1. Lect. 1: Oct 14, 2013 Computer Networking Prof. Hanoch Levy (hanoch at cs.tau.ac.il )hanoch at cs.tau.ac.il Teaching Assistant: Allon Wagner 1

2. Lect. 1: Oct 14, 2013 Course Information Lectures: Wednesday 12 - 15 Dach 005 Exercises: Monday 10 – 11, 11 – 12 Shenkar – Physics 104 Web site: http://www.cs.tau.ac.il/~allonwag/comnet2014A/index.html 1.An Engineering Approach to Computer Networking / Keshav 2.Computer Networks / Tanenbaum 3.Data Networks / Bertsekas and Gallager A Top-down Approach to Computer Networking / Kurouse-Ross Books: 2/71

3. Lect. 1: Oct 14, 2013 Practical Information Homework assignment: Mandatory Both theoretical and programming Grades: Final Exam: 60% theory exercises: 20% Programming exercises: 20% 3/71

4. Lect. 1: Oct 14, 2013 Motivation Today ’ s economy manufacturing, distributing, and retailing goods but also creating and disseminating information publishing banking film making …. part of the ‘ information economy ’ Future economy is likely to be dominated by information! 4/71

5. Lect. 1: Oct 14, 2013 Information? A representation of knowledge Examples: books bills CDs & DVDs Can be represented in two ways analog (waves/atoms) digital (bits) the Digital Revolution convert information as waves/atoms to info as bits use networks to move bits around instead of atoms 5/71

6. Lect. 1: Oct 14, 2013 The Challenges t represent all types of information as bits. t move the bits u In large quantities, u everywhere, u cheaply, u Securely, u with quality of service,  …. 6/71

7. Lect. 1: Oct 14, 2013 Today’s Networks are complex! t hosts t routers t links of various media t applications t protocols t hardware, software Tomorrow ’ s will be even more! 7/71

8. Lect. 1: Oct 14, 2013 8 Backbone ISP ISP Internet Physical Infrastructure Residential access Cable Fiber DSL Wireless Campus access, e.g., m Ethernet m Wireless r The Internet is a network of networks r Each individually administrated network is called an Autonomous System (AS) 8/71

9. Lect. 1: Oct 14, 2013 This course ’ s Challenge To discuss this complexity in an organized way, that will make today ’ s computer networks (and their limitations) more comprehensive. identification, and understanding relationship of complex system ’ s pieces. Problems that are beyond a specific technology 9/71

10. Lect. 1: Oct 14, 2013 Early communications systems I.e. telephone point-to-point links directly connect together the users wishing to communicate use dedicated communication circuit if distance between users increases beyond the length of the cable, the connection is formed by a number of sections connected end-to-end in series. 10/71 Circuit switching

11. Lect. 1: Oct 14, 2013 Data Networks set of interconnected nodes exchange information sharing of the transmission circuits= "switching". many links allow more than one path between every 2 nodes. network must select an appropriate path for each required connection. 11/71

12. Lect. 1: Oct 14, 2013 Qwest backbone http://www.qwest.com/largebusiness/enterprisesolutions/networkMaps/preloader.swf 12/71

13. Lect. 1: Oct 14, 2013 Networking Issues - Telephony  Addressing - identify the end user phone number 1-201-222-2673 = country code + city code + exchange + number  Routing - How to get from source to destination. Telephone circuit switching: Based on the phone number.  Information Units - How is information sent telephone Samples @ Fixed sampling rate. not self descriptive! have to know where and when a sample came 13/71

14. Lect. 1: Oct 14, 2013 Networking Issues - Internet  Addressing - identify the end user IP addresses 132.66.48.37, Refer to a host interface = network number + host number  Routing- How to get from source to destination Packet switching: move packets (chunks) of data among routers from source to destination independently.  Information Units - How is information sent. Self-descriptive data: packet = data + metadata (header). 14/71

15. Lect. 1: Oct 14, 2013 Telephone networks support a single, end-to- end quality of service but is expensive to boot Internet supports no quality of service but is flexible and cheap Future networks will have to support a wide range of service qualities at a reasonable cost 15/71

16. Lect. 1: Oct 14, 2013 History 1961-1972: Early packet-switching principles 1961: Kleinrock - queuing theory shows effectiveness of packet-switching 1964: Baran - packet-switching in military networks 1967: ARPAnet – conceived by Advanced Research Projects Agency 1969: first ARPAnet node operational 1972: ARPAnet demonstrated publicly NCP (Network Control Protocol) first host-host protocol first e-mail program ARPAnet has 15 nodes 16/71

17. Lect. 1: Oct 14, 2013 History 1972-1980: Internetworking, new and proprietary nets 1970: ALOHAnet satellite network in Hawaii 1973: Metcalfe ’ s PhD thesis proposes Ethernet 1974: Cerf and Kahn - architecture for interconnecting networks late70 ’ s: proprietary architectures: DECnet, SNA, XNA late 70 ’ s: switching fixed length packets (ATM precursor) 1979: ARPAnet has 200 nodes 17/71

18. Lect. 1: Oct 14, 2013 Cerf and Kahn ’ s internetworking principles: minimalism, autonomy - no internal changes required to interconnect networks best effort service model stateless routers decentralized control Defines today ’ s Internet architecture 18/71

19. Lect. 1: Oct 14, 2013 History 1980-1990: new protocols, proliferation of networks 1983: deployment of TCP/IP 1982: SMTP e-mail protocol defined 1983: DNS defined for name-to-IP-address translation 1985: FTP protocol defined 1988: TCP congestion control new national networks: CSnet, BITnet, NSFnet, Minitel 100,000 hosts connected to confederation of networks 19/71

20. Lect. 1: Oct 14, 2013 History 1990 - : commercialization and WWW early 1990 ’ s: ARPAnet decommissioned 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) early 1990s: WWW hypertext [Bush 1945, Nelson 1960 ’ s] HTML, http: Berners-Lee 1994: Mosaic, later Netscape late 1990 ’ s: commercialization of WWW 20/71

21. Lect. 1: Oct 14, 2013 Demand and Supply Huge growth in users The introduction of the web Faster home access Better user experience. Infrastructure Significant portion of telecommunication. New evolving industries Although, sometimes temporary setbacks 21/71

22. Lect. 1: Oct 14, 2013 Internet: Users 22/71

23. Lect. 1: Oct 14, 2013 Penetration around the Globe (2009) http://www.internetworldstats.com/stats.htm 23/71

24. Lect. 1: Oct 14, 2013 Users around the Globe (2002/5/9) 24/71

25. Lect. 1: Oct 14, 2013 Technology: Modem speed 25/71

26. Lect. 1: Oct 14, 2013 Today ’ s options Modem: 56 K ISDN: 64K – 128K Frame Relay: 56K ++ Today High Speed Connections Cable, ADSL, Satellite. All are available at 5Mb (2005) 30 Mb (2009) OBSOLETE 26/71

27. Lect. 1: Oct 14, 2013 Coming soon (1999) 27/71

28. Lect. 1: Oct 14, 2013 Today (2005) 28/71

29. Lect. 1: Oct 14, 2013 Why do we need Standards Networks (and other media) support communication between different entities Need agreement to ensure correct, efficient and meaningful communication 29/71

30. Lect. 1: Oct 14, 2013 Various Organizations Issue Standards IEEE (Institute for Electrical and Electronic Engineers) IETF (Internet Engineering Task Force) ITU (International Telecommunications Union) ISO (International Organization for Standardization) W3C (World Wide Web Consortium) 30/71

31. Lect. 1: Oct 14, 2013 Protocol Layers A way for organizing structure of network The idea: a series of steps  … Or at least our discussion of networks 31/71

32. Lect. 1: Oct 14, 2013 Protocol Layering Necessary because communication is complex Intended primarily for protocol designers Divides the problem into intellectually manageable pieces Provides a conceptual framework that can help us understand protocols Think of layering as a guideline, not a rigid specification Understand that optimizations may violate strict layering Should be invisible to users 32/71 Layering in protocols ~ Functions in programs

33. Lect. 1: Oct 14, 2013 Mail system functionality 33/71

34. Lect. 1: Oct 14, 2013 How do we Communicate? Send a mail from Alice to Bob Alice in Champaign, Bob in Hollywood Example: US Postal Service Bob Champaign, Illinois Hollywood, California Alice 34/71

35. Lect. 1: Oct 14, 2013 What does Alice do? Bob ’ s address (to a mailbox) Bob ’ s name – in case people share mailbox Postage – have to pay! Alice ’ s own name and address in case Bob wants to return a message In case the mail has to be returned. Bob 100 Santa Monica Blvd. Hollywood, CA 90028 Alice 200 Cornfield Rd. Champaign, IL 61820 35/71

36. Lect. 1: Oct 14, 2013 What does Bob do? Install a mailbox Receive the mail Get rid of envelope Read the message Bob 100 Santa Monica Blvd. Hollywood, CA 90028 Alice 200 Cornfield Rd. Champaign, IL 61820 36/71

37. Lect. 1: Oct 14, 2013 Layers: Person delivery of parcel Post office counter handling Ground transfer: loading on trucks Airport transfer: loading on airplane Airplane routing from source to destination each layer implements a service via its own internal-layer actions / intra layer peering relying on services provided by layer below Peer entities 37/71

38. Lect. 1: Oct 14, 2013 Advantages of Layering 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 Disadvantage: low efficiency 38/71

39. Lect. 1: Oct 14, 2013 Protocols A protocol is a set of rules and formats that govern the communication between communicating peer set of valid messages - syntax meaning of each message – semantics Necessary for any function that requires cooperation between peers 39/71 e.g: Every car drives on the right

40. Lect. 1: Oct 14, 2013 A protocol provides a service For example: the post office protocol for reliable parcel transfer service Peer entities use a protocol to provide a service to a higher-level peer entity E.g, truck company (drivers) uses a protocol to present post offices with the abstraction of an unreliable parcel transfer service Protocols 40/71

41. Lect. 1: Oct 14, 2013 Protocol Layers A network that provides many services needs many protocols Some services are independent, But others depend on each other A Protocol may use another protocol as a step in its execution for example, ground transfer is one step in the execution of the example reliable parcel transfer protocol This form of dependency is called layering Post office handling is layered above parcel ground transfer protocol. 41/71

42. Lect. 1: Oct 14, 2013 Open protocols and systems A set of protocols is open if protocol details are publicly available changes are managed by an organization whose membership and transactions are open to the public A system that implements open protocols is called an open system International Organization for Standards (ISO) prescribes a standard to connect open systems open system interconnect (OSI) Has greatly influenced thinking on protocol stacks 42/71

43. Lect. 1: Oct 14, 2013 ISO OSI reference model Reference model formally defines what is meant by a layer, a service etc. Service architecture describes the services provided by each layer and the service access point Protocol architecture set of protocols that implement the service architecture compliant service architectures may still use non- compliant protocol architectures 43/71

44. Lect. 1: Oct 14, 2013 The seven Layers Presentation Application Session Transport Network Data Link Physical Presentation Application Session Transport Network Data Link Physical Network Data Link Physical End system Intermediate system There are only 5 !! Application 44/71

45. Lect. 1: Oct 14, 2013 The seven Layers - protocol stack Presentation Application Session Transport Network Data Link Physical Presentation Application Session Transport Network Data Link Physical data DH+data+DT bits data AH PH SH TH Network Data Link Physical dataNH Session and presentation layers are not so important, and are often ignored Session and presentation layers are not so important, and are often ignored 45/71

46. Lect. 1: Oct 14, 2013 עיקרון השכבות Application Transport Network Data-Link Application Transport Network Data-Link Network Identical message Source Destination בשכבה X מתקבלת הודעה זהה להודעה ששכבה X מסרה בצד המקור 46/71

47. Lect. 1: Oct 14, 2013 Postal network Application: people using the postal system Session and presentation: chief clerk sends some priority mail, and some by regular mail ; translator translates letters going abroad. Transport layer: mail clerk sends a message, retransmits if not acked Network layer: postal system computes a route and forwards the letters datalink layer: letters carried between intermediate stops (e.g connecting flights) physical layer: carrying the letter itself between intermediate stops (planes, trains, automobiles) 47/71

48. Lect. 1: Oct 14, 2013 Internet protocol stack application: supporting network applications ftp, smtp, http transport: host-host data transfer tcp, udp network: routing of datagrams from source to destination ip, routing protocols link: data transfer between neighboring network elements ppp, ethernet physical: bits “ on the wire ” application transport network link physical 48/71

49. Lect. 1: Oct 14, 2013 application transport network Link physical application transport network Link physical source destination M M M M H t H t H n H t H n H l M M M M H t H t H n H t H n H l message segment datagram frame Protocol layering and data 49/71

50. Lect. 1: Oct 14, 2013 Physical layer L1 Physically Moves bits between physically connected end-systems Standard prescribes coding scheme to represent a bit shapes and sizes of connectors bit-level synchronization Internet technology to move bits on a wire, wireless link, satellite channel etc. 50/71

51. Lect. 1: Oct 14, 2013 Datalink layer L2 (Reliable) communication over a single link. Introduces the notion of a frame set of bits that belong together Idle markers tell us that a link is not carrying a frame Begin and end markers delimit a frame Internet a variety of datalink layer protocols most common is Ethernet (+access) others are FDDI, SONET, HDLC 51/71

52. Lect. 1: Oct 14, 2013 Datalink layer (contd.) Datalink layer protocols are the first layer of software Very dependent on underlying physical link properties Usually bundle both physical and datalink in hardware. Ethernet (broadcast link) end-system must receive only bits meant for it need datalink-layer address also needs to decide who gets to speak next these functions are provided by Medium ACcess sublayer (MAC = layer 1.5) 52/71 An interesting story in evolution

53. Lect. 1: Oct 14, 2013 Network layer L3 Carries data from source to destination. Logically concatenates a set of links to form the abstraction of an end-to-end link Allows an end-system to communicate with any other end-system by computing a route between them Hides idiosyncrasies of datalink layer Provides unique network-wide addresses Found both in end-systems and in intermediate systems 53/71

54. Lect. 1: Oct 14, 2013 Network layer types In datagram networks provides both routing and data forwarding In connection-oriented network separate data plane and control plane data plane only forwards and schedules data (touches every byte) control plane responsible for routing, call- establishment, call-teardown (doesn ’ t touch data bytes) 54/71

55. Lect. 1: Oct 14, 2013 Internet network layer is provided by Internet Protocol (IP) found in all end-systems and intermediate systems provides abstraction of end-to-end link segmentation and reassembly packet-forwarding, routing, scheduling unique IP addresses can be layered over anything, but only best-effort service Network layer (contd.) 55/71

56. Lect. 1: Oct 14, 2013 At intermediate systems participates in routing protocol to create routing tables responsible for forwarding packets schedules the transmission order of packets chooses which packets to drop Network layer (contd.) At end-systems primarily hides details of datalink layer segments and reassemble detects errors 56/71

57. Lect. 1: Oct 14, 2013 Transport layer L4 Reliable end-to-end communication. creates the abstraction of an error-controlled, flow-controlled and multiplexed end-to-end link (Network layer provides only a ‘ raw ’ end-to-end service) Some transport layers provide fewer services e.g. simple error detection, no flow control, and no retransmission Internet TCP provides error control, flow control, multiplexing UDP provides only multiplexing 57/71

58. Lect. 1: Oct 14, 2013 Transport layer (contd.) Error control GOAL: message will reach destination despite packet loss, corruption and duplication ACTIONS: retransmit lost packets; detect, discard, and retransmit corrupted packets; detect and discard duplicated packets Flow control match transmission rate to rate currently sustainable on the path to destination, and at the destination itself Multiplexes multiple applications to the same end-to-end connection adds an application-specific identifier (port number) so that receiving end-system can hand in incoming packet to the correct application 58/71

59. Lect. 1: Oct 14, 2013 Session layer Not common Provides full-duplex service, expedited data delivery, and session synchronization Internet doesn ’ t have a standard session layer 59/71

60. Lect. 1: Oct 14, 2013 Duplex if transport layer is simplex, concatenates two transport endpoints together Expedited data delivery allows some messages to skip ahead in end-system queues, by using a separate low-delay transport layer endpoint Synchronization allows users to place marks in data stream and to roll back to a prespecified mark Session layer (cont.) 60/71

61. Lect. 1: Oct 14, 2013 Presentation layer Usually ad hoc Touches the application data (Unlike other layers which deal with headers) Hides data representation differences between applications characters (ASCII, unicode, EBCDIC.) Can also encrypt data Internet no standard presentation layer only defines network byte order for 2- and 4-byte integers 61/71

62. Lect. 1: Oct 14, 2013 Application layer The set of applications that use the network Doesn ’ t provide services to any other layer 62/71

63. Lect. 1: Oct 14, 2013 עיקרון השכבות VoIP UDP Network (IPv4) Ethernet Application Transport Network Data-Link Network Source Destination Email(smtp)ftp TCP WiFiModem 63/71

64. Lect. 1: Oct 14, 2013 עיקרון השכבות Network Source Destination app1 UDP Network (IPv4) Ethernet app2app3 TCP WiFiModem app1 UDP Network (IPv4) Ethernet app2 app3 TCP WiFiModem 64/71

65. Lect. 1: Oct 14, 2013 Discussion Layers break a complex problem into smaller, simpler pieces. Why seven layers? Need a top and a bottom  2 Need to hide physical link; so need datalink  3 Need both end-to-end and hop-by-hop actions; so need at least the network and transport layers  5 65/71

66. Lect. 1: Oct 14, 2013 Introduction and Layering1 Data Link: Multi Access2 Hubs, Bridges and Routers3 Scheduling and Buffer Management4 Switching Fabrics5 Routing6 Reliable Data Transfer7 End to End Window Based Protocols8 Flow Control9 Multimedia and QoS10 Network Security11 Distributed Algorithms12 Course outline 66