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Introduction to Networks and the Internet CMPE 80N Winter 2004 Lecture 2 CMPE 80N - Introduction to Networks and the Internet 1 Last class… • What’s a computer network? • Why networks? • Examples of networks: – Postal system. – Telephone network. • Telephone network: – Voice. – Real-time. CMPE 80N - Introduction to Networks and the Internet 2 Last class (cont’d) • The evolution of the telephone system. • Addressing. • Data networks. CMPE 80N - Introduction to Networks and the Internet 3 Data Networks • Components: – End systems (or hosts), – Routers/switches/bridges, and – Links (twisted pair, coaxial cable, fiber, radio, etc.). CMPE 80N - Introduction to Networks and the Internet 4 Communication Model Network Source CMPE 80N - Introduction to Networks and the Internet Destination 5 Connecting End Systems Dedicated link Multiple access / shared medium CMPE 80N - Introduction to Networks and the Internet 6 Connecting End Systems (cont’d) Router Switched network Router: switching element; a.k.a., IMPs (Interface Message Processors) in ARPAnet’s terminology. CMPE 80N - Introduction to Networks and the Internet 7 Types of Data Networks • Several ways to classify data networks. • For example, according to “coverage”: – Local Area Networks (LANs) typically provide networking capabilities within a building, campus. • Typically within 5-mile radius. – Wide-Area Networks (WANs) span greater geographic distances (e.g., world-wide). – Metropolitan Area Networks (MANs) span more restricted distances, e.g., geographic regions (e.g., Los Nettos network in Southern California, etc.) CMPE 80N - Introduction to Networks and the Internet 8 The Internet Backbone Regional Stub CMPE 80N - Introduction to Networks and the Internet 9 Types of Networks (cont’d) • Classification according to type of connection. – Dedicated link. – Shared medium (multiple access). – Switched point-to-point. CMPE 80N - Introduction to Networks and the Internet 10 Types of Networks (cont’d) • Classification according to topology… • What is network topology? – The way network elements are interconnected. CMPE 80N - Introduction to Networks and the Internet 11 Network Topologies: Examples Star Ring Tree Irregular CMPE 80N - Introduction to Networks and the Internet 12 More Concepts… • Network protocols. • Layering. • Network architecture. CMPE 80N - Introduction to Networks and the Internet 13 Network Protocols • Diplomats use rules, called protocols, as guides for formal interactions. • A communication protocol is a set of rules that specify the format and meaning of messages exchanged between computers across a network. • A set of related protocols that are designed for compatibility are called protocol suite. CMPE 80N - Introduction to Networks and the Internet 14 Human and Computer Protocols Human Protocol Hi Hi Got the time? Computer Protocol Web client open connection OK Web server send me data 2:00 <data> time CMPE 80N - Introduction to Networks and the Internet 15 Layering • What is it? • Building complex systems is hard! – Approach: “Divide and conquer”. – Split job into smaller jobs, or layers. • Analogy to other fields. – Building a house: digging, foundation, framing, etc. – Car assembly line… • Basic idea: each step dependent on the previous step but does not need to be aware of how the previous step was done. CMPE 80N - Introduction to Networks and the Internet 16 Analogy: Air Travel • The problem: air travel. • Decomposed into series of steps: Arrival at airport Departure from airport Check-in Baggage claim Boarding Deplane Takeoff Landing Traveling CMPE 80N - Introduction to Networks and the Internet 17 Arrival Departure Check-in Baggage claim Boarding Deplane Takeoff Landing intermediate air traffic sites Airplane routing Arriving airport Departing airport More on the air travel analogy… Airplane routing Traveling CMPE 80N - Introduction to Networks and the Internet 18 Layered Protocol Design • Layering model is a solution to the problem of complexity in network protocols • The model divides the network protocols into layers, each of which solves part of the network communication problem – Each layer has its own protocol! • Each layer implements a service to the layer above – Relying on services provided by the layers below. CMPE 80N - Introduction to Networks and the Internet 19 Layers • Layers are the different components that need to be designed/implemented when designing/implementing networks. • Each layer responsible for a set of functions. • Top layer relies on services provided by bottom layer. • Layer makes it service available to higher layer through an interface. CMPE 80N - Introduction to Networks and the Internet 20 Network Architecture • Set of layers, what their functions are, the services each of them provide, and the interfaces between them. • A.k.a, protocol stack. • Examples: – ISO-OSI 7 layer architecture. – TCP-IP architecture (Internet). CMPE 80N - Introduction to Networks and the Internet 21 Network Architecture • Set of layers, what their functions are, the services each of them provide, and the interfaces between them. CMPE 80N - Introduction to Networks and the Internet 22 Example 1: ISO OSI Architecture • ISO: International Standards Organization • OSI: Open Systems Interconnection. Application Presentation Session Transport Network Data link Physical CMPE 80N - Introduction to Networks and the Internet 23 Layers of Interest in ISO Model • Layer 7: Application – Application-specific protocols (e.g. ftp, http, smtp) • Layer 4: Transport – Delivery of data between computers (end-to-end). • Layer 3: Network – Data routing across a network. • Layer 2: Data Link – Reliable transmission over physical medium. • Layer 1: Physical - Transmission of bits between two nodes. CMPE 80N - Introduction to Networks and the Internet 24 Example 2: TCP/IP Architecture • Model employed by the Internet. TCP/IP Application Application Presentation Transport Session Transport Internet Network Access Physical CMPE 80N - Introduction to Networks and the Internet ISO OSI Network Data link Physical 25