Chapter 1 Introduction

Transcription

1 Sungkyunkwan University Chapter 1 Introduction Prepared by C. Rajesh and H. Choo 2017-Fall Computer Networks Copyright Networking Laboratory 1/52

2 Chapter 1 Outline 1.1 Overview of the Internet 1.2 Protocol Layering 1.3 Internet History 1.4 Standards and Administration 1.5 Summary 2017-Fall Computer Networks Networking Laboratory 2/64

3 Objective We introduce local area networks (LANs) and wide area networks (WANs) and show that an internet or the Internet is a combination of these networks. We introduce the concept of protocol layering to show how the task to be done by the Internet is divided into smaller tasks. We also discuss TCP/IP protocol suite and show the duty of each layers. We give a brief history of the Internet. We introduce the administration of the Internet and define the standards and their lifetime Fall Computer Networks Networking Laboratory 3/64

4 1.1 Overview of the Internet We start our journey by first defining a network. We show how we can connect networks to create small internetworks. Finally, we show the structure of the Internet and open the gate to study the Internet in the next ten chapters Fall Computer Networks Networking Laboratory 4/64

5 1.1 Overview of the Internet Networks A network is the interconnection of a set of devices capable of communication In this definition, a device can be a host such as a large computer, desktop, laptop, workstation, cellular phone, or security system A device in this definition can also be a connecting device such as a router, a switch, a modem that changes the form of data, and so on 2017-Fall Computer Networks Networking Laboratory 5/64

6 1.1 Overview of the Internet How does Internet work? (1/2) Video Content Simple explanation of how the internet really works To Understand networks, inter-networks, data packets, peering and internet exchanges Link: Fall Computer Networks Networking Laboratory 6/64

7 1.1 Overview of the Internet How does Internet work? (2/2) 2017-Fall Computer Networks Networking Laboratory 7/64

8 1.1 Overview of the Internet Local Area Network A LAN (Local Area Network) is usually privately owned and connects some hosts in a single office, building, or campus LANs are discussed in more detail in Chapters 5 and 6 [Figure 1.1 An Isolated LAN in the past and today] 2017-Fall Computer Networks Networking Laboratory 8/64

9 1.1 Overview of the Internet Wide Area Network A WAN (Wide Area Network) is also an interconnection of devices capable of communication There are some differences between a LAN and a WAN LAN WAN It is normally limited in size, spanning an office, a building, or a campus It interconnects hosts It is normally privately owned by the organization that uses It has a wider geographical span, spanning a town, a state, a country, or even the world It interconnects connecting devices such as switches, routers, or modems It is normally created and run by communication companies and leased by an organization that uses it We see two distinct examples of WANs today Point-to-Point WANs Switched WANs 2017-Fall Computer Networks Networking Laboratory 9/64

10 1.1 Overview of the Internet Wide Area Network: Point-to-Point WAN A point-to-point WAN is a network that connects two communicating devices through a transmission media (cable or air). [Figure 1.2 A point-to-point WAN] 2017-Fall Computer Networks Networking Laboratory 10/64

11 1.1 Overview of the Internet Wide Area Network: Switched WAN A switched WAN is a network with more than two ends. A switched WAN, as we will se shortly, is used in the backbone of global communication today We can say that a switched WAN is a combination of several point-to-point WANs that are connected by switches [Figure 1.3 A switched WANs] 2017-Fall Computer Networks Networking Laboratory 11/64

12 1.1 Overview of the Internet Internetwork (1/2) When two or more networks are connected, they make an internetwork or internet Figures 1.4 and 1.5 show examples of internet [Figure 1.4 An internetwork made of two LANs and one point-to-point WAN] 2017-Fall Computer Networks Networking Laboratory 12/64

13 1.1 Overview of the Internet Internetwork (2/2) [Figure 1.5 A heterogeneous network made of four WANs and three LANs] 2017-Fall Computer Networks Networking Laboratory 13/64

14 1.1 Overview of the Internet Switching (1/3) An internet is a switched network in which a switch connects at least two links together. A switch needs to forward data from a link to another link when required Video Content Simple explanation of Circuit-Switched and Packet-Switched Network Fall Computer Networks Networking Laboratory 14/64

15 1.1 Overview of the Internet Switching (2/3) 2017-Fall Computer Networks Networking Laboratory 15/64

16 1.1 Overview of the Internet Switching (3/3) Explain what do you mean by Circuit Switched and Packet Switched network? Give example of each type? A dedicated connection, called a circuit, is always available between the two end systems; the switch can only make it active or inactive Classical telephone networks in past used circuit switching network The communication between the two ends is done in blocks of data called packets Instead of the continuous communication we see between two telephone sets when they are being used, we see the exchange of individual data packets between the two computers A router in a packet-switched network has a queue that can store and forward the packet The communication between the two ends is done in blocks of data called packets Internet is an example of a Packet Switched Network 2017-Fall Computer Networks Networking Laboratory 16/64

17 1.1 Overview of the Internet Switching: Circuit-Switched Network A dedicated connection, called a circuit, is always available between the two end systems; the switch can only make it active or inactive We have used telephone sets instead of computers as an end system because circuit switching was very common in telephone networks in the past, although part of the telephone network today is a packet-switched network [Figure 1.6 A circuit-switched telephone network] 2017-Fall Computer Networks Networking Laboratory 17/64

18 1.1 Overview of the Internet Switching: Packet-Switched Network The communication between the two ends is done in blocks of data called packets Instead of the continuous communication we see between two telephone sets when they are being used, we see the exchange of individual data packets between the two computers A router in a packet-switched network has a queue that can store and forward the packet In Chapter4, we discuss packet-switched networks in more detail [Figure 1.7 A packet-switched computer network] 2017-Fall Computer Networks Networking Laboratory 18/64

19 1.1 Overview of the Internet The Internet An internet (note the lower case i) is two or more networks that can communicate with each other The most notable internet is called the Internet (uppercase I), and is composed of thousands of interconnected networks [Figure 1.8 A conceptual view of the Internet today] 2017-Fall Computer Networks Networking Laboratory 19/64

20 1.1 Overview of the Internet Accessing the Internet (1/2) The Internet today is an internetwork that allows any user to become part of it The user, however, needs to be physically connected to an ISP The physical connection is normally done through a point-to-point WAN In Chapters 6 and 7, we discuss the technical details of the connection 2017-Fall Computer Networks Networking Laboratory 20/64

21 1.1 Overview of the Internet Accessing the Internet (2/2) Using Telephone Networks Dial-up Service DSL Using Cable Networks Using Wireless Networks Direct Connection to the Internet 2017-Fall Computer Networks Networking Laboratory 21/64

22 1.1 Overview of the Internet Hardware and Software For communication to happen, we need both hardware and software This is similar to a complex computation in which we need both a computer and a program In the next section, we show how these combinations of hardware and software are coordinated with each other using protocol layering 2017-Fall Computer Networks Networking Laboratory 22/64

23 1.2 Protocol Layering A word we hear all the time when we talk about the Internet is protocol A protocol defines the rules that both the sender and receiver and all intermediate devices need to follow to be able to communicate effectively When communication is simple, we may need only one simple protocol When communication is complex, we need a protocol at each layer, or protocol layering 2017-Fall Computer Networks Networking Laboratory 23/64

24 1.2 Protocol Layering Scenarios: First Scenario Communication is so simple that it can occur in only one layer Communication between Maria and Ann takes place in one layer, face to face, in the same language, as shown in Figure 1.9 [Figure 1.9 A single-layer protocol] 2017-Fall Computer Networks Networking Laboratory 24/64

25 1.2 Protocol Layering Scenarios: Second Scenario We assume that Ann is offered a higher-level position in her company, but needs to move to another branch located in a city very far from Maria They communicate through postal regular mail with encryption/decryption mechanism for security Postal carrier facility [Figure 1.10 A three-layer protocol] 2017-Fall Computer Networks Networking Laboratory 25/64

26 1.2 Protocol Layering Scenarios: Principles of Protocol Layering The first principle dictates that if we want bidirectional communication, we need to make each layer so that it is able to perform two opposite tasks, one in each direction Example The third layer task is to listen(in one direction) and talk(in the other direction) The second layer needs to be able to encrypt and decrypt The first layer needs to send and receive mail The second important principle that we need to follow in protocol layering is that the two objects under each layer at both sites should be identical Example The object under layer 3 at both sites should be a plaintext letter The object under layer 2 at both sites should be a ciphertext letter The object under layer 1 at both sites should be a piece of mail 2017-Fall Computer Networks Networking Laboratory 26/64

27 1.2 Protocol Layering Scenarios: Logical Connection Logical connection refers to the connection between two systems at the same level of TCP/IP model. The following figure represents a Logical connection. [Figure 1.11 Logical connection between peer layers] 2017-Fall Computer Networks Networking Laboratory 27/64

28 1.2 Protocol Layering TCP/IP Protocol Suite TCP/IP(Transmission Control Protocol/Internet Protocol) TCP/IP is a protocol suite used in the Internet today It is a hierarchical protocol made up of interactive modules, each of which provides a specific functionality The original TCP/IP protocol suite was defined as four software layers Today, TCP/IP is thought of as a five-layer model [Figure 1.12 Layers in the TCP/IP protocol suite] 2017-Fall Computer Networks Networking Laboratory 28/64

29 1.2 Protocol Layering Internet Protocol (1/2) Video Content The Internet Protocol is responsible for addressing hosts and for routing datagrams (packets) from a source host to a destination host across one or more IP networks The Internet Protocol defines the format of packets and provides an addressing system that has two functions: identifying hosts; and providing a logical location service Link: Fall Computer Networks Networking Laboratory 29/64

30 1.2 Protocol Layering Internet Protocol (2/2) 2017-Fall Computer Networks Networking Laboratory 30/64

31 1.2 Protocol Layering TCP/IP Protocol Suite: Layered Architecture (1/5) To show how the layers in the TCP/IP protocol suite are involved in communication between two hosts We assume that we want to used the suite in a small internet made up of three LANs(links), each with a link-layer switch We also assume that the links are connected by one router, as shown in Figure 1.13 in next page Let us assume that computer A communicates with computer B As the figure shows, we have five communicating devices in this communication 2017-Fall Computer Networks Networking Laboratory 31/64

32 1.2 Protocol Layering TCP/IP Protocol Suite: Layered Architecture (2/5) Source host(computer A), the link-layer switch in link 1, the router, the link-layer switch in link 2, and the destination host(computer B) Each device is involved with a set of layers depending on the role of the device in the internet [Figure 1.13 Communication through an internet] 2017-Fall Computer Networks Networking Laboratory 32/64

33 1.2 Protocol Layering TCP/IP Protocol Suite: Layered Architecture (3/5) The two hosts are involved in all five layers The source host needs to create a message in the application layer and send it down the layers so that it is physically sent to the destination host The destination host needs to receive the communication at the physical layer and then deliver it through the other layers to the application layer [Figure 1.13 Communication through an internet] 2017-Fall Computer Networks Networking Laboratory 33/64

34 1.2 Protocol Layering TCP/IP Protocol Suite: Layered Architecture (4/5) The router is involved only in three layers There is no transport or application layer in a router as long as the router is used only for routing [Figure 1.13 Communication through an internet] 2017-Fall Computer Networks Networking Laboratory 34/64

35 1.2 Protocol Layering TCP/IP Protocol Suite: Layered Architecture (5/5) A link-layer switch in a link, however, is involved only in two layers Although each switch in the above figure has two different connections, the connections are in the same link, which uses only on set of protocols [Figure 1.13 Communication through an internet] 2017-Fall Computer Networks Networking Laboratory 35/64

36 1.2 Protocol Layering TCP/IP Protocol Suite: Layers in the TCP/IP Protocol Suite We briefly discuss the functions and responsibilities of layers in the TCP/IP protocol suite Each layer is discussed in detail in the next six chapters of the book Figure 1.14 shows logical connections in our simple internet Logical connections [Figure 1.14 Logical connections between layers of the TCP/IP protocol suite] 2017-Fall Computer Networks Networking Laboratory 36/64

37 1.2 Protocol Layering TCP/IP Protocol Suite: Logical Connections To better understand the duties of each layer, we need to think about the logical connections between layers The domain of duty of the top three layers is the internet And the domain of duty of the two lower layers is the link Figure 1.15 shows the identical objects below each layer related to each device Identical objects (messages) Identical objects (segment or user datagram) Identical objects (datagram) Identical objects (datagram) Identical objects (frame) Identical objects (frame) Identical objects (bits) Identical objects (bits) [Figure 1.15 Identical objects in the TCP/IP protocol suite] 2017-Fall Computer Networks Networking Laboratory 37/64

38 1.2 Protocol Layering TCP/IP Protocol Suite: Description of each layer in TCP/IP (1/2) Application Layer Communication at the application layer is between two processes To communicate, a process sends a request to the other process and receives a response Process-to-process communication is the duty of the application layer Transport Layer The transport layer is responsible for giving services to the application layer: to get a message from an application program running on the source host and deliver it to the corresponding application program on the destination host Network Layer The network layer is responsible for creating a connection between the source computer and the destination computer The communication at the network layer is host-to-host 2017-Fall Computer Networks Networking Laboratory 38/64

39 1.2 Protocol Layering TCP/IP Protocol Suite: Description of each layer in TCP/IP (2/2) Data-link Layer There may be several overlapping sets of links that a datagram can travel from the host to the destination The routers are responsible for choosing the best links When the next link to travel is determined by the router, the data-link layer is responsible for taking the datagram and moving it across the link Physical Layer The physical layer is responsible for carrying individual bits in a frame across the link 2017-Fall Computer Networks Networking Laboratory 39/64

40 1.2 Protocol Layering TCP/IP Protocol Suite: Encapsulation and Decapsulation One of the important concepts in protocol layering in the Internet is encapsulation/decapsulation Encapsulation at the Source Host At the source, we have only encapsulation Decapsulation and Encapsulation at Router We have both decapsulation and encapsulation because the router is connected to two or more links Decapsulation at the Destination Host Each layer only decapsulates the packet received Removes the payload, and delivers the payload to the next-higher layer protocol until the message reaches the application layer 2017-Fall Computer Networks Networking Laboratory 40/64

41 1.2 Protocol Layering TCP/IP Protocol Suite: Addressing Any communication that involves two parties needs two addresses Source address and destination address Although it looks as if we need five pairs of addresses, one pair per layer We normally have only 4 because the physical layer does not need them Because the unit of data exchange at the physical layer is a bit, which definitely cannot have an address [Figure 1.17 Addressing in the TCP/IP protocol suite] 2017-Fall Computer Networks Networking Laboratory 41/64

42 1.2 Protocol Layering TCP/IP Protocol Suite: Multiplexing and Demultiplexing Since the TCP/IP protocol suite uses several protocols at some layers, we can say that we have multiplexing at the source and demultiplexing at the destination Multiplexing : A protocol at a layer can encapsulate a packet from several next-higher layer protocols(one at a time) Demultiplexing : A protocol can decapsulate and deliver a packet to several next-higher layer protocols(one at a time) [Figure 1.18 Multiplexing and demultiplexing] 2017-Fall Computer Networks Networking Laboratory 42/64

43 1.2 Protocol Layering The OSI Model Established in 1947, International Organization for Standardization(ISO) is multinational body dedicated to world wide agreement on international standards An ISO standard that covers all aspects of network communications is the Open System Interconnection(OSI) model It was first introduced in the late 1970s [Figure 1.19 The OSI model] 2017-Fall Computer Networks Networking Laboratory 43/64

44 1.2 Protocol Layering The OSI Model: OSI versus TCP/IP OSI versus TCP/IP When we compare the two models, we find that two layers, session and presentation, are missing from the TCP/IP protocol The application layer in TCP/IP protocol suite is usually considered to be the combination of three layers in the OSI model [Figure 1.20 TCP/IP and OSI model] 2017-Fall Computer Networks Networking Laboratory 44/64

45 Practice Problem Separate the following application layer protocols based on its underlying transport protocol (UDP-Based / TCP-Based)? HTTP, DNS, SMTP, FTP, DHCP, SNMP, SSL, NTP, Telnet. What are different Transport layer Standard Protocols in TCP/IP Model? List at least 3 differences between TCP and UDP Fall Computer Networks Networking Laboratory 45/64

46 1.3 Internet History History of the Internet 1 (1/2) Video Content Short video of the internet's 40 year history, from the first message sent over the ARPANET to being the centre of our digital lives Link: Fall Computer Networks Networking Laboratory 46/64

47 1.3 Internet History History of the Internet 1 (2/2) This brief history makes it clear how the Internet has evolved from a private network to a global one in less than forty years 2017-Fall Computer Networks Networking Laboratory 47/64

48 1.3 Internet History History of the Internet 2 (1/2) Video Content This video clip is an animated documentary explaining the inventions from time-sharing to filesharing, from Arpanet to Internet The clip shows a brief overview of this history and shall animate people to go on discovering the history of the internet Link: Fall Computer Networks Networking Laboratory 48/64

49 1.3 Internet History History of the Internet 2 (2/2) This brief history makes it clear how the Internet has evolved from a private network to a global one in less than forty years 2017-Fall Computer Networks Networking Laboratory 49/64

50 1.3 Internet History The Development of Packet Switching : : Keinrock - queuing theory Bursty traffic Demonstrated effectiveness of packet-switching 1964 : Baran packet switching in military nets 1967 : ARPAnet by Advanced Research Projects Agency 1969 : First ARPAnet node operational 1972 ARPAnet public demonstration NCP (Network Control Protocol) first host-host protocol First program ARPAnet has 16 nodes 2017-Fall Computer Networks Networking Laboratory 50/64

51 1.3 Internet History Proprietary Networks and Internetworking: : ALOHAnet satellite network in Hawaii Multiple access 1974 : Cerf and Kahn-architecture for interconnection 1976 : Ethernet networks (internetting) 1979 : ARPAnet has 200 nodes 2017-Fall Computer Networks Networking Laboratory 51/64

52 1.3 Internet History A Proliferation of Networks : : 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 2017-Fall Computer Networks Networking Laboratory 52/64

53 1.3 Internet History The Internet Explosion : 1990s Early 1990 s : ARPAnet decommissioned 1991 : NSF lifts restrictions on commercial use of NSFnet : Cerf and Kahn-architecture for interconnection networks Early 1990 s : Web Hypertext HTML, HTTP 1994 : Mosaic, later Netscape Late 1990 s : commercialization of the web Late 1990 s 2000 s More killer apps : instant messaging, P2P file sharing Network security to forefront Backbone link running at Gbps 2017-Fall Computer Networks Networking Laboratory 53/64

54 1.4 Standards and Administration In the discussion of the Internet and its protocol, we often see a reference to a standard or an administration entity In this section, we introduce these standards and administration entities for those readers that are not familiar with them 2017-Fall Computer Networks Networking Laboratory 54/64

55 1.4 Standards and Administration Internet Standards An Internet standard is a thoroughly tested specification that is useful to and adhered to by those who work with the Internet It is a formalized regulation that must be followed There is a strict procedure by which a specification attains Internet standard status A specification begins as an Internet draft Upon recommendation from the Internet authorities, a draft may be published as a Request for Comment (RFC) RFCs go through maturity levels and are categorized according to their requirement level 2017-Fall Computer Networks Networking Laboratory 55/64

56 1.4 Standards and Administration Internet Standards: Maturity Levels (1/3) An RFC, during its lifetime, falls into one of six maturity levels [Figure 1.21 Maturity levels of an RFC] 2017-Fall Computer Networks Networking Laboratory 56/64

57 1.4 Standards and Administration Internet Standards: Maturity Levels (2/3) Proposed Standard It is a specification that is stable, well understood, and of sufficient interest to the Internet community At this level, the specification is usually tested and implemented by several different groups Draft Standard A proposed standard is elevated to draft standard status after at least two successful independent and interoperable implementations Internet Standard A draft standard reaches Internet standard status after demonstrations of successful implementation Historic The historic RFCs are significant from a historical perspective 2017-Fall Computer Networks Networking Laboratory 57/64

58 1.4 Standards and Administration Internet Standards: Maturity Levels (3/3) Experimental An RFC classified as experimental describes work related to an experimental situation that does not affect the operation of the Internet Informational An RFC classified as informational contains general, historical, or tutorial information related to the Internet It is usually written by someone in a non-internet organization, such as a vender 2017-Fall Computer Networks Networking Laboratory 58/64

59 1.4 Standards and Administration Internet Standards: Requirement Levels Required An RFC is labeled required if it must be implemented by all Internet systems to achieve minimum conformance Elective An RFC labeled elective is not required and not recommended However, a system can use it for its own benefit Limited Use An RFC labeled limited use should be used only in limited situations Not Recommended An RFC labeled not recommended is inappropriate for general use 2017-Fall Computer Networks Networking Laboratory 59/64

60 1.4 Standards and Administration Internet Administration (1/3) The Internet, with its roots primarily in the research domain, has evolved and gained a broader user base with significant commercial activity Various groups that coordinate Internet issues have guided this growth and development [Figure 1.22 Internet administration] 2017-Fall Computer Networks Networking Laboratory 60/64

61 1.4 Standards and Administration Internet Administration (2/3) ISOC (Internet Society) The ISOC is an international, nonprofit organization formed in 1992 to provide support for the Internet standards process IAB (Internet Architecture Board) The IAB is the technical advisor to the ISOC IETF (Internet Engineering Task Force) The IETF is a forum of working groups managed by the IESG (Internet Engineering Steering Group) IETF is responsible for identifying operational problems and proposing solutions to these problem IRTF (Internet Research Task Force) The IRTF is a forum of working groups managed by the IRSG (Internet Research Steering Group) 2017-Fall Computer Networks Networking Laboratory 61/64

62 1.4 Standards and Administration Internet Administration (3/3) IANA (Internet Assigned Numbers Authority) The IANA, supported by the U.S. government, was responsible for the management of Internet domain names and addresses until October 1998 ICANN (Internet Corporation for Assigned Names and Numbers) The ICANN, a private nonprofit corporation managed by an international board, assumed IANA operations NIC (Network Information Center) The NIC is responsible for collecting and distributing information about TCP/IP protocols 2017-Fall Computer Networks Networking Laboratory 62/64

63 1.5 Summary A network is a set of devices connected by communication links Today when we speak of networks, we are generally referring to two primary categories LAN and WAN Most end users who want Internet connection use the services of Internet service providers(isps) A protocol is a set of rules that governs communication TCP/IP is a hierarchical protocol suite made of five layers We discuss the technical detail of networks in next Chapters 2017-Fall Computer Networks Networking Laboratory 63/64

64 Practice Problem List out the main differences between LAN and WAN? LAN WAN What is an OSI Model? List out the main differences between TCP/IP and OSI Model? 2017-Fall Computer Networks Networking Laboratory 64/64