Computer Networks Architecture Concepts Habib Youssef Ph D

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 April 1999 Computer Networks: Architecture & Concepts/Habib Youssef 1

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

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

Communication Protocols l l 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. April 1999 Computer Networks: Architecture & Concepts/Habib Youssef 4

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 l April 1999 This is the message body itself. This is where the protocol is determined to be character oriented or bit oriented. Computer Networks: Architecture & Concepts/Habib Youssef 5

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. April 1999 Computer Networks: Architecture & Concepts/Habib Youssef 6

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

Most Important Standards Organizations l l 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) April 1999 Computer Networks: Architecture & Concepts/Habib Youssef 8

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. April 1999 Computer Networks: Architecture & Concepts/Habib Youssef 9

Layer Functions 7 6 5 4 3 2 1 April 1999 Application Presentation Session Transport Network Data Link Physical ftp, telnet, email, www, etc. Data representation Negotiation and connection End-to-end delivery Addresses and best path (routing) Access to media (transfer of frames) Binary transmission and cabling Computer Networks: Architecture & Concepts/Habib Youssef 10

Layer Functions Application Presentation Session Transport Network Data Link Physical Host A April 1999 segments packets frames bits Application Presentation Session Transport Network Data Link Physical Host B Computer Networks: Architecture & Concepts/Habib Youssef 11

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

Data Encapsulation Example data segment header data network segment data header Frame Network Segment header Data Frame trailer 0111111101010110100010110101 April 1999 Data Segment Packet Frame Bits Computer Networks: Architecture & Concepts/Habib Youssef 13

Summary l l l 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 deencapsulation at layer interfaces Most network manager tasks configure the lower three layers April 1999 Computer Networks: Architecture & Concepts/Habib Youssef 14

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

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

Application Layer (cont. ) Network Applications Internetwork 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 (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) April 1999 l l l l Computer Networks: Architecture & Concepts/Habib Youssef 17

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

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

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

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

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

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

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

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

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

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

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

PAR Technique l l 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. 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. April 1999 Computer Networks: Architecture & Concepts/Habib Youssef 29

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

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

Summary l l l 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 » Connection synchronization » Flow control » Error recovery » Reliability through windowing April 1999 Computer Networks: Architecture & Concepts/Habib Youssef 32

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

Physical and Data-Link Standards l l 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. 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. April 1999 Computer Networks: Architecture & Concepts/Habib Youssef 34

LAN Data-Link Sublayers Network LLC Logical Link Control Data Link MAC Media Access Control Physical MAC Frame 802. 2 LLC April 1999 Packet or datagram Computer Networks: Architecture & Concepts/Habib Youssef 35

LAN Data-Link Sublayers l l l 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. April 1999 Computer Networks: Architecture & Concepts/Habib Youssef 36

LAN Data-Link Sublayers l l 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 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. April 1999 Computer Networks: Architecture & Concepts/Habib Youssef 37

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

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

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

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. April 1999 Computer Networks: Architecture & Concepts/Habib Youssef 41

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 April 1999 Computer Networks: Architecture & Concepts/Habib Youssef 42

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. April 1999 Computer Networks: Architecture & Concepts/Habib Youssef 43

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

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. April 1999 Computer Networks: Architecture & Concepts/Habib Youssef 45

Summary l l l 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 deencapsulation at layer interfaces. Client-Server paradigm constitutes the foundation on which distributed algorithms are built. April 1999 Computer Networks: Architecture & Concepts/Habib Youssef 46