Transcript ICOM 6115
ICOM 6115 – Computer Networks and the WWW Manuel Rodriguez-Martinez, Ph.D. Lecture 3 ICOM 6115 ©Manuel Rodriguez-Martinez Lecture Objectives • Close some gaps from Hardware Lecture • Understand the Architecture of Networking Software • Client – Server model for communications • Design Principles – Layering – Vertical and Horizontal Communication – Finite State Machines ICOM 6115 ©Manuel Rodriguez-Martinez Wireless Networks • Fundamental idea: Network without wires – Cheaper to deploy – Less of a hassle to people • Most successful ones: based on radio – each host has • Radio modem + antenna – Access point are used to connect wired and wireless parts ICOM 6115 ©Manuel Rodriguez-Martinez Examples Configurations Access Point Fully Wireless ICOM 6115 Wireless + Wires ©Manuel Rodriguez-Martinez Existing technologies • Bluetooth – Localized connectivity (few meters) – Bandwidth – 2Mbps • IEEE 802.11 – LAN connectivity – Bandwidth – • 802.11b – 11Mbps • 802.11a – 54Mbps • 3G (Cellular) – WAN – Bandwidth – less than 1Mbps • Centennial Flex – 144Kpbs ICOM 6115 ©Manuel Rodriguez-Martinez Metropolitan Area Networks (MAN) • Networks that are – bigger than LANs – Not as big as WANs – Mostly dead until Cable TV became ISP • Used to provide connectivity for cities – Broadband Systems • Cable and DSL are current players • Next Big Player? : IEEE 802.16 – Wireless Local Loop (Wireless Broadband) ICOM 6115 ©Manuel Rodriguez-Martinez Cable TV MAN (Cable Modem) Typical Bandwidth: 128Kbps – 1Mbps ICOM 6115 ©Manuel Rodriguez-Martinez Wireless Local Loop (IEEE 802.16) Bandwidth: 150Mbps, 100Mbps, or 50Mbps ICOM 6115 ©Manuel Rodriguez-Martinez Future Trends: Home Area Networks Intelligent Home High Speed Line Home Wireless LAN ICOM 6115 ©Manuel Rodriguez-Martinez Design Issues for Networking Software • What are the programming models? • What are communications protocols? • What are the principles that guide protocols design? • What is the impact of hardware characteristics on networking software • What are the performance trade-offs? • What is the operating systems support for networking? ICOM 6115 ©Manuel Rodriguez-Martinez Client-Server Model • Dominant paradigm for programming networked application • Client application – Used by the user to obtain a given service from the network • Web browser, E-mail, News, SSH client (Open SSH) • Server Application – Provides a well-defined service • Data or computation service • Web Server, Time server, Parallel Machine, SSH Server ICOM 6115 ©Manuel Rodriguez-Martinez Client-Server Interaction Req Reply Web Server Web Surfers ICOM 6115 ©Manuel Rodriguez-Martinez Request-Reply Interaction • Client requests a given data or service • Server replies with either – Requested data or service – Error indication ICOM 6115 ©Manuel Rodriguez-Martinez Peer-to-Peer Model • Old and New model – Existed since the early 70’s • Distributed Databases – Rediscovered in the 90’s • Napster • Applications can act as both client and server – Get data from some site – Serve data to others ICOM 6115 ©Manuel Rodriguez-Martinez Peer-to-Peer Interaction Anyone can be a server and a client (dual role) ICOM 6115 ©Manuel Rodriguez-Martinez Peer-to-Peer Exchange ICOM 6115 ©Manuel Rodriguez-Martinez Peer-to-Peer tend branch out ICOM 6115 ©Manuel Rodriguez-Martinez Client-Server vs. P2P • Client-Server – simpler – highly scalable – Fast – But covers little of the network • P2P – Can access more sites – More complex to program – Can be very slow (too much branching out) • Scalability problems ICOM 6115 ©Manuel Rodriguez-Martinez Networking Protocols • Networking protocol – a set of rules, data formats and algorithms that govern a given communications process Ex.: Generic Request-Reply protocol scheme ICOM 6115 ©Manuel Rodriguez-Martinez Protocol Design Principles • Use Layering to simplify design and implementation • Understand the type of Service – Connection vs. connectionless – Best-effort vs. Guaranteed services • QoS and Differentiated Services • Understand the performance characteristics of network – Bandwidth, throughput, delay, delay x bandwidth • Develop a sound Mathematical model – Finite State Machines, Graph and Queuing Theory ICOM 6115 ©Manuel Rodriguez-Martinez Protocol Layering • Divide the problem into well-defined subproblems and solve each one – Divide and Conquer • Organize solutions into layers of services – Protocol Stack • Each layer must solve a well-defined issue – Data Link – deals with moving packets between network cards. – Network Layer – deals with moving packets between hosts (possibly on different LANs) ICOM 6115 ©Manuel Rodriguez-Martinez Example: TCP/IP Protocol Stack Application Layer Transport Layer FTP SSH TCP UDP Network Layer IP Data Link Layer Ethernet Physical Layer ICOM 6115 Fiber HTTP PPP Cooper ©Manuel Rodriguez-Martinez Air Service Primitives • Primitives are the set of operations provided by a given layer – Similar to methods in a class – Abstract the what from the how? – Modular Design • Can change implementation of primitives • Primitives form the interface for interaction between layers • Principle of Vertical Communication ICOM 6115 ©Manuel Rodriguez-Martinez Vertical Communication ICOM 6115 ©Manuel Rodriguez-Martinez Data Encapsulation • Packets have – Header – control information • Source, destination, flags – Trailer (optional) – more control information – Payload – space where the data transmitted by the packet is held Header Payload Packet Organization ICOM 6115 ©Manuel Rodriguez-Martinez Trailer Data Encapsulation • The packet for one layer becomes the payload in the packet of the lower layer. – Sometimes more than packet might be needed at lower layer – Lower layers should not care about structure of payload – Not 100% true • Some routers inspect payload – Security – Differentiated services ICOM 6115 ©Manuel Rodriguez-Martinez Encapsulation and De-capsulation Sender SSH TCP IP 802.11 Bit Pipe ICOM 6115 ©Manuel Rodriguez-Martinez Receiver More on Encapsulation • Sometimes a packet at layer N won’t fit on one packet at the lower layer – Must be broken and re-assembled at the destination • Horizontal Communication – The packet sent by a given layer X should be understood only by the layer X at the receiver ICOM 6115 ©Manuel Rodriguez-Martinez More on Encapsulation ICOM 6115 ©Manuel Rodriguez-Martinez