Digitally Stimulated...!

Configuring OSPF

2013-06-06T08:10:00.000-07:00

Dear Students , you go through this video uploaded by me. I have worked on the same file sent by you on 06th June 2013.
I hope it will help.

Provide a feedback...This is my blog ..You may go through it for any further knowledge in networking and other related subjects.

2013-04-26T17:58:00.001-07:00

BSNL Recruitment 2013 – Recruitment for Telecom Technical Assistant Posts:
Bharat Sanchar Nigam Ltd (BSNL) proposes to recruits Telecom Technical Assistants for a number Telecom Circles in its various Secondary Switching Areas (SSAs).
Eligible candidates can apply through the prescribed application format on or before 13-05-2013. For more information about age limit, educational qualification, how to apply, and other details are mentioned below…
BSNLVacancy Details:
Name of Posts: Telecom Technical Assistant (TTA)
Age Limit: Candidates age should be between 18 years and 27 years as on 13-05-2013. Age relaxation will be applicable as per rules.
Educational Qualification: Candidate must possess 3 years Diploma in Engineering in any of the discipline in Telecom/ Electrical/ Electronics and Communications/ IT/ Computer/ Radio/ Instrument/ M.Sc (Electronics) from a recognized University/ Institution.
Application Fee: Candidates need to pay the fee in the form of Bank Draft/ Pay Order for Rs. 500/- in favor of “The Accounts Officer (Cash) O/o GM, BSNL of respective SSA or Original Cash receipt of Rs.500/ – paid at the departmental cash counter of respective SSA Head quarters. Fee exempted for SC/ PH candidates.
Selection Process: The mode of selection is through competitive exam followed by a medical test.
How to Apply: Eligible candidates may apply through prescribed application format, fill that form completely, affix passport size photograph on it, along with self attested copies of all the certificates/ testimonials and other documents, recent photograph and Demand Draft towards Application Fee must be sent in a sealed cover super scribed with “Application for Direct Recruitment to the cadre of Telecom Technical Assistants” along with two self addressed envelope and send to the concerned SSA for which the candidate wishes to apply should reach the office on or before 13-05-2013.
Important Dates:
Last Date for Receipt of Application: 13-05-2013.
Date of Examination: 30-06-2013 from 10.00 am to 01.00 pm
For more details regarding age limit, educational qualification, selection process,Exam format, number of vacancies, how to apply, application form and other details are available in the following link…

Click her for Advt. & Application of West Bengal State----The last date here is 15-05-2013

Click here for Advt & Application of Haryana State

Click here for Advt & Application of Tamilnadu State

Click here for Advt & Application of Kerala State

Click here for Advt & Application of J &K State

Click here for Advt & Application of Andhra Pradesh State

Click here for Advt & Application of Himachal Pradesh State

Click here for Advt & Application form of Rajasthan State

Click here for Advt & Application form of Maharashtra State

Click here for Advt & Application form of Gujarat State

Click here for Advt & Application form of Uttarkhand State

Click here for Advt & Application form of Karnataka State

Note : Please be informed that you may visit www.bsnl.co.in and get into the site of any circle/state through drop-down selector for getting respective advertisement and information for that circle/state.
Visit www.wb.bsnl.co.in for latest updates for West Bengal Circle.
Stay tuned with my blog for model questions......! Any further question? Just leave a comment.....

How Internet works?

2012-06-01T07:55:00.000-07:00

The awesomeness of the Internet can't be captured by any single lecture or a video. There are a lot of hardwares, softwares, protocols, policies, devices, whole lot of human thinking that makes it possible to connect to any part of the world in just fractions of a second.
Here, I present two incredible videos ( taken from Youtube) which attempts to demystify Internet in simple layman's language.That's it !

Animation :TCP vis-a-vas UDP

2012-05-28T09:35:00.001-07:00

TCP is a heavyweight, connection oriented Transport layer protocol.When a file or message send it will get delivered unless connections fails. If connection lost, the server will request the lost part. There is no corruption while there is transfer of message. The message will be in ordered way.Used for bigger segments. Examples of applications using TCP are World Wide Web (Apache TCP port 80), e-mail (SMTP TCP port 25 Postfix MTA), File Transfer Protocol (FTP port 21) and Secure Shell (Open SSH port 22) etc.
UDP is lightweight, connectionless Transport layer protocol.Once we send a data or message, we don't know if it'll get there, it could get lost on the way. There may be corruption on the way to the destination.The received message may or may not in ordered way.Used for smaller segments.Examples of applications using UDP are Domain Name System (DNS UDP port 53), streaming media applications such as IPTV or movies, Voice over IP (VoIP), Trivial File Transfer Protocol (TFTP) and online multiplayer games etc.
Understand the two protocols through the animations below.
That's it !
TCP Connection:

TCP Flow:

UDP Flow:

Animation:The journey of an E-Mail...

2012-05-28T08:43:00.002-07:00

Technology has given us an instant means of sending letters i.e. E-mail. Whereas E-mail is fast but the hand written traditional letters carry much-much affection. I still remember those days when I was in school, watching my parents waiting for a letter from our loved ones. While Email gives you instant gratification, still the real love is carried by the traditional hand written letters with the touch and the fragrance of the real loved ones.Both the ways are great ways of communication.The post offices facilitates the journey of our traditional letters.Have we ever wondered how an E-mail travels through Internet. The protocols that facilitates this are the SMTP(Simple mail transfer protocol) and the POP(Post Office Protocol).
There are loads of literature in Internet describing these protocols. I here present an animated version of the whole explanation, to make the understanding clear.That's it !

Increase Internet speed by 20%...

2012-05-22T20:15:00.000-07:00

Microsoft reserves 20% of the bandwidth for their own purposes like Windows Updates, questioning the PC etc. That 20 % can be retrieved back for your use !

Go to Start and the click Run and type “gpedit.msc” (without the quotes). This leads to the opening of the group policy editor. Then go to -->Local Computer Policy -->Computer Configuration -->Administrative Templates -->Network -->QoS Packet Scheduler -->Limit Reservable Bandwidth.
Double click on Limit Reservable Bandwidth. It will be shown that it is not configured, but you will get the whole truth, if you click ‘Explain’ tab. You will see that by default , the packet scheduler limits the system to 20% of the bandwidth, but this setting can be changed. The trick is to ENABLE reservable bandwidth, and then set it to ZERO. Thus, nothing will be reserved and you can use the whole bandwidth for Internet. Watch the video below for further clarity. Enjoy the extra speed ....That's it !

Understand ARP through animation

2012-05-20T20:27:00.000-07:00

All interfaces in the network are identified by an IP address. The IP header encapsulated at the Network layer carries the ultimate source and destination IP addresses. However, for actual transmission, these IP datagrams are encapsulated in Data Link layer frames. The header in this layer carries the hardware addresses of the immediate source and destination.
(For clear understanding refer to my earlier blog on TCP-IP data and data flow). The protocol that creates the association between Hardware addresses and IP address is called Address Resolution Protocol (ARP). The protocol provides answer for a single question for an interface: I know the destination’s IP address, what is its hardware (MAC) address? There are a lot of literatures in the Internet to explain ARP. I just provide here small animation for a better idea. The animation provides a clear reason, about why IP address is preferred over MAC address, to deliver packet over internet. I believe the animation will help to understand the basic concept of ARP. That’s it!

TCP-IP and the DATA Flow....

2012-05-16T08:59:00.001-07:00

In this post, I am not going to discuss in details about how a packet flow through network using TCP-IP layered protocol. My aim here is to share what I understand as to how TCP-IP protocol stack modifies a data and helps it to reach final destination. Please do comment and share, if my knowledge needs modification anywhere. Read on…..

As in my some earlier blog, I have already told that each layer of TCPIP protocol suite does some exercise on the data packet to make it actually deliverable over the network. Let us try to understand this by one simple example. Please refer to the flash play below for the example.

Let say, the green Computer (of the network at the left) with IP address 162.103.1.103 is the source, which wishes to send a data to the yellow Computer with IP address 175.95.1.52 (of the network at the right) which is the destination over a Ethernet network, consisting of switches and routers. Let us now examine what layers are involved and what activities are involved at each node, from source to destination.

Source PC with IP address 162.103.1.103 :

Application layer: This layer will form the data intended to be actually read by the destination PC and this layer also defines the application and format the data accordingly. For example, if the sender PC uses a web-browser to communicate with PC at the destination, then it will use the application layer protocol “HTTP” (Hyper text transfer protocol), if it intends to send mail, it will use protocol “SMTP” (Simple mail transfer protocol). There are lot of protocols here, but to keep it simple, let us under stand that this layer in the source PC will define application, the data format and the actual data, intended to be read only by the destination PC.

DATA

Transport Layer: This layer helps to identify the application for which the data belongs and hence provides end to end data transfer. The identifier of the application is known as the “Port Number”, which is of 16 bits. For example when you are browsing web, the destination port number will be 80. There are specific port numbers for specific standard application. For a newbie, it suffices to understand that port numbers help to identify and differentiate among different processes in one computer. Essentially, this layer adds one header to the original data; which carry certain information needed to deliver correctly to the right application properly. This header is one of the two type’s viz. TCP (Transmission Control Protocol) or UDP (User Datagram protocol). The application decides on the type of Transport layer header.

TCP or UDP

DATA

---> Known as the Segment

Each of the type of header has the most important entries of source and destination port numbers each of 16 bits along with some other information. Just have a look at the TCP and UDP headers, to understand the difference.

TCP header has got certain extra information like Sequence number and acknowledgement number, which guarantees the receipt of the data by the recipient application, whereas UDP header has no such field. Thus, TCP provides end to end reliable data connection and therefore called connection oriented protocol. UDP does not provide such reliability, but as the header is small, and there is no wastage of time in receiving acknowledgement and sending subsequent data, the delivery is faster. Therefore, it can be interpreted that applications like e-mail, File transfer protocol which need reliability uses TCP header and applications requiring faster delivery and can do without reliability like VoIP(Voice over Internet Protocol), DNS query(converting domain names to IP address) uses UDP.

Internet/Network Layer: Whereas Transport layer helps to identify the process or application, Network layer helps to identify the source and destination PC over the network. This layer again adds one header to the segment carrying certain more information, to make data find its route to the destination computer. The mostly used routed protocol here is the IP header. (IPversion4 in particular; work and implementation is going on for IPversion6)

IPv4 Header

TCP or UDP

DATA

Known as the Datagram.

Whatever is the case, this header gives identification to the computers involved and some other information, helping it’s to find its path to the destination in this wide network.Just have a look at the IPv4 header. It is of minimum 40 bytes and 60 bytes in size.

The most important fields in the IP header are the Source IP address and the Destination IP address. In our example those fields will be 162.103.1.103(the source IP) and 175.95.1.52(the destination IP).

Network Interface Layer: This layer encompasses the Data link and Physical layers of OSI model. This layer is a liaison between the software layers above and the media below. In our example of Ethernet link, this layer adds one header and one trailer.

Preamble

Start Frame Delimiter

Destination MAC

Source MAC

Type

IPv4 Header

TCP or UDP

DATA

Frame Check Sequence

7 bytes 1 byte 6 bytes 6 bytes 2byte <-------Payload-------------> 2bytes ---

<-----------------------------Known as Frame-------------------------------------------------------->

The most important information being carried over here are the hardware addresses, i.e. the MAC(media access control) addresses. Here these MAC addresses will be point to point. In our example the Source MAC address will be of the source computer and the destination MAC address will be of the Router, which it gets from its ARP (Address resolution protocol) table, which maps IP address to MAC address. Finally all this information after being converted to electrical signal will be received by the router-A via the switch.
Router-A : -

Let us see what happens at Router-A after the receipt of the frame. Router-A will tear the Frame and look into the IP header. Then it will look at the destination IP address and then looks into its routing table. The routing table consists of Next HOP router address for a Destination IP address, so basically it answers a question of the IP packet---For a given destination IP address, where should the packet be forwarded next? In the real scenario the router-A may be connected to many routers. Routing tables are built either manually or dynamically using certain routing protocols. In our example, the router –A decides to forward the packet next to Router-C. So, Network layer at Router-A decides the next hop, recalculates IP header likewise, with same source and destination address. The Network Interface layer at Router-A then re-frames the packet with Source MAC address of router-A and destination MAC address of router-C. It is then sent to router-C.

Router-C:

Router C will again strip off the frame header and trailer and looks into the IP header; decides the next hop router, which is router-F. Reframe the packet likewise and the packet reaches router-F.

Router-F: Router-F will strip off frame header and trailer, to find that the destination IP address lies in its network only. So, it will frame the packet with source MAC address of itself and destination MAC of the destination computer (67:E6:32:77:FA:CC) and finally the frame will reach the destination computer.

Destination Computer with IP address175.95.1.52 : -

The destination computer will strip off frame header and trailer and look into the IP header. Eureka! It discovers that the packet is meant for it only. It now has the explicit right to strip off the Network/IP header and look further into Transport layer header and see into the port address, to identify the application for which the data is meant for ( Different web-pages in a same computer are also differentiated by port numbers). Finally the transport layer header (TCP or UDP) is stripped off and the data is sent to the relevant application for final processing.

From this explanation, I hope it is clear that the information in lower two layers of TCP/IP model i.e. the Network Interface and Network/Internet layers are meant for all the devices along the path. Therefore they are known as the point to point layers. The information in the upper two layers of TCPIP model viz. the Transport layer and the Application layer, are meant only for the final host. The intermediate devices, has nothing to do with the information carried on these layers, and therefore they are known as host to host layers. That’s it !

The Cloud Storage Options..G-Drive and others

2012-05-13T10:53:00.003-07:00

The much awaited cloud based storage of the Google-team, the Google-drive has been launched on 24th April,2012, for which many were eagerly waiting.

The service is offering 5GB of on-line storage space for documents,videos,photos,PDFs and other files. The great thing is that the Google Docs utility is in-built with it. With Google Docs you can maintain on-line word docs, spreadsheets, Presentations, edit them from anywhere or download them in the format in which you want. With Google-drive , one can share any file with anybody and work with others in real time. Anybody can make changes in the shared file and work upon a single project.
It's very useful for a group of people working on the same project, separated geographically. If you want beyond 5 GB storage, you have to go for paid services. For further details of this wonderful Cloud storage of the wonder internet company Google, just check it at www.drive.google.com or login to your G-mail account / go to Google and click on Documents or Drive. G-Drive is available for PC,Mac,Android,i-phone and i-pad.

And one more thing; if you want much more cloud storage without much fanfare of Google , you may try www.cx.com, which offers 10 GB of free storage. The other options are Dropbox and Skydrive. Dropbox offer free storage of 2GB, but can be easily increased to 16 GB, by referring to some friends.Skydrive offers 7 GB free storage and you can access files and folders of all your other PC’s right from within your browser. You just need to have SkyDrive on these machines and you can then easily access any of their files from any other computer, anywhere simply using your Windows Live ID.

SkyDrive is an absolute must-have service for Microsoft Office users because it gives you the ability to edit documents in the web browser while preserving all the formatting.

My point is that, these on-line cloud storages are very important in this age of highly mobile life.You have the freedom of accessing them anywhere and also no fear of Hard-disk crash. You can at-least save the scanned copies of your important certificates and documents in the cloud. That's it !

Make your Windows PC faster......

2012-05-09T12:43:00.000-07:00

We all are sometimes tired of the sluggish performance of our Windows PC. Our own PC becomes a a necessary evil.Do not worry, there are lot of ways to tune your PC,for delivering best performance.
Here I present some ways to make PC start and run faster.

The obvious ways:

1) Disk Cleanup : This utility is inbuilt in your system

Go to Start>>All Programs>>Accessories>>System Tools >>Disk Cleanup

Run this to free up extra space.

2) Disk Defragmenter: After repetitive usage, files are staggered in various sectors of the Hard disk, which make the job of CPU difficult and hence time consuming to access those files. Disk defragmenter utility rearranges files in contiguous storage locations.

Go to Start>>All Programs>>Accessories>>System Tools >>Disk Defragmenter.

Run this for faster access.

3) Slow startup problem : - This is a common problem when a computer takes too much time to boot up (possibly after switching on your PC, you can watch a part of a movie between two commercials). This is simply because your PC has been directed to startup with a lot of applications. Want to get rid of this problem?

Go to Start>> Run>> type “msconfig” in the box that appears>> Click “Startup”>> uncheck the applications that are unwanted during startup, the click ‘Apply” and then “OK”. You will be prompted for a restart. Do that and see the magic….When I say unwanted startup applications, it means applications like “Yahoo-Messenger”, “PCsuite” etc which are unwanted in your system tray and which may be opened from Start>>All programs, if required. The catch here is to keep only the system files and uncheck the others (i.e. those which you can identify as a layman).

4) Loading of “Start” menu is slow : Go to Start>>Run>>type “regedit” in the box>>Go to HKEY_CURRENT_USER>>Control Panel>>Desktop. Look for Menu Show Delay, and double click to edit the value. Default value may be 400. The lower the number specified, the faster the Start Menu will load. Change it to 0. Click OK.

5) Slow loading of “My Computer” Window

Now this is one common problem, where once you double click “My computer”, it takes too much time to load, as somebody is searching something with a torch.

To get rid of this problem

Go to Tools >> Folder Options >> View and uncheck ‘Automatically search for network folders and printers”

Not so obvious but powerful ways:

6) Defraggler

It is an alternative to Windows Defragmenter and much better. Defraggler is free, works wonderfully and can speed up defragmentation manifold. I always choose to use defraggler, instead of Windows Defragmenter. So, have Defraggler.

7) CCleaner

It does what it says. This is basically the best single lightweight utility to speed-up your computer. It is an all in one application which can delete unnecessary file (job of disk cleanup), uninstall programs at your command (job of add remove programs of windows), remove unwanted registry entries; clean up cookies and cleanup temporary files from other applications. This is a small piece of application, which I run once a week, to keep my PC faster, clearer and hence stronger. So,have Ccleaner. जैसा नाम वैसा काम।

8) Revo Uninstaller

It sometimes happen that you are unable to install certain programs through add remove utility. This can be done by Revo Uninstaller. Personally,I use Revo uninstaller (the freeware only) for uninstalling any program, because there is no leftovers of that program after uninstall(which is there in case of traditional add remove utility)

Revo Uninstaller runs the selected program's built-in uninstaller, but after the uninstall has completed, it will search and remove files or registry entries that the uninstaller may have left on the user's hard drive.

Revo Uninstaller also cleans out:

§ Files in the temporary folder

§ Entries in the Windows start-up applications folder

§ Browser history and cache of Internet Explorer, Firefox, Opera andNetscape

§ The recently opened file list in Microsoft Office applications

So, get Revo Uninstaller

Now, some advices to keep PC clean & fast…..

a) Junk & unnecessary registry entries should be removed periodically. Ccleaner can be used for this purpose,

b) One should not keep installing softwares. Install a program if it has got real purpose for you.

c) System tray should be kept free as far as possible. This reduces startup time.

d) Get a genuine anti-virus program. Not the free ones, but the paid ones. It will surely secure your PC from attacks. My choices are Quick Heal and Kaspersky.
e) Before opening any application, let the computer boots up completely. Do not be in a hurry.
f)Do not set wallpaper, which is of large file size. It is better to do without wallpaper if RAM size is low.
g) Make it a habit to empty recycle bin regularly, as the files remain in your Hard-disk till you empty recycle bin.
h) Do not overcrowd your desktop with lot of files, shortcuts etc. Each shortcut on the desktop uses up to 500bytes of RAM.
i) Disable the tray icon option, while installing softwares, as they uses RAM and also slow down booting up of the computer.
j) Keep your computer dust-free as dust jam and slow down the cooling fan, leading to heating of CPU and thus affecting CPU speed. Compresses air should be used to blow out any dust from the CPU and do not use Vacuum cleaner. The main point here is to keep the RAM area uncluttered.

Remember to enjoy and learn with you PC to the fullest. Do it safely and surely. That’s it !

Hubs, Switches & Routers..the basic differences

2012-05-09T08:47:00.002-07:00

In Networking, Hubs ,switches and routers are the very basic and important devices.I have tabulated the basic differences among them, without going into much details.

SL. No.	Parameter	HUBS	SWITCHES	ROUTERS
1	Operates in OSI layer	Physical	Data Link	Network
2	Work based on address	Nothing(Does not care about address)	48 bits MAC address/Hardware address (Address embedded in NIC card of our computers)	IP address
3	Operation	Broadcast frames to all the computers connected to its ports.	Initially it has no knowledge of the identities (MAC addresses) of the computers connected. So, for the first few transactions of packets, it will broadcast to learn which PC is connected in which port, to fill a table called MAC table. Afterwards, it unicast frames to the correct PC, by referring to the table	The most intelligent one of all. It maintains routing table which contains the next hop router IP address for a given destination network IP address. So, in a very layman’s way we can say that it reads the IP header and answers a question “ For the given destination IP address on the IP header of the packet, what should be the next hop router”. Routing tables are built using routing protocols like RIP,OSPF, BGP etc. as per the situation.

For a clearer understanding of the above concepts, there are following animations.....In case of any confusion, Please do comment..That's it !

“How to type the language you speak”

2012-05-05T12:53:00.000-07:00

Can you type in English? If your answer is yes, you can type in the script of Hindi (Devanagari), Bengali or any Indian language. I will explain in easy steps and show certain snapshots of my computer screen for better and clear understanding.

Step-1

1. Go to Start-> Control Panel> Regional & Language Options>Click on Languages Tab

Tick the Check box to Install files for complex scripts...and click OK.

2. Click OK

3. You will be required to place the Windows XP CD in the CD drive or give I386 folder path to enable Indic languages including Hindi

Now you will need to Reboot the System.

Step 2

Go to Start-> Control Panel> Regional & Language Options>Click on Languages Tab > Click on Details > Click on Advanced

Tick the Check box “Extend support of advanced text services to all programs”

Go to Start-> Control Panel> Regional & Language Options>Click on Languages Tab > Click on Details and Add Devnagari –INSCRIPT keyboard layout

Step 3

Go to website http://www.msn.co.in/ilit

Click on Hindi >> Install Desktop version >> Install Now
Hindi.exe file will be downloaded
Double click Hindi.exe Setup. Once the installation process is complete, Microsoft Indic Language Input Tool has been successfully installed will be displayed.

This is the website preview.

This is the preview of the Hindi.exe file, which you need to run.
I have also Bengali.exe downloaded here.

Now, you can open any application like Microsoft Word and choose any language from the from the system tray. You can toggle between the languages as you type. As you type you will get drop-downs for the choice of spellings. Just go through the snapshots below and nothing will remain unclear..I have typed in Bengali also..my mother tongue.

Here I open a MS word file and chose Hindi from system tray.

Here I chose Microsoft Indic Language tool.

Here I start typing.... You just type the phonetic of the word you need to type. Just like "aap" for "आप".
See the drop down list appearing to help in selecting the correct spelling.

See how easy it is....

By following the same method for other language you can type in any Indian language. Just as ,I have typed in Bengali..
Any problem?..Leave a comment.
That's it !

OSI & TCP-IP, Part-2

2012-05-04T00:08:00.000-07:00

The OSI & the TCPIP
    First of all we must understand that internet works with packet switching technology, where the information is broken down into packets. Each packet will then trace any path to the destination. Along the path from the source to the destination, it will come across many nodes. The nodes may be any network device but it must understand the language of the layered structured model (TCPIP in the case of internet).
    At every node, each layer of the protocol suite will do some exercise on the packet, as per the requirement. I mean to say that, the layers will impose some rules on the packet, to make it actually deliverable over the network.
  As OSI is the most logical standard, it will be discussed first and then it will be seen how 4 layers TCP-IP fits into this 7 layers OSI model. OSI or TCPIP is not a single protocol but a collection of many protocols at different layers. They have been developed over years and still improving as per the need of the modern networking community.
We should be kept informed that all the developments in internet have been contributed by users only and the good thing is that anybody can do that! ( thanks to IETF )
The OSI model has got 7-layers as depicted below. The counting is from the lowest layer. So Physical layer is 1st layer, Data-link is 2nd, Network is the 3rd and so-on. We shall try to understand one by one.

The Application(7th) Layer :- Whenever we want to communicate over internet, we first open web-browser, instant messenger etc. All the softwares that help to build these come under Application layer. So we can say that this layer provides human interface to the network. As an analogy with the postal network, we can say that the plain paper over which we write, falls under the Application layer.

The popular protocols in this layer are 1) Hypertext transfer protocol or HTTP, due to which we are able to view webpage. 2) Domain Name Service or DNS is the way by which Internet domain names are located and translated into Internet Protocol addresses.

The Presentation (6th) layer: - This layer ensures readability of the data at both ends.

The main functions are: -

a) Data/File formatting (ASCII, EBCDIC)

b) Translation of data into formats understood by the local machine to maintain cross platform compatibility.

c) Encryption, to keep sensitive data (like password) secure or scramble data into a format that can be understood by receiving machine only. There is usage of certain algorithm for this.

d) Compression of data like audio, video and picture into their respective formats like .mpeg, .avi, .jpeg etc.

As an analogy, the language that you write on the letter comes under this layer. You have to write the language that the receiver understands, so the language ensures readability at both ends.

The Session Layer (5^th) Layer: - This layer maintains session/communication links between end machines. It establishes, manages & terminates the connections between the local & remote applications. As an analogy whenever you lift telephone to talk to somebody, you first of all say “Hello”, this indicates the beginning of a session and when you say “Ok Bye”, which indicates the end of the conversation session. This session layer does similar type of job. As you know more about the working of Internet, you shall understand that the actual session aspects of these protocols are not used. Actually session layer protocols are rarely used and their duties now fall on the application layer. With that being said, there are other services of session layer which are of much use. These services are: -

1) Authentication 2) Permissions 3) Organization of Data flow

To be very true, with the advent of multimedia services in Internet like Video, Live Tv, Web-conferencing, online video game, the protocols in this layer are very important now a days. Certain protocols in this layer are RTCP (Real-time transport control protocol), SQL, RADIUS, KERBEROS etc.

The Transport (4^th ) Layer: - This layer guarantees end to end data transfer between the correct processes in the two communicating devices. It takes care of reliability through acknowledgement mechanism and flow control through Sliding window mechanism. This layer defines one of the most important address of the network, the 16 bits “Port address”. The port address represents the address of the process in a computer. For example your computer may be running different applications (or different webpages, instant messenger etc are open), then those will have different port addresses. Important two protocols in this layer are TCP or Transmission Control Protocol & UDP or User Datagram Protocol. TCP has got acknowledgement mechanism in-built, and therefore the connection oriented whereas in UDP, there is no acknowledgement mechanism and therefore connectionless. I will describe the details in my other blogs.

Network (3^rd ) Layer: - This layer is responsible for routing the packet systematically from source to the destination, along the correct path. Here another important address of the network is defined, the IP address ( 32 bits in IPv4 and 128 bits in IPv6). IP address is the identity of the computer or the device in the internet ( port address is the process. One important network device called “Router” exists here. The main protocol here is the IP(Internet Protocol) and there are certain auxiliary protocols having specific functions like ICMP, IGMP,ARP,RARP.....

The post offices correspond to routers and the postal address with PIN code to the IP address, in our analogy for postal network.

Data Link (2^nd) Layer : - The job of this layer to make the packet actually deliverable over the network. It is just like the postal stamp in our postal network, without which, the letter will not move. We must understand that the packet may go through different types of media (may be Cu wire, OFC, microwave, satellite, radio waves etc) along the path to the destination and hence the requirements or the protocols are also different. Data link layer protocols govern how to format the packet into frame for different media. This layer tries to ensure reliable transfer of frames over point to point link through flow control and error control. This layer acts as a connecting layer between the software processes of the layers above it and the physical layer below it. It releases the upper layers from the responsibility of putting data into the network & recovering data from the network. The important protocol in this layer is the Ethernet. This layer again defines hardware address or 48 bits MAC address (if it is Ethernet), which identify the machine over point to point link.

Physical (1^st) Layer: -This layer is responsible for transmitting raw bit stream over physical medium. So when you say physical medium, it can be a copper wire, where bits are sent as voltages, it can be wireless link through which bits are sent using some kind of frequency modulation and so on. It can also be some kind of encoding like differential Manchester for example in Ethernet protocol, before actually sending data over physical link.

Comparison of TCP/IP and OSI :- TCP/IP does not conflict much with the OSI standards because the two protocol stacks were developed concurrently. In some ways, TCP/IP contributed to OSI, and vice-versa.

The main differences between the OSI architecture and that of TCP/IP relate to the layers above the transport layer (layer 4).OSI has both, the session layer and the presentation layer, whereas TCP/IP combines both into an application layer. The other things remain same.

Remember TCP/IP is not a single protocol, but a collection of many protocols at every layer, and therefore its is called TCP/IP protocol suite. The name TCP/IP was coined after the most important protocols in this suite the “Transmission Control Protocol” and the “Internet Protocol”.

A point to note: - The upper layers from Application, Presentation, Session and the Transport are host to host layers. The information in these layers is meant for the end processes only and the intermediate nodes have nothing to do with them. The lower layers Network, Data-Link and physical are point to point layers. The information in these layers are for actual point to point delivery and finally to the destination. As an analogy with our postal network, the actual letter-pad, the content are meant for the final receiver only and the post-offices, stamp, the post-man are for point to point delivery. This whole matter can be understood by understanding the actual routing of packet through internet. For this my blog on Routing may be referred. Till then, have a visual understanding of the layers through the animation below. For any query, you may always drop in a comment. That’s it !

OSI & TCP-IP, Part-1

2012-05-03T23:27:00.003-07:00

I have already mentioned that TCP-IP is the protocol based on which Internet works. TCP-IP is not a single protocol, but a collection of many standard protocols, and therefore called TCP-IP protocol suite. The term TCP-IP was coined from the most important protocols in the suite the “Transmission Control Protocol” & the “Internet protocol”. It was developed (and still developing) and implemented in the late 1970’s. OSI or Open system Interconnection was proposed in 1978 by ISO (International Standard Organization, which is a 7-layered reference model. Now, let me try to explain the similarities and differences between the two, which can be summarized in following points:-

1) TCP-IP was born first (in late1970’s) and then the OSI (in1978).

2) Both the protocols explain about how two computers or networks should communicate in a logical way.

3) Both the protocol has got layered structure. OSI has 7 layers and TCP-IP has 4.

4) Though OSI is a more logical way of carrying out the layering, TCP-IP is the accepted protocol for the working of Internet. Actually, the point is that when OSI was proposed in 1978, Internet was already working fine with TCP-IP, and it became baseless to disturb the already functional and useful application i.e. Internet.

As OSI has a very sound logical base as far as layering is concerned, today any protocol developed in communication, is compared with OSI for a better understanding, like CCS7, TCP-IP, and many more. Just have a look at the layers…..I will explain them in my next blog.

Layering? :-

Having said that, let us see what is layering and why this is being done. Layering is done simplify the understandability and implementation of the whole complex job of communication between computer networks. The idea is to clearly demarcate the types of jobs need to be done to achieve the ultimate goal of transferring the data among two or more Computers. A change in one layer is not going to affect the other layers. This is just like running an organization or a college, where the jobs of the Dean and the security guard are different .One’s way of doing the job is not going to affect that of the other, but for the ultimate job of running the organization, both are needed.

So, when a software geek is developing applications in Apple IOS, Anroid or Java he is not going to worry about how these will reach to others at the very physical level. The data may take any path like Fibres, plain Cu wires or radio frequencies. The engineers working in these physical paths need not to worry about the applications being developed. Any question?..Just drop a commentThat’s it!

The Internet & The TCP-IP

2012-04-30T11:43:00.000-07:00

I have been and will always be overwhelmed by the way this huge infrastructure called “Internet” works. Formally the definition of Internet is “The network formed by the cooperative interconnection of a large number of computer networks”. Please mind the words “cooperative interconnection”, from which you can draw at least three inferences:

1) That the two computers (or networks) first agree upon the fact that they wish to share data.

2) That the language (technically called the protocol) that the two computers (or networks) use to talk is same.

3) And that you cannot identify a single owner of the Internet.

The works in computer networks started in the late 1960s. The purpose was to connect certain computers so as to achieve certain goals and that’s too in the laboratories and research institutions. This gave rise to different islands of networks using different types of protocols (or you may call them rules) to let their computers communicate among themselves. This led to networks which were proprietary in nature and there was cross platform incompatibility. I mean to say that, an IBM (or DEC) computer can communicate with an IBM (or DEC) computer only. As, necessity (but you need to be crazy also) is the mother of all inventions, it was required to interconnect different types of networks to share more information and knowledge.

This requirement needs to have a globally single protocol and thus TCP-IP was born. Work on TCPIP began in the 1970s, by ARPA (Advanced Research Project Agency) and funded by US Military and thus the first network which used TCP-IP was called ARPANET. Gradually the use of TCP-IP as a protocol in networks increased and it became the de-facto protocol (the standard) of the whole internet we use today. So, simply you can say that all the computers around the world speak the language of TCP-IP and if a computer does not understand TCP-IP it cannot communicate over Internet. That’s it!