Lecture 1 - FITstaff.fit.ac.cy › com.cl › acoe412 › lecture1.pdf · Lecture 1 Introduction...

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1Dr. L. Christofi Spring 2009

Lecture 1

Introduction

Network Models

ACOE412

Data Communications

Spring 2009


0. Overview0. Overview

In this lecture we will cover the following topics:

1. Introduction

1.1 Introduction to data communications and networks

1.2 Networks

1.3 The Internet

1.4 Protocols & Standards

1.5 Summary (part 1)

2. Network Models

2.1 Layered tasks

2.2 OSI model

2.3 Layers in the OSI model

2.4 TCP/IP protocol suite

2.5 Addressing

2.6 Summary (part 2)

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1.0 INTRODUCTION1.0 INTRODUCTION

The term The term telecommunicationtelecommunication means communication at a means communication at a

distance. distance.

The word The word datadata refers to information presented in whatever refers to information presented in whatever

form is agreed upon by the parties creating and using the form is agreed upon by the parties creating and using the

data. data.

Data communicationsData communications are the exchange of data between two are the exchange of data between two

devices via some form of transmission medium such as a wire devices via some form of transmission medium such as a wire

cable. cable.

ComponentsData RepresentationData Flow

Topics discussed in this section:Topics discussed in this section:


Components of data communication

A data communication system has 5 components:

- Message: info (data) to be communicated- Sender: device that sends the data message- Receiver: device that receives the message- Medium: transmission medium (physical path) by which a message travels from the transmitter to the receiver

- Protocol: set of rules that governs data communications

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Data representation

• Text: bit pattern

• ASCII: 128 different symbols (7 bits)

• Extended ASCII: size of each pattern is 1 byte (8 bits)

• Unicode: 65.536 symbols (16 bits)

• ISO: 4.294.967.296 symbols (32 bits)

• Numbers: decimal numbers converted directly to binary

• Images: divided into a matrix of pixels

• Audio: representation of sound by an analog or a digital signal

• Video: represented by an analog or digital signal


Direction of data flow

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1.2 NETWORKS1.2 NETWORKS

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

nodesnodes) connected by communication ) connected by communication linkslinks. .

A node can be a computer, printer, or any other A node can be a computer, printer, or any other

device capable of sending and/or receiving data device capable of sending and/or receiving data

generated by other nodes on the network.generated by other nodes on the network.

Network Criteria

Physical StructuresCategories of Networks



Network criteria

• Performance—Can be measured in may ways

• transit time: amount of time required for a message to travel from one device to another

• response time: time elapsed between an inquiry and a response

• Number of users

• Type of transmission medium

• Hardware capabilities and software efficiency

• Reliability—A measure of frequency of failure and the time needed to recover, network robustness

• Security—Protecting of data from unauthorized users

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Physical Structures

Types of connections: point-to-point and multipoint


Physical Topology

Physical topology refers to the way in which a network is

laid out physically.

Network topology is the geometric representation of the

relationship of all the links and linking devices (nodes)

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Topology categories

Number of links = n*(n-1)/2

Mesh Star

Number of links = n

Bus

Number of links = n+1

Ring

Number of links = n


A hybrid topology

A star backbone with three bus networks

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Categories of networks

• Local Area Networks (LANs)— Usually privately owned and links the devices in a single office, building or campus

— Most common LAN topologies are bus, ring and star

— Speeds of 100Mbps-1Gbps

• Metropolitan Area Networks (MANs)— Designed to extend over a city— May be owned by a large private organization or a service provider (telephone company)

• Wide Area Networks (WANs)— Provide long-distance transmission of data, voice, image and video info over large geographical areas that may comprise a country or a continent

• Internetworks— When two or more networks are connected they become an internetwork or internet


WAN examples

A switched WAN and a

point-to-point WAN

An heterogenous network

made of 4 WANs and 2 LANs

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An heterogeneous network

made of four WANs and two LANs


Comparison of LANs, MANs, & WANs

LANs: 1 – 1000 Mbps

MANs: 10 – 40 Gbps

WANs: Tbps

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1.3 THE INTERNET1.3 THE INTERNET

The The InternetInternet has revolutionized many aspects of our daily has revolutionized many aspects of our daily

lives. lives.

It has affected the way we do business as well as the way we It has affected the way we do business as well as the way we

spend our leisure time. spend our leisure time.

The Internet is a communication system that has brought a The Internet is a communication system that has brought a

wealth of information to our fingertips and organized it for ourwealth of information to our fingertips and organized it for our

use. use.

A Brief HistoryThe Internet Today (ISPs)



A brief history

• Mid-1960s— Standalone devices— ARPA (Advanced Research Projects Agency) was interested in finding a way to connect computers to share information

— Backbones: None - Hosts: None

• 1967— ARPA presented its ideas for ARPANET— Backbones: None - Hosts: None

• 1969— The first physical network was constructed — Backbones: 50Kbps ARPANET - Hosts: 4

• 1972— The first e-mail program was created by Ray Tomlinson of BBN— Backbones: 50Kbps ARPANET - Hosts: 23

• 1973— Development began on the protocol later to be called TCP/IP (by Vint Cerf and Bob Kahn)

— Backbones: 50Kbps ARPANET - Hosts: >23

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Hierarchical organization of Internet


The Internet today (ISPs)

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1.4 PROTOCOLS AND STANDARDS1.4 PROTOCOLS AND STANDARDS

In this section, we define two widely used terms: In this section, we define two widely used terms: protocolsprotocols

and and standardsstandards. First, we define protocol, which is . First, we define protocol, which is

synonymous with rule. Then we discuss standards, which synonymous with rule. Then we discuss standards, which

are agreedare agreed--upon rules.upon rules.

Protocols

StandardsStandards OrganizationsInternet Standards



Protocols

• A protocol is a set of rules that governs data communications

• It defines what is communicated, how it is communicated and when it is communicated

• Key elements of a protocol:—Syntax

• Structure or format of data, meaning the order in which they are presented

—Semantics• Refer to the meaning of each section of bits, how a particular pattern is interpreted and what action to be taken

—Timing• Refers to when data should be sent and how fast can they be sent

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Standards

• Standards are essential in creating and maintaining an open and competitive market for equipment manufacturers

• Required to guarantee national and international interoperability of data and telecommunications technology and processes

• Categories of data communications standards

—De facto:

• Standards that have not been approved by an organizational body but have been adopted through widespread use, eg. model TCP/IP)

—De jure:

• Those that have been legislated by an official recognized body, eg.

OSI model


Standards organizations

• Standards creation committees

— ISO (International Organization for Standardization)

— ITU-T (International Telecommunications Union – Telecommunications Standards)• Initially known as CCITT (Consultative Committee for International Telegraphy and Telephony)

— ANSI (American National Standards Institute)

— IEEE (Institute of Electrical and Electronics Engineers)

— EIA (Electronic Industries Association

• Forums

— Made up of representatives from interested corporations to speedacceptance and use of new technologies in the telecom industry

• Regulatory Agencies

— Governmental agencies: to protect public interest by regulating radio, TV and wire/cable communications

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Internet standards

• An Internet standard is a thoroughly tested specification used by those who work with the Internet

• A specification begins with an Internet draft

—Working document with no official status and a 6-month lifetime

—Upon recommendation from the Internet authorities a draft may be published as a Request for Comment(RFC)


1.5 SUMMARY (part 1)

• Data communication is the transfer of data from one device to another via some form of transmission medium.

• A data communications system must transmit data to the correct destination in an accurate and timely manner.

• The five components that make up a data communications system are the message, sender, receiver, medium, and protocol.

• Text, numbers, images, audio, and video are different forms of information.

• Data flow between two devices can occur in one of three ways: simplex, half-duplex, or full-duplex.

• A network is a set of communication devices connected by media links.

• In a point-to-point connection, two and only two devices are connected by a dedicated link. In a multipoint connection, three or more devices share a link.

• Topology refers to the physical or logical arrangement of a network. Devices may be arranged in a mesh, star, bus, or ring topology.

• A network can be categorized as a local area network (LAN), a metropolitan-area network (MAN), or a wide area network (WAN).

• A LAN is a data communication system within a building, plant, or campus, or between nearby buildings.

• A MAN is a data communication system covering an area the size of a town or city.

• A WAN is a data communication system spanning states, countries, or the whole world.

• An internet is a network of networks.

• The Internet is a collection of many separate networks.

• TCP/IP is the protocol suite for the Internet.

• There are local, regional, national, and international Internet service providers (ISPs).

• A protocol is a set of rules that governs data communication; the key elements of a protocol are syntax, semantics, and timing.

• Standards are necessary to ensure that products from different manufacturers can work together as expected.

• The ISO, ITU-T, ANSI, IEEE, and EIA are some of the organizations involved in standards creation.

• Forums are special-interest groups that quickly evaluate and standardize new technologies.

• A Request for Comment (RFC) is an idea or concept that is a precursor to an Internet standard.

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2.0 NETWORK MODELS

• A network uses a combination of hardware and software to send data from one location to another—Hardware consists of the physical equioment that carries signals from one point of the network to another

—The task of sending a piece of information from one point in the worls to another can be broken into several tasks, each performed by a separate software package• Each piece of software uses the services of another software package o do its job

• At the lowest layer, a signal is sent from the source to the destination computer

• In this part we will see a general idea of layers of a network and discus the functions of each one


2.1 LAYERED TASKS2.1 LAYERED TASKS

We use the concept of We use the concept of layerslayers in our daily life. As an in our daily life. As an

example, let us consider two friends who communicate example, let us consider two friends who communicate

through postal mail. The process of sending a letter to a through postal mail. The process of sending a letter to a

friend would be complex if there were no services available friend would be complex if there were no services available

from the post office. from the post office.

Sender, Receiver, and CarrierHierarchy


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Tasks involved in sending a letter

carrier

• The task of transporting the

letter between the sender

and the receiver is done by

the carrier.

• The tasks must be done in

the order given in the

hierarchy.


2.2 THE OSI MODEL2.2 THE OSI MODEL

Established in 1947, the International Standards Established in 1947, the International Standards

Organization (Organization (ISOISO) is a multinational body dedicated to ) is a multinational body dedicated to

worldwide agreement on international standards. worldwide agreement on international standards.

An ISO standard that covers all aspects of network An ISO standard that covers all aspects of network

communications is the Open Systems Interconnection communications is the Open Systems Interconnection

((OSIOSI) model. It was first introduced in the late 1970s. ) model. It was first introduced in the late 1970s.

Layered Architecture

Peer-to-Peer ProcessesEncapsulation


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Seven layers of the OSI model


Peer-to-peer processes

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Encapsulation

• The process starts at layer 7

(application layer), then moves

from layer to layer in descending,

sequential order.

• At each layer, a header is added

to the data unit.

• At layer 2, a trailer is added as

well.

• When the formatted data unit

passes through the physical layer

(layer 1) it is changed into an

electromagnetic or optical signal

and transported along a physical

link

• At the destination the reverse

process is performed


2.3 LAYERS IN THE OSI MODEL2.3 LAYERS IN THE OSI MODEL

In this section we briefly describe the functions of each In this section we briefly describe the functions of each

layer in the OSI model.layer in the OSI model.

Physical Layer

Data Link LayerNetwork LayerTransport LayerSession Layer

Presentation LayerApplication Layer


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Physical layer

The physical layer is responsible for movements ofindividual bits from one hop (node) to the next.

Note


Data link layer

The data link layer is responsible for moving frames from one hop (node) to the next.

Note

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Hop-to-hop delivery


Network layer

The network layer is responsible for the delivery of individual packets from

the source host to the destination host.

Note

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Source-to-destination delivery


Transport layer

The transport layer is responsible for the delivery of a message from one process to another.

Note

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Reliable process-to-process delivery


Session layer

The session layer is responsible for dialog control and synchronization.

Note

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Presentation layer

The presentation layer is responsible for translation, compression, and encryption.

Note


Application layer

The application layer is responsible for providing services to the user.

Note

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Summary of layers


2.4 TCP/IP PROTOCOL SUITE2.4 TCP/IP PROTOCOL SUITE

The layers in the The layers in the TCP/IP protocol suiteTCP/IP protocol suite do not exactly do not exactly

match those in the OSI model. match those in the OSI model.

The original TCP/IP protocol suite was defined as having The original TCP/IP protocol suite was defined as having

four layers: four layers: hosthost--toto--networknetwork, , internetinternet, , transporttransport, and , and

applicationapplication. .

However, when TCP/IP is compared to OSI, we can say However, when TCP/IP is compared to OSI, we can say

that the TCP/IP protocol suite is made of five layers: that the TCP/IP protocol suite is made of five layers:

physicalphysical, , data linkdata link, , networknetwork, , transporttransport, and , and applicationapplication..

Physical and Data Link Layer

Network LayerTransport Layer

Application Layer


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TCP/IP layers


TCP/IP and OSI model

TCP/IP modelOSI

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2.5 ADDRESSING2.5 ADDRESSING

Four levels of addresses are used in an internet employing Four levels of addresses are used in an internet employing

the TCP/IP protocols: the TCP/IP protocols: physicalphysical, , logicallogical, , portport, and , and specificspecific..

Physical Addresses

Logical AddressesPort AddressesSpecific Addresses



Addresses in TCP/IP

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Physical & Logical address

• Physical address—In computer networks a physical address means a MAC (Medium Access Control) address• Also known as Ethernet Hardware Address (EHA) or hardware address or adapter address

—It is a number that acts like a name for a particular network adapter, eg. the network cards

• Logical address

—In computer networks, a logical address refers to a network layer address such as an IP address

—An IP address (Internet Protocol address) is a unique address that certain electronic devices use in order to identify and communicate with each other on a computer network utilizing the Internet Protocol standard (IP)


Port & specific address

• Port address

—TCP and UDP are transport protocols used for communication between computers via ports

— The port numbers are divided into three ranges.

• The Well Known Ports are those in the range 0–1023.

• The Registered Ports are those in the range 1024–49151.

• The Dynamic and/or Private Ports are those in the range 49152–65535. These ports are not used by any defined application.

• Specific address

—This address is used by application processes

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Relationship of layers-addresses in TCP/IP


In the following figure, a node with physical address 10 sends a frame to a

node with physical address 87. The two nodes are connected by a link

(bus topology LAN). As the figure shows, the computer with physical

address 10 is the sender, and the computer with physical address 87 is

the receiver.

Example: Physical address

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As we will see in a later lecture, most LANs use a 48-bit (6-

byte) physical address written as 12 hexadecimal digits; every byte (2 hexadecimal digits) is separated by a colon,

as shown below:

07:01:02:01:2C:4B

A 6-byte (12 hexadecimal digits) physical address.

Example: Physical address


This figure shows a part of

an internet with two routers

connecting three LANs.

Each device (computer or

router) has a pair of

addresses (logical and

physical) for each

connection.

In this case, each computer

is connected to only one

link and therefore has only

one pair of addresses.

Each router, however, is

connected to three

networks (only two are

shown in the figure).

So each router has three

pairs of addresses, one for

each connection.

Example: IP addresses

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This figure shows two

computers communicating via

the Internet.

The sending computer is

running three processes at this

time with port addresses a, b,

and c.

The receiving computer is

running two processes at this

time with port addresses j and k.

Process a in the sending

computer needs to communicate

with process j in the receiving

computer.

Note that although physical

addresses change from hop to

hop, logical and port addresses

remain the same from the

source to destination.

Example: Port addresses


The physical addresses change from hop to hop,

but the logical and port addresses usually remain the same.

Note

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2.6 SUMMARY (part 2)

• The five-layer model provides guidelines for the development of universally compatible networking protocols.

• The physical, data link, and network layers are the network support layers.

• The application layer is the user support layer.

• The transport layer links the network support layers and the user support layer.

• The physical layer coordinates the functions required to transmit a bit stream over a physical medium.

• The data link layer is responsible for delivering data units from one station to the next without errors.

• The network layer is responsible for the source-to-destination delivery of a packet across multiple network links.

• The transport layer is responsible for the process-to-process delivery of the entire message.

• The application layer enables the users to access the network.


References

• W. Stalling, Local and Metropolitan Area Networks, 6th edition, Prentice Hall, 2000

• F. Halsall, Data Communications, Computer Networks and Open Systems, 4th edition, Addison Wesley, 1995

• B.A. Forouzan, Data Communications and Networking, 4th edition, McGraw-Hill, 2007

• W. Stallings, Data and Computer Communications, 7th edition, Prentice Hall, 2004

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