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Introduction 1-1 Data Networks. Organization: Core lecture, 9 ECTS points Lectures: Tue 10-12 (Günter-Hotz lecture hall), Thu 12- 14 (HS002 except for.

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Presentation on theme: "Introduction 1-1 Data Networks. Organization: Core lecture, 9 ECTS points Lectures: Tue 10-12 (Günter-Hotz lecture hall), Thu 12- 14 (HS002 except for."— Presentation transcript:

1 Introduction 1-1 Data Networks

2 Organization: Core lecture, 9 ECTS points Lectures: Tue (Günter-Hotz lecture hall), Thu (HS002 except for 25th) Tutorial: Fri (HS002, except for May 31 st, June 21 st ) Written exam (25.07), re-exam (beginning of October) Weekly quizzes on Wednesdays: 50% of points to participate in exam Weekly exercises (optional): solutions are discussed in tutorial (sheets are uploaded one week earlier)

3 Data Networks Organization: Questions about the organization: {turrini, spieler, Course webpage: mosi.cs.uni-saarland.de -> teaching you may post live comments during the lecture: everything you want to discuss immediately without interrupting the presentation you may also post interesting links related to the material presented feedback concerning the presentation forum for “dead (not live)” comments/questions

4 Data Networks Literature: Computer Networking by J.F Kurose and K.W. Ross, 6 th edition (Chapter 1-6) (=> Bock & Seip store on campus!) Data Networks by Dimitri P. Bertsekas and Robert G. Gallager, 2 nd edition (Chapter 3)

5 Syllabus 1: Introduction: Broad overview of computer networking and the Internet 2: Application Layer: HTTP, FTP, SMTP, DNS, P2P, … 3: Transport Layer: Multiplexing, TCP, Congestion control, … 4: Network Layer: IP and routing, … 5: Link Layer: Links, Access Networks, LANs, … 6: Wireless Networks 7: Delay Models: Little’s Theorem, Queueing Systems, … Further reading: Computer Networking by J.F Kurose and K.W. Ross, 6 th edition (Chapter 7-9) Multimedia Networking, Security in Computer Networks, Network Management Computer Networks by A. Tanenbaum, 4th ed Computer Networks by L. Peterson, B. Davie, 5th Edition

6 Syllabus What this lecture is (not) about: Fundamental principles of computer networks in general! Internet is just an instance/ an example where we can see how things are implemented in practice. Not: details of most recent developments of the Internet (currently “in”, may be “out” in two years...)

7 Introduction Chapter 1: introduction our goal:  get broad overview and terminology  more depth, detail later in course  approach:  use Internet as example overview:  what’s the Internet?  what’s a protocol?  network edge; hosts (servers, Laptops, smartphones,...)  network core: packet/circuit switching, Internet structure  performance: loss, delay, throughput  security (no details later)  protocol layers  history 1-7

8 Introduction Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge 1.3 network core 1.4 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 networks under attack: security 1.7 history 1-8

9 Introduction What’s the Internet: “nuts and bolts” view  hundreds of millions of connected computing devices:  hosts = end systems  running network apps  communication links  coaxial cable, copper, fiber, radio, …  transmission rate: bandwidth  Packet switches: receive and forward packets (chunks of data)  routers and switches wired links wireless links router mobile network global ISP regional ISP home network (WiFi) institutional network smartphone PC server wireless laptop 1-9

10 Introduction  Internet Service Provider (ISP):  End systems access the Internet through ISPs  Interconnected ISPs (=> “network of networks”)  classification according to size (Tier 3 (local), Tier 2 (national), Tier 1(global/international)  protocols control sending, receiving of msgs  e.g., TCP, IP, HTTP, SMTP, …  Internet standards  different components of the internet have to agree on standards to interoperate  IETF: Internet Engineering Task Force develops and promotes such standards  IETF publishes RFCs (Requests for comments) describing/defining protocols What’s the Internet: “nuts and bolts” view mobile network global ISP regional ISP home network institutional network 1-10

11 What’s the Internet: a service view  Infrastructure that provides services to applications:  Web, VoIP, , distributed games, P2P, social nets,...  applications are distributed (involve multiple hosts exchanging data)  End systems provides applic. programming interface to apps  rules for exchanging data between programms  provides service options, analogous to postal service mobile network global ISP regional ISP home network institutional network Introduction 1-11 The Internet from a different perspective:

12 "Questions?" raise hand “Yes?" ask Introduction a human analogy: Hi Got the time? 2:00 time What’s a protocol? 1-12 answer teacher “broadcast”

13 Introduction a human protocol and a computer network protocol: Hi Got the time? 2:00 TCP connection response Get time TCP connection request What’s a protocol? 1-13

14 Introduction What’s a protocol? network protocols:  communication between machines rather than humans  all communication activity in Internet governed by protocols protocols define format, order of messages sent and received among network entities, and actions taken on message transmission or receipt 1-14

15 Introduction Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge 1.3 network core 1.4 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 networks under attack: security 1.7 history 1-15 just a quick overview; no technical details!

16 Introduction A closer look at network structure:  network edge:  hosts: clients and servers  home-based hosts: desktop computers, laptops, smartphones, tablets  servers often reside in large data centers (Web, ) mobile network global ISP regional ISP home network institutional network 1-16

17 Introduction Non-traditional end systems IP picture frame Web-enabled toaster + weather forecaster Internet phones Internet refrigerator Slingbox: watch, control cable TV remotely 1-17 Tweet-a-watt: monitor energy use

18 Introduction A closer look at network structure:  network edge:  hosts: clients and servers  access networks: physical connection of end system to first router (“edge router”); wired or wireless communication links  network core:  interconnected routers  network of networks mobile network global ISP regional ISP home network institutional network 1-18

19 Introduction Access networks and physical media How to connect end systems to edge router? different types  residential access nets  institutional access networks (school, company)  mobile access networks 1-19 edge router

20 Access net: digital subscriber line (DSL) DSL Internet access obtained from local telephone company => ISP Market share in Germany 86% (in 2012) use existing telephone line (copper wire, analog transmission) to DSL access multiplexer (DSLAM) of phone company DSLAM usually located in the central office (CO)„Vermittlungsstelle“ (or it is an outdoor DSLAM) data over DSL line goes to Internet voice over DSL line goes to telephone net

21 Introduction Access net: digital subscriber line (DSL) central office ISP telephone network DSLAM voice, data transmitted at different frequencies over dedicated line to central office  use different frequencies for telephone and Internet data => splitter separates rec. signal & forwards data to DSL modem  DSLAM separates the incoming data/phone signals and translates it into digital format  rates are either limited by ISP or because of the distance to CO DSL modem splitter DSL access multiplexer 1-21

22 Introduction cable modem splitter … cable headend CMTS ISP cable modem termination system  make use of the cable television infrastructure  residence: needs cable modem to exchange data with cable modem termination system (CMTS)  splitter often integrated in cable modem  both optical fibre and coaxial cable are employed (HFC: hybrid fiber coax) Access net: cable network 1-22

23 Introduction data, TV transmitted at different frequencies over shared cable distribution network cable modem splitter … cable headend CMTS ISP cable modem termination system  network of cable/fiber attaches homes to ISP router  homes share access network to cable headend  => transm. rate decreases in case of high traffic  => requested data packets are sent to all connected participants of a group  unlike DSL, which has dedicated access to central office Access net: cable network 1-23

24 Introduction Access net: home network to/from headend or central office cable or DSL modem router wired Ethernet (100 Mbps) wireless access point (54 Mbps) wireless devices often combined in single box 1-24

25 Introduction Enterprise access networks (Ethernet)  typically used in companies, universities, etc  transmission rates:  10 Mbps to 100Mbps (users),  1Gbps, 10Gbps (servers)  today, end systems typically connect into Ethernet switch Ethernet switch institutional mail, web servers institutional router institutional link to ISP (Internet) 1-25

26 Introduction Wireless access networks  wireless access network connects end system to router  via “access point”; uses radio signals to transmit data  access point shared by several end systems wireless LANs:  IEEE technology (WiFi)  up to 54 Mbps transmission rate  range: typically a few 10 meters wide-area wireless access  use infrastructure of cellular telephony  connect to base stations  range: few 10’s of km to Internet 1-26 distinguish between maximal bandwidths

27 Physical media Introduction  bit: sent by propagating electromagnetic waves (analog signal) or optical pulses (digital signal) between transmitter/receiver pairs  physical link: what lies between transmitter & receiver  distinguish:  guided media: signals propagate in solid media: copper, fiber-optic, coaxial  unguided media: signals propagate freely, e.g., radio waves twisted pair (TP) copper wire  two insulated copper wires arranged in regular spiral pattern  least expensive, most commonly used  10 Mbps to 10 Gpbs  Ethernet, DSL 1-27

28 Introduction Physical media: coax, fiber coaxial cable:  two concentric copper conductors  used for HFC (hybrid fibre coaxial) access via (cable internet) fiber optic cable:  glass fiber carrying light pulses (digital signal)  high-speed point-to-point transmission (10’s-100’s Gpbs)  low error rate ( immune to electromagnetic noise)  transmitters, receiver, switches are costly  long distance link (oversea)  prevalent in Internet backbone 1-28

29 Introduction Physical media: radio radio link types:  terrestrial radio channels  short distance (e.g. Bluetooth)  LAN (e.g., WiFi)  cellular access (wide–area wireless access)  satellite links  used if DSL or cable is not available  transmission rate:10’s of Mbps  > 270 msec signal propagation delay (DSL has ony 20 ms)  typically using a geostationary satellite  location needs to be in the footprint of the satellite  influenced by meteorological factors 1-29

30 Introduction Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge  end systems, access networks, links 1.3 network core  packet switching, circuit switching, network structure 1.4 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 networks under attack: security 1.7 history 1-30

31 Introduction  mesh of interconnected routers  What do routers do? packet-switching:  hosts run network apps and break application-layer messages into packets  forward packets from one router to the next, across links on path from source to destination  packets may be buffered and queue while passing network nodes The network core 1-31

32 Host: sends packets of data host sending function:  takes application message  breaks into smaller chunks, known as packets, of length L bits (packetization)  transmits packet into access network at transmission rate R (bits/sec)  link transmission rate = link bandwidth R: link transmission rate host 1 2 two packets, L bits each packet transmission delay time needed to transmit L-bit packet into link L (bits) R (bits/sec) = = How many seconds does it take to transmit one L-bit paket?

33 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 access network at transmission rate R (bits/sec)  transmission delay = time for pushing the packet‘s bits into the link  propagation delay = traveling across the wire R: link transmission rate host 1 2 two packets, L bits each

34 Introduction Packet-switching: store-and-forward mechanism  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 one-hop numerical example:  L = 7.5 Mbits  R = 1.5 Mbps  one-hop transmission delay = 5 sec more on delay shortly … 1-34 source R bps destination L bits per packet R bps  end-end delay (two links with bandwidth R)= 2L/R (assuming zero propagation delay)

35 Introduction Packet-switching: store-and-forward  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 1-35 source R bps destination L bits per packet R bps  Question: What is the end-end delay if a packet is sent via N links (and N-1) routers?  end-end delay = 2L/R (assuming zero propagation delay) N x L/R

36 Introduction Packet Switching: queueing delay, loss 1-36 queuing and loss:  routers have one buffer per outgoing link => store packets that the router is about to send into the link  If arrival rate (in bits) 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 A B C R = 100 Mb/s R = 1.5 Mb/s D E queue of packets waiting for output link

37 Network Layer 4-37 Key functions in paket switching forwarding : move packets from router’s input to appropriate router output routing: determines source- destination route taken by packets  routing algorithms routing algorithm local forwarding table header value output link dest address in arriving packet’s header

38 Introduction Paket vs. circuit switching two fundamental approaches for moving data through a network: packets switching and circuit switching in packet-switched networks resources are NOT reserved (=> no guarantees!) restaurant analogy: just go there without reservation! - in circuit-switched networks resources are reserved - links are separated into circuit segments - fraction of each links transmission capacity is reserved for the duration of the connection restaurant analogy: reserve a table in advance!

39 Introduction Alternative core: circuit switching resources (buffers, links, transmission rate) are reserved for “call” between source & destination:  Here, 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) constant transmission rate  circuit segment idle if not used by call (no sharing)  no store and forward => transmission time independent of number of links 1-39 Commonly used in traditional telephone networks

40 Introduction Circuit switching: FDM versus TDM Frequency-division multiplexing frequency time Time-division multiplexing frequency time 4 users Example: 1-40

41 Introduction Packet switching versus circuit switching example:  users share 1000 kb/s link  each user: wants to transmit 100 kb/s when “active” active 10% of time  circuit-switching:  can have at most ? users  packet switching:  with 35 users, probability > 10 active at same time is less than.0004 packet switching allows more users to use network! N users 1000 kb/s link Q: how did we get value ? Q: what happens if > 35 users ? … => 3 times more users at the same performance with prob 99,96 % 10

42 Introduction  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  Problem: How to provide circuit-like behavior?  bandwidth guarantees needed for audio/video streaming  still an unsolved problem... packet switching Packet switching versus circuit switching 1-42

43 Internet structure: network of networks  End systems connect to Internet via access ISPs (Internet Service Providers)  Residential, company and university ISPs  Access ISPs in turn must be interconnected.  So that any two hosts can send packets to each other Let’s now take a stepwise approach to describe the current Internet structure.

44 Internet structure: network of networks Question: given thousands of access ISPs, how to connect them together? access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … …

45 Internet structure: network of networks Option: connect each access ISP to every other access ISP? access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … … … … … … connecting each access ISP to each other directly doesn’t scale: O(N 2 ) connections.

46 Internet structure: network of networks access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … Option: connect each access ISP to a single global transit ISP? Access ISPs (customers) have to pay global ISP for traffic => customer and provider ISPs need economic agreement. global ISP

47 Internet structure: network of networks access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … But if one global ISP is viable business, there will be competitors …. ISP B ISP A ISP C

48 Internet structure: network of networks access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … But if one global ISP is viable business, there will be competitors …. which must be interconnected ISP B ISP A ISP C IXP peering link Internet exchange point (multiple ISPs peer together)

49 Internet structure: network of networks access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … … and regional networks may arise to connect access nets to ISPS ISP B ISP A ISP C IXP regional net

50 Internet structure: network of networks access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net … … … … … … … and content provider networks (e.g., Google, Microsoft,...) may run their own network, to bring services, content close to end users ISP B ISP A ISP B IXP regional net Content provider network

51 Introduction Internet structure: network of networks  Tier-1 commercial ISPs: national & international coverage, providers of Internet backbone (backbone is the core of the actual internet)  content provider network (e.g, Google): private network that connects it data centers to Internet, often bypassing tier-1, regional ISPs 1-51 access ISP access ISP access ISP access ISP access ISP access ISP access ISP access ISP Regional ISP IXP Tier 1 ISP Google IXP at center: small # of well- connected large networks

52 Introduction Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge  end systems, access networks, links 1.3 network core  packet switching, circuit switching, network structure 1.4 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 networks under attack: security 1.7 history 1-52

53 Introduction How do loss and delay occur? packets queue in router buffers  packet arrival rate to link (temporarily) exceeds output link transmission rate  packets queue, wait for turn A B packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers 1-53

54 Introduction Four sources of packet delay d proc : nodal processing  examine header of packet  check for bit-level errors  determine output link  typically < 1/100 millisec (ms) A B propagation transmission nodal processing queueing d queue : queueing delay  time waiting at output link for transmission  depends on congestion level of router  1/1000 – 1 ms d nodal = d proc + d queue + d trans + d prop 1-54

55 Introduction d trans : transmission delay:  L: packet length (bits)  R: link bandwidth (bps)  d trans = L/R d prop : propagation delay:  d: length of physical link  s: propagation speed in medium (~2x10 8 meters/sec)  d prop = d/s  in wide area networks: order of milliseconds otherwise negligible Four sources of packet delay propagation nodal processing queueing d nodal = d proc + d queue + d trans + d prop 1-55 A B transmission

56 Introduction Caravan analogy  “propagation speed” of cars: 100 km/hr  cars have fixed order  toll booth: on arrival, first car waits for others; takes 12 sec to service a car (bit 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 toll booth toll booth ten-car caravan 100 km 1-56 highway

57 Introduction Caravan analogy (more)  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 2nd booth before all cars serviced at first booth?  A: Yes! after 7 min, 1st car arrives at second booth; three cars still at 1st booth. => this situation arises in packet-switched networks: bits arrive at the router before the last bit is pushed into the link at the source router toll booth toll booth ten-car caravan 100 km 1-57

58 Introduction cw/index.html

59  total delay from source to destination  N-1 routers on the path between source host and destination host  assume no queueing  assume d proc is processing delay at each router (and source host)  transmission rate out of each router and out of source host is R  => d trans = L/R (L is size of packet)  propagation delay d prop of each link  What is the end-to-end delay? End-to-end delay Introduction 1-59 d end-to-end = N ( d proc + d trans + d prop )

60 Introduction  R: link bandwidth (bits/sec)  L: packet length (bits)  a: average packet arrival rate (in packets/sec)  λ= a x L is arrival rate (bits/sec) traffic intensity = λ/R  λ /R ~ 0: avg. queueing delay small  λ /R 1: avg. queueing delay large  λ /R > 1: more “work” arriving than can be serviced, average delay infinite! average queueing delay La/R ~ 0 La/R subject of intense research => more about this in a couple of weeks Queueing delay (revisited)

61 Introduction Packet loss  queue that precedes the link in buffer has finite capacity  packet arriving to full queue dropped (=> lost)  lost packet may be retransmitted by previous node, by source end system, or not at all A B packet being transmitted packet arriving to full buffer is lost buffer (waiting area) 1-61 * Check out the Java applet for an interactive animation on queuing and loss

62 Introduction “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 (=> 3N packets in total)  router i will return packets to sender  time interval between start of transmission and reply (response time) 3 probes 1-62

63 Introduction “Real” Internet delays, routes 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 traceroute: gaia.cs.umass.edu to 3 delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu * means no response (probe lost, router not replying) trans-oceanic link 1-63 * Do some traceroutes from exotic countries at

64 Introduction 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 server has file of F bits to send to client link bandwidth R s bits/sec link bandwidth R c bits/sec Bits can be seen as fluid that is pumped into pipe, bandwidth corresponds to link capacity! 1-64 e.g. file of F bits is transferred within T seconds => average throughput? F/T

65 Introduction Throughput (more)  R s < R c What is average (approx) end-end throughput? R s bits/sec R c bits/sec  R s > R c What is average (approx) end-end throughput? R s bits/sec R c bits/sec 1-65 File of size F needs F/min{Rc, Rs} time to be transmitted, since at both links we cannot transmit faster than at rate min{Rc, Rs} (think about the last bit of the file!)

66 Introduction Throughput (more)  R 1,..., R N What is average end-end throughput? link on end-end path that constrains end-end throughput bottleneck link 1-66 min{R 1,..., R N }

67 Introduction Throughput: Internet scenario 10 connections (fairly) share backbone bottleneck link R bits/sec RsRs RsRs RsRs RcRc RcRc RcRc R  10 simultaneous downloads involving 10 client-server pairs  all through a link with rate R  per-connection end-end throughput?  => link may be a bottleneck  in practice: R c or R s is often bottleneck (because link in the core has very high rate) min{R c,R s,R/10}

68 Introduction Bits and Bytes, Kilo, Mega, Giga 1-68 In concrete examples, we might have to convert between bits and bytes, kilo-x, mega-x, giga-x, tera-x 1 bit is either a 1 or 0 (b) 8 bits = 1 byte (B) 1024 bytes = 1 Kibibyte (KiB) = 2^10 bytes 1024 Kibibytes = 1 Mebibyte (MiB) = 2^20 bytes 1024 Mebibytes = 1 Gibibyte (GiB) = 2^30 bytes 1024 Gibibytes = 1 Tebibyte (TiB) = 2^40 bytes Common prefixes: - kilox (Kx) -> 1,000 =10^3 (one thousand) - megax (Mx) -> 1,000,000=10^6 (one million) - gigax (Gx) -> 1,000,000,000=10^9 (one billion) - terax (Tx) ->1,000,000,000,000= 10^12 (one trillion) upper case/lower case

69 Introduction Bits and Bytes, Kilo, Mega, Giga 1-69 In concrete examples, we might have to convert between bits and bytes, kilo-x, mega-x, giga-x, tera-x 10 Mb to KB = 1500 KB to Mb = 1 GiB to MB = 1 TB to GiB = (10^12)/2^30 GiB ≈ GiB (10*10^6)/(8*10^3) KB = 1250 KB (1500*10^3*8)/10^6 Mb = 12 Mb (2^30)/10^6 MB ≈ MB

70 Introduction Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge  end systems, access networks, links 1.3 network core  packet switching, circuit switching, network structure 1.4 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 networks under attack: security 1.7 history 1-70

71 Introduction Protocol “layers” Networks are complex, with 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? 1-71

72 Introduction Organization of air travel  a series of steps/ actions ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain if trip was bad) baggage (claim) gates (unload) runway landing airplane routing 1-72

73 Introduction ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival airport intermediate air-traffic control centers airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing ticket baggage gate takeoff/landing airplane routing Layering of airline functionality layers: each layer implements a service  via its own internal-layer actions  relying on services provided by layer below 1-73

74 Introduction Why layering? dealing with complex systems:  allows to identify the relationships of the complex pieces of the system  modularization eases maintenance, updating of system  e.g., change in gate procedure (say, order in which passengers are boarding) doesn’t affect rest of system 1-74

75 Introduction Network protocols  application: supporting network applications  FTP, SMTP, HTTP, DNS application transport network link physical 1-75 Internet protocol stack

76 Introduction Network protocols  application: supporting network applications  FTP, SMTP, HTTP, DNS  transport: process-process data transfer  TCP (guaranteed delivery, congestion control),  UDP (connectionless)  transport-layer packets = segments application transport network link physical 1-76 Internet protocol stack

77 Introduction Network protocols  application: supporting network applications  FTP, SMTP, HTTP  transport: process-process data transfer  TCP, UDP  transport-layer packets = segments  network: routing of datagrams from source to destination  IP Protocol, routing protocols application transport network link physical 1-77 Internet protocol stack

78 Introduction Network protocols  application: supporting network applications  FTP, SMTP, HTTP  transport: process-process data transfer  TCP, UDP  transport-layer packets = segments  network: routing of datagrams from source to destination  IP, routing protocols  link: data transfer between neighboring network elements  Ethernet, (WiFi), PPP  physical: bits “on the wire” application transport network link physical 1-78 Internet protocol stack

79 Introduction Network protocols application transport network link physical 1-79 Internet protocol stack messages segments datagrams frames packets are called...

80 Introduction source application transport network link physical HtHt HnHn M segment HtHt datagram destination application transport network link physical HtHt HnHn HlHl M HtHt HnHn M HtHt M M network link physical link physical HtHt HnHn HlHl M HtHt HnHn M HtHt HnHn M HtHt HnHn HlHl M router switch Encapsulation message M HtHt M HnHn frame 1-80 Paket switches implement only the bottom layers – they are ‘transparent‘ to the hosts and routers! Encapsulation (slightly) increases frame size. extract enclosed datagram

81 Introduction Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge  end systems, access networks, links 1.3 network core  packet switching, circuit switching, network structure 1.4 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 networks under attack: security 1.7 history 1-81

82 Introduction Network security  field of network security:  how bad guys can attack computer networks  how we can defend networks against attacks  how to design architectures that are immune to attacks => part of security course offered every two years at UdS 1-82

83 Introduction Bad guys: put malware into hosts via Internet  malware (software doing bad things) can get in host from:  virus: corrupts or modifies files on target host; typically user runs infected program; self-replicating infection but cannot be spread without a human action  worm: exploits security vulnerabilities to spread passively (travel without any human action); does not attach itself to an existing program; takes advantage of system's transport features, which is what allows it to travel unaided  spyware can record keystrokes, web sites visited, upload info to collection site 1-83

84 Introduction Denial of Service (DoS): attackers make resources (server, bandwidth) unavailable to legitimate users - vulnerability attack: send message to vulnerable application => service stops or host crashes - bandwidth flooding: send so many (fake) packets that target’s access link becomes clogged (‘verstopft’) - connection flooding: establish large number of TCP connections (=> Chapter 3) Bad guys: attack server, network infrastructure 1-84

85 Introduction target Distributed Denial of Service (DDoS) bandwidth flooding: 1. select target 2. break into hosts around the network 3. send packets to target from compromised hosts Bad guys: attack server, network infrastructure 1-85 make sure that aggregate traffic rate is approx. equal to access rate of server

86 Introduction Bad guys can sniff packets packet “sniffing”:  broadcast media (shared ethernet, wireless)  network interface reads/records all packets (e.g., including passwords!) passing by A B C src:B dest:A payload  best defense is strong encryption => cryptography lecture at UdS 1-86

87 Introduction Bad guys can use fake addresses IP spoofing: send packet with false source address (e.g. C pretends to be B ) A B C src:B dest:A payload 1-87  flood victim with fake traffic; attacker does not care about responses to the attack packets  each spoofed packet appears to come from a different address (=> filtering is difficult!)  best defense is end-point authentication (determine identity of sender with certainty)

88 Introduction Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge  end systems, access networks, links 1.3 network core  packet switching, circuit switching, network structure 1.4 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 networks under attack: security 1.7 history 1-88

89 Introduction Internet history  early 1960s: telephone network was dominant communication network (circuit switching!!!) ... paket switching was invented (Paul Baran)  1961: Kleinrock - queueing theory shows effectiveness of packet-switching  1964: Baran - packet- switching in military nets  1969: ARPAnet - first packet-switched computer network at MIT  1972:  NCP (Network Control Protocol) first host-host protocol; predecessor of TCP/IP  first program (1971)  file transfer (1973) : Early packet-switching principles 1-89

90 Introduction Internet history  1961: Kleinrock - queueing theory shows effectiveness of packet-switching  1964: Baran - packet- switching in military nets  1969: ARPAnet - first packet-switched computer network at MIT : Early packet-switching principles 1-90 nodes and connections of the ARPA-net in 1974  1972:  NCP (Network Control Protocol) first host-host protocol; predecessor of TCP/IP  first program (1971)  file transfer (1973)

91 Introduction  1970: ALOHAnet satellite network in Hawaii (wireless paket- based radio network)  : growing number of other stand-alone packet- switching networks  1974: Cerf and Kahn invented architecture for interconnecting networks => early TCP  1976: Ethernet for wire-based shared broadcast networks  1979: ARPAnet had 200 nodes : Growing number of networks Internet history 1-91

92 Introduction  1983: deployment of TCP/IP in ARPAnet (replacing NCP)  1982: smtp protocol defined  1983: DNS defined for name-to-IP-address translation  1985: ftp protocol defined  1988: TCP congestion control : new protocols and growths of networks Internet history 1-92

93 Introduction  early 1990’s: ARPAnet decommissioned (replaced by a new network of the NSF)  early 1990s: World Wide Web started as a CERN-project (Switzerland)  purpose: share information among researchers.  HTML, HTTP  Mosaic, later Netscape  late 1990’s: commercialization of the Web  1993: CERN announced that WWW is free to anyone late 1990’s – 2000’s:  more killer apps: instant messaging, P2P file sharing (Napster!!!)  about 50 million hosts, 100 million users  thousands of startups creating Internet products and services  Internet stocks collapsed in  some winners: Microsoft, Cisco, Yahoo, e-Bay, Google, Amazon 1990, 2000’s: commercialization, the Web, new apps Internet history 1-93

94 Introduction 2005-present  ~350 million hosts in 2005, ~750 million hosts in 2010  Aggressive deployment of broadband access (DSL, Cable)  Increasing availability of high-speed wireless access  Emergence of online social networks:  Facebook: since October 2012 one billion users (~ number of habitants in Europe and the US)  Service providers (Google, Microsoft) create their own networks  Bypass Internet, providing “instantaneous” access to search, , etc.  E-commerce, universities, enterprises running their services in “cloud” (e.g. and Web hosting)=> end users access cloud-based applications through a web browser Internet history 1-94

95 Introduction 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  security  history you now have:  context, overview, “feel” of networking  more depth, detail to follow! 1-95


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