1. April 1999Computer Networks: Architecture & Concepts/Habib Youssef1 Computer Networks: Architecture & Concepts Habib Youssef, Ph.D. youssef@ccse.kfupm.edu.sa Department of Computer Engineering King Fahd University of Petroleum & Minerals Dhahran, Saudi Arabia

2. April 1999Computer Networks: Architecture & Concepts/Habib Youssef2 Computer Network? l An interconnected collection of autonomous computers and computer resources

3. April 1999Computer Networks: Architecture & Concepts/Habib Youssef3 Simple Data Communication Model Transceiver Transport System Digital Analog/Digital Digital 001101 Data Network Public Telephone Network

4. April 1999Computer Networks: Architecture & Concepts/Habib Youssef4 Communication Protocols l To provide error-free and convenient information transfers, the network communication is regulated by a set of rules and conventions called network protocols. l Protocols define connectors, cables, signals, data formats, error control techniques, and algorithms for message preparation, analysis and transfer.

5. April 1999Computer Networks: Architecture & Concepts/Habib Youssef5 Protocol Data Units (PDU) l Protocol entities exchange PDUs »Each PDU must contain two major parts: –Header: l Identifies how the following parts are to be handled and routed. –Message: l This is the message body itself. l This is where the protocol is determined to be character oriented or bit oriented.

6. April 1999Computer Networks: Architecture & Concepts/Habib Youssef6 OSI Reference Model of ISO l 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.

7. April 1999Computer Networks: Architecture & Concepts/Habib Youssef7 Reference Model

8. April 1999Computer Networks: Architecture & Concepts/Habib Youssef8 Most Important Standards Organizations l ITU-T: International Telecommunication Union (a United Nations specialized agency, was created on March 1, 1993) l ISO: International Organization for Standardization (an international voluntary, nontreaty organization, founded in 1946) l IETF: Internet Engineering Task Force (responsible for publishing RFCs (Requests For Comments)) l 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)

9. April 1999Computer Networks: Architecture & Concepts/Habib Youssef9 ISO OSI Reference Architecture l 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.

10. April 1999Computer Networks: Architecture & Concepts/Habib Youssef10 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 Layer Functions

11. April 1999Computer Networks: Architecture & Concepts/Habib Youssef11 Application Application Presentation Presentation SessionSession Transport Transport NetworkNetwork Data LinkData Link PhysicalPhysical Layer Functions bits frames packets segments Host A Host B

12. April 1999Computer Networks: Architecture & Concepts/Habib Youssef12 Data Encapsulation Frames Bits Packets Data Salams 7. application 6. presentation 5. session 4. transport

13. April 1999Computer Networks: Architecture & Concepts/Habib Youssef13 Data Encapsulation Example segment data header network segment data header header data Frame Network Segment Data Frame header header header trailer Data Segment Packet Frame Bits 01111111010101101000100100010110101

14. April 1999Computer Networks: Architecture & Concepts/Habib Youssef14 Summary l Internetworking evolved to support current and future applications l The OSI reference model organizes network functions into seven layers l Data flows from upper-level user applications to lower-level bits transmitted over network media l Peer-to-peer functions use encapsulation and de- encapsulation at layer interfaces l Most network manager tasks configure the lower three layers

15. April 1999Computer Networks: Architecture & Concepts/Habib Youssef15 Application, Presentation, and Session Layers

16. April 1999Computer Networks: Architecture & Concepts/Habib Youssef16 Application Layer Computer Applications l Word Processing l Presentation Graphics l Spreadsheet l Database l Design/Manufacturing l Project Planning l Others Network Applications l Electronic mail l File Transfer l Remote Access l Client/Server Process l Information Location l Network Management l Others

17. April 1999Computer Networks: Architecture & Concepts/Habib Youssef17 Application Layer (cont.) Network Applications (For enterprise communication) l Electronic mail l File Transfer l Remote Access l Client/Server Process l Information Location l Network Management l Others Internetwork Applications (Extend beyond the enterprise) l Electronic Data Interchange l World Wide Web l E-mail Gateways l Special-Interest Bulletin Boards l Financial Transaction Services l Internet Navigation Utilities l Conferencing (Video, Voice, Data)

18. April 1999Computer Networks: Architecture & Concepts/Habib Youssef18 Presentation Layer l Text l Data »ASCII »EBCDIC »Encrypted l Sound l Video »MIDI (Musical Instrument Digital Interface) »MPEG (Motion Picture Experts Group) »QuickTime

19. April 1999Computer Networks: Architecture & Concepts/Habib Youssef19 Presentation Layer l Graphics l Visual Images »PICT(format to transfer QuickDraw graphics between Macintosh or PowerPC programs) »TIFF (Tagged Image File Format) »JPEG (Joint Photographic Experts Group) »GIF l Provides code formatting and conversion for applications

20. April 1999Computer Networks: Architecture & Concepts/Habib Youssef20 Session Layer l Coordinates applications as they interact on different hosts Service Request Service Reply

21. April 1999Computer Networks: Architecture & Concepts/Habib Youssef21 Session Layer (contd.) l Network File System (NFS) –Allows transparent access to remote network resources l Structured Query Language (SQL) l Remote-Procedure Call (RPC) –RPC procedures are built on clients and executed on servers l X Window System –Allows intelligent terminals to communicate with remote UNIX machines l AppleTalk Session Protocol (ASP) –Establishes and maintains sessions between an AppleTalk client and server l DNA Session Control Protocol (SCP)

22. April 1999Computer Networks: Architecture & Concepts/Habib Youssef22 Transport Layer

23. April 1999Computer Networks: Architecture & Concepts/Habib Youssef23 Transport Layer Overview l Segments upper-layer applications l Establishes an end-to-end connection l Sends segments from one end host to another l Ensures end-to-end data reliability

24. April 1999Computer Networks: Architecture & Concepts/Habib Youssef24 Segment Upper-Layer Applications l Transport segments share traffic stream Application Data Application Data port port Electronic mail File transfer Terminal session Application Presentation Session Transport

25. April 1999Computer Networks: Architecture & Concepts/Habib Youssef25 Establishes Connection sender receiver synchronize Negotiate connection synchronize Acknowledge Connection established Data transfer (send segments)

26. April 1999Computer Networks: Architecture & Concepts/Habib Youssef26 Establishes Connection sender receiver transmit not ready ready Resume Transmission Buffer full process segments Buffer OK

27. April 1999Computer Networks: Architecture & Concepts/Habib Youssef27 Reliability with Windowing l 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. l Windowing is a method to control the amount of information transferred end-to- end. Some protocols measure information in terms of number of packets

28. April 1999Computer Networks: Architecture & Concepts/Habib Youssef28 Reliability with Windowing senderreceiversender receiver Send 1 Send 2 Send 1 Send 2 Send 3 Window size 1 Window size 3 Receive 1 Receive 2 Receive 3 Receive 1 Receive 2 ACK 2 ACK 3 ACK 4 Send 4

29. April 1999Computer Networks: Architecture & Concepts/Habib Youssef29 PAR Technique l 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. l The sender keeps the record of each segment it sends and waits for an acknowledgement. l The sender also starts a timer when it sends a segment, and it retransmits a segment it the timer expires before an acknowledgement arrives.

30. April 1999Computer Networks: Architecture & Concepts/Habib Youssef30 PAR Technique (contd.) send 1 send 2 send 3 Ack 4 send 4 send 5 send 6 Ack 5 send 5 Ack 7 sender receiver 1 2 3 4 5 6 X

31. April 1999Computer Networks: Architecture & Concepts/Habib Youssef31 Transport to Network Layer End-to-end segments Routed packets

32. April 1999Computer Networks: Architecture & Concepts/Habib Youssef32 Summary l Presentation layer formats and converts network application data to represent text, graphics, images, video, and audio. l Session-layer functions coordinate communication interactions between applications. l Reliable transport-layer functions include »Multiplexing »Connection synchronization »Flow control »Error recovery »Reliability through windowing

33. April 1999Computer Networks: Architecture & Concepts/Habib Youssef33 Physical and Data Link Layers

34. April 1999Computer Networks: Architecture & Concepts/Habib Youssef34 Physical and Data-Link Standards l 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. l The physical layer specifies the electrical, mechanical, procedural, and functional requirements for activating, maintaining, and deactivating the physical link between end systems. l These requirements and characteristics are codified into standards.

35. April 1999Computer Networks: Architecture & Concepts/Habib Youssef35 LAN Data-Link Sublayers Logical Link Control Media Access Control MAC Frame 802.2 LLC Packet or datagram Network Physical Data Link LLC MAC

36. April 1999Computer Networks: Architecture & Concepts/Habib Youssef36 LAN Data-Link Sublayers l LLC refers upward to higher-layer software functions. l MAC refers downward to lower-layer hardware functions. l LAN protocols occupy the bottom two layers of OSI reference model: the physical layer and data link layer.

37. April 1999Computer Networks: Architecture & Concepts/Habib Youssef37 LAN Data-Link Sublayers l The IEEE 802 committee subdivided the data link layer into two sublayers: »The logical link control (LLC) sublayer »The media access control (MAC) sublayer l The LLC sublayer provides for environments that need connectionless or connection- oriented services and the data link layer. l The MAC sublayer provides access to the LAN medium in an orderly manner.

38. April 1999Computer Networks: Architecture & Concepts/Habib Youssef38 LLC Sublayer Functions l Enable upper layers to gain independence over LAN media access. l Allow service access points (SAPs) from interface sublayers to upper-layer functions. l Provide optional connection, flow control, and sequencing services.

39. April 1999Computer Networks: Architecture & Concepts/Habib Youssef39 Client-Server Model

40. April 1999Computer Networks: Architecture & Concepts/Habib Youssef40 Client Server Model l Client-Server paradigm is the primary pattern of interactions among cooperating applications. l This model constitutes the foundation on which distributed algorithms are built.

41. April 1999Computer Networks: Architecture & Concepts/Habib Youssef41 What is the Client-Server Paradigm? l The paradigm divides communicating applications into 2 broad categories, depending on whether the application waits for communication or initiates it. »An application that initiates a communication is called a client. »End users usually invoke a client software when they use a network service.

42. April 1999Computer Networks: Architecture & Concepts/Habib Youssef42 Client Server Model (cont.) l Server: Any program that offers a service reachable over the network »If a machine’s primary purpose is to support a particular server program, the term server is usually applied to both, the machine and the server program l Client: An executing program becomes a client when it sends a request to a server and waits for a response

43. April 1999Computer Networks: Architecture & Concepts/Habib Youssef43 Client Server Model (cont.) l A server is any program that waits for incoming communication requests from a client. »Each time a client application needs to contact a server, it sends a request and awaits a response. »The server receives a client’s request, performs the necessary computation, and returns the result to the client. »When the response arrives at the client, the client continues processing.

44. April 1999Computer Networks: Architecture & Concepts/Habib Youssef44 Client Server Model (cont.) Request Reply Machine Running Client Application Machine Running Server Application Client Program Server Program

45. April 1999Computer Networks: Architecture & Concepts/Habib Youssef45 Client Server Model (cont.) l A Misconception: »Technically, a server is a program and not a piece of hardware. »However, computer users frequently (mis)apply the term to the computer responsible for running a particular server program. –For example, Web Server, is usually a computer running the http server program.

46. April 1999Computer Networks: Architecture & Concepts/Habib Youssef46 Summary l Internetworking evolved to support current and future applications. l The OSI reference model organizes network functions into seven layers. l Data flows from upper-level user applications to lower-level bits transmitted over network media. l Peer-to-peer functions use encapsulation and de- encapsulation at layer interfaces. l Client-Server paradigm constitutes the foundation on which distributed algorithms are built.