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Chapter 1. Introduction

Chapter 1. Introduction. Wen-Shyang Hwang KUAS EE. Introduction. Distributed system a collection of independent computers appears to its users as a single coherent system. Often a middleware on top of the operating system. Computer Networks the coherence and middleware are absent.

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Chapter 1. Introduction

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  1. Chapter 1. Introduction Wen-Shyang Hwang KUAS EE.

  2. Introduction • Distributed system • a collection of independent computers appears to its users as a single coherent system. • Often a middleware on top of the operating system. • Computer Networks • the coherence and middleware are absent. • computers are separated but interconnected. • user has to log onto the remote machine to run a program • Computer Center • a room with a large computer for users • Client-server model • Peer-to-peer (P2P)

  3. Network Hardware • Transmission technology • Broadcast networks: Broadcasting and multicasting • Point-to-point networks: unicasting • Scale • Local Area Network (LAN) • Ethernet, IEEE 802.3 • Token bus, IEEE 802.5 • Metropolitan Area Network (MAN) • Cable TV, head end • WiMAX, IEEE 802.16 • Wide Area Network (WAN) • Switching element (router), • routing algorithm • Store-and-forward or packet-switched • Wireless Networks (Bluetooth and IEEE 802.11) • Home Networks and internetworks (gateway)

  4. Switching Terms • Switching Nodes: • Intermediate switching device that moves data • Not concerned with content of data • Stations: • End devices that wish to communicate • Each station is connected to a switching node • Communications Network: • A collection of switching nodes

  5. Techniques Used in Switched Networks • Circuit switching • Dedicated communications path between two stations • E.g., public telephone network • Packet switching • Message is broken into a series of packets • Each node determines next leg of transmission for each packet

  6. Phases of Circuit Switching • Circuit establishment • An end to end circuit is established through switching nodes • Information Transfer • Information transmitted through the network • Data may be analog voice, digitized voice, or binary data • Circuit disconnect • Circuit is terminated • Each node deallocates dedicated resources • Characteristics • Inefficient • Channel capacity dedicated for duration of connection • Utilization not 100% • Delay prior to signal transfer for establishment • Once established, network is transparent to users • Information transmitted at fixed data rate with only propagation delay

  7. Packet Switching

  8. Packet Switching Networks - Datagram • Datagram • Each packet treated independently, without reference to previous packets • Each node chooses next node on packet’s path • Packets don’t necessarily follow same route and may arrive out of sequence • Exit node restores packets to original order • Responsibility of exit node or destination to detect loss of packet and how to recover • Advantages: • Call setup phase is avoided • Because it’s more primitive, it’s more flexible • Datagram delivery is more reliable

  9. Packet Switching Networks – Virtual Circuit • Virtual Circuit • Preplanned route established before packets sent • All packets between source and destination follow this route • Routing decision not required by nodes for each packet • Emulates a circuit in a circuit switching network but is not a dedicated path • Packets still buffered at each node and queued for output over a line • Advantages: • Packets arrive in original order • Packets arrive correctly • Packets transmitted more rapidly without routing decisions made at each node

  10. Effect of Packet Size on Transmission

  11. Network Software - 1 • Protocol hierarchies • Protocol is an agreement between the communicating parties • Layers or levels, protocol stack • Peers (Fig 1-13) • Packet header • Design issues • Addressing, • Error control • Flow control • Multiplexing, demultiplexing • Routing

  12. Network Software - 2 • Connection-oriented and connectionless services • Quality of service • Datagram service • Acknowledged datagram service • Request-reply service • Service Primitives • Listen • Connect • Receive • Send • Disconnect

  13. Reference models • OSI reference model (Open System Interconnection) • Application • Presentation • Session • Transport • Network • Data link • Physical • TCP/IP reference model • Application • Transport • Internet • Host-to-Network

  14. TCP/IP Layers • Physical layer (All layers are relative with wireless • Network access layer networks in multimedia Communication) • Internet layer • Host-to-host, or transport layer • Application layer

  15. TCP/IP addressing

  16. Protocol Data Units (PDUs)

  17. TCP/IP Layers • Physical layer covers the physical interface between a data transmission device and a transmission mediumor network • Physical layer specifies: • Characteristics of the transmission medium • The nature of the signals • The data rate • Other related matters (coding, Radio Frequence…) • Network access layer concerned with the exchange of data between an end system and the network to which it's attached • Software used depends on type of network • Circuit switching • Packet switching (e.g., X.25) • LANs (e.g., Ethernet) • Others (WiFi, WiMAX, Bluetooth…)

  18. TCP/IP Layers • Internet Protocol (IP) • Provides routing functions to allow data to traverse multiple interconnected networks • Implemented in end systems and routers (mesh wireless network) • Transport Layer • Commonly uses transmission control protocol (TCP) • Provides reliability during data exchange • Completeness • Order • Application Layer • Supports user applications • Uses separate modules that are particular to each different type of application

  19. Common TCP/IP Applications • Simple mail transfer protocol (SMTP) • File Transfer Protocol (FTP) • TELNET

  20. Layers of the OSI Model • Application • Presentation • Session • Transport • Network • Data link • Physical

  21. OSI Layers • Application Layer • Provides access to the OSI environment for users • Provides distributed information services • Presentation Layer • Provides independence to the application processes from differences in data representation (syntax) • Session Layer • Provides the control structure for communication between applications • Establishes, manages, and terminates connections (sessions) between cooperating applications • Transport Layer • Provides reliable, transparent transfer of data between end points • Provides end-to-end error recovery and flow control

  22. OSI Layers • Network Layer • Provides upper layers with independence from the data transmission and switching technologies used to connect systems • Responsible for establishing, maintaining, and terminating connections • Data Link Layer • Provides for the reliable transfer of information across the physical link • Sends blocks (frames) with the necessary synchronization, error control, and flow control • Physical Layer • Concerned with transmission of unstructured bit stream over physical medium • Deals with accessing the physical medium • Mechanical characteristics • Electrical characteristics • Functional characteristics • Procedural characteristics

  23. Example Networks • The Internet • ARPANET • NSFNET • ANSNET • E-mail, News, Remote login, File transfer, WWW • ISP’s POP (Point of Presence) • Connection-Oriented Networks • X.25 • Frame Relay • ATM • Virtual circuits, cell • ATM reference model • AAL (ATM adaptation layer) • Ethernet • Wireless LAN: IEEE 802.11, WiFi • Access point, Ad hoc network, multipath fading

  24. Asynchronous Transfer Mode (ATM) • Also known as cell relay • Resembles packet switching • transfer data in discrete chunks • allows multiple logical connections to be multiplexed over a single physical interface • Fixed-size cells simplify processing at ATM nodes

  25. ATM Terminology • Virtual channel connection (VCC) • Logical connection in ATM • Basic unit of switching in ATM network • Analogous to a virtual circuit in packet switching networks • Exchanges variable-rate, full-duplex flow of fixed-size cells • Virtual path connection (VPC) • Bundle of VCCs that have the same end points • Advantages: • Simplified network architecture • Increased network performance and reliability • Reduced processing and short connection setup time • Enhanced network services

  26. Call Establishment

  27. Virtual Channel Connection • Between end users • carry end-to-end user data or control signaling between two users • Between an end user and a network entity • Used for user-to-network control signaling • Between two network entities • Used for network traffic management and routing functions • Virtual Path/Virtual Channel Characteristics • Quality of service • Specify parameters such as cell loss ratio and cell delay variation • Cell sequence integrity • Traffic parameter negotiation and usage monitoring • Virtual channel identifier restriction within a VPC

  28. ATM Cell Header Format • Generic flow control (GFC) – • 4 bits, used only in user-network interface • Used to alleviate short-term overload conditions in network • Virtual path identifier (VPI) – • 8 bits at the user-network interface, • 12 bits at network-network interface • Routing field • Virtual channel identifier (VCI) – • 8 bits, used for routing to and from end user • Payload type (PT) – • 3 bits, indicates type of information in information field • Cell loss priority (CLP) – • 1 bit, provides guidance to network in the event of congestion • Header error control (HEC) – • 8 bit, Error code

  29. ATM Service Categories • Real-time service • Constant bit rate (CBR) • Real-time variable bit rate (rt-VBR) • Non-real-time service • Non-real-time variable bit rate (nrt-VBR) • Available bit rate (ABR) • Unspecified bit rate (UBR)

  30. Examples • CBR applications • Videoconferencing • Interactive audio (e.g., telephony) • Audio/video distribution (e.g., television, distance learning, pay-per-view) • Audio/video retrieval (e.g., video-on-demand, audio library) • UBR applications • Text/data/image transfer, messaging, distribution, retrieval • Remote terminal (e.g., telecommuting)

  31. Wireless LAN– IEEE 802.11 Single cell Multiple cells Ad Hoc

  32. IEEE 802.11 Architecture

  33. Storage Area Networks

  34. LAN Topologies

  35. Frame Transmission on Bus LAN

  36. Frame Transmission Ring LAN

  37. Network Standardization • De facto (Latin for “ from the fact”) • The standard have just happened • IBM PC, UNIX • De jure (Latin for “by law”) • Legal standards adopted by some authorized standardization body • CCITT, ISO, ANSI, IEEE, NIST • IAB, IRTF, IETF for Internet – RFC (Request for Comments) • Proposed standard • Draft standard • RFC • Metric units • Kilo, Mega, Giga, Tera, Peta, Exa, zetta, Yotta • 103, 106, 109, 1012, 1015, 1018, 1021, 1024

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