1. Chapter 1 Introduction Computer Networks CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 1

2. Introduction Chapter 1 CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Uses of Computer Networks Network Hardware Network Software Reference Models Example Networks Network Standardization Metric Units

3. Uses of Computer Networks Computer networks are collections of autonomous computers, e.g., the Internet They have many uses: Business Applications » Home Applications » Mobile Users » These uses raise: Social Issues » This text covers networks for all of these uses CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF

4. request response Business Applications Companies use networks and computers for resource sharing with the client- server model: Other popular uses are communication, e.g., email, VoIP, and e-commerce CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 4

5. Home Applications Homes contain many networked devices, e.g., computers, TVs, connected to the Internet by cable, DSL, wireless, etc. Home users communicate, e.g., social networks, consume content, e.g., video, and transact, e.g., auctions Some application use the peer-to-peer model in which there are no fixed clients and servers: CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 5

6. 1. Interactions between persons and remote databases WWW, digital libraries, peer-to-peer file sharing 2. Person to person communications or Social networks Email, instant messaging, Twitter, Facebook, wikis, blogs, etc. 3. Electronic Commerce Bill paying, online auctions (ebay), online stores, etc. 4. Entertainment Music, radio, film, TV (IPTV), games 5. Ubiquitous computing ( embedded into daily life) Smart homes, security systems, RFID Network Uses CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 6

7. Mobile Users Tablets, laptops, and smart phones are popular devices; WiFi hotspots and 3G cellular provide wireless connectivity. Mobile users communicate, e.g., voice and texts, consume content, e.g., video and Web, and use sensors, e.g., GPS. Wireless and mobile are related but different: CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 7

8. Sales of mobile devices are greater than desktops Connectivity to the Internet Cellular networks – operated by telephone companies, mobile and smart phones for texting WI-Fi Hotspots (based on 802.11 standard) – used for “hand held” and tracking devices, important to military, ebooks GPS ( global positioning systems) Google maps, etc… M-commerce ( mobile commerce)- text messages used in payment, bitcoins Senor networks ( cars, animals) Wearable computers ( google glass, motorola…) Mobile Uses CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 8

9. Computer networks allow users to distribute and view content in ways that were not possible until recently. This has resulted in many unsolved social, political and ethical issues: Social networks, message boards, content sharing sites, allow people to share views, etc…. Some network operators block content, charge different rates to some clients, provide better service to others, etc. These practices are opposed by network neutrality. Music, films are distributed in violation of copyright; now automated systems search for violators under the Digital Millennium Copyright Act. It has become easy to “snoop” ( employer’s accessing employee email, etc.) Government vs. citizens’ rights. Social Issues CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 9

10. Location privacy- tracking through mobile devices Anonymous messages – threats, bullying Ability to find information but some is misleading or wrong Electronic junk mail or spam Botnets, viruses and other malware can be used for identity theft (spoofing and phishing), to collect bank account number, passwords Botnets or zombies which distribute spam and viruses to computers CAPTCHAS are used to prevent computers form impersonating people Computer gambling Social Issues CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 10

11. Social Issues Summarized CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Network neutrality – no network restrictions- treat all data equally Content ownership, e.g., DMCA takedowns Anonymity and censorship Privacy, e.g., Web tracking and profiling Theft, e.g., botnets and phishing http://www.wired.com/opinion/2013/11/so-the-internets-about-to-lose-its-net-neutrality /

12. Technical issues in Network design: Two types of transmission technology: broadcast links and point-to-point links Point-to-point links connect individual machines, sending packets. usually unicast (one sender, one receiver) Broadcast shared and received among many machines (eg wireless)can be addresses to all or a subset ( multicast) Network can also be classified by scale or rough physical size: Personal area networks Long range ( local, metropolitan, wide area) Internets – connection of 2 or more networks The Internet – global network of networks Future – Interplanetary Internet – connects networks across space. Network Hardware CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 12

13. Network Hardware CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Networks can be classified by their scale: ScaleType Examples VicinityPAN (Personal Area Network) »Bluetooth (e.g., headset) BuildingLAN (Local Area Network) »WiFi, Ethernet CityMAN (Metropolitan Area Network) » Cable, DSL CountryWAN (Wide Area Network) »Large ISP PlanetThe Internet (network of all networks) The Internet!

14. Personal Area Network CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Connect devices over the range of a person Example of a Bluetooth (wireless) PAN: advantage- no wires needed

15. Local Area Networks Connect devices in a home or office building –privately owned Called enterprise network in a company CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Wireless LAN with 802.11 Wired LAN with switched Ethernet 15

16. WiFi or IEEE 802.11 is the standard for wireless LANs Wireless LANs Access point (AP), wireless routers, or base stations relay packets between computers and the Internet. Wired LANs use different technologies, and media (copper wire, fiber, etc.) Ethernet or IEEE 802.3 is the most common Usually connected to a switch through a port Switches can be connected together to form larger networks Local Area Networks CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 16

17. Many devices are capable of being networked: computers, DVDs, phones and other consumer electronics, such as cameras, appliances such as clocks and radios and infrastructures such as utility meters and thermostats. Some unique properties of home networks: 1.Networked devices must be easy to install 2.Network and devices must be foolproof 3.Devices must be economical 4.Must allow for expansion 5.Must be secure and reliable Google is moving toward the “Internet of Things” with the purchase of NESTNEST LANs in the Home CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 17

18. Metropolitan Area Networks CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Connect devices over a metropolitan area High speed wireless MANs based on IEEE 802.16 – called WIMAX Example MAN based on cable TV:

19. Connect devices over a country- span large geographic areas Example WAN connecting three branch offices: Wide Area Networks (1) CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 19

20. Wide Area Networks (2) An ISP (Internet Service Provider) network is also a WAN. Customers buy connectivity from the ISP to use it. CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 20

21. Wide Area Networks (3) A VPN (Virtual Private Network) is a WAN built from virtual links that run on top of the Internet. CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 21

22. WANs connect devices, called hosts, through subnets Subnets consist of: Transmission lines that move bits between machines Switches or routers – that connect two or more transmission lines Some differences from a LAN: Usually the components in a WAN are owned by different entities ( such as a phone company owning a leased line) and are not private Routers usually connect different kinds of networking technologies (heterogeneous) instead of usually homogeneous equipment as in a LAN Subnets can be made up of computers as in a LAN, but often connect larger LANs, forming internetworks. Wide Area Networks CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 22

23. Network Software CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Protocol layers » Design issues for the layers » Connection-oriented vs. connectionless service » Service primitives » Relationship of services to protocols »

24. 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 Example Layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below Kurose Introduction CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 24

25. Most networks are organized as a stack of layers or levels, each one built upon and communicating with the one below it. Each layer offers services to a higher layer, (like a virtual machine) providing information hiding and encapsulation. A Protocol is an agreement between communicating parties on how communication is to proceed. The entities which communicate are called peers ( software, hardware or humans). There are 5 layer (Internet or TCP/IP) and 7 layer (OSI) models Between each pair of adjacent layers is an interface Protocol Layers CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 25

26. Protocol Layers (1) CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Protocol layering is the main structuring method used to divide up network functionality. Each protocol instance talks virtually to its peer Each layer communicates only by using the one below Lower layer services are accessed by an interface At bottom, messages are carried by the medium

27. Protocol Layers (2) Example: the philosopher-translator-secretary architecture Each protocol at different layers serves a different purpose CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 27

28. Protocol Layers (3) Each lower layer adds its own header (with control information) to the message to transmit and removes it on receive Layers may also split and join messages, etc. CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 28

29. Design Issues for the Layers CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Each layer solves a particular problem but must include mechanisms to address a set of recurring design issues IssueExample mechanisms at different layers Reliability despite failuresCodes for error detection/correction (§3.2, 3.3) Routing around failures (§5.2) Network growth and evolutionAddressing (§5.6) and naming (§7.1) Protocol layering (§1.3) Allocation of resources like bandwidth Multiple access (§4.2) Congestion control (§5.3, 6.3) Security against various threatsConfidentiality of messages (§8.2, 8.6) Authentication of communicating parties (§8.7)

30. A packet is a message at the network layer Datagram service is unreliable or unacknowledged message delivery service ( eg. Telegeam or email) Connection oriented –modeled after the phone system Connectionless – modeled after the postal system A Service is a set of primitives or operations that a layer provides to the one above it. ( Like an object in OOP). A Protocol is a set of rules governing the format and meaning of the packets or messages that are exchanged. Protocols implement the services Some Definitions CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 30

31. Connection-Oriented vs. Connectionless Service provided by a layer may be kinds of either: Connection-oriented, must be set up for ongoing use (and torn down after use), e.g., phone call Connectionless, messages are handled separately, e.g., postal delivery CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 31

32. Service Primitives (1) A service is provided to the layer above as primitives Hypothetical example of service primitives that may provide a reliable byte stream (connection-oriented) service: CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 32

33. Service Primitives (2) Hypothetical example of how these primitives may be used for a client-server interaction CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Client Server LISTEN (0) ACCEPT RECEIVE SEND (4) DISCONNECT (6) CONNECT (1) SEND RECEIVE DISCONNECT (5) Connect request Accept response Request for data Reply Disconnect (2) (3) 33

34. Relationship of Services to Protocols CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Recap: A layer provides a service to the one above[vertical] A layer talks to its peer using a protocol [horizontal]

35. Reference Models CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Reference models describe the layers in a network architecture OSI reference model » TCP/IP reference model » Model used for this text » Critique of OSI and TCP/IP »

36. OSI Reference Model A principled, international standard, called the seven layer model to connect different systems: CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF – Provides functions needed by users – Converts different representations – Manages task dialogs – Provides end-to-end delivery – Sends packets over multiple links – Sends frames of information – Sends bits as signals 36

37. OSI Architecture The OSI 7-layer Model OSI – Open Systems Interconnection

38. Description of Layers Starting from the bottom up: (Remember: “Please Do Not Throw Sausage Pizza Away”) Physical Layer Handles the transmission of raw bits over a communication link Data Link Layer Collects a stream of bits into a larger aggregate called a frame Network adaptor along with device driver in OS implement the protocol in this layer Frames are actually delivered to hosts Network Layer Handles routing among nodes within a packet-switched network Unit of data exchanged between nodes in this layer is called a packet The lower three layers are implemented on all network nodes CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 38

39. Description of Layers Transport Layer Implements a process-to-process channel Unit of data exchanges in this layer is called a message Session Layer Provides a name space that is used to tie together the potentially different transport streams that are part of a single application Presentation Layer Concerned about the format of data exchanged between peers Application Layer Standardize common type of exchanges, includes protocols such as FTP, HTTP, etc. The transport layer and the higher layers typically run only on end-hosts and not on the intermediate switches and routers CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 39

40. 7 Layer Model LayerFunctions 7ApplicationHow application uses network 6PresentationHow to represent & display data 5SessionHow to establish communication 4TransportHow to provide reliable delivery (error checking, sequencing, etc.) 3NetworkHow addresses are assigned and packets are forwarded 2Data LinkHow to organize data into frames & transmit 1PhysicalHow to transmit “bits” CN5E by Tanenbaum & Wetherall, © Pearson Education- Prentice Hall and D. Wetherall, 2011, modified by SJF 40

41. OSI Headers Multiple Nested Headers Each layer (except the physical) places additional information in a header before sending data to a lower layer. The header corresponding to the lowest level protocol occurs first. CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 41

42. OSI Model http://computer.howstuffworks.com/osi1.htm CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 42

43. The OSI (Open System Interconnection) model has 7 layers and can be summarized as follows: 1.A layer should be created where a different abstraction is needed. 2.Each layer should perform a well defined function 3.The function of each layer should be based on standard protocols. 4.The layer boundaries should minimize the information flow across the interfaces. 5.The number of layers should be large enough to accommodate the necessary functions and small enough not to be cumbersome. This model is widely used and specifies what each layer should do. OSI -7 Layer Model CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 43

44. Three concepts are central to this model: 1.Services 2.Interfaces 3.Protocols The main contribution of this model is that it makes the distinction among these 3 concepts explicit. Each layer performs a service for the layer above it. The layer’s interface tells the processes above it how to access it. Peer protocols can be used or changed by the layers. OSI -7 Layer Model CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 44

45. Internet Architecture Also called the TCP/IP Architecture Evolved from the packet switched ARPANET ( Advanced Research Projects Agency) of the Department of Defense. Influenced the OSI model Usually shown as a 4 or 5 layer model CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 45

46. Internet Architecture Special Features 1.Does not imply strict layering 2.Has “hourglass shape” design philosophy- with IP as its central feature ( See protocol graph) 3.To propose a new protocol, both a protocol specification and at least one representative implementations must be provided. CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 46

47. Internet Architecture Internet Protocol Graph Alternative view of the Internet architecture. The “Network” layer shown here is sometimes referred to as the “sub-network” or “link” layer.

48. Internet Architecture 1.At lowest or Network Layer there are many protocols, called NET 1, NET 2, NET 3, etc., implemented by a combination of hardware (Ethernet or Fiberoptics) 2.Internet Layer - Internet Protocol (IP) supports connection of multiple networks 3.Transport Layer –reliable Transmission Control Protocol (TCP) and unreliable User Datagram Protocol (UDP) –alternative logical channels to applications. 4.Application Layer – FTP, SMTP, Telnet, HTTP CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 48

49. Internet Architecture Application Layer Transport Layer Internet Layer Network Layer 4 or 5 Layer Internet Model Physical layer (implied) CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 49

50. Protocols in TCP/IP Reference Model A four layer model derived from experimentation; omits some OSI layers and uses the IP as the network layer. CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF IP is the “narrow waist” of the Internet Protocols are shown in their respective layers 50

51. This model was defined by Cerf and Kahn and defined as a standard in the Internet community. The protocols came first and the model was a description of the existing protocols The original TCP/IP model did not distinguish between services, interfaces and protocols. TCP/IP Reference Model CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 51

52. Application Transport Internet Link (Physical ) implied TCP/IP 7Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical OSI Comparison of OSI and TCP/IP CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 52 Not present in model

53. Model Used in this Book CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF It is based on the TCP/IP model but we include the physical layer and look beyond Internet protocols.

54. Critique of OSI & TCP/IP CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF OSI: + Very influential model with clear concepts Models, protocols and adoption all bogged down by politics and complexity TCP/IP: + Very successful protocols that worked well and thrived Weak model derived after the fact from protocols

55. Example Networks CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF The Internet » 3G mobile phone networks » Wireless LANs » RFID and sensor networks »

56. Internet (1) CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Before the Internet was the ARPANET, a decentralized, packet- switched network based on Baran’s ideas. ARPANET topology in Sept 1972. Nodes are IMPs, or early routers, linked to hosts 56 kbps links

57. Internet (2) CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF The early Internet used NSFNET (1985-1995) as its backbone; universities connected to get on the Internet NSFNET topology in 1988 T1 links (1.5 Mbps)

58. Internet (3) CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF The modern Internet is more complex: ISP networks serve as the Internet backbone ISPs connect or peer to exchange traffic at IXPs Within each network routers switch packets Between networks, traffic exchange is set by business agreements Customers connect at the edge by many means Cable, DSL, Fiber-to-the-Home, 3G/4G wireless, dialup Data centers concentrate many servers (“the cloud”) Most traffic is content from data centers (esp. video) The architecture continues to evolve

59. Internet (4) CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Architecture of the Internet 59

60. 3G Mobile Phone Networks (1) CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 3G network is based on spatial cells; each cell provides wireless service to mobiles within it via a base station

61. 3G Mobile Phone Networks (2) Base stations connect to the core network to find other mobiles and send data to the phone network and Internet CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 61

62. 3G Mobile Phone Networks (3) CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF As mobiles move, base stations hand them off from one cell to the next, and the network tracks their location Handover

63. Wireless LANs (1) CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF In 802.11, clients communicate via an AP (Access Point) that is wired to the rest of the network.

64. Wireless LANs (2) CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Signals in the 2.4GHz ISM band vary in strength due to many effects, such as multipath fading due to reflections requires complex transmission schemes, e.g., OFDM

65. Wireless LANs (3) CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Radio broadcasts interfere with each other, and radio ranges may incompletely overlap CSMA (Carrier Sense Multiple Access) designs are used

66. RFID and Sensor Networks (1) CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Passive UHF RFID networks everyday objects: Tags (stickers with not even a battery) are placed on objects Readers send signals that the tags reflect to communicate

67. RFID and Sensor Networks (2) CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Sensor networks spread small devices over an area: Devices send sensed data to collector via wireless hops

68. Network Standardization CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF Standards define what is needed for interoperability Some of the many standards bodies: BodyAreaExamples ITUTelecommunicationsG.992, ADSL H.264, MPEG4 IEEECommunications802.3, Ethernet 802.11, WiFi IETFInternetRFC 2616, HTTP/1.1 RFC 1034/1035, DNS W3CWebHTML5 standard CSS standard

69. Metric Units CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF The main prefixes we use: Use powers of 10 for rates, powers of 2 for storage E.g., 1 Mbps = 1,000,000 bps, 1 KB = 1024 bytes “B” is for bytes, “b” is for bits PrefixExp.prefixexp. K(ilo)10 3 m(illi)10 -3 M(ega)10 6 μ(micro)10 -6 G(iga)10 9 n(ano)10 -9 T(era)10 12

70. End Chapter 1 CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011, modified by SJF 70