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Understanding Computer Networks: Architecture and Concepts

This text explores communication networks, computer architecture, data communication models, network services, protocols, OSI reference model, and important standards organizations in the field of computer networking.

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Understanding Computer Networks: Architecture and Concepts

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  1. Computer Networks: Architecture & Concepts Abdulaziz Almulhem Communication Networks

  2. Communication • People need to communicate with each other. • Why? To exchange information. • What? Voice, Sound, Graphics, Pictures, Text, or Data • One way is to use the postal service. Communication Networks

  3. Communication (cont.) • Better, pull wires between each two people. (point-to-point communication) • cost is high and resources are wasted • complexity (mesh, drop and add) • We need to build a shared communication media (links) • Efficient • needs management (data may wait) Communication Networks

  4. Communication (cont.) • We build communication networks. • These are arrangements of hardware and software that allow users to exchange information. (computer net) • Thus we have two types of nodes: • terminal nodes • communication nodes Communication Networks

  5. Computer Network? • An interconnected collection of autonomous computers and computer resources communication node Shared medium Terminal node Communication Networks

  6. Simple Data Communication Model 001101 Analog/Digital Digital Transceiver Transport System Transceiver Data Network Digital Public Telephone Network 001101 Communication Networks

  7. Network Services • The objective is to provide services to the users. • Information transportation • signaling • billing • A service is the execution of a sequence of basic actions on network resources. (how to place a phone call?) Communication Networks

  8. Network Services (cont.) • Scripts are executed by the communicating entities only. • These scripts could be very complex. • It is more efficient to have a modular construction of scripts: • action it performs • interaction to other modules Communication Networks

  9. Network Services (Cont.) • Advantages of such modular: • reusability • upgradability • interoperability • The general organization of services into simpler services is called the network architecture. Communication Networks

  10. Communication Protocols • To provide error-free and convenient information transfers, the network communication is regulated by a set of rules and conventions called network protocols. • Protocols define connectors, cables, signals, data formats, error control techniques, and algorithms for message preparation, analysis and transfer. Communication Networks

  11. Protocol Data Units (PDU) • Protocol entities exchange PDUs • Each PDU must contain two major parts: • Header: • Identifies how the following parts are to be handled and routed. • Message: • This is the message body itself. • This is where the protocol is determined to be character oriented or bit oriented. Communication Networks

  12. OSI Reference Model of ISO • Architecture/structure that defines communication tasks and which would: • Serve as a reference model for international standards • would facilitate efficient internetworking among systems from different technologies, manufacturers, administrations, nationalities, and enterprises. Communication Networks

  13. Reference Model Communication Networks

  14. Most Important Standards Organizations • ITU-T: International Telecommunication Union (a United Nations specialized agency, was created on March 1, 1993) • ISO: International Organization for Standardization (an international voluntary, nontreaty organization, founded in 1946) • IETF: Internet Engineering Task Force (responsible for publishing RFCs (Requests For Comments)) • IEEE: Institute of Electrical and Electronic Engineers (ATM Forum: This organization is not a standard organization. After ITU defined the ATM concept in Nov 1990, ATM Forum was initiated in October 1991 to accelerate the deployment of ATM products and services. ATM Forum develops implementation agreements and publishes them as “specifications” on its web site: www.atmforum.com) Communication Networks

  15. ISO OSI Reference Architecture • The architecture is layered to reduce complexity. • Each layer offers certain services to the layer immediately above it. • Each layer shields the higher layer from the details of implementation of how the services are offered. • Layer "n" on one station carries on a conversation with layer "n" on another network station. Communication Networks

  16. Layer Functions 7 Application ftp, telnet, email, www, etc. 6 Presentation Data representation 5 Session Negotiation and connection 4 Transport End-to-end delivery 3 Network Addresses and best path (routing) 2 Data Link Access to media (transfer of frames) 1 Physical Binary transmission and cabling Communication Networks

  17. Layer Functions Application Application Presentation Presentation Session Session TransportTransport NetworkNetwork Data LinkData Link PhysicalPhysical segments packets frames bits Host AHost B Communication Networks

  18. Data Encapsulation Salams Salams Data 7. application 6. presentation 5. session 4. transport Packets Frames Data Bits Communication Networks

  19. Data Encapsulation Example data Data Segment Packet Frame Bits segment data header network segment data header header Frame Network Segment Data Frame header header header trailer 01111111010101101000100100010110101 Communication Networks

  20. Summary • Internetworking evolved to support current and future applications • The OSI reference model organizes network functions into seven layers • Data flows from upper-level user applications to lower-level bits transmitted over network media • Peer-to-peer functions use encapsulation and de-encapsulation at layer interfaces • Most network manager tasks configure the lower three layers Communication Networks

  21. Interfaces and Services • Each layer in the OSI layered architecture has a function (service) to be provided to the upper layer through some interface (service access point). • The upper layer can request a service from the lower layer through SAP. Communication Networks

  22. Interface and services (cont.) • When layer n+1 requests a service from layer n, Layer n will encapsulate the PDU of layer n+1 into a new PDU to be handed to layer n-1. • Services provided by each layer: • Connection-oriented (telephone) • Connectionless (post) Communication Networks

  23. Service Primitives • Layer services are specified by a set of operations available to the layer above it. • These operations either: • Ask for the service • report the status of the service Communication Networks

  24. Service Primitives (cont.) Layer n+1 Request Confirm Layer n Indication Response Communication Networks

  25. Services and Protocols • Services are set of operations provided to upper layers or user. • Protocols are sets of rules governing how the same peers should be communicating. • Protocols are transparent from user and may change without changing services. Communication Networks

  26. Protocols and Services Session Session Transport Transport Services Network Network Protocols Communication Networks

  27. Application, Presentation, and Session Layers Communication Networks

  28. Computer Applications Word Processing Presentation Graphics Spreadsheet Database Design/Manufacturing Project Planning Others Network Applications Electronic mail File Transfer Remote Access Client/Server Process Information Location Network Management Others Application Layer Communication Networks

  29. Network Applications (For enterprise communication) Electronic mail File Transfer Remote Access Client/Server Process Information Location Network Management Others Internetwork Applications (Extend beyond the enterprise) Electronic Data Interchange World Wide Web E-mail Gateways Special-Interest Bulletin Boards Financial Transaction Services Internet Navigation Utilities Conferencing (Video, Voice, Data) Application Layer (cont.) Communication Networks

  30. Presentation Layer • Text • Data • ASCII • EBCDIC • Encrypted • Sound • Video • MIDI (Musical Instrument Digital Interface) • MPEG (Motion Picture Experts Group) • QuickTime Communication Networks

  31. Presentation Layer • Graphics • Visual Images • PICT(format to transfer QuickDraw graphics between Macintosh or PowerPC programs) • TIFF (Tagged Image File Format) • JPEG (Joint Photographic Experts Group) • GIF • Provides code formatting and conversion for applications Communication Networks

  32. Session Layer • Coordinates applications as they interact on different hosts (dialogue control and synchronization) Service Request Service Reply Communication Networks

  33. Session Layer (contd.) • Network File System (NFS) • Allows transparent access to remote network resources • Structured Query Language (SQL) • Remote-Procedure Call (RPC) • RPC procedures are built on clients and executed on servers • X Window System • Allows intelligent terminals to communicate with remote UNIX machines • AppleTalk Session Protocol (ASP) • Establishes and maintains sessions between an AppleTalk client and server • DNA Session Control Protocol (SCP) Communication Networks

  34. Transport & Network Layers Communication Networks

  35. Transport Layer Overview • Segments upper-layer PDUs • Establishes an end-to-end connection • Sends segments from one end host to another • Ensures end-to-end data reliability Communication Networks

  36. Segment Upper-Layer PDUs Application Electronic mail File transfer Terminal session • Transport segments share traffic stream Presentation Session Transport Application Data Application Data port port Communication Networks

  37. Acknowledge Establishes Connection receiver sender synchronize Negotiate connection synchronize Connection established Data transfer (send segments) Communication Networks

  38. receiver sender Establishes Connection transmit Buffer full process segments Buffer OK not ready ready Resume Transmission Communication Networks

  39. Reliability with Windowing • In the most basic form of reliable connection-oriented transfer, data segments must be delivered to the recipient in the same sequence that they were transmitted. • Windowing is a method to control the amount of information transferred end-to-end. Some protocols measure information in terms of number of packets Communication Networks

  40. receiver receiver sender sender Reliability with Windowing Window size 1 Send 1 Receive 1 ACK 2 Send 2 Receive 2 ACK 3 Window size 3 Send 1 Receive 1 Send 2 Receive 2 Send 3 Receive 3 ACK 4 Send 4 Communication Networks

  41. PAR Technique • Reliable delivery guarantees that a stream of data sent from one machine will be delivered through a functioning data link to another machine without duplication or data loss. Positive acknowledgement with retransmission is one technique that guarantees reliable delivery of data streams. • The sender keeps the record of each segment it sends and waits for an acknowledgement. • The sender also starts a timer when it sends a segment, and it retransmits a segment it the timer expires before an acknowledgement arrives. Communication Networks

  42. receiver sender 1 2 3 4 5 6 1 2 3 4 5 6 PAR Technique (contd.) send 1 send 2 send 3 Ack 4 send 4 send 5 send 6 Ack 5 send 5 Ack 7 X Communication Networks

  43. End-to-end segments Transport to Network Layer Routed packets Communication Networks

  44. Network Layer • Controlling the operation of the network. • How to route data from source to destination? • Static routing tables • Dynamic routing tables • Datagram is similar to a postal letter. Communication Networks

  45. Summary • Presentation layer formats and converts network application data to represent text, graphics, images, video, and audio. • Session-layer functions coordinate communication interactions between applications. • Reliable transport-layer functions include • Multiplexing • Flow control • Error recovery • Reliability through windowing Communication Networks

  46. Physical and Data Link Layers Communication Networks

  47. Physical and Data-Link Standards • The data link layer provides data transport across a physical link. To do so, the data link layer handles physical addressing, network topology, line discipline, error notification, orderly delivery of frames , and optional flow control. • The physical layer specifies the electrical, mechanical, procedural, and functional requirements for activating, maintaining, and deactivating the physical link between end systems. • These requirements and characteristics are codified into standards. Communication Networks

  48. LAN Data-Link Sublayers LLC Network Logical Link Control Data Link MAC Media Access Control Physical MAC Frame802.2 LLCPacket or datagram Communication Networks

  49. LAN Data-Link Sublayers • LLC refers upward to higher-layer software functions. • MAC refers downward to lower-layer hardware functions. • LAN protocols occupy the bottom two layers of OSI reference model: the physical layer and data link layer. Communication Networks

  50. LAN Data-Link Sublayers • The IEEE 802 committee subdivided the data link layer into two sublayers: • The logical link control (LLC) sublayer • The media access control (MAC) sublayer • The LLC sublayer provides for environments that need connectionless or connection-oriented services and the data link layer. • The MAC sublayer provides access to the LAN medium in an orderly manner. Communication Networks

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