Computer Network

Prepared by Hannyzzura Pal

Resources

Data Communication & Networking, 2nd. Ed., Forouzan, B.A., McGraw-Hill, 2001

Computer Networks, 4th, Ed., Tanenbaum, A.S., Prentice Hall, 2002

Selected papers


Syllabus

Basic introduction Network concepts Network models Signals Encoding & modulating Data transmission Transmission media Multiplexing Error detection & correction Data link control Switching techniques


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


Network models

OSI model 7 layers

Application Presentation Session Transport Network Data link Physical

TCP/P 5 layers

Application Transport Network Data link Physical


Signals

Analog signalsDigital signalsPeriodic & aperiodic signalsComposite signals

Frequency signals bandwidth


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


Data transmission

Digital data Parallel, serial

DTE-DCE EquipmentInterface standards

EIA-449, EIA-530, X.21

Modems


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


Multiplexing

FDMWDMTDM


Error detection & correction

Types of error Single-bit, burst error

Redundancy Detection CRC

Error correction Single-bit Hamming code


Data link control

Flow control Stop-and-wait Sliding window

Error control ARQ (Automatic Repeat Request) Stop-and-wait ARQ Sliding window ARQ


Switching techniques

Circuit switchingPacket switching

approaches Datagram Virtual circuit

Message switching


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(mainframes); now has become obselete Had been replaced by a large number of interconnected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


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


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



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)



5 main components involve: Message Sender Receiver Transmission medium Protocol

A set of rules which allows communicating devices to ‘talk’ to each others


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?


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


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


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


Social issues

Widespread of networking technology introduce new social, ethical, political problems Obscene and abusive images and messages Offensive forum Cyber-terrorism, cyber-warfare


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


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


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


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


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


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


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


Wireless networks

What is wireless networking?What is mobile computing?


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


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


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


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


Standards organizations

International Standards Organization (ISO)Inter. Telecommunications Union-

Telecommunications Standards Sector (ITU-T)

Computer Network

Documents

Transcript of Computer Network