dsi 07 datacommnet

7/30/2019 DSI 07 DataCommNet

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Data Communications and

Networking


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IntroductionData Communication

NetworksProtocols and Standards

Standard Organizations


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Why study data

communicationsICT is the fastest growing technologies in our

culture today

Data communications and networking are

important elements that enable information to be

shared

It is important to understand the concepts and

mechanisms of these technologies - what they do

and when to use


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Data Communication

Data communication is the exchange of data

between two devices via some form of

transmission medium

The communicating devices are part of the

communication system made up of hardware and

software


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Data Communication

Characteristics of effective Data Comm Systems

Delivery

The system must deliver data to the correct destination

Accuracy The system must deliver data accurately

Timeliness

The system must deliver data in a timely manner


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Data Communication

Components

1

2 3

4

5 5


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Data Communication

Components

Message the information (data) to be communicated; text,numbers, pictures, sound, video, etc or combination

(data refers to facts, concepts and instructions presented in

whatever form agreed upon by the parties creating and using thedata)

Sender the device that sends the message; computer,workstation, telephone handset, video camera, etc

Receiverthe device that receives the message; computer,workstation, telephone handset, video camera, etc

Medium the physical path for the transmission; copper wire,fiber-optic cable, laser, radio waves, etc

Protocol the set of rules that govern data communications;agreement between the communicating devices


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Networks

Definition

A network is a set of devices (often referred to as

nodes) connected by media links

A node can be a computer, printer, or any otherdevices capable of sending and/or receiving data

generated by other nodes on the network.

The links connecting the devices are called

communication channels.

Networks promotes distributed processing a task is divided among multiple computers


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Networks

Advantages of distributed processing

Security/encapsulation a system designer can limit the kinds ofinteraction that a given user can have with the entire system

Distributed databases

storage capacity can be at differentlocations

Faster problem solving concurrent processing by manycomputers in solving a problem is faster than a single computer

Security through redundancy multiple computers running the

same program improve security Collaborative processing multiple computers/users can interact

on a single task


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Networks

Network Criteria

To be considered effective and efficient


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Networks

Network Criteria

Performance

number of users, type of transmission medium, hardware and

software Reliability

frequency of failure, recovery time of a network after a failure,

contingency plan on catastrophe

Security

unauthorized access, viruses


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Protocols and Standards

A protocol is a set of rules (conventions) that

govern all aspects of data communication

Defines whatis communicated, howit is communicated

and when it is communicated The key elements syntax(structure/format); semantics

(meaning of the structure); timing(when to send and how fast)

A standard provides a model for development

that makes it possible for a product to workregardless of manufacturers


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Protocols and Standards

De jure

legislated by official bodies

De facto industry standard, proprietary & non-proprietary


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ISO dedicated to a worldwide agreement on internationalstandards

ITU-T related to the UN for telecommunications

ANSI

US non-profit org, representing US to ISO and ITU-T

IEEE largest professional society developing standards forcomputing, communication, electrical engineering, electronics

EIA - non-profit org, promoting standards for electronics

manufacturing


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Forums

Frame Relay Forum

(DEC, Nortel, Cisco, etc)

ATM Forum and ATM Consortium

(PBX exchange manufacturers, telecom providers, etc)

ISOC/IETF

deals with the progress of the Internet


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Basic Concepts

Line Configuration

Topology

Transmission Mode

Categories of Networks

Internetworks


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Line Configuration

defines the attachment of communication devices to a link

a linkis a physical communication pathway that transfers data

from one device to another


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Line Configuration

Point-to-point A dedicated link between two devices, i.e. the entire capacity of

the channel is reserved for transmission

e.g. wire


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Line Configuration



e.g. wire


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Line Configuration



e.g. microwave and satellite links, etc.


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Line Configuration

Multipoint (aka multidrop) more than two devices share a single link

spatially shared several devices can share the link simultaneously

time-shared devices take turn to use the link


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Topology

defines the physical or logical arrangement of links in a

network

geometric representation of the relationship of all links and nodes


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Topology - Mesh

each node has a dedicated point-to-point link to every

other node


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Topology Mesh

Advantages each connection can carry its own data load eliminating traffic

problems

if one link becomes unusable, it does not incapacitate the entire

system robust

a dedicated line guarantees security

easy fault identification and fault isolation - reroutable

Disadvantages the amount of cabling and number of i/o ports required

expensive


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Topology Star

Each device has a dedicated point-to-point link only to a

central controller (or hub).


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Topology Star

Advantages only one link and one I/O port required per device

less expensive than mesh topology

if one link fails, only that link is affected robust

easy fault identification and fault isolation (as long as the hub is working)

Disadvantages if the hub fails, the network is down

requires more cabling than tree, ring and bus topologies


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Topology Tree

A variation of a star

majority of devices are connected tosecondary hubs (active/passive) than a central hub (active).


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Topology Tree

Advantages generally similar to star

secondary hubs allow more devices to be connected increase

the distance

allows the network to isolate and prioritize communications from

different computers

Disadvantages generally similar to star


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Topology Bus

One long cable (the backbone) link all the devices in the

network multipoint


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Topology Bus

Advantages easy installation

use less cabling than mesh, star or tree

Disadvantages difficult reconfiguration and fault isolation

a fault or break in the bus cable stops all transmission


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Topology Ring

Each device is linked only to its immediate neighbors


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Topology Ring

Advantages each device incorporates a repeater

easy to install and reconfigure

Disadvantages in unidirectional traffic, a break in the ring can disable the entire

network (some implementations use a dual ring or a switch)


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Topology Hybrid

combination of several topologies as subnetworks linked

together in a larger topology.


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Transmission Modes

the direction of signal flow between two linked

devices.


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Transmission Mode

simplex the communication is unidirectional only of the twodevices on a link can transmit, the other receive


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Transmission Mode

half-duplex each device can both transmit and receive, but notat the same time.


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Transmission Mode

full-duplex (or duplex) both devices can transmit andreceive simultaneously


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Categories of Networks

Determined by its size, ownership, distance covered and

physical architecture


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Networking

Point to point communication not usually practical

Devices are too far apart

Large set of devices would need impractical number of

connectionsSolution is a communications network

Wide Area Network (WAN)

Local Area Network (LAN)


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Usually privately owned and links the devices in a single

office,

building or

campus


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Local Area Networks

Smaller scope

Building or small campus

Usually owned by same organization as attached

devicesData rates much higher

Usually broadcast systems

Now some switched systems and ATM are being

introduced


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Size limited to a few

kilometers

Common topologies

are bus, ring and

star

High data rate

4/10/16 Mbps to

100 Mbps or

gigabits


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LAN Configurations

Switched

Switched Ethernet

May be single or multiple switches

ATM LAN Fibre Channel

Wireless

Mobility

Ease of installation


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Wide Area Networks

Large geographical area

Crossing public rights of way

Rely in part on common carrier circuits

Alternative technologies

Circuit switching

Packet switching

Frame relay

Asynchronous Transfer Mode (ATM)


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Wide Area Network (WAN)

long-distance transmission over large geographical areas(continent/world)

utilize public,

leased or private

communication incombinations

An enterprise

network is a WAN

owned by one

company


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Circuit Switching

Dedicated communications path established for

the duration of the conversation

e.g. telephone network


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Packet Switching

Data sent out of sequence

Small chunks (packets) of data at a time

Packets passed from node to node between

source and destinationUsed for terminal to computer and computer to

computer communications


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Frame Relay

Packet switching systems have large overheads

to compensate for errors

Modern systems are more reliable

Errors can be caught in end systemMost overhead for error control is stripped out

Asynchronous Transfer


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Asynchronous Transfer

Mode

ATM

Evolution of frame relay

Little overhead for error control

Fixed packet (called cell) length

Anything from 10Mbps to Gbps

Constant data rate using packet switching

technique

Metropolitan Area


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Metropolitan Area

Networks

MAN

Middle ground between LAN and WAN

Private or public network

High speed

Large area

Metropolitan Area


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Metropolitan Area

Network (MAN)Extend over entire city, may be wholly owned by a private

company, popular service SMDS


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Internetworks

internet network of networks

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