Computer Network (EC-354)

Computer network: computers interconnected by some transmission lines.

There may be some intermediate devices like Hub, Switch, Router etc.

Audio, Video and Data services are conversing and supported by computer network these days.

Distributed systems: Railway Ticket Reservation Systems, Banking system

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Networking Evolution

SPUTNIK

First satellite Launched by then Soviet Union in 1957

Seen as a defeat by the US

Spurred on by President Kennedy and his vision to put man on

the moon by the end of the decade, two new agencies were

formed NASA and ARPA in the DoD (Department of Defense)

ARPA was the founding agency of ARPANET which eventually

led to the Internet

In 1969 four computers of four US universities were connected using ARPANET

IBM developed SNA TIME SHARE developed TIMENET ISO gave OSI reference model

Networking Evolution

1972 Ethernet specification formulated by Matcalfe.

1983 TCP/IP became official protocol on ARPANET

1991 WWW application was invented by CERN Physicists Tim-Berner-Lee

1992 MOSAIC released first GUI browser

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A Communications Model

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Data Communications Model

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Types of Communication networks

Analog (AM/FM)

Digital (GSM/CDMA etc.)

Backbone/ Backhaul (Optical Fiber Network)

Access (GSM, WiFi, LAN etc.)

Broadcast (TV, FM, AM radio, one to many)

Multicast (Selected group only)

Unicast (one to one)

Computer network (LAN & WLAN)

Internet

Circuit switched (Conventional Telephone networks/PSTN)

Packet switched (Internet)

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DATA COMMUNICATIONS

The term telecommunication means communication at a distance.

The word data refers to information presented in whatever form is agreed upon by the parties creating and

using the data.

Data communications are the exchange of data between two devices via some form of transmission medium such as

a wire cable.

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Components of a data communication system

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Data flow (simplex, half-duplex, and full-duplex)

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NETWORKS

A network is a set of devices (often referred to as nodes) connected by communication links.

A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by

other nodes on the network.

A link can be a cable, air, optical fiber, or any medium which can transport a signal carrying information.

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Network Evaluation Criteria

Performance

Depends on Network Elements/devices

Measured in terms of Delay and Throughput

Reliability

Failure rate of network components

Measured in terms of availability/robustness

Security

Data protection against corruption/loss of data due to: Errors

Malicious users

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Types of connections: point-to-point and multipoint

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Types of network topologies

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A fully connected mesh topology (five devices)

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A star topology connecting four stations

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A bus topology connecting three stations

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A ring topology connecting six stations

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A hybrid topology: a star backbone with three bus networks

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Comparative analysis of the network topologies

Mesh Star Bus Ring

Installation cost high medium low medium

Network Efficiency high high low low

Network Reliability high high low low

Fault isolation in link yes yes no no

Categories of Networks (based on coverage area)

Local Area Networks (LANs)

Short distances

Designed to provide wired local interconnectivity

Wireless Local Area Network (WLAN)

Provides wireless connectivity over small area, Ex. WiFi

Wide Area Networks (WANs)

Long distances

Provide connectivity over large areas

Metropolitan Area Networks (MANs)

Provide connectivity over areas such as a city, a campus

Personal Area Network (PAN)

Provides connectivity over very small area, Ex. Bluetooth

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An isolated LAN connecting 12 computers to a hub in a closet

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WANs: a switched WAN and a point-to-point WAN

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A heterogeneous network made of four WANs and two LANs

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Transmission Media

Twisted pair STP: shielded twisted pair UTP: unshielded twisted pair

(e.g. Telephone cable, Ethernet 10BaseT (RJ45))

Coaxial cable Thin (similar to TV cable) Thick (e.g., 10Base5, ThickNet)

Optical Fiber (preferred for backbone network)

Wireless (Connectionless/ connection oriented)

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Electromagnetic Spectrum

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Broadband Network

Provides multimedia integrated services (Transportation through same medium)

Voice

Video

Data

Transports very high data rate signals

Examples :- B-ISDN, WiMAX, Optical transmission lines, Leased lines etc.

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Broadband Network (Cont.)

Broadband networks can be classified as Wide Area Network (WAN) (Transports signals over long

distances) Optical fiber backbone network Lease lines Satellites Communication Telecommunication networks (BS to BS or backbone network)

Access network (BS or local exchange to customer) Cable modem , DSL & ADSL Wireless Local Loop (WLL) WiMAX

Telecommunication Networks from BS to MS (3G networks like UMTS/CDMA 2000)

BS=Base Station

MS= Mobile Station 27 OPM

Broadband Wireless Access (BWA) Technologies

WiMAX stands for Worldwide Interoperability for Microwave Access

WiMAX forum is a non-profitable group

WiMAX forum ensures the interoperability of devices developed by various vendors using IEEE 802.16 specifications

WiMAX forum Promote the development and deployment of WiMAX systems

LTE (Long Term Evolution) rival technology to WiMAX, developed by Ericsson company.

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Types of Services based on data rate & delay

CBR (constant bit rate): Ex. Audio call 64 Kbps

VBR(Variable bit rate): Ex. Real time Video transmission

ABR (Available bit rate:-minimum guarantee rate): file transfer

UBR (Unspecified bit rate: Traffic is allocated to all, no guarantee of minimum bit rate), Ex. Web browsing

Services based on type of QoS (Quality of Service)

UGS (Unsolicited Grant Service):Ex. Audio without silent suppression

ertps (extended real time polling service):Ex. Audio with silent suppression

rtps (real tile polling service):Ex. Real time Video

nrtps (non real time polling service):Ex. non-real time video

BE (Best Effort service):Ex. Web services

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Computer Network Devices Hub

Device that acts as a central point for LAN cables Takes incoming data from one port & sends to all other ports Not preferred due to congestion in network by broadcast nature of the

device

Switch

Moves data from input to output port, preferred over Hub. Analyzes packet to determine destination port and makes a virtual

connection between the ports.

Repeater/ Regenerator

Regenerates data passing through it Bridge

Connects two LANs or two segments of a LAN Connection at data link layer (layer 2)

Router

Determines the next network point to which a packet should be forwarded Connects different types of local and wide area networks at network layer

(layer 3)

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OSI reference model

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Developed by ISO (International Standard Organization) OSI (Open System InterConnection)

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OSI cont.

Application Layer: provides a means for similar or dissimilar application processes to exchange information.

Presentation Layer: presentation of information in a way that is meaningful to the network devices.

Session Layer: organize and synchronize a given dialog occurring between devices and to manage the data exchange.

Transport Layer: responsible for providing data transfer between two users at an agreed-upon level of quality.

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OSI cont.

Network Layer: responsible for establishing, maintaining and terminating the network connection, routing data from one

network device to another.

Data Link Layer: responsible for providing reliable data transmission.

Physical layer: responsible for the transmission of bit streams across a transmission channel.

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TCP/IP (Internet) Reference model

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TCP/IP ref. model

The functions of session and presentation layers clubbed with application layer

Functions of transport layer are same in the OSI ref. model

Internet layer uses IP addresses for routing and destination device identification.

Host to network layer combines functions of physical and data link layers

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Packet Encapsulation

The data is sent down the protocol stack at transmitter

Each layer adds header to SDU (Service Datagram Unit) passed from upper layer

At receiver the headers are removed in reverse order

22Bytes 20Bytes 20Bytes 4Bytes

46 to 1500 Bytes 36 OPM