Computer Network

Computer Network

Resources • Data Communication & Networking, 2nd. Ed., Forouzan, B.A., McGraw-Hill, 2001 • Computer Networks, 4th, Ed., Tanenbaum, A.S., Prentice Hall, 2002 • Selected papers Prepared by Hannyzzura Pal

Syllabus • Basic introduction • Network concepts • Network models • Signals • Encoding & modulating • Data transmission • Transmission media • Multiplexing • Error detection & correction • Data link control • Switching techniques Prepared by Hannyzzura Pal

Network concepts • Line configuration • Point-to-point, Multipoint • Topology • Tree, Bas, Mesh, Ring, Star • Transmission mode • Simplex, Half-duplex, full-duplex • Types of networks • LAN, WAN, MAN Prepared by Hannyzzura Pal

OSI model 7 layers Application Presentation Session Transport Network Data link Physical TCP/P 5 layers Application Transport Network Data link Physical Network models Prepared by Hannyzzura Pal

Signals • Analog signals • Digital signals • Periodic & aperiodic signals • Composite signals • Frequency signals • bandwidth Prepared by Hannyzzura Pal

Encoding & modulating • 4 types • Digital-digital • Unipolar, polar, bipolar • Analog-digital • PAM, PCM, sampling rate • Digital-analog • ASK, FSK, PSK, QAM • Analog-analog • AM, FM, PM Prepared by Hannyzzura Pal

Data transmission • Digital data • Parallel, serial • DTE-DCE Equipment • Interface standards • EIA-449, EIA-530, X.21 • Modems Prepared by Hannyzzura Pal

Transmission media • Guided media • Twisted-pair, coaxial, optical fiber • Unguided media • Terrestrial microwave, satellite, cellular telephony, wireless • Transmission impairment • Attenuation, distortion, noise • Performance • Throughput, propagation speed, propagation time • Wavelength • Shannon capacity Prepared by Hannyzzura Pal

Multiplexing • FDM • WDM • TDM Prepared by Hannyzzura Pal

Error detection & correction • Types of error • Single-bit, burst error • Redundancy Detection • CRC • Error correction • Single-bit • Hamming code Prepared by Hannyzzura Pal

Data link control • Flow control • Stop-and-wait • Sliding window • Error control • ARQ (Automatic Repeat Request) • Stop-and-wait ARQ • Sliding window ARQ Prepared by Hannyzzura Pal

Switching techniques • Circuit switching • Packet switching • approaches • Datagram • Virtual circuit • Message switching Prepared by Hannyzzura Pal

Flash Back • The past 3 centuries dominated by single technology • 18th century – mechanical system within Industrial Revolution • 19th century – steam engine • 20th century – information gathering, processing, and distribution; telephone networks; radio & TV; communication satellites • Computer technology made a spectacular progress in short time • First 2 decades, computer systems are highly centralized (mainframes); now has become obselete • Had been replaced by a large number of interconnected computers doing the job Prepared by Hannyzzura Pal

The importance! • Can a network design support company’s expansion? • PC evolution • Increase non-computer users awareness to usage of computers; PC more user-friendly; does not burden on users • Previously, PC does not allows data sharing • Data being exchange through physical transmission medium such as via sea, air, road etc; time-consuming, • Created another inconveniences – allow users’ error, virus spreading Prepared by Hannyzzura Pal

What is Data Communication? • Telecommunication – communicating via distances • Data communication – the process involving data exchanges (binary data) between 2 devices via transmission medium • Local data communication, remote data communication Prepared by Hannyzzura Pal

What is Data Communication? • How effective your data communication systems? • Depends on • Delivery – correct destination, intended recipient • Accuracy – data received must be the one that was sent • Timeliness – must reach destination in time; very important in real-time transmission (audio, video data) Prepared by Hannyzzura Pal

What is Data Communication? • 5 main components involve: • Message • Sender • Receiver • Transmission medium • Protocol • A set of rules which allows communicating devices to ‘talk’ to each others Prepared by Hannyzzura Pal

What is Networks? • A network is a set of devices connected by a media links (channels); interconnected collection of autonomous computers • Two computers are connected when they able to communicate with each other, exchanging information • What’s the different between a computer network and a distributed system? Prepared by Hannyzzura Pal

Distributed systems • Existence of multiple autonomous computers is transparent to the user • Users type in command, run the program • OS will determine which processor will run the program • Computer networks • User explicitly log onto a machine; explicitly submit jobs remotely, explicitly moves files around and generally handle all the network management personally • Thus, a distributed system s a software system built on top of a network Prepared by Hannyzzura Pal

Uses of computer networks • To companies • Resource sharing – regardless of physical location of the resource and the user • To provide high reliability – alternative sources of supply • Saving money – client-server architecture • More scalable – allowing extension of network Prepared by Hannyzzura Pal

Uses of computer networks • To people • Access to remote information • Online payment, online banking, online shopping • Online personalized newspaper • Online digital library • WWW • Person-to-person communication • Email • Virtual meeting • Interactive entertainment • Video on demand (killer application) – possible to select any movie or television program in any country and have it displayed on the screen instantly Prepared by Hannyzzura Pal

Social issues • Widespread of networking technology introduce new social, ethical, political problems • Obscene and abusive images and messages • Offensive forum • Cyber-terrorism, cyber-warfare Prepared by Hannyzzura Pal

Network criteria • What is an effective and efficient networks? • Performance – measured by transit time or response time • Number of concurrent users – too many will slow down response time • Types of transmission medium • Hardware • Software • Transform raw data to transmittable signals • To route signals to destination • To ensure signals are error free • Transformation to original data Prepared by Hannyzzura Pal

Network criteria • Reliability • Failure frequency • Recovery time after a failure • Catastrophic disaster • Security • Ensure no unauthorized access • User authentication – password, encryption • Host authentication • Virus protected Prepared by Hannyzzura Pal

Performance evaluation • Transit time • Time required for a message to travel from one device to another • Response time • Elapsed time between an enquiry and a response Prepared by Hannyzzura Pal

Network hardware • 2 types of transmission technology • Broadcast network • Single communication channel shared by all machines on the network • Packets sent will be received by all the others • Address field attached to packet will determined who can have the packet • Multicasting – transmission to a subset of the machines • Generally used by smaller, geographically localized networks Prepared by Hannyzzura Pal

Point-to-point network • Consists of many connections between individual pairs of machines • A packet will be routed to any intermediary machines which exist between the source and the intended recipient based on certain algorithm • Generally used by large dispersed networks Prepared by Hannyzzura Pal

Local Area Network (LAN) • Privately-owned network • Single building or campus; few kilometers in size • Connecting PCs and workstations • Allowing sharing of resources and information exchange • LANs are distinguished according to • Their size • Their transmission technology • Single cable attaching all machines (bus, ring) • Bus – master-slave / CS; ring – token ring • Their topology Prepared by Hannyzzura Pal

Wide Area Network (WAN) • Spans a large geographical area • Consists of a collection of machines intended for running user programs (hosts) • Hosts are connected by subnet which carries messages from host to host • Subnet • Transmission line • Switches (router) – specializes computers/device to connect two or more transmission lines • Packet forwarding based either on point-to-point, store-and-forward or packet-switching principles • Nearly all WAN applied the store-and-forward principle • Point-to-point need to based on certain topology either ring, star, tree, mesh, irregular, intersection ring Prepared by Hannyzzura Pal

Wireless networks • What is wireless networking? • What is mobile computing? Prepared by Hannyzzura Pal

Protocols • A system may consists of several entities – anything capable of sending and receiving information such as application programs, browser, ftp packages, dbms, email sw • To reduce design complexity, networks are organized as a series of layers • Each layer will offer services to the higher layers • For 2 entities to send stream of bits, they must agree on a protocol – defines what is communicates, how it is communicated and when it is communicated • Between each pair of adjacent layers, there is an interface which defines the operations and services the lower layer offers to the upper layer • A set of layers and protocols is called NETWORK ARCHITECTURE Prepared by Hannyzzura Pal

Interfaces and services • Services are available at SAP (Service Access Points) • The layer n SAPs are the places where layer n + 1 can access the services offered • 2 layers to exchange information • Has to had an agreed upon set of rules about the interface • Layer n+1entity pass IDU (interface Data Unit) to layer n entity through SAP • IDU consists of control information and SDU (Service Data Unit) which information will be passed across the network to the peer entity Prepared by Hannyzzura Pal

Types of services • 2 types of services • Connection-oriented services • Need to establish the connection, use the connection and terminate connection when finish • Reliable – data will not lose; acknowledgement required • Eg: File trasfer • Connectionless services • No prior establishment required • Data not guarantee to arrive at the intended machine • Also known as datagram service • Eg : Electronic mail Prepared by Hannyzzura Pal

Standards • Products may be used on each other regardless of its manufacturers • Provides guidelines to manufacturers, vendors, service providers to ensure connectivity • 2 types : de jure & de facto • De facto: • proprietary – invented by commercial orgs and fully owned by them – also called closed standards • Nonproprietary – developed by groups or committees and passed it to public domain – also called open standards Prepared by Hannyzzura Pal

Standards organizations • International Standards Organization (ISO) • Inter. Telecommunications Union-Telecommunications Standards Sector (ITU-T) Prepared by Hannyzzura Pal

Computer Network