Understanding the OSI model and its layers

The OSI model is the part of the Open Systems Interconnection project at the International Organisation for Standardisation.

The OSI model characterizes and provides a standard set of protocols for communication functions of a telecommunication or network system regardless to its underlying architecture.

It provides interoperability and helps in easy troubleshooting of the network.
The OSI model is not a protocol, it is a network architecture that is flexible, robust and inter-operable.

It is divided into seven different layers:

  • Physical Layer
  • Data link Layer
  • Network Layer
  • Transport Layer
  • Session Layer
  • Presentation Layer
  • Application Layer

Lets look into each layer one by one,

Layer 7: Application layer

  • The application layer is the layer close to the user, which means both the application layer and the user interact with the software application.
  • It acts as a interface between application and user.
  • Application-layer functions include identifying communication partners, determining resource availability, and synchronising communication.

Layer 6: Presentation layer

  • The presentation layer handles the delivery and formatting of information. this layer presents data for the application or the network.
  • It converts data into the standard format.
  • It performs functions such as encryption, decryption, data compression, data decompression and character encoding.
  • Protocols used are eXternal Data Representation (XDR), Network Data Representation (NDR), X.25 Packet Assembler/Dis-assembler Protocol (PAD), Lightweight Presentation Protocol (LPP), Internet key exchange (IKE)

Layer 5: Session layer

  • Its main function is to manage communication sessions – continuous exchange of information.
  • It provides the mechanism for opening, closing and managing a session between end-user application processes.
  • It creates a session ID for each application and keeps the data separate for each.
  • In case of a connection loss this protocol will try to recover the connection.
  • If a connection is not used for a long duration, then session-layer protocol will close or re-open it.
  • It provides either full duplex or half-duplex operation and provides synchronisation points in the messages exchanged.
  • Protocols used are ADSP, ASP, H.245, ISO-SP, iSNS, L2F, L2TP, NetBIOS, PAP, PPTP, RPC, RTCP, SMPP, SCP, SOCKS, ZIP, SDP, SIP.

Layer 4: Transport layer

  • Transport layer provides functions and procedures for transferring data to the destination.
  • Its the bridge between hardware and software layer. The heart of the OSI layer.
  • The transport layer controls link through flow control, segmentation/de-segmentation, and error control.
  • This layer can keep track of the segments and re-transmit those that fail delivery.
  • The transport layer also provides the acknowledgement signal on successful transmission of data and sends the next data if no errors occurred.
  • It creates segments of the data dividing them into smaller layer.
  • Responsible for process to process delivery.
  • Protocols used are TCP and UDP.

Layer 3: Network Layer

  • The Network layer is responsible for the delivery of individual packets from the source host to destination.
  • It is used to communicate between different network.
  • This layer uses logical addressing (adds IP address in the header).
  • It decides the path in which the information must flow.
  • The main functions are Routing and forwarding data, logical addressing, error detection, sequencing of data and flow control.
  • Data is in the form of packets.
  • Protocols used are RIP, OSPF, BGP, EIGRP, Apple Talk
  • Devices: Router, Firewalls, L3 switch

Layer 2: DataLink Layer

  • This layer is responsible for moving frames from one node to another.
  • It is responsible for communication with the Local Area Network.
  • Data shared is in the form of Frames.
  • Responsibility of this layer are framing, physical addressing, flow control, error control, access control.
  • Physical addressing – also called as MAC addressing or Layer 2 addressing.
  • It is divided into two sublayers : Logical Link Control (LLC) and Media Access Control (MAC).
  • MAC address is a 48 bit hexadecimal address.
  • Protocols used are ARP, RARP, ICMP, IGMP, HDLC, PPP.
  • Devices: NIC, Switch, Bridge.

Layer 1: Physical layer

  • The Physical layer is responsible for movement of individual bits from one hop to another.
  • It coordinates the function required to carry a bit stream over a physical medium.
  • Main functions are modification of data into digital signals, establish and termination of connection, effectively share resources among multiple users.
  • Devices: NIC, HUB, Repeaters and Modem.

Remembering the OSI Model 7 layers – 8 mnemonic tricks:

From Application to Physical:

All People Seem To Need Data Processing
All Pros Search Top Notch Donut Places
A Penguin Said That Nobody Drinks Pepsi
A Priest Saw Two Nuns Doing Pushups

From Physical to Application:

Please Do Not Throw Sausage Pizza Away
Pew! Dead Ninja Turtles Smell Particularly Awful
People Don’t Need To See Paula Abdul
Pete Doesn’t Need To Sell Pickles Anymore

Password-protect your MS-Word document

Microsoft Word utility is a commonly used application and many time you feel the need to Password-protect your MS-Word document . Sometimes, we wish only a selected group of people to have access to the data in our Word documents.

Password-protect your MS-Word documentThe MS-Word in Office 365 gives you several tools to encrypt and Password-protect your MS-Word document . Here is how you can do it:

Step-1: Open the document you want to protect in MS Word.
Step-2: Click on ‘File’ and go to Info, click on ‘Protect Document’ next.
Step-3: Now, click on ‘Encrypt with Password’ option.
Step-4: The ‘Encrypt Document’ window will open next; you’ve to give a password for the document. The password is case-sensitive. After creating the password, click ‘OK’.
Step-5: Type the password again for the confirmation. Click ‘OK’.
Step-6: Save the document again and close it.
Step-7: Open the document again. Now, to access the document, you will have to use the password. Type in password and  click ‘OK’ to open the document.

If you want to remove the password, here are the steps:

Step-1: Click on ‘File’ and then click on ‘Protect Document’.
Step-2: Click on ‘Encrypt with Password’. At the next window, delete the dots that are hiding your password and then click ‘OK’.
Step-3: Save the document again and close it. When you open it the next time, you don’t have to enter the password and you can access it directly.

Note: The password that you use should ideally be complex and yet easy to remember. Because if you happen to forget it, there is no way you can retrieve or reset it, and hence, you will lose access to your own document. So, make sure that the password you give is easy to memorize. You can even write it down somewhere. This will help in case you forget it in the future.

Filter spam and annoying calls on android phones

filter spam and annoying calls

You’re in the middle of something important or just hanging out with friends and a spam call has buzzed on your smartphone.  We’ve all been there and it can be pretty annoying. Google has now come with a feature in its Phone app which will at least warn you about these irritating calls. So here are a few steps that you need to follow to turn on this option on your Android smartphone:

Steps to Filter spam and annoying calls

Step 1: Open the default Phone app on your smartphone
Step 2: Tap on the three dots toggle on the right hand side
Step 3: Click on More
Step 4: You’ll need to click on the Settings option
Step 5: Now, here you will see the Caller ID & Spam option. Turn it off/on depending on the setting active on your phone.

Here it’s important to know that the caller ID and Spam option is by default on. In case it’s off, just turn it on.

There is another option available on the Phone app to filter spam and annoying calls. You need to follow the following steps to do so:

Step 1: Open the Phone app on your phone
Step 2: Go to Recent Calls

Step 3: Select a call from the list you want to mark as Spam

Step 4: After that, tap on the Block/report Spam option

Step 5: The app will ask you to check if you want to block the number

Step 6: If you do get the option, then you can also choose Report call as spam

Step 7: If that option isn’t available, then you can simply choose to block a particular number which is making those irritating calls.


Note: You will need a smartphone that is running Android 6.0 or above.

While the calls might not stop totally, at least they will bother you less.

Story of internet – The Network of Networks

A journey into story of internet

Everyone of us use Internet… But do you know how it originated and transformed to what it is today???

Here you go… Lets have a peek into the Bygone times,

Around 1960’s, the theories related to the internet started. In July 1961, Leonard Kleinrock at MIT published the first paper on packet switching theory. In August 1962, the articles written by J.C.R. Licklider of MIT stated Galactic network concept (the first noted description of interactions through network) – Concept similar to todays internet.

Later in October 1962, Licklider – First head of computer research program at DARPA, convinced his successors at DARPA, Ivan Sutherland, Bob Taylor, and MIT researcher Lawrence G. Roberts, of the importance of this networking concept.

In 1964, Leonard Kleinrock published a book on packet switching theory. Kleinrock convinced Roberts of the theoretical feasibility of communications using packets rather than circuits, which was a major step towards the developement of the computer networking.

In 1965, Roberts connected the TX-2 computer in Mass to the Q-32 in California with a low speed dial-up telephonic line building the first ever wide-area computer network (However small). But using circuit switching!!!.. which was inadequate for the job. Finally he agreed on Leonard Kleinrock on packet switching.

Later Roberts joined DARPA in 1966. In 1967, He suggested the plan of ARPANET and presented paper in a conference where he got some more info regarding the researches going on parallely in other organisations. August 1968, DARPA structured ARPANET and the key component was IMPs (Interface message processors)

In 1969, UCLA (Kleinrock’s laboratory where he developed packet switching theory) was selected as a first node of the ARPANET, therefore the first host computer was connected. One month later, SRI (Stanford Research Institute) became the second node (due to the project on Augmentation of Human Intellect carried out at SRI).

First host to host message was sent from UCLA to SRI.

Later two more nodes were added at the end of 1969, network creation started!

In 1970, initial ARPANET host to host protocal was release by S. Crocker, it was called as Network Control Protocol(NCP). The first international public demonstration of the ARPANET was held at ICCC – International Computer Conference in 1972 (In the same year Email concept was introduced).

The typical ARPANET grew into an internet. It was based on the idea that there would be multiple independent networks connected to other forming the internetworking architeture. For these different networks to communicate an open architecture was required. But the NCP had no ability to address different networking concept, It had a limitation that all the networks had to be build in a similar manner. The assumption was that the ARPANET cannot be changed.

This was a major draw back as it had no error control and any devition from the traditinal ARPANET would not work.

In later stages two organizations, International Organization for Standardization (ISO) and International Telegraph and Telephone Consultative Committee (CCITT) defined similar kind of networking model which supported the open architecture concept, these concepts put together formed the OSI Reference model. A turning point in the story of the internet. Having this as a reference different network can be created independently and could communicate which each other. The internetworking was finally possible.

Meanwhile Kahn from DARPA also devloped a similar model to OSI called te TCP/IP model. This new protocol was more over a communication protocol were as NCP just acted like a device driver.

Initially the internet was used only in defence and TOP 20 organizations.A major motivation for both the ARPANET and the Internet was the resource sharing. However, while file transfer and remote login (Telnet) were very important applications, electronic mail probably had the most significant impact of the innovations from that era.

When desktop computers first appeared, it was thought by some that TCP was too complex to run on a personal computer. David Clark and his research group at MIT explained that a simple implementation of TCP was possible. They demostrated an implementation, first for the Xerox Alto and then for the IBM PC. That implementation confirmed the interoperable with other TCPs and showed that workstations as well as large time-sharing systems could be a part of the Internet.

The development of Local area networks, PCs and workstations in the 1980s allowed the Internet to flourish at a greater extent. Ethernet technology, developed by Bob Metcalfe at Xerox PARC in 1973, is now probably the dominant network technology in the Internet. Having many networks has resulted in a number of new concepts and changes to the underlying network technology. First, it resulted into classification of networks inorder accommodate the range of networks into Class A, Class B and Class C.

Later to make it easy for people to use the network, hosts were assigned names, so that it was not necessary to remember the numeric addresses. Originally, there were a very few limited number of hosts, so it was easy to maintain a single table of all the hosts and their associated names and addresses. But as the network grew into having a large number of independently managed networks, having a single table of hosts was no longer making sense, and the Domain Name System (DNS) was invented by Paul Mockapetris of USC/ISI.

The increase in te size of network also challenged the router capability, to overcome this the hierarchical model of routing was replaced with IGP – Interior Gateway protocol and EGP – Exterior gateway protocol. Thus, by 1986, Internet was well established as a technology supporting the community of researchers and developers and was beginning to be used by other communities for daily computer network communications. Hence stared the cyber era.

Right now 80% of the people in the world use internet.

As the network grew larger many researches are carried on, new protocols and technologies evolve along with the threats as well. Thereby increasing the need for the network security.


Linux basic commands for Beginners-Part 2

Welcome to the next part of linux basic commands.

In case you have missed the previous post, or need a quick review on where we started, here is the link.

Continuing from the last post in Basic linux commands series, I am going to mention the most commonly used commands by a Linux BEGINNER.

linux basic commands

Changing the hostname

#hostnamectl  set-hostname  yourhostname.domain

The hostname can be with or without domain name.

Checking OS details


In systems based on redhat , this command will show you the OS, kernel, vendor details.

Configuring date and time


This command shows you the date and time currently in your OS.


It provides more details on the timezone and the NTP status.

#timedatectl set-time 12:00

the above command will change the time to 12 o clock.

#timedatectl  set-time  2018-07-01 

This changes the date to 7th of july 2018.

Note that the command to change date and time is same. And the syntax for date and time should be strictly followed to avoid the errors.

Kernel details

#uname  -r

Shows the kernel name.

#uname  -a

Shows kernel name, version, architecture and other details.

Current directory name


Prints the current working directory on screen. In other words shows your current location in directory hierarchy.


#shutdown -h 12:00

The system will shutdown at 12’o clock.

#shutdown -h now

The system will shutdown instantly.

Power off and reboot


powers off the OS.


reboots the system.

You may wonder what is the difference between “shutdown and poweroff”, the first one is a systematic process whereas the later powers off the OS without closing any running programs or saving changes.

Other useful Linux basic commands


Shows the name of user logged in that terminal first.


Shows last successful login attempts of all user accounts.


Gives the list of accounts which failed the login.


displays the name of current terminal.

#su username

switches to the user account mentioned in place of “username”.


These linux basic commands are good to start with , if you further want to explore then you can use this site link.

Blue screen errors in windows and how to fix it.

There are multiple types of blue screen or blue screen of death errors in a Microsoft windows based OS. Before fixing it, it is neccessary that you should know the types.

If you get only blue screen without the error codes, probably the problem is with video card or the monitor. Check your video card and monitor in this case.

If you are getting a blue screen and then your computer suddenly reboots without being able to read the text in the blue screen, follow the steps below. when you are unable to get into Windows to perform the steps below, boot the computer into Safe Mode.

If you are unable to boot into Safe Mode, you may have corrupt Windows system files, a defective memory chip or a damaged hard drive. You should run hardware diagnostic tests to determine if the memory or hard drive is causing the blue screen errors.

**right-click on My Computer or Computer, from the start menu or desktop.
**Click the Properties option.
**In the System Properties window, click the Advanced tab.
**On the Advanced tab, go to Startup and Recovery section and click the Settings button.
**In the Startup and Recovery window, uncheck the Automatically restart check box.
**Click OK.

Blue screen errors

Windows NT, 2000, XP, Vista, and later versions of Windows have a blue screen error that is similar to the example shown below. These error messages often contain more detailed information and will contain information that you can search and find. If you’re not getting a blue screen error that looks like the example below, refer the fatal exception error troubleshooting.


blue screen error

Locate the line containing all “capital letters with underscores” instead of spaces, such as the above example, BAD_POOL_HEADER. Write this information down. If you do not see anything written in all caps with underscores like this, skip this step.
Get either the STOP: error message at the top of the error, or in the “Technical Information:” portion of the error. For example, in the above error, it is STOP: 0x00000019, write the first portion of this error message down.
Finally, if technical information is shown, write down the file and the address.

Once you have the above information, you can start troubleshooting the issue.

For information on slow running computers refer this link.

Now apply for the passport from anywhere using app!

In a welcoming step taken by Government of India, now the Indian citizen can “apply for the passport” from anywhere in country. The government of India has added new features in the “mPassportSeva” app and will now allow citizens to apply for fresh passports from the app itself from anywhere in country. Released on July 11 2013, this mobile app and has been recently updated on June 5. On the occasion of the ‘6th Passport Seva Divas’ on June 26, External Affairs Minister Sushma Swaraj announced the new developments.The app is available for free download on both Android and iOS and has been downloaded over 1 million times on Android. Note that the app is released by ‘Consular, Passport and Visa (CPV) Division’ and not by any other government agency. Be sure to download the right app, there are several fake apps floating on Google Playstore.

What are the new services?

apply for the passport
The updated version of the “mPassportSeva” app allows users to apply for the passport along with PCC form filing, online payment for the application form, appointment scheduling/rescheduling or cancellation facilities. Additionally, citizens can apply for a re-issue of a new passport in lieu of an existing passport for any of the following reasons: change in existing personal details, validity expired or due to expire, validity expired more than three years ago, exhaustion of pages, damaged passport and lost passport.

Other services include — issue of Police Clearance Certificate (PCC) along with background verification for Global Entry Program (GEP).

How to use the mPassportSeva app to apply for a passport on your mobile?

Note that there is no separate process to apply for a passport via mPassportSeva app exclusively. The process is exactly similar to the existing system that is being followed by ‘Passport Seva’ website. In other words, there is no change in the application, documentation or verification process of getting the passport and it’s just that the mPassportSeva app is a new way for making the task easier.

The mobile app has a new interface and here is how to apply for a fresh passport from the app:

** open the app, tap on New User Registration.
** Select the Passport Office from the list as per the city of your residence.
** Enter personal details like name, date-of-birth, email id.
** Think about a unique login ID and check for its availability. Add a strong password. (similar to opening an email ID). You can also keep your email ID as a login ID for the app.
** Add a security question and answer. This will help if you forget your password.
** After the confirmation , add the text written inside the small image (Captcha code) and submit.

After that, you can apply for the passport by activating the account. Check for the email sent by the passport office and click on the verification link. On clicking the verification link, it will direct you to a webpage and you will be asked to enter your Login ID for confirmation.
Close the app and relaunch it again. Then go to “Existing User” and enter your Login ID, the password and Captcha code. After that you will be greeted with a screen saying Apply for “Fresh Passport” along with other option. Click on it and fill the form and follow the steps.


For the online passport application click here

PC shortcut keys

PC Shortcut keys provide an easier to navigate through the computer and open launch applications quickly. Shortcut keys are generally accessed by using the Alt key , Command key (on Apple computers), Ctrl key, or Shift key in conmbination with another key. Commonly listing a shortcut is listing the modifier key(alt,shift or ctrl), a plus symbol, and another key. In other words, “Ctrl+S” is telling you to press and hold the Ctrl key, and then press the S key too.

PC shortcut keys
Common PC shortcut keys

Below is a list of some of the most commonly used basic shortcut keys that work with almost every computer and software programs. It is highly advised that all users keep a good note of these shortcut keys or try to memorize them. It will highly increase your productivity.

Tip: Some special characters are also located on the number keys (below the F1 – F12 keys). You can enter these special characters by pressing the Shift key and the number key that has the special character mentioned on it.

Shortcut Keys     Description

Alt+F                File menu options in current program.
Alt+E               Edit options in current program
Alt+Tab          Switch between open programs
F1                    Universal Help in almost every Windows program.
F2                   Rename a selected file
F5                   Refresh the current program window
Ctrl+N          Create a new or blank document in some software programs.
Ctrl+O          Open a file in current software program
Ctrl+A           Select all text.
Ctrl+B          Change selected text to be Bold
Ctrl+I           Change selected text to be in Italics
Ctrl+U          Change selected text to be Underlined
Ctrl+F          Open find window for current document or window.
Ctrl+S          Save current document file.
Ctrl+X         Cut selected item.
Shift+Del    Cut selected item.
Ctrl+C         Copy selected item.
Ctrl+Ins      Copy selected item
Ctrl+V         Paste
Shift+Ins    Paste
Ctrl+Y         Redo last action
Ctrl+Z         Undo last action
Ctrl+K         Insert hyperlink for selected text
Ctrl+P         Print the current page or document.
Home          Goes to beginning of current line.
Ctrl+Home Goes to beginning of document.
End              Goes to end of current line.
Ctrl+End    Goes to end of document.
Shift+Home Highlights from current position to beginning of line.
Shift+End     Highlights from current position to end of line.
Ctrl+Left-arrow   Moves one word to the left at a time.
Ctrl+Right-arrow  Moves one word to the right at a time.
Ctrl+Esc        Opens the START menu
Ctrl+Shift+Esc Opens Windows Task Manager
Alt+F4           Close the currently active program
Alt+Enter      Open the Properties for the selected item (file, folder, shortcut, etc.)


This list of PC shortcut keys will save you a lot of time. For Troubleshooting the PC speed issues visit this link.

Huge discount on laptops for students!!

If you are a student looking for budget friendly purchase yet a laptop with decent configurations, this can be your shot! Paytm mall is offering Huge discount on laptops. This offer has already started drawing attention to a wide group of students.

huge discount on laptops

The offer details

Paytm Mall, the e-commerce wing of Paytm, has started “Campus Lap-Shop” campaign and offering several offers and discounts. Offers under these campaign will be valid till August 10.

As part of the campaign, students can get upto Rs 20,000 cashback on the entire range of laptops.

There are different categories of Laptops – for engineers & coders, Laptops for law and art students, Laptops for architects & designers, and Laptops for business & management students.

Laptops for engineers & coders starts at a price of Rs 34,990. Maximum cashback in this category is Rs 6,500 on HP Pavilion – 15-cc129tx Core i5 (8th Gen) and Lenovo Ideapad 320E (80XL0414IN) Intel Core i5 (7th Gen).

For art and law students category the starting price is Rs 23,990. Dell Inspiron, Lenovo Ideapad 320, Acer Aspire E 15 are some of the laptops offered under this category.

Laptops for architects & designers include HP 15-bs 180tx Notebook Core i5, ASUS VivoBook S15 K510UQ-BQ668T Core i5 (8th Gen), and many others. The Price for this category starts at Rs 39,990.

Business and management students category will be getting huge discount on laptops too at a starting price of Rs 23,990. The maximum cashback of Rs 11,000 is offered on Microsoft Surface Pro.

Shopping vouchers of up to Rs 30,000 across categories that include fashion, movies, smart speakers & printer is also being offered by Paytm Mall. Brands like Allen Solly, Red Tape, Amazon Echo and Microsoft Office will be distributing these vouchers

Also, the online retailer is offering no-cost EMI option on purchase of laptops during this sale. The customers will get an extra 10% cashback doing payment using ICICI Bank credit card. The offer for ICICI Bank customers is valid till July 15, 2018.


Click on this link for more info.

Mobile number portability might not be an option soon for Indian Mobile phone customers

The mobile number portability might raise concerns for the mobile phone users in the coming year.Mobile number portability

NEW DELHI: The mobile phone users planning to change service provider while keeping the old number will have difficulties after March next year.

Mobile number portability (MNP), as it’s called, is functioning properly right now but the two companies which is responsible for the service in India — MNP Interconnection Telecom Solutions and Syniverse Technologies — have written to the Department of Telecommunications (DoT) that the almost-80% reduction in porting charges since January this year has resulted into daily losses and they have to close services once their licence terms come to an end in March 2019, said people with the concern of the matter.

If this happens, customers who want to change their service provider due to billing issues, poor call qualities or irrelevant tariffs will have no option to do so — at least in the near term.


A DoT official said the policy for mobile number portability might change if the issue isn’t settled in time.

Monthly MNP requests have increased tremendously in near past. With the entry of Reliance Jio Infocomm and exits by Reliance Communications, Tata Teleservices, Aircel and Telenor India, the older operators Bharti Airtel, Vodafone India and Idea Cellular are dropping tariff rates to retain or attract customers.

MNP Interconnection(which handles east and south India), has said it will halt its operation and surrender the lincense, while Syniverse Technologies, which handles north and western India, has mentioned its alarming financial problems to DOT due to the Telecom Regulatory Authority of India (Trai) order to reduce charges down to Rs 4 per transaction from a previous charge of Rs 19.

Both the companies has handled more than 370 million porting requests until March this year. They have also moved court against the regulator, on the grounds of arbitrary and non-transparent transactions. The case will be heard next on July 4.
“We have written to DoT that our company will not be able to provide MNP services mainly because the tariff has been revised to as low as Rs 4, which has made the business unsustainable as we’re facing losses on a daily basis and can’t even pay salaries,” said a senior executive at MNP Interconnection Telecom Solutions to ET on the condition of anonymity.