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Copyright UTL Technologies Ltd 2011 All rights reserved

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An Introduction to Networking


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A network is an interconnection of a group of computersthat can communicate and share resources such as hard

disks and printers.

A network is a group of computers and other devices that

are connected by some type of transmission media.

The initial idea of a network was perceived by Departmentof Defense (DOD) in USA for the purpose of security.

Some advantages of networks are:

Sharing of information across the network

Optimum utilization of hardware resources

Centralization of data management

Introducing Networks


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How Networks Are Used

File services: capability of a server to share data files,

applications, and disk storage space.

Print services: used to share printers across a network.

Communications services: Allow remote users to connect to theremote network.

Mail services: Transfer of e-mail between users on a network.

Internet services: Supplying Web pages, file transfer

capabilities, and a means for directly logging on to other

computers on the Internet.

Management services: centrally administer management

tasks on the network like Traffic monitoring and control.


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Internetworking services are the services in a networkingenvironment that are accessible to users within an intranet

or the Internet.

The following are some of the services provided by the

Internetworking servers:

File TransferWWW

E-mail

Understanding Internetworking Servers


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Network Topologies


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Network topology is a schematic layout or a map of the

arrangement of nodes over a network.

This layout also determines the manner in which information

is exchanged within the network.

There are five types of network topologies:

Bus

Star

Ring

Mesh

Cellular

Network Topologies


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The bus topology connects all the nodes on a network to a

main cable called bus.

In the bus topology, each packet that is placed on the bus

contains the address of the destination node and is

transmitted in both directions along the bus.

A single high capacity cable is required thus requiring

minimum cabling and its cost.

Entire cable setup needs to be reconfigured to add a node.

Time consuming process to troubleshoot as every point

needs to be checked to locate the fault.

Bus Topology

The Bus Topology

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A Terminated Bus Topology

network

Bus Topology (Continued)

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The star topology connects nodes over a network using acentral control unit called the hub.

Nodes to a star-based network can be easily attached to the

hub.

All the nodes are connected to the hub thus requiring lot of

cabling and cost.A faulty hub can disrupt the entire network.

Star Topology

The Star Topology

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A Typical Star Topology Network

Star Topology (Continued)

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The ring topology connects the nodes on a network througha point-to-point connection.

Easy to locate cable faults in a ring.

The entire network stops functioning, if any of the nodes in

the network malfunctions.

Ring Topology

The Ring Topology

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A Typical Ring Topology Network

Ring Topology (Continued)

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The mesh topology involves point-to-point connectionbetween every node in the network.

High reliable as network connectivity does not depend on

any one node.

Useful for large network connections.

Involves high installation and setup costs due to elaboratecabling required to connect each node with the other node.

Difficult to manage as the size of the network increases.

Mesh Topology

The Mesh Topology

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The cellular topology is a wireless topology, wheregeographic area is divided into cells or regions.

In cellular topology, each cell is a separate entity that is

controlled by a central station.

Operates on wireless media, thus do not require cabling.

Easy to install as only requirement is the availability of acentral location and signal strength.

Cellular Topology

Cell Node

The Cellular Topology

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Network Categories

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The resources and software capabilities that nodes in a

network share are commonly known as services.

Networks are categorized as:

Peer-to-peer

Client / Server

Network Categories

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In a peer-to-peer network, there is no specific distinctionbetween a client and a server.

Every computer can communicate directly with every other

computer.

By default, no computer has more authority than another.

Every computer is capable of sending and receivinginformation to and from every other computer.

The following figure illustrates the peer-to-peer network:

Peer-to-Peer Networks

The Peer-to-Peer Network

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Resource sharing on a Simple Peer-to-Peer Network

Peer-to-Peer Networks (Continued)

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In a client / server network, the requests are processedcentrally by one or more servers.

The server is a system with high processing power, which

provides services for the other computers in a network.

The client is a system that accesses resources available on

a server.In a client / server network setup, the server is responsible

for processing the requests sent by the clients.

Client / Server Networks

The Client / Server Network The Client-Server Network Setup

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Resource sharing on a Client / Server Network

Client / Server Networks (Continued)

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Advantages of using client/server networks over peer-to-peernetworks:

User logon accounts and passwords can be assigned in one place.

Access to multiple shared resources can be centrally granted to a

single user or groups of users.

Problems can be tracked, diagnosed, and often fixed from onelocation.

Servers are optimized to handle heavy processing loads and

dedicated to handling requests from clients, enabling faster

response time.

Because of their efficient processing and larger disk storage,

servers can connect more than a handful of computers on anetwork.

To function as a server, a computer must be running a network

operating system (NOS).

Client / Server Networks (Continued)

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ClientServer

Network interface card (NIC)

NOS

Connectivity device

Elements of Client / Server Networks

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Network Operating Systems

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Network Operating System (NOS) is an enhanced versionof an operating system, with features that allow the

management and connectivity of nodes within a network.

NOS allows the sharing of information and resources based

on the accessibility privileges allocated to each user or

node.Popular NOSs include:

Windows Server 2008 R2

UNIX

Linux

Network Operating System

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Centrally manage network resources, such as programs, data,and devices.

Allow remote users to connect to a network.

Allow users to connect to other networks.

Secure access to a network.

Data backup & restore.

Allow for simple additions of clients and resources.

Monitor status and functionality of network elements.

Distribute programs and software updates to clients.

Provide fault tolerance in case of a hardware or softwareproblem.

Functions of Network Operating System

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Windows Server 2008 R2 is a 64-bit operating system. It isa Microsoft product, which operates on single and

multiprocessor systems.

The features of the Windows Server 2008 R2 operating

system are as follows:

Active DirectoryVirtual Private Networks (VPNs)

Terminal services

NTFS

Windows Deployment Services

Hyper VIPv6 Implementation

Windows Server 2008 R2

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Bell Labs launched the UNIX network operating system.Many versions of UNIX, such as Sun Solaris, AIX UNIX, HP

UNIX, and BSD, are available in the market.

Some of the features of UNIX, which allow networking at the

operating system level, are:

Internet-based servicesCompatibility with different protocols

Network security

UNIX

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The Linux network operating system, developed by LinusTorvalds, is based on the UNIX architecture.

Linux is an open source operating system in which the

source code or the program of the operating system is

available free of cost.

This provides flexibility to the user to modify the operatingsystem according to individual requirements.

Linux provides services like Apache, Samba and NFS.

LINUX

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Types of Network

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Depending on the size and the area that networks cover,the networks are primarily categorized into the following

types:

Local Area Networks (LANs)

Wide Area Networks (WANs)

Types of Network

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A LAN is a small-scale network that extends over relativelysmall distances.

The following figure depicts a typical LAN setup:

Local Area Network

Typical LAN Setup

Node1

Node 2 Node 3

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A Wide Area Network (WAN) provides network connectivityspanning across large geographical area, such as across

states, countries, or across the globe.

The following figure depicts WAN connectivity between two

buildings at Miami and Texas, across the Internet using the

services of a service provider.

Wide Area Network

The WAN Connectivity

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Transmission Basics

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Transmission Direction

There are 3 different transmission modes characterized according tothe direction of the exchanges:

Simplex

Half-Duplex

Full-Duplex (Duplex)

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Simplex: signals may travel in only one direction.

Half-Duplex: signals may travel in both directions over a mediumbut only one direction at a time.

Full-Duplex or Duplex: signals free to travel in both directionsover a medium simultaneously.

Transmission Direction (Continued)

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C


Bandwidth

In computer networking bandwidth refers to the data rate supportedby a network connection.

In the field of electrical engineering, bandwidth represents thedifference between highest and lowest frequencies that a mediumcan transmit.

Bandwidth represents the capacity of the connection.

The greater the capacity, the more likely that greater performancewill follow, though overall performance also depends on other

factors, such as latency.

We most commonly expresses bandwidth in terms of bits persecond (bps).

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Latency

Delay between transmission and receipt of a signal.

Many possible causes:

Cable length

Inter connectivity device e.g. routers.

Round Trip Time (RTT)

Time for packets to go from sender to receiver and back.

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Throughput

In communication networks, network throughput is the average rateof successful message delivery over a communication channel.

The throughput is usually measured in bits per second (bps).

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Baseband

In Baseband networks a digital signal is placed directly on the

transmission medium without requiring a carrier, i.e. withoutmodulation.

Only one signal may be present on the baseband channel at atime.

Baseband networks may use twisted pair, coaxial cable, oroptical fiber for data transmission.

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Broadband

A term used to describe a network that can transmit a wide range

of signals, including audio and video.

Broadband networks are especially useful in the NetworkedWorld, as they can carry many signals at once, resulting in fasterdata transmission.

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Transmission Flaws (Noise)

Electro Magnetic Interference: also called Radio FrequencyInterference RFI) is a disturbance that affects an electrical circuitdue to either electromagnetic induction or electromagneticradiation emitted from an external source such as electricaldevices or cables.

Crosstalk: refers to electromagnetic interference from oneunshielded twisted pair to another twisted pair, normally runningin parallel. In that case signal traveling on a wire or cableinfringes on signal traveling over adjacent wire or cable.

Certain amount of signal noise is unavoidable.

All forms of noise measured in decibels (db).

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Attenuation

Attenuation is a general term that refers to any reduction in thestrength of a signal.

Attenuation occurs with any type of signal, whether digital oranalog. Sometimes called loss, attenuation is a naturalconsequence of signal transmission over long distances.

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Transmission Media

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The physical channel that is used for connecting thecomponents of a network, such as nodes and printers, is

known as transmission medium.

The types of transmission media include the following:

Cables

Wireless

Transmission Media

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Cables are the conventional media used to setup networks.

There are three types of cables:

Coaxial Cables

Twisted Pair Cables

Fiber-optic Cables

Cables

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These cables are designed in such a manner that the centerconductor and the outside braided metal shield share a

common axis.

Coaxial Cables

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These cables use copper wires, which are good conductorsof electricity.

Color-coded pairs of insulated copper wires twisted

together.

Twist ratio: twists per meter or foot.

Higher twist ratio reduces crosstalk and increasesattenuation

Twisted Pair Cables

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Types of Twisted Pair Cables

There are two types of twisted pair cables:

Shielded Twisted Pair Cables (STP)

Unshielded Twisted Pair Cables (UTP)

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These cables consist of multiple twisted pairs (TPs) surroundedby an insulator shield. This insulator shield, in turn, is covered

with a plastic encasement.

Shielded Twisted Pair (STP)

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Shielded Twisted Pair (STP) (Continued)

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These cables consist of a set of twisted pairs that are coveredwith a plastic jacket, as shown in the following figure.

Most common form of cabling found on LANs today.

TIA/EIA 568 standard divides twisted-pair wiring into several

categories: CAT 3, 4, 5, 5e, 6, 6e, 7

Unshielded Twisted Pair (UTP)

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CAT 3 (Category 3): up to 10 Mbps of throughputCAT 4 (Category 4): 16 Mbps throughput

CAT 5 (Category 5): up to 1000 Mbps throughput

CAT 5e (Enhanced Category 5): higher twist ratio

CAT 6 (Category 6): six times the throughput of CAT 5

CAT 6e (Enhanced Category 6): reduced attenuation and crosstalkCAT 7 (Category 7): signal rates up to 1 GHz

Categories of Unshielded Twisted Pair (UTP)

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STP cables are shielded while UTP cables are unshielded.STP cables are more immune to interference and noise than UTPcables.

STP cables are better at maximizing bandwidth compared to UTPcables.

STP cables cost more per meter compared to UTP cables.STP cables are heavier per meter compared to UTP cables.

UTP cables are more prevalent in SOHO networks while STP isused in more high-end networks.

Comparing STP & UTP

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These cables are based on fiber optic technology, which useslight rays instead of electricity to transmit data. The following

figure shows a fiber-optic cable.

Contains glass or plastic fibers at core surrounded by layer of

glass or plastic cladding.

Reflects light back to core.

Fiber-optic

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Fiber-optic cables can be differentiated into the following twocategories:

Single-mode

Multimode

Types of Fiber-optic

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Narrow core through which laser-generated light travels over onepath, reflecting very little.

Accommodates high bandwidths and long distances.

Expensive.

Single Mode Fiber

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Multi-mode optical fiber is a type of optical fiber mostly used forcommunication over short distances, such as within a building oron a campus.

Multi Mode Fiber

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Nearly unlimited throughput.Transmission rates exceed 10 Gigabits per second.

Very high resistance to noise.

Excellent security.

Ability to carry signals for much longer distances before requiringrepeaters than copper cable.

Cost: most expensive transmission medium.

Connector: uses 10 different types of connectors.

Typically use SC, ST & MTRJ connectors.

Noise immunity: unaffected by EMI.

Size and scalability: segment lengths vary from 150 to 40,000

meters.Industry standard for high-speed networking.

Benefits over copper cabling

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The wireless technology helps connect distant networks,

without needing to physically set up cables between thedestination and the source point.

In a wireless setup, the atmosphere is used to transmit and

receive signals in the form of electro-magnetic waves through

an antenna.

These electro-magnetic waves can be transmitted throughdifferent types of wireless transmission carriers, which include

the following:Radio: Radio transmissions operate on radio waves. Radio wavesare only limited to low transmission capacities, from 1 Mbps to 10Mbps.

Microwave: Microwaves transmit data over a higher bandwidth ascompared to radio transmissions.Infrared: Infrared transmissions use infrared radiation to transmitdata. Infrared is an electro-magnetic radiation.

Wireless Transmission

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Connectors

&Media Converters

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Connectors for Coaxial Cable

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RJ45 Connector for UTP Cable

Connectors for UTP Cable

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MTRJSC

ST

Connectors for Fiber-optic Cable

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Media Converters

Media converters are simple networking devices that

make it possible to connect two dissimilar media typessuch as twisted pair with fiber optic cabling.

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OSI Reference Model

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Established in 1947, the International Standards Organization

(ISO) is a multinational body dedicated to worldwide agreement on

international standards.

An ISO standard that covers all aspects of network

communications is the Open Systems Interconnection (OSI)

model. It was first introduced in the late 1970s.

The OSI Model

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ISO is the organization.

OSI is the model

Note:

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The OSI Model

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Application

Presentation

Session

Transport

Network

Data Link

Physical

Reduces complexity (one bigproblem to seven smaller ones)

Standardizes networking

Simplifies teaching and learning

Why a Layered Network Model?

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OSI layers

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An exchange using the OSI model

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Physical layer

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The physical layer is responsible

for the movement of individual bits from

one node to the next.

Note:

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Data link layer

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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

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Network layer

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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

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Transport layer

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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 of a message

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Session layer

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Session layer is responsible for

establishing, managing, and

terminating the communication between

the two nodes.

Note:

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Presentation layer

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Presentation layer is responsible for

encoding & decoding, compression

& decompression, encryption &

decryption of data.

Note:

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Application layer

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Application layer provides the

interface between the user and the

network.

Note:

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Summary of layers

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Application Layer

Provides network access to application

programs (such as electronic mail, file

transfer)

7 Application

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Presentation Layer

Network access to application programs

Ensures data is readable by

receiving system Format of data

Negotiates data transfer syntax for

application layer

7 Application

6 Presentation Data representation

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Session Layer

Inter-host communication Establishes, manages, and

terminates sessions between

applications

7 Application

6 Presentation

5 Session

Network services to applications

Data representation

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Transport Layer

7 Application

6 Presentation

5 Session

Transport4

Inter-host communication


Data representation

End-to-end connection reliability

Concerned with data transport issues

between hosts

Data transport reliability Establishes, maintains, and

terminates virtual circuits

Error detection and recovery

Information flow control

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Network Layer

7 Application

6 Presentation

5 Session

Transport4

Network3



Data representation


Addresses and best path

Define Logical addressing and pathselection between two end systems

Routing of packets

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Data Link Layer

7 Application

6 Presentation

5 Session

Transport4

Network3

Data Link2



Data representation



Access to media

Physical addressing, errornotification, flow control

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Physical Layer

7 Application

6 Presentation

5 Session

Transport4

Network3

Data Link2

Physical1



Data representation



Access to media

Binary transmission

Wires, connectors, data rates

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7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

Host A

Communication

Application

Presentation

Session

Transport

Network

Data Link

PhysicalBits

Frames

Packets

Segments

Host B

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Data Encapsulation

Application

Presentation

Session

Transport

Network

Physical

Data Link

Application

Presentation

Session

Transport

Network

Physical

Data Link

Host A Host B

Data} {

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Application

Presentation

Session

Transport

Network

Physical

Data Link

Application

Presentation

Session

Transport

Network

Physical

Data Link

Data} {Data

Network

Header

Host A Host B

Data Encapsulation (Continued)

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Application

Presentation

Session

Transport

Network

Physical

Data Link

Application

Presentation

Session

Transport

Network

Physical

Data Link

Data} {Data

Network

Header

Frame

Header

Frame

TrailerDataNetwork

Header

Host A Host B


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Application

Presentation

Session

Transport

Network

Physical

Data Link

Application

Presentation

Session

Transport

Network

Physical

Data Link

Data} {Data

Network

Header

Frame

Header

Frame

TrailerDataNetwork

Header

0101101010110001

Host A Host B


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Host Layers

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

Host layers: Provide accurate

data delivery between computers.}

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Media Layers

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

Host layers: Provide accurate

data delivery between computers.

Media layers: Control physical

delivery of messages over thenetwork.

}}

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Physical Layer

The Physical layer specifies the electrical, mechanical,

procedural, and functional requirements for activating,

maintaining, and deactivating a physical link between end

systems.

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Data Link Layer

Data Link layer is divided into two sub layers:

Media Access Control (MAC)

Logical Link Control (LLC)

The Data Link layer is responsible for the following aspects of

communication:Providing unique identification (MAC address) to each

node on the network.

Transforming data bits from the Physical layer into groups

called frames.

Detecting errors that occur during a transmission.

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Data Link La er (Contin ed)


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The Data Link Layer and its Sub Layers

Data Link Layer (Continued)

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Logical Link Control (LLC):

Provides interface to Network layer protocols.

Manages flow control.

Media Access Control (MAC):

Manages access to physical layer.Appends destination computers physical address onto

data frame (MAC address, Data Link layer address, or

hardware address).

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MAC Address (Physical Address, Hardware Address)

24 bits

ROM

RAM

24 bits

0000.0c12. 3456

Serial NumberVendor Code

MAC address is burned into ROM on a network interface card

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A NICs MAC address


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Network Layer


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This layer is responsible for the following functions:

Providing unique logical addresses to each node on thenetwork.

Transmitting data across networks.

Controlling network traffic.

Best Path Determination.

Network Layer

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Which Path?Which Path?

Layer 3 functions to find the best path through the internetwork.

Network Layer : Best Path Determination

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Transport Layer


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Establishes an end-to-end connection.

Sends segments from one end host to another.Ensures data reliability.

Organizing messages into segments or breaking large

segments into smaller segments.

Delivering segments to the recipients.

Providing error control.

Transport Layer


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Transport Layer (Continued)


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Transmit

Buffer FullNot ReadyStopProcess

Segments

Buffer OK

ReadyGo

Resume Transmission

ReceiverSender


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Window Size = 1

Sender

Send 1 Receive 1

Receiver

Ack 2

Send 2 Receive 2

Ack 3

Sender

Send 1

Send 2Receive 1Receive 2

Receiver

Window Size = 3

Send 3 Receive 3Ack 4

Send 4


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Sender Receiver

Send 2Send 1

Send 3

Ack 4

Send 5

Send 4

Send 6

Ack 5

Send 5Ack 7

1 2 3 4 5 6 7 1 2 3 4 5 6 7


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Transport Layer To Network Layer


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End-to-End Segments

Routed Packets

Transport Layer To Network Layer

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Session Layer


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Service Request

Service Reply

Establishes, manages, and terminates sessions between applications.

Session Layer

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Presentation Layer


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ASCIIEBCDIC

Encrypted

Text Data

login:

PICTTIFF

JPEGGIF

Graphics Visual images

Sound

VideoMPEG

QuickTime

MIDI

Provides code formatting and conversion for applications.

Presentation Layer

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Application Layer


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Word Processor

Presentation Graphics

Spreadsheet

Database

Design/Manufacturing

Others

COMPUTERAPPLICATIONS

Electronic Mail

File Transfer

Remote Access

Client-Server Process

Network Management

Others

NETWORKAPPLICATIONS INTERNETWORK

APPLICATIONS

Electronic Data Interchange

World Wide Web

E-Mail Gateways

Special-Interest Bulletin Boards

Financial Transaction Services

Internet Navigation UtilitiesConferencing (Voice, Video, Data)

Others

Provides the interface between the user and the network.

Application Layer

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Functions of the OSI Layer


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Functions of the OSI Layer

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Summary


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OSI reference model describes building blocks of functions for

program-to-program communications between similar ordissimilar hosts.

Summary

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What is Protocol?


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A protocol is a set of established and agreed-upon rules

required to enable effective communication on a network.Protocols can either be developed by a vendor or by anetworking standard organization.

A protocol suite is a hierarchical collection of protocols.

Some of the protocol suites are:

TCP/IP Protocol SuiteIPX/SPX Protocol Suite

AppleTalk Protocol Suite

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Introduction to TCP/IP

(DoD Model)

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TCP/IP Model (DoD Model)


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The DoD model is basically a condensed version of the OSI

model.Its composed of four, instead of seven, layers:

1) Process/Application layer

2) Host-to-Host layer (Transport layer)

3) Internet layer

4) Network Access layer

/ ( )

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Comparing The OSI Model and TCP/IP Model


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TCP/IP Protocol Suite


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Application Layer


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The TCP/IP protocol suite combines all application related

issues into one layer and ensure this data is properly packagedbefore passing it on to the next layer.

Handles high-level protocols, issues of representation, encoding,decoding and session control.

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Application Layer Protocols


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Host-to-Host Layer (Transport Layer)


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The main purpose of the Host-to-Host layer is to shield the

upper- layer applications from the complexities of the network.

This layer says to the upper layer, Just give me your datastream, with any instructions, and Ill begin the process of gettingyour information ready to send.


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Internet Layer


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The purpose of the Internet layer is to send packets from a

network host and have them arrive at the destination nodeindependent of the path taken.

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Internet Layer Protocols


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Network Access Layer


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.

The network access layer is concerned with all of the issues that an

IP packet requires to actually make a physical link to thetransmission media.

It includes the LAN and WAN technology details, and all the detailscontained in the OSI physical and data link layers.

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Network Access Layer Protocols


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Transmission Control Protocol

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Transmission Control Protocol (TCP)


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Creates a reliable connection between two computers.

TCP is one of the main protocol in TCP/IP protocol suite.

Whereas the IP protocol deals only with packets, TCP enablestwo hosts to establish a connection and exchange streams of

data.

TCP guarantees delivery of data and also guarantees thatsegment will be delivered in the same order in which they weresent.

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A packet in TCP is called a

segment.

Note:

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Key Features of TCP


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TCP 3 way Handshake


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TCP 3 way Handshake (Continued)


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Stream delivery


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TCP segment format


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Control field


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Description of flags


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Description of flags (Continued)


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Encapsulation and decapsulation


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A TCP Connection


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TCP is connection-oriented.

A connection-oriented transport protocol establishes a virtualpath between the source and destination.

All of the segments belonging to a message are then sent overthis virtual path.

A connection-oriented transmission requires three phases:Connection establishment

Data transfer

Connection termination

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Connection establishment using three-way handshaking


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The bytes of data being transferred in

each connection are numbered by TCP.

The numbering starts with a randomlygenerated number.

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The value of the acknowledgment field

in a segment defines the number of the

next byte a party expects to receive.

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Connection termination using three-way handshaking


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Example1


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Suppose a TCP connection is transferring a file of 5000 bytes.

The first byte is numbered 10001. What are the sequencenumbers for each segment if data is sent in five segments, eachcarrying 1000 bytes?

Solution

The following shows the sequence number for each segment:

Segment 1 Sequence Number: 10,001 (range: 10,001 to 11,000)





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Aborting a connection


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Error Control


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TCP provides reliability using error control, which detects

corrupted, lost, out-of-order, and duplicated segments.

Error control in TCP is achieved through the use of thechecksum, acknowledgment, and time-out.

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N t


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Data may arrive out of order and be

temporarily stored by the receiving TCP, but

TCP guarantees that no out-of-ordersegment is delivered to the process.

Note:

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In modern implementations, a

retransmission occurs if the

retransmission timer expires.

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No retransmission timer is set for an

ACK segment.

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Normal operation


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Lost segment


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The receiver TCP delivers only ordered

data to the process.

Note:

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Fast retransmission


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Lost acknowledgment


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Flow Control & Congestion Control


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Flow control regulates the amount of data a source can send

before receiving an acknowledgment from the destination.

For that TCP defines a window size depending on the capabilityof receiving host.

Congestion control refers to the mechanisms and techniques to

keep the load below the capacity.

There are two algorithms for Congestion control in TCP:

slow start algorithm

congestion avoidance algorithm

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Slow start, exponential increase algorithm


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Note:


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In the slow start algorithm, the size of

the congestion window increases

exponentially until it reaches athreshold.

Note:

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Congestion avoidance, additive increase algorithm


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Note:


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In the congestion avoidance algorithm

the size of the congestion window

increases additively untilcongestion is detected.

Note:

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T k t k f ll th diff t t h i d i

State Transition


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To keep track of all the different events happening during

connection establishment, connection termination, and datatransfer, the TCP software is implemented as a finite statemachine.

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User Datagram Protocol (UDP)


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UDP uses a simple transmission model without implicit hand-

shaking dialogues for providing reliability, ordering, or dataintegrity.

Thus, UDP provides an unreliable service and datagram's mayarrive out of order, appear duplicated, or go missing withoutnotice.

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Comparison of TCP and UDP


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Addresses in TCP/IP


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Three different levels of addresses are used in an internet:

Physical address (MAC Address)Logical address (IP Address)

Port Address (Port Numbers)

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Addresses in TCP/IP


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TCP and the upper layers dont use MAC and IP addresses to

Port Numbers


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TCP and the upper layers don t use MAC and IP addresses tounderstand the sending hosts address as the Data Link andNetwork layer protocols do. Instead, they use port numbers.

TCP and UDP must use port numbers to communicate with theupper layers because theyre what keep track of differentapplications' conversations crossing the network simultaneously.

Originating source port numbers are dynamically assigned bythe operating system of the source host and will equal somenumber starting at 1024.

These port numbers identify the source and destinationapplication or process in the TCP segment.

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The port numbers are divided into three ranges:

Port Numbers (Continued)


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The port numbers are divided into three ranges:

Well Known PortsRegistered Ports

Dynamic or Private Ports

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The port numbers in the range from 0 to 1023 are the well-

Well Known Ports (01023)


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The port numbers in the range from 0 to 1023 are the wellknown ports. They are used by system processes that provide

widely-used types of network services.

Registered Ports (102449151)

Dynamic or Private Ports (4915265535)

The ranges of port number from 1024 to 49151 are theregistered ports. They are assigned by IANA for specific service

upon application by a requesting entity.

The range above the registered ports contains dynamic or

private ports that cannot be registered with IANA. It is used forcustom or temporary purposes and for automatic allocation byoperating system.

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Relationship of layers and addresses in TCP/IP


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Example1


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In Figure 2.18 a node with physical address 10 sendsa frame to a node with physical address 87. The two

nodes are connected by a link. At the data link level

this frame contains physical (link) addresses in the

header. These are the only addresses needed. The restof the header contains other information needed at

this level. The trailer usually contains extra bits

needed for error detection.

See Next Slide

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Figure 2.18 Physical addresses


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Example2


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Most local area networks use a 48-bit (6 bytes)physical address written as 12 hexadecimal digits,

with every 2 bytes separated by a colon as shown

below:

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

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

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Example3


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In Figure 2.19 we want to send data from a node withnetwork address A and physical address 10, located on one

LAN, to a node with a network address P and physical

address 95, located on another LAN. Because the two devices

are located on different networks, we cannot use link

addresses only; the link addresses have only localjurisdiction. What we need here are universal addresses that

can pass through the LAN boundaries. The network (logical)

addresses have this characteristic.

See Next Slide

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Example3(Continued)


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The packet at the network layer contains the logicaladdresses, which remain the same from the original source to

the final destination (A and P, respectively, in the figure).

They will not change when we go from network to network.

However, the physical addresses will change as the packet

moves from one network to another. The boxes labeled routersare internetworking devices, which we will discuss later.

See Next Slide

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Figure 2.19 IP addresses


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F 2 20 h l f l

Example5


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Figure 2.20 shows an example of transport layer

communication. Data coming from the upper layers

have port addresses j and k ( j is the address of the

sending process, and k is the address of the receiving

process). Since the data size is larger than the networklayer can handle, the data are split into two packets,

each packet retaining the service-point addresses ( j

and k). Then in the network layer, network addresses

(A and P) are added to each packet.

See Next Slide

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Example5(Continued)


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The packets can travel on different paths and arrive atthe destination either in order or out of order. The two

packets are delivered to the destination transport layer,

which is responsible for removing the network layer

headers and combining the two pieces of data fordelivery to the upper layers.

See Next Slide

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Figure 2.20 Port addresses


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Port No TCP UDP Protocol / Application Comment

Well Known Port Numbers


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pp

20 FTP Data Transfer21 FTP Control Commands

22 Secure Shell (SSH) Secure Remote Login

23 TELNET Remote Login

25 SMTP Sending Mails

43 WHOIS Search WHOIS

Database

53 DNS Resolves Domain

Names

67 DHCP Server

68 DHCP Client

69 TFTP Insecure File Transfer

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Well Known Port Numbers (Continued)


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80 HTTP Retrieving Web Pages88 Kerberos Authentication

110 POP3 Receiving Mails

123 Network Time Protocol Synchronize Time

137 NetBIOS Name Service Resolves NetBIOS

Names

138 NetBIOS Datagram

Service

139 NetBIOS Session Service

143 Internet Message Access

Protocol

Retrieving Mails

161 Simple Network

Management Protocol

Network Mgt.

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179 BGP (Border GatewayProtocol) Routing Protocol forISPs

389 Lightweight Directory

Access Protocol

Directory Services

443 HTTPS HTTP Secure

445 Windows SMB FileSharing Service

File Sharing inWindows

500 Internet Security

Association and Key

Management Protocol

(ISAKMP)

Used in IPSec VPNs

514 Syslog Sending Log Messages

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520 Routing InformationProtocol (RIP) Routing Protocol forSmall Networks

546 DHCPv6 client For IPv6 Addressing

547 DHCPv6 server For IPv6 Addressing

860 iSCSI For Accessing Storage

over the networks

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Registered Ports


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1293 IPSec (Internet Protocol

Security)

Encrypting IP Packets

1503 Windows Live Messenger Chat Messenger

6891-

6900

Windows Live Messenger File Transfer

6901 Windows Live Messenger Voice Calls1645 RADIUS Authentication

Protocol

Default Port for Cisco

and Juniper Networks

RADIUS servers

1646 RADIUS Accounting

Protocol

Default for Cisco and

Juniper Networks

RADIUS servers

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Registered Ports (Continued)


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1755 Microsoft Media Services Media Services

1812 RADIUS Authentication

Protocol

Microsoft

Implementation

1813 RADIUS Accounting

Protocol

Microsoft

Implementation

2049 Network File System Available in Linux

3389 Microsoft Terminal Server Remote Desktop

Protocol

3544 Teredo Tunnelling IPv4 To IPv6 Tunnelling

5050 Yahoo! Messenger Chat Messenger

5060 Session Initiation

Protocol (SIP)

Used in Cisco VOIP

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Registered Ports (Continued)


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5355 LLMNR (Link-Local

Multicast Name

Resolution)

Allows hosts to

perform name

resolution for hosts on

the same local link

(only provided by

Windows Vista and

Server 2008)

7777 Windows Backdoor

Program tini.exe

Trojan Horse

19294,

19295,

19302

Google Talk Voice and

Video connections

Chat Messenger

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The combination of IP address and port number. e.g. 201.0.0.1:80

Socket


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Unicast: These are sent to a single destination host.

Unicast, Multicast and Broadcast


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Multicast: These are packets sent from a single source host andtransmitted to many devices on different networks.

Broadcast (layer 2): These are sent to all hosts on a LAN.

Broadcasts (layer 3): These are sent to all hosts on the network.

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A broadcast domain a logical division of a computer network, in

Broadcast Domain


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b oadcas do a a og ca d s o o a co pu e e o ,

which all nodes can reach each other by broadcast at the data linklayer.

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In TCP/IP communications, a datagram (packet) on a local-area

ARP (Address Resolution Protocol )


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, g (p )

network must contain both a destination MAC address and adestination IP address.

There needs to be a way to automatically map IP to MACaddress.

ARP associates an IP address with its MAC address. On a typicalphysical network, such as a LAN, each device on a link isidentified by a physical or MAC address that is usually imprintedon the NIC.

The TCP/IP suite has a protocol, called Address ResolutionProtocol (ARP), which can automatically obtain MAC addressesfor local transmission.

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Used b a sending host hen it kno s the IP address of the

Address Resolution Protocol (Continued)


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Used by a sending host when it knows the IP address of the

destination but needs the MAC address.

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ARP operation


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Each device on a network maintains



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Each device on a network maintains

its own ARP table.

A device that requires an IP andMAC address pair broadcasts an

ARP request.

If one of the local devices matchesthe IP address of the request, itsends back an ARP reply thatcontains its IP-MAC pair.

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ARP is a broadcast protocol every host on the network receives



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p y

the request.

Each host checks the request against its IP address the rightone responds.

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An ARP request is broadcast;

an ARP reply is unicast.

Note:

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Four cases using ARP


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RARP finds the IP address for a machine that only knows its

RARP (Reverse Address Resolution Protocol)


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RARP finds the IP address for a machine that only knows its

MAC address.

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ARP and RARP


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ICMP is a network protocol used for reporting errors that might

ICMP (Internet Control Message Protocol)


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p p g g

have occurred while transferring data packets over networks.

ICMP is designed for network diagnosis and to find out as to whatwent wrong in the data communication.

ICMP can be used to report:errors in the underlying communications of networkapplications.

availability of remote hosts.

Best known example of ICMP in practice is the ping utility,that uses ICMP protocol.

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ICMP In Action


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When Host A sends a packet destined for Host B, the Lab_B routerwill send an ICMP destination unreachable message back to thesending device (Host A in this example).

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HTTP

Application Layer Protocols


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FTPTFTP

TELNET

SSH

DNS

SMTPPOP

IMAP

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Web servers implement this protocol.

HTTP (Hyper Text Transport Protocol )


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p p

The underlying protocol used by the World Wide Web.

HTTP defines how messages are formatted and transmitted,and what actions Web servers and browsers should take inresponse to various commands.

For example, when you enter a URL in your browser, thisactually sends an HTTP command to the Web server directing itto fetch and transmit the requested Web page.

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FTP protocol is used for downloading and uploading files over

FTP (File Transfer Protocol)


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p g p g

the Internet.

FTP works in the same way as HTTP for transferring Webpages from a server to a user's browser.

FTP is most commonly used to download a file from a serverusing the Internet or to upload a file to a server (e.g. uploading adocument file to a server).

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It can do nothing but send and receive files.

TFTP (Trivial File Transfer Protocol)


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TFTP has no directory-browsing abilities.

Theres no authentication as with FTP, so its insecure.

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It allows a user to remotely access the resources of anothers stem on the net ork

TELNET


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system on the network.

Telnet is a text-mode type program.

Telnet is not secure.

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SSH (Secure Shell)

SSH is a network protocol that allows you to remotely accessthe resources of another system on the network


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the resources of another system on the network.

Allows data to be exchanged using a secure channel betweentwo networked devices.

SSH was designed as a replacement for Telnet which send

information, notably passwords, in plaintext, rendering themsusceptible to packet analysis.

The encryption used by SSH is intended to provideconfidentiality and integrity of data over an unsecured network,

such as the Internet.

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A Domain Name Server (DNS) lookup is the conversion of adomain name into its respective IP address

DNS (Domain Name Service)


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domain name into its respective IP address.

Domain names are alphabetic, they're easier to remember.

The Internet however, is really based on IP addresses, Everytime you use a domain name, therefore, a DNS service must

translate the name into the corresponding IP address.

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For example, the domain name www.example.com mighttranslate to 198 105 232 4

DNS (Continued)


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translate to 198.105.232.4.

If one DNS server doesn't know how to translate a particulardomain name, it asks another one, and so on, until the correctIP address is returned.

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Domain name space


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Domain names and labels


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FQDN


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Hierarchy of name servers


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The domain name space (tree) is divided into two differentsections:

DNS In The Internet


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Generic domainsCountry domains

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DNS used in the Internet


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Generic domains


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Generic Domain Labels


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Generic Domain Labels (Continued)


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Country Domains


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In Linux and Windows, the nslookup utility can be used to

retrieve address/name mapping The following shows how we

Example3


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retrieve address/name mapping. The following shows how we

can retrieve an address when the domain name is given.

$ nslookup india.comName: india.com

Address: 153.18.8.1

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Note:


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DNS can use the services of UDP or

TCP using the well-known port 53.

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Every operating system has a hosts file.

The Hosts File


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The hosts file stores information on where to find or locate aparticular computer on the network.

It basically maps hostnames or domain names to IP addresses.

One can think of it as the local system version of the DomainName System (DNS).

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Depending upon your operating system, the hosts file can befound at different locations:

The Hosts File (Continued)


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Microsoft Windows \windows\system32\drivers\etc

Unix & Linux \etc

The hosts file can be tweaked to carry out a number of

interesting things:

Block certain websites.

Redirecting the user to an embarrassing website eachtime he enters the address of a regular website.

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SMTP is used for sending email messages.

SMTP (Simple Mail Transfer Protocol)


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Most e-mail systems that send mail over the Internet use SMTPto send messages from one server to another; the messagescan then be retrieved with an e-mail client using either POP orIMAP.

In addition, SMTP is generally used to send messages from amail client to a mail server. This is why you need to specify boththe POP or IMAP server and the SMTP server when youconfigure your e-mail application.

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Note:

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Cnw n+ 3rd Dec 2012 Cnw Batch (2)

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