DataCommChapter 1

8/14/2019 DataCommChapter 1

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Chapter 1 Part A

Data CommunicationsandNetworks Overview


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Chapter 1: Data Communications and NetworkingOverviewChapter 2: Data Communications Fundamental

Chapter 3: Characteristics of Data Communication

NetworksChapter 4: Reliable Data CommunicationsChapter 5: Multiple Access NetworksChapter 6: Internetworking Protocols

SyllabusSyllabus


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1-1 DATA COMMUNICATIONS1-1 DATA COMMUNICATIONS

The termThe term telecommunicationtelecommunication means communication at ameans communication at adistance. The worddistance. The worddatadata refers to information presented inrefers to information presented inwhatever form is agreed upon by the parties creating andwhatever form is agreed upon by the parties creating and

using the data.using the data. Data communicationsData communications are the exchange ofare the exchange of

data between two devices via some form of transmissiondata between two devices via some form of transmission

medium such as a wire cable.medium such as a wire cable.


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Figure 1.1 Five components of data communication

What is data communications?Exchange of data between two devices via a transmissionmediumAny transfer of data within a computer, between computer andany other devices

Exchange of digitally encoded information between two Sides


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Data Representation

Text represented as a bit pattern; codes oftenused: ASCII; Extended ASCII; Unicode; ISO

Numbers represented by binary equivalent

Images bit patterns representing pixels

Audio

Video


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Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)


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1-2 NETWORKS1-2 NETWORKS

AA networknetwork is a set of devices (often referred to asis a set of devices (often referred to as nodesnodes))connected by communicationconnected by communication linkslinks. A node can be a. A node can be acomputer, printer, or any other device capable of sendingcomputer, printer, or any other device capable of sending

and/or receiving data generated by other nodes on theand/or receiving data generated by other nodes on the

network.network.


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Categories of Network

Based on size, ownership, distance covered, and

physical architecture:

Local Area Network (LAN) smaller

geographical area Metropolitan Area Network (MAN) network

extended over an entire city

Wide Area Network (WAN) largegeographical area


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Figure 1.3 Types of connections: point-to-point and multipoint


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Figure 1.4 Categories of topology


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Figure 1.5 A fully connected mesh topology (five devices)


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Figure 1.6 A star topology connecting four stations


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Figure 1.7 A bus topology connecting three stations


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Figure 1.8 A ring topology connecting six stations


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Figure 1.9 A hybrid topology: a star backbone with three bus networks


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Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet


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Figure 1.11 WANs: a switched WAN and a point-to-point WAN


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Figure 1.12 A heterogeneous network made of four WANs and two LANs


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1-3 THE INTERNET1-3 THE INTERNET

TheThe InternetInternet has revolutionized many aspects of our dailyhas revolutionized many aspects of our dailylives. It has affected the way we do business as well as thelives. It has affected the way we do business as well as the

way we spend our leisure time. The Internet is away we spend our leisure time. The Internet is acommunication system that has brought a wealth ofcommunication system that has brought a wealth of

information to our fingertips and organized it for our use.information to our fingertips and organized it for our use.


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Figure 1.13 Hierarchical organization of the Internet


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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:protocolsprotocolsandand 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 agreed-upon rules.are agreed-upon rules.


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Protocols and Standards

Why do we need Protocol and Standard?

Protocol set of rules that govern data

communication; defines what, how, and when(Key elements syntax, semantics, timing)

Standard provides a model for development;allows for interoperability


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Protocols

When two computers across a network exchange data, procedures

involved can be quite complex.

These computers cannot simply send bit streams to each other and

expect to be understood.

There must be a high degree of cooperation between the two

computer systems.

For communication to occur, the entities must agree on a protocol,

what is communicated, how it is communicated, and when it is

communicated


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Key Elements of a Protocol

Syntax

Format of the data blocks

e.g. What are the fields, how many bits per field, etc.

Semantics

Control information for coordination & operation

Defines functions of the fields, what does each field do?

This include error handling information

Timing

Speed matching/synchronizing so that packets can be received properly

(especially to know where the protocol frame starts and ends)

Sequencing so that frames or packets can be received in order

(especially for packet-based switching)

f1 f2 f3


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Basic Protocol Architecture

Application Layer

Support for different user applications

e.g. e-mail, file transfer

Transport Layer

Reliable data exchange Independent of network being used

Independent of application

Network Access Layer

Exchange of data between the computer and the network

Sending computer provides address of destination so that data

can be routed

May invoke levels of service e.g. priority

Dependent on type of network used (Ethernet LAN, ATM, WLAN)


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Standards

A set of agreed-upon rules/protocols which are essential in creating

and maintaining an open and competitive market for equipmentmanufacturers and other service providers, also in guaranteeing

international interoperatibility of data and telecommunications

technology and processes

Standard Organization:

CCITT International Telegraph and Telephone Consultative

Committee in Europe [now ITU-T (International

Telecommunication Union Telecommunication standardization

sector)]

ISO International Standards Organization


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Standards

Advantages

Ensures a large market for equipment and software

Allows products from different vendors to communicate

Disadvantages

Freeze technology May be multiple standards for the same thing


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Chapter 1 Part B

Data Communications andNetworks Overview


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2-1 LAYERED TASKS2-1 LAYERED TASKS

We use the concept ofWe use the concept of layerslayers in our daily life.in our daily life.s an example, let us consider two friends whos an example, let us consider two friends who

communicate through postal mail. The processcommunicate through postal mail. The process

of sending a letter to a friend would beof sending a letter to a friend would becomplex if there were no services availablecomplex if there were no services available


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Fi ure 2.1 Tasks involved in


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2-2 THE OSI MODEL2-2 THE OSI MODEL

Established in 1947, the InternationalEstablished in 1947, the International

Standards Organization (Standards Organization (ISOISO) is a multinational) is a multinationalbody dedicated to worldwide agreement onbody dedicated to worldwide agreement oninternational standards. An ISO standard thainternational standards. An ISO standard thatcovers all aspects of network communicationscovers all aspects of network communications

is the Open Systems Interconnection (is the Open Systems Interconnection (OSIOSI))


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Motivation of OSI Model

Provides a common set of convention, to makecommunication among heterogeneous machinespossible.

If functions of each layer are well-defined,standards can be developed independently and

simultaneously for each layer that means fasterstandardization process.

If the boundaries between layers are well-defined,changes in standards in one layer need not affect

another layer easier to introduce new standards the task of communication between applications

on different computer is too complex to be handleas a unit. Problem can be decomposed intomanageable parts


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ISO is the organization.OSI is the model.

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Figure 2.2 Seven layers of the OSI


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Figure 2.3 The interaction between layers in the OSI

the same set of

layered functions must

exist in 2 systems(transmitting and

receiving sides)

communication is

achieved by having

The corresponding

(peer) layers in 2

Systems

communicate

telecom networksmainly concernthe lowest 3 layers


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Figure 2.4 An exchange using the OSI

2 3 A S OS O


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2-3 LAYERS IN THE OSI MODEL2-3 LAYERS IN THE OSI MODEL

In this section we briefly describe the functionsIn this section we briefly describe the functions

of each layer in the OSI model.of each layer in the OSI model.


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Figure 2.5 Physical


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

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Figure 2.6 Data link


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

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Figure 2.7 Hop-to-hop


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Figure 2.8 Network


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The network layer is responsible for thedelivery of individual packets from

the source host to the destination host.

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Figure 2.9 Source-to-destination


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Figure 2.10 Transport


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

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Figure 2.11 Reliable process-to-process delivery of a


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Figure 2.12 Session


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The session layer is responsible for dialogcontrol and synchronization.

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Figure 2.13 Presentation


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The presentation layer is responsible fortranslation, compression, and encryption.

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Figure 2.14 Application


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The application layer is responsible forproviding services to the user.

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Fi 2 15 S f


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Figure 2.15 Summary of


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Th b i f ti f h l


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The basic functions of each layer aresummarized below:

1. Physical- Concerned with transmission of raw bit stream overphysical medium; deals with mechanical, electrical, functional andprocedural properties of interfaces and physical medium

2. Link- Responsible for node-to-node validity and integrity of thetransmissions; send blocks of data [frames] with synchronization

3. Network- Provide upper layers with data transmission andswitching technologies used to connect systems; establishes theroute between sender and receiver

4. Transport- Provide end-to-end error recovery and flow control

5. Session- Provide coordination for communication betweenapplications; establishes, manages and terminates connectionsbetween cooperating applications

6. Presentation- Manages the way data is represented to theapplication processes from difference in data representation

7. Application- Defines the rules for applications to gain entranceinto the communication system

2 4 TCP/IP PROTOCOL SUITE2-4 TCP/IP PROTOCOL SUITE


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2-4 TCP/IP PROTOCOL SUITE2-4 TCP/IP PROTOCOL SUITE

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

exactly match those in the OSI model. Theexactly match those in the OSI model. Theoriginal TCP/IP protocol suite was defined asoriginal TCP/IP protocol suite was defined ashaving four layers:having four layers: host-to-networkhost-to-network,, internetinternet,,transporttransport, and, and applicationapplication. However, when. However, when

TCP/IP is compared to OSI, we can say that theTCP/IP is compared to OSI, we can say that theTCP/IP protocol suite is made of five layers:TCP/IP protocol suite is made of five layers:

TCP/IP Model


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TCP/IP Model

Everyone believed that the OSI model would become the

ultimate standard for computer communication before1990, but this did not happen

TCP/IP protocol suite became the dominant commercialarchitecture because it was used and tested extensivelyin the Internet, while the OSI model was never fullyimplemented

As TCP/IP was developed concurrently with the OSImodel, it does not contain specific protocols relating toall the OSI layers

The TCP/IP suite is made of five layers

The three top-most layers in the OSI model arerepresented by the applications layer

The OSI model specifies functions associated with eachlayer, whereas TCP/IP layers contain relativelyindependent protocols that can be mixed and matched

Fi 2 16


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Figure 2.16 TCP/IP and OSI

TCP/IP M d l


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TCP/IP Model

TCP/IP M d l


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TCP/IP Model

TCP/IP Model


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TCP/IP Model

n Application Layer- contains a selection of application

protocols [e.g. FTP, SMTP, HTTP, SNMP and TELNET]

n Transport Layer- represented by 2 transport protocols:

i. TCP [Transmission Control Protocol]

ii. UDP [User Datagram Protocol]

- these are process-to-process protocols responsiblefor delivery of a message from a process [runningprogram] to another process

- TCP provides a reliable connection-oriented service- UDP provides an unrealiable connectionless service

by delivering the UDP datagrams on a best-effort basis[when error correction is not needed or for a single shortrequest/response message exchange between two

application protocols]

TCP/IP Model


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TCP/IP Model

n Network Layer

- The main protocol is IP [Internet Protocol] andother supporting protocols: ARP, ICMP and IGMP

- IP is an unreliable and connectionlessprotocol - a best-effort delivery service, it does itsbest to get a transmission through to itsdestination

- IP transport data in packets called datagrams[each=IP header + TCP or UDP packet] which

travel along different routes to destination- IP is a host-to-host protocol, meaning that it

can only deliver a packet from one device toanother by routing across multiple networks

TCP/IP Model


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TCP/IP Model

n Data Link Layer

- also known as network access layer, and isconcerned with the exchange of data between anend system and a network

- main functions are:

i. Framing IP datagrams into a stream ofbits

ii. Specifying the MAC [Medium AccessControl] methods to the networks

iii. Specifying MAC [hardware] and CRC inthe frame

- HDLC [High-level Data Link Control] and ARQ[Automatic Repeat Request] are the two

important protocols at this layer

TCP/IP Model


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TCP/IP Model

n Physical Layer

- defines the interface between devices andtransmission media [type of connectors], type ofmedia, transmission rate, type of encoding forrepresenting data bits in electrical or opticalsignals, network topology, communication mode

[e.g. fullduplex service] and etc

n There are no specific protocols defined for thelowest two layers

n

Hence, they support all of the standard andproprietary LAN or WAN protocols or technologies

2-5 ADDRESSING2-5 ADDRESSING


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2 5 ADDRESSING2 5 ADDRESSING

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

employing the TCP/IP protocols:employing the TCP/IP protocols:physicalphysical,, logicallogical,,

Figure 2 17 Add i


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Figure 2.17 Addresses in

Figure 2 18 Relationship of layers and addresses in


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Figure 2.18 Relationship of layers and addresses in

Example


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In Figure 2.19 a node with physical address 10sends a frame to a node with physical address87. The two nodes are connected by a link(bus topology LAN). As the figure shows, the

computer with physical address 10 is thesender, and the computer with physical

Example

Figure 2 19 Physical


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Figure 2.19 Physical

Example


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Most local-area networks use a 48-bit(6-byte) physical address written as 12 hexadecimaldigits; every byte (2 hexadecimal digits) isseparated by a colon, as shown below:

Example

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

A 6-byte (12 hexadecimal digits) physical

Example


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Figure 2.20 shows a part of an internet withtwo routers connecting three LANs. Eachdevice (computer or router) has a pair oaddresses (logical and physical) for each

connection. In this case, each computer isconnected to only one link and therefore hasonly one pair of addresses. Each router,however, is connected to three networks (only

two are shown in the figure). So each route

p

Figure 2 20 IP


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Figure 2.20 IP

Example


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Figure 2.21 shows two computerscommunicating via the Internet. The sendingcomputer is running three processes at thistime with port addresses a, b, and c. The

receiving computer is running two processesat this time with port addresses j and k.Process a in the sending computer needs tocommunicate with process j in the receiving

computer. Note that although physicaladdresses change from hop to hop, logical

p

Figure 2 21 Port


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Figure 2.21 Port


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The physical addresses will change from hop tohop,

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Example


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p

port address is a 16-bit address representedby one decimal number as shown.

753

A 16-bit port address representedas one single number.


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The physical addresses change from hop to hop,but the logical and port addresses usually remain

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