link transmission rate R " aka link capacity, (wrongly called link bandwidth) 2 host 1 two packets, L bits each R: link transmission rate packet transmission delay time needed to transmit L-bit packet into link = = L (bits) R (bits/sec) From Computer Networking, by Kurose&Ross Introduction

13 Physical Media! bit (or symbol): propagates between transmitter/receiver pairs! physical link: what lies between transmitter & receiver! guided media: " signals propagate in solid media: copper, fiber, coax! unguided media: " signals propagate freely, e.g., radio Twisted Pair (TP)! two insulated (unshielded) copper wires " Category 3: traditional phone wires, 10 Mbps Ether " Category 5: 100Mbps, 1 Gbps Ether " Category 6: 10 Gbps From Computer Networking, by Kurose&Ross Introduction 1-25 Physical Media: coax, fiber Coaxial cable:! two concentric copper conductors! bidirectional! broadband: Copper core " multiple channels on cable " HFC Insulating material Braided outer conductor Protective plastic covering Fiber optic cable:! glass fiber carrying light pulses, each pulse a bit! high-speed operation: " high-speed point-to-point transmission (e.g., 10 s-100 s Gbps transmission rate)! low error rate: " repeaters spaced far apart " immune to electromagic noise Core (glass) From Computer Networks, by Tanenbaum Prentice Hall Cladding (glass) Jacket (plastic) From Computer Networking, by Kurose&Ross Introduction

14 Light Ray Propagation in a Fiber Air/silica boundary Silica α 1 Air β 1 α 2 β 2 n 1 n 2 Three examples of a light ray from inside a silica fiber impinging on the air/silica boundary at different angles α 3 β 3 Light source Light trapped by total internal reflection! Refraction law: n 1 sin α = n 2 sin β n (refraction index) = c / v c is the speed of light in vacuum, v in the medium! When β = 90, we get sin α c = n 2 / n 1 (with n 2 < n 1 ) c = ± m/s In silica (n = 1.5): v = ± m/s! For α > α c, there is no refraction (pure reflection)! From From Computer Computer Networks, Networking, by Tanenbaum by Kurose&Ross Prentice Hall Introduction 1-27 Types of Optical Fibers Multi-mode fiber (Multiple propagation modes) A light pulse, a symbol, spreads out, leading to symbol interference (Inter)modal (delay) dispersion, proportional to length n 2 < n 1 n 1 64 µ Single-mode fiber 2.4 µ No more delay dispersion, longer distances possible Multi-mode fiber with graded index (i.e., variable n 1 ) No From delay Computer dispersion Networking, by Kurose&Ross either, why? Introduction

15 Physical media: radio! signal carried in electromagic spectrum! no physical wire! bidirectional! propagation environment effects: " reflection " obstruction by objects " interference Radio link types:! terrestrial microwave " e.g. up to 45 Mbps channels! LAN (e.g., Wifi) " 11, 54, 200, >1000 Mbps! wide-area (e.g., cellular) " 3G, 4G cellular: Mbps! satellite " Kbps to 45Mbps channel (or multiple smaller channels) " 270 msec end-end delay " geosynchronous versus low altitude From Computer Networking, by Kurose&Ross Introduction 1-29 Chapter 1: roadmap 1.1 What is the Inter? 1.2 Network edge - end systems, works, links 1.3 Network core - packet switching vs circuit switching, work structure 1.4 Delay, loss and throughput in works 1.5 Protocol layers, service models 1.6 History From Computer Networking, by Kurose&Ross Introduction

16 The work core! mesh of interconnected routers! packet-switching: hosts break application-layer messages into packets " forward packets from one router to the next, across links on path from source to destination " each packet transmitted at full link capacity From Computer Networking, by Kurose&Ross Introduction 1-31 Packet-switching: store-and-forward L bits per packet source R bps R bps des+na+on! takes L/R seconds to transmit (push out) L-bit packet into link at R bps! store and forward: entire packet must arrive at router before it can be transmitted on next link! end-end delay = 2L/R (assuming zero propagation delay) for 2 hops! one-hop numerical example: # L = 7.5 Mbits # R = 1.5 Mbps # one-hop transmission delay = 5 sec! more on delay shortly From Computer Networking, by Kurose&Ross Introduction

17 Packet Switching: queueing delay, loss A R = 100 Mb/s statistical multiplexing C B queue of packets waiting for output link R = 1.5 Mb/s queuing and loss: If arrival rate (in bps) to link exceeds transmission rate of link for a period of time: # packets will queue, wait to be transmitted on link # packets can be dropped (lost) if memory (buffer) fills up statistical multiplexing on link: # no fixed pattern on link, link shared on demand From Computer Networking, by Kurose&Ross Introduction 1-33 D E Two key work-core functions routing: determines source-destination route taken by packets # routing algorithms forwarding: moves packets from router s input to appropriate router output routing algorithm local forwarding table header value output link dest address in arriving packet s header From Computer Networking, by Kurose&Ross Introduction

18 Alternative core: circuit switching End-end resources allocated to, reserved for call between source & dest:! in diagram, each link has four circuits " call gets 2 nd circuit in top link and 1 st circuit in right link.! dedicated resources: no sharing " circuit-like (guaranteed) performance! circuit segment idle if not used by call (no sharing)! commonly used in traditional telephone works From Computer Networking, by Kurose&Ross Introduction 1-35 Network Core: Circuit Switching work resources (e.g., link 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 From Computer Networking, by Kurose&Ross Introduction

19 Circuit Switching: FDM versus TDM FDM (Frequency Division Multiplexing) Example: 4 users frequency TDM (Time Division Multiplexing) time frequency time From Computer Networking, by Kurose&Ross Introduction 1-37 WDM: Wavelength Division Multiplexing Same principle as FDM, used in fibers, (λ is the color of light ) In Dense WDM: 100 Gbps/λ, and λ per fiber From From Computer Computer Networks, Networking, by Tanenbaum by Kurose&Ross Prentice Hall Introduction

20 Packet switching versus circuit switching Packet switching allows more users to use work!! 1 Mbps link, shared! each user: " 0.1 Mbps when active " active 10% of time.. N users 1 Mbps link! circuit-switching: " 10 users max!! packet switching: " even with 35 users, probability of 10+ users active at same time is less than Q: how did we get value ? Q: how many users max? From Computer Networking, by Kurose&Ross Introduction 1-39 Packet switching versus circuit switching Is packet switching a slam dunk winner?! great for bursty data " resource sharing " simpler, no call setup! excessive congestion possible: packet delay and loss " protocols needed for reliable data transfer, congestion control! Q: How to provide circuit-like behavior? " data rate guarantees needed for audio/video apps " still a not so well solved problem (see book chapter 9) Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)? From Computer Networking, by Kurose&Ross Introduction

21 Inter structure: work of works! End systems connect to Inter via s (Inter Service Providers) # Residential, company and university s! Access s in turn must be interconnected # So that any two hosts can send packets to each other! Resulting work of works is very complex # Evolution was driven by economics and national policies! Let s take a stepwise approach to describe current Inter structure From Computer Networking, by Kurose&Ross Introduction 1-41 Inter structure: work of works Question: given millions of s, how to connect them together? From Computer Networking, by Kurose&Ross Introduction

22 Inter structure: work of works Option: connect each to every other? connecting each to each other directly doesn t scale: O(N 2 ) connections. From Computer Networking, by Kurose&Ross Introduction 1-43 Inter structure: work of works Option: connect each to a global transit? Customer and provider s have economic agreement global From Computer Networking, by Kurose&Ross Introduction

23 Inter structure: work of works But if one global is viable business, there will be competitors A B C From Computer Networking, by Kurose&Ross Introduction 1-45 Inter structure: work of works But if one global is viable business, there will be competitors which must be interconnected Inter exchange point A IXP IXP B C peering link From Computer Networking, by Kurose&Ross Introduction

24 Inter structure: work of works and regional works may arise to connect s to global s A IXP IXP B C regional From Computer Networking, by Kurose&Ross Introduction 1-47 Inter structure: work of works and content provider works (e.g., Google, Microsoft, Akamai) may run their own work, to bring services, content close to end users A B B From Computer Networking, by Kurose&Ross Introduction 1-48 IXP Content provider work IXP regional 24

25 Inter structure: work of works Tier 1 Tier 1 Google IXP IXP IXP Regional Regional! at center: small # of well-connected large works " tier-1 commercial s (e.g., Sprint, AT&T, NTT, Orange, Deutsche Telekom, ), national & international coverage " content provider work (e.g, Google): private work that connects its data centers to Inter, often bypassing tier-1, regional s From Computer Networking, by Kurose&Ross Introduction 1-49 Tier-1 : e.g., Sprint POP: point-of-presence to/from backbone peering to/from customers From Computer Networking, by Kurose&Ross Introduction

26 Inter structure: work of works A packet passes through many works! Path results from interdomain routing local Tier-3 Tier-2 local local Tier-2 local Tier-1 local Tier-1 Tier-2 local Tier-1 Tier-2 local Tier-2 local From Computer Networking, by Kurose&Ross Introduction 1-51 Chapter 1: roadmap 1.1 What is the Inter? 1.2 Network edge - end systems, works, links 1.3 Network core - packet switching vs circuit switching, work structure 1.4 Delay, loss and throughput in works 1.5 Protocol layers, service models 1.6 History From Computer Networking, by Kurose&Ross Introduction

27 How do loss and delay occur? packets queue in router buffers! packet arrival rate to link (temporarily) 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 From Computer Networking, by Kurose&Ross Introduction 1-53 Four sources of packet delay A transmission propagation B nodal processing queueing d nodal = d proc + d queue + d trans + d prop d proc : nodal processing # check bit errors # determine output link # typically < msec d queue : queueing delay # time waiting at output link for transmission # depends on congestion level of router From Computer Networking, by Kurose&Ross Introduction

28 Four sources of packet delay A transmission propagation B nodal processing queueing d nodal = d proc + d queue + d trans + d prop d trans : transmission delay: # L: packet length (bits) # R: link rate (bps) # d trans = L/R d trans and d prop very different d prop : propagation delay: # d: length of physical link # s: propagation speed in medium (~2x10 8 m/sec) # d prop = d/s From Computer Networking, by Kurose&Ross Introduction 1-55 Caravan analogy ten-car caravan toll booth 100 km 100 km toll booth! Car ~ bit; caravan ~ packet! cars propagate at 100 km/hr! toll booth takes 12 sec to service car (bit transmission time)! Q: How long until caravan is lined up before 2 nd toll booth?! time to push (transmit) entire caravan through toll booth onto highway = 12 x 10 = 120 sec! time for last car to propagate from 1 st to 2 nd toll both: 100km/(100km/hr) = 1 hr! A: 62 minutes From Computer Networking, by Kurose&Ross Introduction

29 Caravan analogy (more) 100 km 100 km ten-car caravan toll booth toll booth! suppose cars now propagate at 1000 km/hr! and suppose toll booth now takes one min to service a car! Q: Will cars arrive to 2 nd booth before all cars serviced at 1 st booth? # A: Yes! after 7 min, 1 st car arrives at second booth; three cars still at 1 st booth # This happens frequently with packets over work links From Computer Networking, by Kurose&Ross Introduction 1-57 Queueing delay (revisited)! R: link rate (bps)! L: packet length (bits)! a: average packet arrival rate average queuing delay! La/R ~ 0: avg. queuing delay small! La/R > 1: avg. queuing delay large! La/R > 1: more work arriving than can be serviced, average delay infinite! traffic intensity = La/R Typical delay versus throughput curve La/R ~ 0 La/R > 1 From Computer Networking, by Kurose&Ross Introduction

30 Real Inter delays and routes! what do real Inter delay & loss look like?! traceroute program: provides delay measurement from source to router along end-end Inter path towards destination! For all k: " sends three packets (probes) that will reach router k on path towards destination " router k will return packets to sender " sender times interval between transmission and reply 3 probes 3 probes 3 probes From Computer Networking, by Kurose&Ross Introduction 1-59 Real Inter delays, routes traceroute: gaia.cs.umass.edu to 3 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. ( ) 16 ms 11 ms 13 ms 5 jn1-so wae.vbns. ( ) 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. ( ) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant. ( ) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant. ( ) 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. ( ) 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 link * means no response (probe lost, router not replying) From Computer Networking, by Kurose&Ross Introduction

31 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 (rarely), by source end system, or not at all A buffer (waiting area) packet being transmitted B packet arriving to full buffer is lost From Computer Networking, by Kurose&Ross Introduction 1-61 Throughput! throughput: rate (in bits/sec) at which bits are transferred between sender/receiver " instantaneous: rate at given point in time practically, over a short period of time " average: rate over longer period of time server, with file of F bits to send to client server sends bits (fluid) into pipe link capacity R s bits/sec pipe that can carry fluid at rate R s bits/sec) link capacity R c bits/sec pipe that can carry fluid at rate R c bits/sec) From Computer Networking, by Kurose&Ross Introduction

32 Throughput (more)! R s < R c What is max end-end throughput? R s bits/sec R c bits/sec! R s > R c What is max end-end throughput? R s bits/sec R c bits/sec bottleneck link link on end-end path that constrains end-end throughput From Computer Networking, by Kurose&Ross Introduction 1-63 Throughput: Inter scenario 10 connections (fairly) share backbone bottleneck link R bits/sec R s R s R s R R c R c R c! per-connection end-end throughput: min (R c, R s, R/10)! in practice: R c or R s is often bottleneck From Computer Networking, by Kurose&Ross Introduction

33 Chapter 1: roadmap 1.1 What is the Inter? 1.2 Network edge - end systems, works, links 1.3 Network core - packet switching vs circuit switching, work structure 1.4 Delay, loss and throughput in packet-switched works 1.5 Protocol layers, service models 1.6 History From Computer Networking, by Kurose&Ross Introduction 1-65 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 work? Or at least our discussion of works? From Computer Networking, by Kurose&Ross Introduction

34 The philosopher-translator-secretary analogy Location A «App» 1 I like rabbits Message Philosopher J aime les lapins 3 Location B Translation service 2 L: Dutch Ik hou van konijnen Information for the remote translator Translator L: Dutch Ik hou van konijnen 2 Secretarial service 3 Fax #--- L: Dutch Ik hou van konijnen Information for the remote secretary Secretary Fax #--- L: Dutch Ik hou van konijnen 1 Telecom service From From Computer Computer Networks, Networking, by Tanenbaum by Kurose&Ross Prentice Hall Introduction 1-67 Another analogy: Organization of air travel ticket (purchase) baggage (check) gates (load) runway takeoff ticket (complain) baggage (claim) gates (unload) runway landing airplane routing airplane routing airplane routing a series of steps From Computer Networking, by Kurose&Ross Introduction

35 Layering of airline functionality ticket (purchase) ticket (complain) ticket baggage (check) baggage (claim) baggage gates (load) gates (unload) gate runway (takeoff) runway (land) takeoff/landing airplane routing airplane routing airplane routing airplane routing airplane routing departure airport intermediate air-traffic control centers arrival airport Layers: each layer implements a service " via its own internal-layer actions " relying on services provided by layer below From Computer Networking, by Kurose&Ross Introduction 1-69 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? From Computer Networking, by Kurose&Ross Introduction

36 Inter layers! application: supporting work applications " HTTP, FTP, SMTP,! transport: process-process data transfer " TCP, UDP! work: routing of datagrams from source to destination " IP, routing protocols! link: data transfer between neighboring work elements " Ether, WiFi,! physical: bit encoding/decoding application transport work link physical From Computer Networking, by Kurose&Ross Introduction 1-71 ISO/OSI reference model (1978)! ISO proposed two more layers " presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machinespecific conventions " session: synchronization, checkpointing, recovery of data exchange! Inter stack missing these layers! " these services, if needed, must be implemented in application " needed? application presentation session transport work link physical From Computer Networking, by Kurose&Ross Introduction

37 message segment H t datagram H n H t frame H l H n H t M M M M source application transport work link physical Encapsulation link physical switch H l H t H n H t H n H t M M M M destination application transport work link physical H n H t H l H n H t M M work link physical H n H t M router From Computer Networking, by Kurose&Ross Introduction 1-73 Chapter 1: roadmap 1.1 What is the Inter? 1.2 Network edge - end systems, works, links 1.3 Network core - packet switching vs circuit switching, work structure 1.4 Delay, loss and throughput in packet-switched works 1.5 Protocol layers, service models 1.6 History From Computer Networking, by Kurose&Ross Introduction

38 Inter History : Early packet-switching principles! 1961: L. Kleinrock - queuing theory shows effectiveness of packetswitching! 1964: P. Baran idea of packet-switching in military s, also for voice! 1967: ARPA conceived by US DoD s Advanced Research Projects Agency! 1969: first ARPA node operational! 1972: " ARPA public demonstration " NCP (Network Control Protocol) first host-host protocol " first program " ARPA has 15 nodes From Computer Networking, by Kurose&Ross Introduction 1-75 Growth of the ARPANET SRI UTAH SRI UTAH MIT SRI UTAH ILLINOIS MIT LINCOLN CASE UCSB UCSB SDC UCSB SDC CARN STAN UCLA UCLA RAND BBN (a) (b) MCCLELLAN SRI UTAH NCAR GWC LINCOLN CASE ILLINOIS RADC AMES USC CARN UCSB LINC MIT MITRE STAN SDC ETAC UCLA RAND TINKER BBN HARVARD NBS (d) SRI UCLA RAND BBN HARVARD BURROUGHS (c) LBL MCCLELLAN UTAH ILLINOIS MIT AMES TIP CCA BBN AMES IMP HARVARD LINC X-PARC ABERDEEN STANFORD NBS FNWC RAND ETAC TINKER ARPA MITRE RADC UCSB UCSD SAAC BELVOIR CMU UCLA SDC USC NOAA GWC CASE (e) (a) Dec (b) July (c) March (d) April (e) Sept From From Computer Computer Networks, Networking, by Tanenbaum by Kurose&Ross Prentice Hall Introduction

39 ARPANET in 1975 From Computer Networking, by Kurose&Ross Introduction 1-77 Inter History : Interworking, new and proprietary s! 1970: ALOHA satellite work in Hawaii! 1974: Cerf and Kahn - architecture for interconnecting works! 1976: Ether at Xerox PARC! late 70 s: proprietary architectures (DEC, SNA, XNA) then ISO reference model! late 70 s: switching fixed length packets in telecom s (X25, ATM precursor)! 1979: ARPA has 200 nodes Cerf and Kahn s interworking principles: " minimalism, autonomy - no internal changes required to interconnect works " best effort service model " stateless routers " decentralized control define today s Inter architecture From Computer Networking, by Kurose&Ross Introduction

40 Inter History : new protocols, a proliferation of works! 1982: smtp protocol defined! 1983: deployment of TCP/IP! 1983: DNS defined for name-to-ip-address translation! 1985: ftp protocol defined! 1988: congestion control added to TCP! new national works: CS (1981), BIT (1981), NSF (1985), Minitel (1982 -> 2012!)! 100,000 hosts connected to confederation of works From Computer Networking, by Kurose&Ross Introduction 1-79 Inter History 1990, 2000 s: commercialization, the Web, new apps! Early 1990 s: ARPA decommissioned! 1991: NSF lifts restrictions on commercial use of NSF (decommissioned, 1995)! early 1990s: Web " hypertext [Bush 1945, Nelson 1960 s] " HTML, HTTP: Berners-Lee " 1994: Mosaic browser, later Netscape " late 1990 s: commercialization of the Web Late 1990 s 2000 s:! more killer apps: instant messaging, P2P file sharing! work security to forefront! est. 50 million hosts, 100+ million users! backbone links running at Gbps From Computer Networking, by Kurose&Ross Introduction

41 Inter History 2005-present! Aggressive deployment of broadband! Increasing ubiquity of high-speed wireless! Emergence of online social works: " Facebook: 2.2 billion users in 2018! Service providers (Google, Microsoft) create their own works " Bypass Inter, providing instantaneous to search, video, , etc.! E-commerce, universities, enterprises running their services in cloud (e.g., Amazon EC2)! Inter of Things (IoT)! July 2018: " ~23 billion connected devices (PCs, smartphones, tablets, sensors) " ~4.1 billion Inter users " ~5.1 billion mobile telephony (3G and beyond) users " ~1.9 billion web sites From Computer Networking, by Kurose&Ross Introduction 1-81 Introduction: Summary Glanced through a ton of material!! Inter overview! what s a protocol?! work edge, core, work " packet-switching versus circuit-switching " Inter structure! performance: loss, delay, throughput! layering, service models! history You now have:! context, overview, feel of working! more depth, detail to follow! From Computer Networking, by Kurose&Ross Introduction