ARPANET

Network Topology:

Network topology is the layout of a network. It consists of two parts; physical and logical. The physical part describes the physical layout of a network while the logical part describes how the data flows in that network. Both, physical and logical parts are also known as the physical topology and the logical topology.

Physical part (Topology) + Logical part (Topology) = Network Topology

History of Computer Networking:

A computer network is a group of computers that has the potential to transmit, receive and exchange voice, data, and video traffic. 

The network and data communication are the essential factors to rise information technology in the world as technology's advancement is on the system, including the gadgets. ARPANET began the networking long ago.

In 1957, when SPUTNIK Satellite was launched by Russia. An agency named ADVANCED RESEARCH PROJECT AGENCY (ARPA) was started by American, and its first satellite was launched within 18 months after establishment. Then they used ARPANET to share the information on another computer. America's Dr. LIED LIEDER has this all responsibility. Then, ARPANET came to India in 1969, and its name changed from Indian to NETWORK.

For the United States Department of Defense, the funding of the design of the Advanced Research Projects Agency Network (ARPANET) was began by ARPA. In 1969, the network began to develop on the basis of the developed designs in the 1960s. The below table contains a complete history of computer networking:

Year	Event
1961	In this year, Leonard Kleinrock proposed the earliest computer networks, which was the idea of ARPANET.
1965	In 1965, Donald Davies coined the term "packet" to describe how to send data between computers on a network.
1969	Although In 1966, the development of ARPANET began, officially started ARPANET in 1969. It was considered one of the first computer networks in which first two nodes, UCLA and SRI (Stanford Research Institute) were connected, and to use packet switching. To provide and define information about network protocols, procedures, and computer communications, the first RFC surfaced as a document in April 1969.
1969	On 29 August 1969, the first IMP and network switch were sent to UCLA. On ARPANET, the first data transmission was sent by using it.
1970	NCP, stands for NetWare Core Protocol, released by Steve Crocker and a team at UCLA for use with NetWare.
1971	In 1971, the first e-mail was sent to across a network to other users by Ray Tomlinson.
1973	While working at Xerox PARC, Robert Metcalfe developed the Ethernet in 1973. In the same year, ARPA deployed the first international network connection, known as SATNET. In 1973, VoIP technology and capabilities were officially introduced, which made a VoIP call. However, until 1995, the software was not available for users that could make VoIP calls.
1974	In this year, the use of first router was began, but they were not considered true IP routers.
1976	Originally called a gateway, Ginny Strazisar develop the first true IP router.
1978	In 1978, the TCP/IP protocol was developed and invented by Bob Kahn for networks; it was developed with help from Vint Cerf.
1981	In the United States, between IBM mainframe systems, BITNET was created in 1981 as a network. The U.S. National Science Foundation developed the CSNET (Computer Science Network) in the same year 1981.
1983	For using TCP/IP, ARPANET finished the transition. The first DNS implement by Jon Postel and Paul Mockapetris in 1983.
1986	This is the year in which a backbone for ARPANET, the National Science Foundation Network was came online, which finally took the place of ARPANET in 1990s. In the same year, with the original BITNET, BITNET II was introduced to deal with bandwidth issues.
1988	In 1988, the first T1 backbone was included with ARPANET. AT&T, Lucent, and NCR introduced the WaveLAN network technology in 1988. In 1988, for the first time, the explanation of network firewall technology was published. In the same year, Digital Equipment Corporation developed it. This paper had the detail about the first firewall, known as a packet filter firewall.
1990	The first network switch was developed and introduced by a U.S. network hardware company named Kalpana in 1990.
1996	In 1996, an IPv6 was introduced as an improvement over IPv4, as well as embedded encryption, improved routing.
1997	In June 1997, the 802.11 standards, containing transmission speeds up to 2 Mbps, for Wi-Fi were introduced.
1999	The 802.11a standard, containing transmission speeds up to 25 Mbps to use the 5 GHz band, was officially made in 1999. Another standard 802.11b was available to use for the public in mid-1999, which offered transmission speeds up to 11 Mbps. In September 1999, for use with 802.11b, the WEP encryption protocol was released.
2003	802.11g devices, contained transmission speeds up to 20 Mbps, were available to the public in January 2003. In the same year, for use with 802.11g, the WPA encryption protocol is released.
2004	In 2004, as a replacement for WPA, the WPA2 encryption protocol was introduced. By 2006, WPA2 certification was compulsory for all Wi-Fi devices.
2009	The 802.11n standard can operate on the 2.4 GHz and 5 GHz bandwidths and offers higher transfer speeds over 802.11a and 802.11g. Officially, it was made in 2009.
2018	In January 2018, WPA3 encryption was released by the Wi-Fi Alliance, which comprises security enhancements over WPA2.

List of Abbreviations and Acronyms

 

3GPP 3G Partnership Project Protocols

6LoWPAN IPv6 over Low power Wireless Personal Area Networks

ACID Atomicity, Consistency, Isolation and Durability of transactions

ADAS Advance Driver Assistance Systems

ADC Analog-to-Digital Converter

ADFG Acrylic Data Flow Graph

ADSL Asymmetric Digital Subscriber Line

AES Advanced Encryption 128- or 192- or 256- bit key length Algorithm

AES-CCM AES with CCM

API Application Programming Interface 

AQI Air Quality Index

ARP Address Resolution Protocol

ASCII American Standard Code for Information Interchange

ASIC Application Specific Integrated Circuit

ATM Automated Teller Machine 

AWS Amazon Web Services

BB BeagleBone

BI Business Intelligence

BJT Bipolar Junction Transistor

xx List of Abbreviations and Acronyms

Bootpc Bootstrap Protocol Client

Bootps Bootstrap Protocol Server

BP Business Process

BT BR Bluetooth Basic data rate in 1.0, 2.0, 3.0 or 4.0 device

BT EDR Bluetooth Enhanced Data Rate

BT LE Bluetooth Low Energy

CA Certification Authority

CAN Controller Area Network bus

CAP Consistency, Availability and Partitions

CBC Cryptographic Block Cipher for block ciphers with a block length of 

128 bits

CCD Charge Coupled Device 

CCM Counter with CBC-MAC

CEP Complex Event Processing

CGA Cryptographically Generated Addresses 

CIDR Classless Inter-Domain Routing 

CIMD Computer Interface to Message Distribution

CoAP Constrained Application Protocol

CORE Constrained RESTful Environment

CRC Cyclic Redundancy Check

CRM Customer Relations Management

CSMA/CD Carrier Sense Multiple Access with Collision Detection

CUP Connected Universe Platform

CVS Concurrent Versions System

CWI Cloud Web Interface

DAG Directed Acrylic Graph

DB Database

DBMS Database Management System

DBP Distributed Business Process

DFG Data Flow Graph

DHCP Dynamic Host Control Protocol 

DLL Dynamically Linked Library

DM Device Management

DNS Domain Name System

DODAG Destination Oriented Directed Acrylic Graph

List of Abbreviations and Acronyms xxi

DoS Denial-of-Service

DSL Digital Subscriber Line

DSP Digital Signal Processor

DSSS Direct Sequence Spread Spectrum 

DTLS Datagram Transport Layer Security

DWI Device Web Interface

ECU Electronic Control Unit

EPC Electronic Product Code

ESP Event Stream Processing

ETL Extract, Transform and Load 

FC Functional Component 

FG Functional Group

FHSS Frequency Hopping Spread Spectrum 

FOTA Firmware Over-The-Air

FPT Phototransistor

FTP File Transfer Protocol

GPIO General Purpose Input-Output

GPRS General Packet Radio Service

GSM Global System for Mobiles

HAB Home Automation Bus

HAN Home Area Network

HDFS Hadoop File System

HLR Home Location Register 

HSPA High Speed Packet Access

HTML HyperText Markup Language

HTTP Hypertext Transfer Protocol

HTTPS HTTP over TLS/SSL

I/O Input-Output

I2C Inter-Integrated Circuit 

IaaS Infrastructure-as-a-Service

IANA Internet Assigned Number Authority 

ICCM Internet Connected Car Maintenance 

ICMP Internet Control Message Protocol

ICSP In-Circuit Serial Programming 

xxii List of Abbreviations and Acronyms

ICT Information and Communications Technology

IDE Integrated Development Environment

IdM Identity Management

IEC International Electrotechnical Commission for Standards

IETF Internet Engineering Task Force

IFTTT If This Then That service

IIC Industrial Internet Consortium 

IIoT Industrial IoT

IM Instant Messaging

IO Input-Output

IoT Internet of Things

IP Internet Protocol

IPSec IP Security Protocol

IPSP Internet Protocol Support Profile 

IPv4 Internet Protocol version 4

IPv6 Internet Protocol version 6 

iq Information/Query

IR-LED Infrared Light Emitting Diode

ISDN Integrated Services Data Network 

ISM Industrial, Scientific and Medical

ISO International Organization for Standardization

JAR Java Archive

JID Jabber ID 

JMS Java Message Service

JSON Java Script Object Notation

KPI Key Performance Indicators

LAN Local Area Network (of Computers)

LED Light Emitting Diode

LIDAR Light + Radar, also Laser Imaging, Detection and Ranging

LIN Local Interconnect Network Bus

LLN Low Power Lossy Networks

LoRaWAN Low-power and Range WAN

LPWAN Low-power WAN

LTE Long Term Evolution

List of Abbreviations and Acronyms xxiii

LWM2M Lightweight M2M Protocol

LWT Last Will and Testament on failure of a session, for example, between 

a client and broker or server

M2M Machine-to-Machine

MAC Media Access Control 

mDNS Multicast Domain Name System

MEMS Micro-Electro-Mechanical Sensor 

MFLOPS Million Floating Point Operations Per Second 

MIME Multipurpose Internet Mail Extension

MINA Multi-Hop Infrastructure Network Architecture 

MIPS Million Instructions Per Second 

MMC Multimedia Card

MO Mobile Origin 

MOSFET Metal-oxide Field Effect Transistor

MOST Media Oriented System Transport

Mote Mobile Terminal

MPLS Multiprotocol Label Switching

MPP Massively Parallel Processing

MQ Message Queue

MQTT Message Queue Telemetry Transport protocol

MS Mobile Station

MSISDN Mobile Station ISDN Number

MT Mobile Terminal 

MTC Machine Type Communication

MTU Maximum Transmission Unit 

MUT Multi-User Chat

NAN Neighbourhood Area Network

ND Neighbour Discovery

NDP Network Discovery Protocol 

NFC Near Field Communication

NFV Network Function Virtualization

NIST National Institute of Standards and Technology

OASIS Organization for the Advancement of Structured Information 

Standards

ODBC Open Database Connectivity

xxiv List of Abbreviations and Acronyms

OID Object Identifier

OLAP On-Line Analytical Processing 

OLTP On-Line Transactions Processing 

OMA Open Mobile Alliance

ONS Object Name Service

ORCHID Overlay Routable Cryptographic Hash Identifier

OS Operating System

OSGi Open Services Gateway initiative

OWASP Open Web Application Security Project

P2P Point-to-Point 

PaaS platform-as-a-service

PAN Personal Area Network

PCI Peripheral Component Interconnect

PCMCIA Personal Computer Memory Card International Association

PDU Protocol Data Unit for a layer

PII Personally Identifiable Information 

PKI Public Key Infrastructure

PPP Point-to-Point Protocol 

PS Participatory Sensing

PSK Pre-Shared Key

pubsub Publication by a service and subscription by end point or client or 

server

PWM Pulse Width Modulator

QoS Quality of Service

QR code Quick Response code

RAM Random Access Memory 

RARP Reverse Address Resolution Protocol

RDMS Relational Database Management System

REST Representational State Transfer

RF Radio Frequency of MHz

RFC IETF Request for Comments standardisation document

RFD Reduced Function Device

RFIC RF Integrated Circuits

RFID Radio Frequency Identification

ROLL Routes Over the Low power and Lossy network

List of Abbreviations and Acronyms xxv

ROM Read Only Memory 

RPC Remote Procedure Call

RPi Raspberry Pi 

RPK Random Pair-wise Keys, Raw-Public-key

RPL IPv6 Routing Protocol for LLNs (Low Power Lossy Networks)

RPM Revolution per Minute

RPMP Re-Planning Manufacturing Process

RTC Real Time Clock

RTOS Real Time Operating System

Rx Receiver

RxD Receiver Data line

SaaS Software as a Service

SASL Simple Authentication and Security Layer

SCADA Supervisory Control and Data Acquisition 

SCL Serial Clock

SCOVARS Supply Chain Order Verification, Automated Reordering and 

Shipping

SD Service Discovery 

SDA Serial Data

SDK Software Development Kit

SHA Secure Hash Algorithm

SIM Subscriber Identity Module (generally a card) in mobile

SLA Service Level Agreement

SMPP Short Message Peer to Peer

SMS Short Message Service 

SNMP Simple Network Management Protocol 

SOAP Simple Object Access Protocol

SPI Serial Peripheral Interface Bus

SPINS Security Protocols in Network of Sensors

SQL Structured Query Language

SS7 Signaling Service Protocol 

SSID Service Set Identifier

SSL Secure Scoket Layer

STP Spanning Tree Protocol 

SWE Sensor Web Enablement services

xxvi List of Abbreviations and Acronyms

TCCICDD Tracking of Customer Carrying Internet Connected Digital Devices

TCP Transmission Control Protocol

TCUP TCS Connected Universe Platform

TFTP Trivial File Transfer Protocol

TLS Transport Layer Security

TLS Transport Layer Security

TLV Tag Length Value

TSDB Time Series Database 

TTP Trusted Third Party 

Tx Transmitter

TxD Transmitter Data line

UART Universal Asynchronous Receiver and Transmitter

UCP/UMI Universal Computer Interface Protocol/Machine Interface

UDP User Datagram Protocol

UI User Interface

UPC Universal Product Code

URI Universal Resource Identifier

URL Universal Resource Locator

USB Universal Serial Bus

V2I Vehicle to Infrastructure Communication 

VLAN Virtual Local Area Network 

W3C World Wide Web Consortium

WAN Wide Area Network

WEP Wired Equivalent Privacy 

WIDL Web Interface Definition Language

Wi-Fi Wireless Fidelity 

WLAN Wireless 802.11 Local Area Network

WPA Wireless Protected Access

WSAPI WebSocket Application Programming Interface

WSN Wireless Sensor Node/Network

WWAN Wireless Wide Area Network

XAAS Everything-as-a-Service 

xep XMPP Extension Protocol

XHTML EXtensible HyperText Markup Language

List of Abbreviations and Acronyms xxvii

XML EXtensible Markup Language

XMPP EXtensible Messaging and Presence Protocol

XMPP-IoT XMPP xeps for the IoT/M2M 

XSF XMPP Standards Foundation

ACN short questions : HTPS vs FTP vs SMTP , IPV6

 Differences : HTPS vs FTP vs SMTP

 

List of features of IPv4:

Address Structure:

An IPv6 address is made of 128 bits divided into eight 16-bits blocks. Each block is then converted into 4-digit Hexadecimal numbers separated by colon symbols.

For example, given below is a 128 bit IPv6 address represented in binary format and divided into eight 16-bits blocks:

0010000000000001 0000000000000000 0011001000111000 1101111111100001 0000000001100011 0000000000000000 0000000000000000         1111111011111011

Each block is then converted into Hexadecimal and separated by ‘:’ symbol:

2001:0000:3238:DFE1:0063:0000:0000:FEFB

1. Larger Address Space

The IPV6 uses four times more bits for addressing a device on the internet as compared to IPV4, and the space provided by it is 3.4 x 10 ^ 38 devices; the address space provided by IPV6 may fulfill the requirement to allocate addresses all over the world means it can be allocated to everywhere on the earth in a square meter, this the main feature of the IPV6.

2. Simplified Header

The header of the IPV6 is twice bigger than the header provided by IPV4 on the other hand, the address provided by it is 4× more than IPV4, IPV6 header is not complex but easy to process while in IPV4, the header is complex, so by simplifying in IPV6 we need to move all the information from the header of it to the end of its header.

3. End-to-end Connectivity

The end-to-end connectivity feature in internet protocol, as of now every system has an IP address which is to be unique it can cross the internet without translating other components, it is fully implemented on the internet each host can access the other host directly, but there may have some restrictions like firewall, and policies of the organization may restrict.

4. Auto-configuration

The auto-configuration is the process to verify uniqueness on a link; it also determines the information that should be auto-configured, it supports stateful configuration mode to keep track of each assignment as well as it also supports the stateless auto-configuration in which there is no need to configure manually because it automatically generates the IPV6 addresses.

5. Faster Routing or Forwarding

The information which is present at the first part of the header is enough to make routing decisions as we know this is the simplified header feature as we have seen above, and due to the information present at header the IPV6 can make routing decisions faster, in this, we can say that IPV6 is faster in routing.

6. IPSec

This is an optional feature provided by IPV6 to give security of IPSec type, which is more secure than IPV4 and IPSec is used at the network or packet processing layer to secure the network.

7. Aggregation

The aggregation is another feature of IPV6, which allows using a single prefix for the entire network, which is easy and flexible to promote efficient and scalable routing.

8. No Broadcast

The IPV6 uses multicast address instead of broadcast address because it does not support the broadcast address, by using multicast address it communicates with the multiple hosts, it also has anycast mode which is a new type of address, a network device sends a packet to a multicast address then the device broadcast the packet to all interfaces which are identified by the address.

9. Anycast Support

Anycast is the featuring provided by IPV6 that is the mode of packet routing; on the internet, by using the anycast mode, the same anycast IP address can assign multiple interfaces, we can say that this is the address we can assign to multiple interfaces or set of interfaces, in this way IPV6 support the anycast.

10. Mobility

This feature of IPV6 allows the host, like a mobile phone, to keep the device connected in different geographic areas by using the same IP address, the mobility in IPV6 can assign an IP address to the mobile node within its home network, and the mobile node of the home address is useful to reach their destination.

11. Enhanced Priority Support

This is another feature of the IPV6 to check the priority support that IPV4 provided the quality of services where it used 6 bits Differential Service Code Point that is DSCP, and 2 bits Explicit Congestion Notification that is ECN but that can be used only when there is an end-to-end devices support so the underlying network like source and destination may support to it.

12. Smooth Transition

The smooth transition is the transition technique in IPV6 which is upgraded from IPV4 based on the up-to-date IPV6 technique, by the feature of the large IP address in IPV6 allow to assign the same IP address globally so devices can send and receive data within the network, the router in it can forward the decisions quickly rather the header is less loaded, and another enhancement is that all routers in one path need to do recalculation for IPV6 packet instead of error detection which is handled by the data link layer.

13. Extensibility

Extensibility is the major advantage of the IPV6; it is extensible so that it can add more information in the options section, the IPV6 has a large size packet where the IPV4 has less than IPV6 so that IPV4 can support 40-byte options only, in this way of adding extension header after the IPV6 header IPV6 can easily be extended, and the size of its extension is mannered by the size of its packets.

Local & Global address:

Global Addressing: A source or a destination needs to have a global address-an address that can be unique in the scope of the network or internationally.

Local Addressing: The identifier that is actually used for data transfer is called the virtual-circuit identifier (VCI). A VCI, unlike a global address, is a small number that has only switch scope; it is used by a frame between two switches. When a frame arrives at a switch, it has a VCI; when it leaves, it has a different VCI.

Difference between Switch and Router:

Router	Switch
The main objective of router is to connect various networks simultaneously.	While the main objective of switch is to connect various devices simultaneously.
It works in network layer.	While it works in data link layer.
Router is used by LAN as well as MAN.	While switch is used by only LAN.
Through the router, data is sent in the form of packets.	While through switch data is sent in the form of  frame.
There is less collision taking place in the router.	While there is no collision taking place in full duplex switch.
Router is compatible with NAT.	While it is not compatible with NAT.
The types of routing are: Adaptive and Non-adaptive routing.	The types of switching are: Circuit, Packet,and Message Switching.

acn 4

 Switching 

acn 3

 

LAYERED TASKS : Open System Interconnection & TCP/IP Model

LAYERED TASKS

We use the concept of layers in our daily life. As an example, let us consider two friends who communicate through postal mail the process of sending a letter to a friend would be complex if there were no services available from the post office.

Sender, Receiver, and Carrier

At the Sender Site

Let us first describe, in order, the activities that take place at the sender site.

• Higher layer. The sender writes the letter, inserts the letter in an envelope, writes the sender and receiver addresses, and drops the letter in a mailbox.

• Middle layer. The letter is picked up by a letter carrier and delivered to the post office.

• Lower layer. The letter is sorted at the post office; a carrier transports the letter.

0n the Way: The letter is then on its way to the recipient. On the way to the recipient's local post office, the letter may actually go through a central office. In addition, it may be transported by truck, train, airplane, boat, or a combination of these.

At the Receiver Site

• Lower layer. The carrier transports the letter to the post office.

• Middle layer. The letter is sorted and delivered to the recipient's mailbox.

• Higher layer. The receiver picks up the letter, opens the envelope, and reads it. 

Reference Models:

In computer networks, reference models give a conceptual framework that standardizes communication between heterogeneous networks.

The two popular reference models are −
•OSI Model
•TCP/IP Protocol Suite

OSI(Open System Interconnection) Model:

• OSI stands for Open Systems Interconnection
• Created by International Standards Organization (ISO)
• Was created as a framework and reference model to explain how different networking technologies work together and interact
• It is not a standard that networking protocols must follow
• Each layer has specific functions it is responsible for
• All layers work together in the correct order to move data around a network

Application Layer: Contains all services or protocols needed by application software or operating system to communicate on the network

Examples
–Firefox web browser uses HTTP (Hyper-Text Transport Protocol)
–E-mail program may use POP3 (Post Office Protocol version 3) to read e-mails and SMTP (Simple Mail Transport Protocol) to send e-mails

Presentation Layer: Concerned with how data is presented to the network
•Handles three primary tasks: 
 Translation , Compression , Encryption

Session Layer

• Responsible for managing the dialog between networked devices
• Establishes, manages, and terminates connections
• Provides duplex, half-duplex, or simplex communications between devices
• Provides procedures for establishing checkpoints,  adjournment,  termination, and restart or recovery procedures

Transport Layer

• Takes data from higher levels of OSI Model and breaks it into segments that can be sent to lower-level layers for data transmission
• Conversely, reassembles data segments into data that higher-level protocols and applications can use
  
• Also puts segments in correct order (called sequencing ) so they can be reassembled in correct order at destination
• Concerned with the reliability of the transport of sent data
• May use a connection-oriented protocol such as TCP to ensure destination received segments
• May use a connectionless protocol such as UDP to send segments without assurance of delivery
• Uses port addressing

Network Layer 

• Responsible for moving packets (data) from one end of the network to the other, called end-to-end communications
• Requires logical addresses such as IP addresses
• Device example: Router
• Routing is the ability of various network devices and their related software to move data packets from source to destination

Data Link Layer

• Is responsible for moving frames from node to node or computer to computer
• Can move frames from one adjacent computer to another, cannot move frames across routers
• Encapsulation = frame
• Requires MAC address or physical address
• Protocols defined include Ethernet Protocol and Point-to-Point Protocol (PPP)
• Device example: Switch,Bridge
• Two sublayers: Logical Link Control (LLC) and the Media Access Control (MAC)

Logical Link Control (LLC)

• Data Link layer addressing, flow control, address notification, error control

Media Access Control (MAC)

• Determines which computer has access to the network media at any given time
• Determines where one frame ends and the next one starts, called frame
• synchronization

Physical Layer

• Deals with all aspects of physically moving data from one computer to the next
• Converts data from the upper layers into 1s and 0s for transmission over media
• Defines how data is encoded onto the media to transmit the data
• Defined on this layer: Cable standards, wireless standards, and fiber optic standards.
• Copper wiring, fiber optic cable, radio frequencies, anything that can be used to transmit data is defined on the Physical layer of the OSI Model
• Device example: Hub, Repeater
• Used to transmit data

An exchange using the OSI model

TCP/IP Model (Transmission Control Protocol/Internet Protocol):
A protocol suite is a large number of related protocols that work together to allow networked computers to communicate

Application Layer

Application layer protocols define the rules when implementing specific network applications Rely on the underlying layers to provide accurate and efficient data delivery
Typical protocols:

• FTP – File Transfer Protocol
• For file transfer
• Telnet – Remote terminal protocol
• For remote login on any other computer on the network
• SMTP – Simple Mail Transfer Protocol
• For mail transfer
• HTTP – Hypertext Transfer Protocol
• For Web browsing

Transport Layer 
•TCP is a connection-oriented protocol

• Does not mean it has a physical connection between sender and receiver
• TCP provides the function to allow a connection virtually exists – also called virtual circuit

•UDP provides the functions:

•   Dividing a chunk of data into segments
•   Reassembly segments into the original chunk
•   Provide further the functions such as reordering and data resend
•   Offering a reliable byte-stream delivery service
•   Functions the same as the Transport layer in OSI
•   Synchronize source and destination computers to set up the session between the respective computers

Internet Layer

• The network layer, also called the internet layer, deals with packets and connects independent networks to transport the packets across network boundaries. The network layer protocols are the IP and the Internet Control Message Protocol (ICMP), which is used for error reporting.

Host-to-network layer
The Host-to-network layer is the lowest layer of the TCP/IP reference model. It  combines  the  link layer and  the  physical layer of  the  ISO/OSI  model.  At this layer, data is transferred between adjacent network nodes in a WAN or between nodes on the same LAN.

OSI Model Vs TCP/IP Model:

Introduction to Computer Networks

Syllabus of unit 1:

DATA COMMUNICATION: Characteristics, Components, Data flow, Network criteria, Topologies, Network model, Layered tasks, ARPANET, OSI model, TCP/IP protocol suite, Addressing 

PHYSICAL LAYER: Transmission Media: Guided and unguided, Connecting devices: Hub, switch, bridge, router, Gateway.

A network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network.

“Computer network’’ means a collection of autonomous computers interconnected by a single technology. Two computers are said to be interconnected if they are able to exchange information.

The connection need not be via a copper wire; fiber optics, microwaves, infrared, and communication satellites can also be used, with  the Internet being the most well-known example of a network of networks.

There is considerable confusion in the literature between a computer network and a distributed system. The key distinction is that in a distributed system, a collection of independent computers appears to its users as a single coherent system. Usually, it has a single model or paradigm that it presents to the users. Often a layer of software on top of the operating system, called middleware, is responsible for implementing  this  model.  A  well-known example of a distributed system is the World Wide Web. It runs on top of the Internet and presents a model in which everything looks like a document (Web page).

A network must be able to meet certain criterias, these are mentioned below:

Performance
Reliability
Scalability 

Performance: It can be measured in the following ways:
Transit time : It is the time taken to travel a message from one device to another.
Response time : It is defined as the time elapsed between enquiry and response.
Other ways to measure performance are :
·       Efficiency of software
·       Number of users        
·       Capability of connected hardware
 

Reliability: It decides the frequency at which network failure take place. More the failures are, less is the network's reliability.

Security: It refers to the protection of data from any unauthorized user or access. While travelling through network, data passes many layers of network, and data can be traced if attempted. Hence security is also a very important characteristic for Networks.

USES OF COMPUTER NETWORKS

1. Business Applications

• To distribute information throughout the company (resource sharing). sharing physical resources such as printers, and tape backup systems, is sharing information

• client-server model. It is widely used and forms the basis of much network usage.

• communication medium among employees. email (electronic mail), which employees generally use for a great deal of daily communication.

• Telephone calls between employees may be carried by the computer network instead of by the phone company. This technology is called IP telephony or Voice over IP (VoIP) when Internet technology is used.

• Desktop sharing lets remote workers see and interact with a graphical computer screen

• Doing business electronically, especially with customers and suppliers. This new model is called e-commerce (electronic commerce) and it has grown rapidly in recent years.

2.Home Applications

• peer-to-peer communication

• person-to-person communication

• electronic commerce

• entertainment.(game playing,)

3.Mobile Users

• Text messaging or texting

• Smart phones,

• GPS (Global Positioning System)

• m-commerce

• NFC (Near Field Communication)

4.Social Issues

With the good comes the bad, as this new-found freedom brings with it many unsolved social, political, and ethical issues. 

Social networks, message boards, content sharing sites, and a  host  of other applications allow people to share their views with  like-minded individuals. As long as the subjects are restricted to technical topics or hobbies like gardening, not too many problems will arise.

The trouble comes with topics that people actually care about, like politics, religion, or sex. Views that are publicly posted may be deeply offensive to some people. Worse yet, they may not be politically correct. Furthermore, opinions need not be limited to text; high-resolution color photographs and video clips are easily shared over computer networks. Some people take a live-and-let-live view, but others feel that posting certain material (e.g., verbal attacks on particular countries or religions, pornography, etc.) is simply unacceptable and that such content must be censored. Different countries have different and conflicting laws in this area. Thus, the debate rages.

Computer networks make it very easy to communicate. They also make it easy for the people who run the network to snoop on the traffic. This sets up conflicts  over  issues  such  as  employee  rights  versus  employer   rights. Many people read and write email at work. Many employers have claimed the right to read and possibly censor employee messages, including messages sent from a home computer outside working hours. Not all employees agree with this, especially the latter part.

Another conflict is centered around government versus citizen’s rights.A new twist with mobile devices is location privacy. As part of the process of providing service to your mobile device the network operators learn where you are at different times of day. This allows them to track your movements. They may know which nightclub you frequent and which medical center you visit.

Phishing ATTACK: Phishing is a type of social engineering attack often used to steal user data, including login credentials and credit card numbers. It occurs when an attacker, masquerading as a trusted entity, dupes a victim into opening an email, instant message, or text message.

BOTNET ATTACK: Botnets can be used to perform distributed denial-of-service attack (DDoS attack), steal data, send spam, and allows the attacker to access the device and its connection.

Data Communications System :

The effectiveness of a data communications system depends on  four fundamental characteristics: delivery, accuracy, timeliness, and jitter.

I. Delivery. The system must deliver data to the correct destination. Data must be received by the intended device or user and only by that device or user.

2 Accuracy. The system must deliver the data accurately. Data that have been altered in transmission and left uncorrected are unusable.

3.Timeliness. The system must deliver data in a timely  manner.  Data delivered late are useless. In the case of video and audio, timely delivery means delivering data as they are produced, in the same order that they are produced, and without significant delay. This kind of delivery is called real-time transmission.

4.Jitter. Jitter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets. For example, let us assume that video packets are sent every 30 ms. If some of the packets arrive with 30-ms delay and others with 40-ms delay, an uneven quality in the video is the result.

A data communications system has five components

1.Message. The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video. 

2 Sender. The sender is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, and so on.

3.Receiver. The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on.

4.Transmission medium. The transmission medium is the physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves.

5.Protocol. A protocol is a set of rules that govern data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating, just as a person speaking French cannot be understood by a person who speaks only Japanese.

Data Flow

Communication between two devices can be simplex, half-duplex, or full-duplex as shown in Figure.

Simplex 

In simplex mode, the communication is unidirectional, as on a one- way street. Only one of the two devices on a link can transmit; the other can only receive (Figure a). Keyboards and traditional monitors are examples of simplex devices.

Half-Duplex

In half-duplex mode, each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa (Figure b). Walkie-talkies and CB (citizens band) radios are both half- duplex systems.

Full-Duplex

In full-duplex, both stations can transmit and receive simultaneously (Figure c). One common example of full-duplex communication is the telephone network. When two people are communicating by a telephone line, both can talk and listen at the same time. The full-duplex mode is used when communication in both directions is required all the time.