Applied Computer Networks. Introduction (2 nd Edition) John Morton

Transcription

1 Applied Computer Networks Introduction (2 nd Edition) John Morton

2 Fred Halsall Some Books Computer Networking and the Internet 5 th Ed, Addison-Wesley, James Kurose and Keith Ross Computer Networking 3 rd Ed, Addison-Wesley Andrew S. Tanenbaum Computer Networks: 4 th Ed, Prentice Hall 2004 William Stallings Data & Computer Communications 6 th Ed, Prentice Hall, Douglas Comer Computer Networks and Internets 3 rd Ed, Prentice Hall, Odom, W Cisco CCNA Exam Certification Guide, Cisco Press, 2002, Selected articles from the technical literature, as directed, e.g. IEEE/ACM Transactions on Networking IEEE Transactions on Communications Computer Networks - Introduction 2

3 Topics Importance of computer networks: an example Basic concepts LAN (Local Area Network) and WAN (Wide Area Network) Computer Networks - Introduction 3

4 Importance of Computer Networks Example: The network in Seaton Delaval plant Connects computers on site Allows information exchange between the production information servers and production lines Automates the information exchange with hauliers Computer Networks - Introduction 4

5 Basic Concepts: Building Blocks (Peterson/Davie, Chapt. 1.1) Nodes: Workstations, Servers Links: RJ 45, Optical Fibre Computer Networks - Introduction 5

6 Basic Concepts: Connectivity Direct Links Point-To-Point N N Multiple Access N N N N Computer Networks - Introduction 6

7 Basic Concepts: Connectivity Indirect Connectivity Switched networks Nodes connected to at least two links that can forward data received on one link out on another are commonly called switches.these nodes form a switched network. The nodes that use the network are commonly called hosts Computer Networks - Introduction 7

8 Indirect Connectivity Basic Concepts: Connectivity Switched network: Hosts and switches H H H S H S S H Computer Networks - Introduction 8

9 Circuit Switching Two main Switching Strategies Uses a dedicated circuit; send/receive a bit stream. The network first establishes a dedicated path (circuit) across a sequence of links between the source and the destination; then the source can send a stream of bits over that circuit. This is how telephone networks work Packet Switching Store-and-forward; send/receive messages (packets). Nodes send blocks of data (packets) to each other. A switch typically stores incoming packets in its memory and then forwards each packet over the appropriate link Computer networks use packet switching rather than circuit switching why? Computer Networks - Introduction 9

10 Basic Concepts: Connectivity Networks connected to other networks to form an Internetwork (Internet for short) A node that is connected to two or more networks is called a router or gateway G G G Computer Networks - Introduction 10

11 Basic Concepts: LAN and WAN Local networks (e.g. Seaton Delaval) are referred to as LANs (Local Area Networks) Geographically much bigger networks that are normally connected through gateways are referred to as WANs (Wide Area Networks) Computer Networks - Introduction 11

12 WAN-Example: P&G in NE UK SEATON (HUGO BOSS) LONGBENTON (ARIEL) COBALT (EMEA Service Centre) BRUSSELS Computer Networks - Introduction 12

13 Reasons for Networking Communication within computer system on chip, on board, between peripherals,... Sharing hardware between systems specialist CPU, peripherals,... Remote access to facilities dial-up access, telnet,... Exchanging and distributing data between systems or applications FTP, EDI,... Computer Networks - Introduction 13

14 More Reasons for Networking Sharing of software between systems FTP, network versions of packages,... Sharing data Distributed data bases, NFS,... Communication and advertising , WWW,... Computer Networks - Introduction 14

15 1 Miniature < 5cm Classification of Networks Interconnected components on a single integrated circuit. 2 Small < 50cm Interconnected components in a piece of equipment, e.g. a bus. 3 Average < 1km Interconnected separate pieces of equipment distributed over a local area, such as a factory site. Local Area Networks - LANs. 4 Large > 1km Interconnected equipment distributed over a wide area. Wide Area Networks - WANS. Computer Networks - Introduction 15

16 Classification of Networks 2 1 & 2 - Homogeneous hardware Closely coupled: Shared memory. Common Clocking. Parallel data transfer. 3 & 4 - Heterogeneous hardware: Loosely coupled => Protocols. Serial data transfer. Physical transfer over distance => errors. Major factors: Reliable transfer. Common interpretation of data and control signals. Computer Networks - Introduction 16

17 Network Standards Closed systems: Proprietary networks. Open Systems: Allow diverse equipment to communicate. International standards required. The evolution of standards: The computer industry. Proprietary standards and closed systems: ECMA: European Computer Manufactures Association EIA: Electrical Industries Association. IEEE: Institute of Electrical and Electronic Engineers Computer Networks - Introduction 17

18 Network Standards 2 Telecommunications industry. Interface standards and multivendor systems: ITU: International Telecommunications Union. CCITT: Consultative Committee of International Telegraph and Telephone ANSI: American National Standards Institute. Integrated computer and telecoms industries. International standards and open systems interconnect: ISO: International Standards Organisation CCITT: Consultative Committee of International Telegraph and Telephone. Computer Networks - Introduction 18

19 The Internet Society Internet Architecture Board (IAB) Responsible for the overall architecture of the internet. Provides guidance to the and broad direction to the IETF Internet Engineering Task Force (IETF) The protocol engineers and development arm of the Internet Membership in a working group is voluntary and open Internet Engineering Steering Group (IESG) Responsible for technical management of IETF activities and the Internet standards process Computer Networks - Introduction 19

20 Request for Comment IETF working groups produce Internet Drafts which progress to be an RFC within 6 months and are open to review and comment by any interested parties RFC progress through Proposed Standard to Draft Standard and finally to an Internet Standard They are given an STD number as well as an RFC number. An obsolete RFC is assigned to the historic state There are also informational, experimental, and best practice statuses for an RFC. Computer Networks - Introduction 20

21 Computer Networks The Layered Model (2 nd Edition) John Morton

22 Layered Architecture (Peterson/Davie Chapt 1.2, Tanenbaum Chapt. 1.4) Networking software is designed in a layered fashion: start with the services offered by the underlying hardware, and add a sequence of software layers, each providing a higher (more abstract) level of service. The services provided by high layers are implemented using services provided by low layers. This is of course the general principle of building any complex software system. Computer Networks - Introduction 22

23 Layered Architecture Application programs Process-to-Process channels Host-to-host connectivity Hardware L3 L2 L1 L0 Application programs Request/reply Message stream Host-to-host connectivity Hardware Computer Networks - Introduction 23

24 Layered Architecture A given layer implements one (or more) protocol. Each protocol defines two interfaces: Service interface: defines operations provided by this protocol for layer Li+1 Peer-to-peer interface: defines messages exchanged with peer (between Li) Note: entities at the same level are called peer entities Li+1 Service interface Li Protocol Protocol Peer-to-peer interface Peer-to-peer Computer Networks - Introduction communication 24

25 Layered Architecture At the hardware level peer-to-peer communication is directly over a link At higher level (say Li), Li to Li communication is only conceptual; in reality it happens by each Li making use of the services of Li-1. A technique known as encapsulation is used for using lower level services: Data Application program Application program Data RRP RRP RRP Data RRP Data HHP HHP HHP RRP Data Computer Networks - Introduction 25

26 Layered Architecture Let us consider how application on host 1 sends a message to an application on host 2 (in practice this would be equivalent to the application making a procedure call to Request Reply Protocol software module): RRP attaches some control information (RRP specific header information) to data so that its peer RRP will know what to do when the data is received by it. This combined message is sent to local Host-to-Host protocol. HHP attaches HHP specific header, and the entire message is sent to host 2 So each layer attaches a header (encapsulates the message) as the message goes down. At host 2, each layer removes its header, performs header specific processing and passes the message up. Computer Networks - Introduction 26

27 Services and Protocols Services: A set of primitives provided to the layer above (Li+1). A definition visible to the user layer. Protocols: A set of rules governing the format and meaning of the frames, packets or messages exchanged by peer entities. An implementation hidden from the user layer. Computer Networks - Introduction 27

28 ISO Model Layers Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 Application Presentation Session Transport Network Data Link Physical Computer Networks - Introduction 28

29 ISO Model Overview 1 1. Physical Layer: Network hardware Mechanical and electrical connections. 2. Data Link Layer: Managed the transmission of data across the physical network Framing, data transparency and error control. 3. Network Layer: These protocols define how addresses are assigned and how data is forwarded from one network to another Routing 4. Transport Layer: Provides reliable, transparent transfer of data between end points. End to end Error recovery and flow control Computer Networks - Introduction 29

30 5. Session Layer: ISO Model Overview 2 Provides the control structure for communication between applications. Establishing, manages and terminates dialogues between application entities. Specification for security details 6. Presentation Layer: Provides independence to the application process from differences in data representation 7. Application Layer: Each protocol specifies how a particular application uses the network. The protocol specifies how an application program on one computer makes a request and how the application on another machine responds Computer Networks - Introduction 30

31 OSI v TCP/IP OSI Application Presentation Session Transport Network Data Link Physical TCP/IP Application TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) Internet Protocol IP Network layer of the Internet Computer Networks - Introduction 31