4.Network Protocols and Architectures

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Data Communications andComputer Networks

Chapter 4

Network Protocols and

Architecture

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Outline:

Protocol CharacteristicsOSI reference model

TCP/IP reference model

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Communicating the Message

In theory, a single communication, such as a musicvideo or an e-mail message, could be sent across anetwork from a source to a destination as onemassive continuous stream of bits.

Problem??

Solution - Data is sent across a network in smallchunks called segmentsSegmentation helps

Interleaving/multiplexing messages (many conversation on onenetwork)

increase the reliability of network communications - If aparticular path becomes congested with data traffic or fails,individual pieces of the message can still be directed to the

destination using alternate pathways. 4


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Components of the Network

Network componentshardware: Devices and media such as laptop,

a PC, a switch, or the cabling used to connectthe devices

software: run on the networked devices todeliver Services and do some processes

Services include many of the common networkapplications

Processes provide the functionality that directs andmoves the messages through the network.

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Cont..

End Devices and their Role in the NetworkEnd devices (host networking context) form

interface with human network &communications network

Role of end devices:

client

server

both client and serversoftware installed on the host determines

which role it plays on the network.6


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Cont..

Servers are hosts that have software installed thatenables them to provide information and services

Clients are hosts that have software installed thatenables them to request and display the information

obtained from the server. Role of an intermediary device

provides connectivity and ensures data flows across network

Network Access Devices (Hubs, switches, and wireless accesspoints)

Internetworking Devices (routers)

Communication Servers and Modems

Security Devices (firewalls)

The management of data as it flows through the

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Cont..

Processes running on the intermediary network devicesperform these functions:

Regenerate and retransmit data signals

Maintain information about what pathways exist through

the network and internetwork Notify other devices of errors and communication

failures

Direct data along alternate pathways when there is alink failure

Classify and direct messages according to QoS priorities

Permit or deny the flow of data, based on securitysettings

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Function of Protocol in Network

Communication

The importance of protocols and how they are used tofacilitate communication over data networks

All communication, whether face-to-face or over anetwork, is governed by predetermined rules called

protocols.A group of inter-related protocols that are necessary to

perform a communication function is called a protocolsuite.

The protocols are viewed as a layered hierarchy, witheach higher level services depending on the functionalitydefined by the protocols shown in the lower levels.

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Standards and Protocols

A standard is - a process or protocol that hasbeen endorsed by the networking industry andratified by a standards organization - such asthe Institute of Electrical and Electronics

Engineers (IEEE) or the Internet EngineeringTask Force (IETF).

The use of standards in developing and

implementing protocols ensures that productsfrom different manufacturers can work togetherfor efficient communications.

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Why Standards?

Communication requires a common language Standards specify how things are done to the

smallest detail

Standardized things are easier to develop inthe future

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Protocols

One form of network standardsA protocol

Is a language spoken between computers toexchange information

Is a formal description of message formats and therules that two computers must follow in order toexchange those messages.

Example: The HTTP protocol defines the formatfor communication between web browsers andweb servers

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Network models

Specify how networks are implemented One famous model is the Open Systems

Interconnection (OSI) reference model

Another famous model is TCP/IP model

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Benefits of using a layered

model

Benefits include assists in protocol design

fosters competition

changes in one layer do not affect other layers provides a common language

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OSI model

Used to specify a networking framework forimplementing protocols

Facilitates communication betweenheterogeneous systems

Implemented by almost most network systems

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Explaining the OSI layer

Breaks network communication to small partsto make it manageable and easier to understand

Consists of seven well defined layers

Prevents changes in one layer from affectingothers

Proprietary - one or a small group ofcompanies controls all usage of the technology

OSI is proprietary, developed by InternationalOrganization for Standardization (ISO)

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Physical

Concerned with transmission of data across media wires

connectors

voltages data rates

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Data link

Concerned with physical addressing

network topology

error notification flow control

reliable transfer of data across media

Divided into two sub layers: Logical Link Control(LLC) and Media Access Control (MAC)

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Network

Concerned with network addressing

best path determination

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Transport

Concerned with transportation with hosts

data transport reliability

establish, maintain, terminate virtual circuits Fault detection, flow control, recovery

information

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Session

Concerned with establishing, managing and terminating

sessions

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Presentation

Concerned with format of data

data structures

data transfer syntax

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Application

Concerned with providing network service toapplications like

Email

File transfer Terminal emulation

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Encapsulation

Data Packets or packets are information sentover a network.

Encapsulation wraps data with the necessaryprotocol information before network transit.

As the data packet moves down through thelayers of the OSI model, it receives headers,trailers, and other information.

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Encapsulation process

As data travels through the layers, the followingprocedures are carried out

Build the data

Package the data for end-to-end transport Add the network IP address to the header

Add the data link layer header and trailer

Convert to bits for transmission

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Build the data

As a user sends an e-mail message, itsalphanumeric characters are converted to datathat can travel across the internetwork

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P k th d t f d t


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Package the data for end-to-

end transport

The data is packaged for internetworktransport.

By using segments, the transport functionensures that the message hosts at both ends ofthe e-mail system can reliably communicate.

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Add th t k IP dd t


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Add the network IP address to

the header

The data is put into a packet or datagram thatcontains a packet header with source anddestination logical addresses

Addresses help network devices send thepackets across the network along a chosen path

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Convert to bits for transmission

The frame must be converted into a pattern of1s and 0s (bits) for transmission on themedium.

A clocking function enables the devices todistinguish these bits as they travel across themedium.

The medium on the physical internetwork can

vary along the path used. Example: The e-mail message can originate on

a LAN, cross a campus backbone, and go out aWAN link until it reaches its destination on

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TCP/IP model

Developed by the U.S. Department of Defense Developed as an open standard anyone can

use it for free

Has four layers

Network access layer

Internet layer

Transport layer

Application layer

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Network access layer

Concerned with Logical addressing Transmission of data across media

wires

connectors voltages

data rates

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Internet layer

Concerned with network addressing

best path determination

Transport layer

Concerned with

-Reliability-Flow control

-Error correction

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Application layer

Concerned with Representation

Encoding

Dialogue control

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OSI and TCP/IP - similarities

Both have layers Both assume packets are switched (called

packet switched), i.e. that packets could takedifferent paths to reach to the same destination.Circuit switched is a case in which all packetstake the same path

Both should be known by network

professionals

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OSI and TCP/IP - differences

TCP/IP combines session, presentation andapplication layers into a single layer

TCP/IP combines physical and data link layerinto a single layer

TCP/IP is the standard in which the internethas grown

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Categorizing protocols

Application protocols work in Application layer

Presentation layer

Session layerTransport protocols work in

Transport layer

Network protocols work in Network layer

Data link layer

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Application layer protocols

Hypertext Transfer Protocol (HTTP) Used for exchanging files (text, graphic

images, sound, video, and other multimediafiles) on the World Wide Web.

File Transfer Protocol (FTP)

Used for transferring files from one computerto another

Simple Mail Transfer (SMTP)

Used for transferring e-mail across theInternet.

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(contd.)

Network File System (NFS) Used to transfer files from one computer to

another

Simple Network Management Protocol(SNMP)

Used to manage a network

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Transport layer protocols

Transmission Control Protocol (TCP) Enables two hosts to establish a connection

and exchange streams of data. It guaranteesdelivery of data and also guarantees that

individual units of data (called packets) will bedelivered in the same order in which they weresent

Net Bios Extended User Interface (NetBEUI) A communication protocol designed by IBM

and often used by Microsoft

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Network protocols

Internet Protocol (IP) Specifies the format of packets and the

addressing scheme. Most networks combine IPwith a Transport Control Protocol (TCP), which

establishes a virtual connection between adestination and a source. IP by itself issomething like the postal system. It allows you

to address a package and drop it in the system,but theres no direct link between you and therecipient

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Network protocols (contd.)

Ethernet The most common local area network (LAN)

protocol

X.25

Common wide area network (WAN) protocol

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Documents

4.Network Protocols and Architectures