Computer Networks - An Overview : An E-Book for your Viva Season

       

         With the semester exams arriving almost 15 days prior to normal schedule, we believe all Engineers are facing time shortage for covering your syllabus. Today, we bring to you an all new E-Book Guide which gives you a Complete Overview of Computer Networks. This book covers all basic information required for understanding the crux of the subject. The contents of the book are lucid and thus would help any lame engineer to grasp the concepts easily. Computer Networks being a very interesting subject is also a scoring subject. TE - IT(sem 1) and TE - Comp(sem 2) introduces Computer Networks into the curriculum  for Pune  University. The subject includes 100 theory paper, 50 marks oral and 25/50 marks internal.

 The book covers all the contents required for you to clear your viva and revise all the important concepts of the subject.

Computer Networks - An Overview

Author : Manoj Pisharody

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The book covers

• A short introduction
• The Physical Layer
• Data Link Layer
• Medium Access Control Sublayer
• The Network Layer
• The Transport Layer
• The Application Layer.

        With the contents well organized, the size of the complete PDF is 131 pages. Easy to learn and easy to grasp, we wish all Engineers best of luck especially for Computer Networks and your Viva season.

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Learn about POP3 and IMAP Protocols : Computer Networks

Article contributed by :

ManojPisharody (BE – IT)

manoj.pisharody99@gmail.com

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The pre-requisite to understand these two protocols is to know what an E-mail is and how it works. So, we would first take a short tour of E-mail.

Electronic Mail or e-mail, as it is often called, is one of the best forms of communication. Several innovations and researches to the field of Computer Networks have brought about many modifications to the traditional e-mail and today E-mail has become the fastest and most efficient way to communicate.

Working of E-mail

An e-mail system supports five basic functions:

Composition (generation of email),
Transfer (sending of email from sender to receiver), 
Reporting (delivery status of the mail at the receiver’s end), 
Displaying (the mail in the receiver’s mailbox) and
Disposition (what does the receiver does with the mail).

But for now, let us make the long story short, and just discuss about the message transfer phase.

To transfer an email from the source machine (say, A) to destination machine (say, B); the source machine establishes a TCP connection to port 25 of the destination machine. The actual transfer is done by a protocol named SMTP (Simple Mail Transfer Protocol). 

This protocol accepts incoming connections and copies them in to the destination machine with the help of a message transfer agent. If the message cannot be delivered, an error report is sent to the source machine.

Final delivery protocols (POP3 & IMAP)

Now that we have seen the basic idea of how a mail is transferred, now it is the optimal time to learn about the delivery protocols.

As we have seen, sending an email needs the source machine to establish a TCP connection with the destination machine. But suppose A wants to send an email to B, but B is offline. In this case, A cannot establish a TCP connection with B and thus, The SMTP protocol fails.

One solution to this problem is to have a message transfer agent residing on an ISP (Internet Service Provider) between the source and destination machines. This agent can remain online 24x7, and thus the source machine can establish a TCP connection with this agent anytime.

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POP3 (Post Office Protocol Version 3)

Now, the problem establishing TCP connection is solved. But, does it solve all the problems in delivering the mail? Certainly not. The problem now arising is how to connect the destination machine to the ISP (on which the message transfer agent resides). Note that this ISP is online throughout, but the destination machine is not. So, there must be a protocol to connect the mail transfer agent’s ISP to the destination machine. This is what POP (Post Office Protocol) is all about. This protocol deals with delivering the mail to the destination. But how? Let’s see.

First, the source establishes a TCP connection with the mail transfer agent’s ISP. The agent copies the mail to the ISP’s mailbox. Now, the role of the source machine is over. Delivering the mail to destination is up to the message transfer agent’s ISP.  Whenever the destination machine comes online, it establishes a TCP connection with the mail transfer agent at port 110. Then the message transfer agent gives the control to the POP3 server and this server completely copies the message to the mailbox of the destination machine. Once this is done, the message is deleted from the message transfer agent’s ISP.

IMAP (Internet Message Access Protocol)

The above protocol works well if there is a single user in the receiver’s ISP. But that must not be the case all the time. Quite often, in big companies or organizations, a single ISP is shared by many users. The mail sent by a source might be important for all the users sharing the ISP. So, in this case, definitely POP3 won’t work. To solve this problem, another protocol named IMAP (Internet Message Access Protocol) is used. Here, whenever a user in the destination ISP comes online, the user establishes a TCP connection to port 110 of the message transfer agent’s ISP.

  The agent approaches the IMAP server which now displays the whole message to the user. The user can either delete after reading, delete before reading, fully or partially download file(s) (if the message contains any files), and so on. Whatever the user does with the message is not the concern of the message transfer agent’s ISP. The agent does not delete the message from its ISP mailbox. So that, if a new user sharing the same destination ISP logs in, the message is displayed to that user too, after the TCP connection is established.

P.T.O.

Key Differences

The key difference between both the protocols is the role of the message transfer agent and the corresponding protocol server. In POP3, the agent deletes the message (file) from its mailbox after the user PC downloads the file. In the contrary, in IMAP, the agent does not delete the message after displaying it to the user.

Another difference is that, in POP3, the only option left with the destination PC is to completely download the file to its PC. But, IMAP provides additional features- the destination user PC can partially/fully download the file, delete before/after reading the message, without loss of data as the message will always remain in the agent’s ISP mailbox.

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Article contributed by :

ManojPisharody (BE – IT)
manoj.pisharody99@gmail.com

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Advance Computer Networks : [BE-IT] Elective

Advance Computer Networks

Unit I Introduction

Requirements , Network architecture , Networking principles, Network services and Layered architecture , Network services and Layered architecture , Future networks ( Internet , ATM , Cable TV, Wireless – Bluetooth, Wi-Fi, WiMax, Cell phone )

Unit II Advanced Technologies

Virtual circuits, Fixed size packets, Small size packets, Integrated service, History, Challenges, ATM Network protocols, IP over ATM, Wireless networks : Wireless communication basics, architecture, mobility management, wireless network protocols. Ad-hoc networks Basic concepts, routing; Bluetooth

(802.15.1), Wi-Fi (802.11), WiMAX (802.16), Optical Network : links, WDM system, Optical LANs, Optical paths and networks.

Unit III Performance of Networks

Control of networks: objectives and methods of control, Circuit switched networks, Datagram and ATM networks. Mathematical background for control of networks like Circuit switched networks, Datagram and ATM networks

Unit IV Advanced Routing - I

Routing architecture , Routing between peers ( BGP) , IP switching and Multi- Protocol Label Switching (MPLS), MPLS Architecture and related protocols , Traffic Engineering (TE) and TE with MPLS , NAT and Virtual Private Networks (L2, L3, and Hybrid), CIDR –Introduction , CIDR addressing, CIDR

address blocks and Bit masks

Unit V Advanced Routing - II

Mobile IP- characteristics, Mobile IP operation, Security related issues. Mobility in networks. Voice and Video over IP (RTP, RSVP, QoS) IPv6: Why IPv6, basic protocol, extensions and options, support for QoS, security, etc., neighbor discovery, auto-configuration, routing. Changes to other protocols. Application

Programming Interface for IPv6.

Unit VI Ad Hoc Networking

An Introduction, A DoD Perspective on Mobile Ad Hoc Networks, DSDV: Routing over a Multihop Wireless Network of Mobile Computers, Cluster-Based Networks, DSR: The Dynamic Source Routing Protocol for Multihop Wireless Ad Hoc Networks

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Computer Networks: A Systems Approach

Larry L. Peterson, Bruce S

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Internetworking with TCP/IP

Douglas E. Comer

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IPV4 and IPV6 : A short Explanation with Animation

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Before we start, let us clear the most essential term for this article : IP

IP- stands for Internet Protocol. It is only because of IP, that we are now able to connect with each other on a network. Now, basically why do we need an IP address to connect on the network? Let us consider a small example, suppose you are away from your hometown and your friends and family would like to reach you through any means of communication like cellphone, letters, emails or post cards , then the first and foremost thing you need to have an address. An address then allows you to be recognized over a network or a region. The above picture will make sense, when you try contacting someone with some means of communication ,say a simple traditional letter or postcard. Here, you need to provide an address, so that your letter will be delivered.

  Eg:

          To,
               Mr. XYZ,
               23/411,  East Street, Bronx ,
               NewYork, USA

 This is a simple traditional address which allows you or a particular person or an organization to be recognized universally.

     In the same way, when you connect to any particular network, the data sent can reach the destination only if it has a particular address or unique end point. This is where , IP plays the role of savior. Every node or peer on a network in the world is uniquely identified by an address, this address is called the IP address. The IP address is a 32 bit address, which means it can have 2 to the power 32 different combinations of addresses,which provides a huge pool for IP addresses.

    So in simple words, we define IP address as : a numerical label assigned to each device (eg: Computer,Printer) participating in the computer network and uses Internet Protocol for communication.

So what is IPV4?

      IPv4 stands for Internet Protocol version 4. It is basically the underlying technology that makes it possible for us to connect our devices to the web. Whenever a device like a computer or a printer try to access the Internet , it is assigned a unique, numerical IP address such as 128.119.213.227. 

    Without IP addresses, computers would not be able to communicate and send data to each other. It’s essential to the infrastructure of the web.

What is IPv6?
Here is a short animation which explores deep into the IPV6, Hit the play button
                             

   IPv6 is the sixth revision to the Internet Protocol and the successor to IPv4. It functions similarly to IPv4 in that it provides the unique, numerical IP addresses necessary for Internet-enabled devices to communicate. However, it does sport one major difference: it utilizes 128-bit addresses.

What is the reason that we are moving away from IPV4 to IPV6?

    The Internet has run out of Internet addresses, sort of.Everyday,more and more number of devices are getting attached to the network and hence more and more addresses have to be allocated to the corresponding new devices. Perhaps you’ve heard the news: the last blocks of IPv4 Internet addresses have been allocated. The fundamental underlying technology that has powered Internet Protocol addresses since the Internet’s inceptionwill soon be exhausted.

A new technology will take its place, though. IPv4′s successor is IPv6, a system that will not only offer far more numerical addresses, but will simplify address assignments and additional network security features.

Q: How does IPv6 solve this problem?

   As previously stated, IPv6 utilizes 128-bit Internet addresses. Therefore, it can support 2^128 Internet addresses — 340,282,366,920,938,000,000,000,000,000,000,000,000 of them to be exact. That’s a lot of addresses, so many that it requires a hexadecimal system to display the addresses. In other words, there are more than enough IPv6 addresses to keep the Internet operational for a very, very long time.

Q: So why don’t we just switch?

   The depletion of IPv4 addresses was predicted years ago, so the switch has been in progress for the last decade. However, progress has been slow — only a small fraction of the web has switched over to the new protocol. In addition, IPv4 and IPv6 essentially run as parallel networks — exchanging data between these protocols requires special gateways.

To make the switch, software and routers will have to be changed to support the more advanced network. This will take time and money.

Q: How will this affect me?

    Initially, it won’t have a major impact on your life. Most operating systems actually support IPv6, including Mac OS X 10.2 and Windows XP SP 1. However, many routers and servers don’t support it, making a connection between a device with an IPv6 address to a router or server that only supports IPv4 impossible. IPv6 is also still in its infancy; it has a lot of bugs and security issues that still need to be fixed, which could result in one giant mess.  

  Nobody’s sure how much the transition will cost or how long it will take, but it has to be done in order for the web to function as it does today.

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Pune University : TE - IT - 2010 Dec : Question Papers

Question Papers for Third Year Engineering  in
 Information Technology :Pune University
     

Subject	Download Link
Software Engineering	Download Now
Operating Systems	Download Now
Theory of Computation	Download Now
Computer Network Technology	Download Now

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Selective Repeat Protocol Video

      A sliding window protocol is a feature of packet-based data transmission protocols. Sliding window protocols are used where reliable in-order delivery of packets is required, such as in the Data Link Layer (OSI model) as well as in the Transmission Control Protocol (TCP).

          Conceptually, each portion of the transmission (packets in most data link layers, but bytes in TCP) is assigned a unique consecutive sequence number, and the receiver uses the numbers to place received packets in the correct order, discarding duplicate packets and identifying missing ones. The problem with this is that there is no limit of the size of the sequence numbers that can be required.

By placing limits on the number of packets that can be transmitted or received at any given time, a sliding window protocol allows an unlimited number of packets to be communicated using fixed-size sequence numbers.

 Working :

           When used as the protocol for the delivery of messages, the sending process continues to send a number of frames specified by a window size even after a frame loss. Unlike Go-Back-N ARQ, the receiving process will continue to accept and acknowledge frames sent after an initial error; this is the general case of the sliding window protocol with both transmit and receive window sizes greater than 1.

The receiver process keeps track of the sequence number of the earliest frame it has not received, and sends that number with every acknowledgement (ACK) it sends. If a frame from the sender does not reach the receiver, the sender continues to send subsequent frames until it has emptied its window. The receiver continues to fill its receiving window with the subsequent frames, replying each time with an ACK containing the sequence number of the earliest missing frame. Once the sender has sent all the frames in its window, it re-sends the frame number given by the ACKs, and then continues where it left off.

              The size of the sending and receiving windows must be equal, and half the maximum sequence number (assuming that sequence numbers are numbered from 0 to n−1) to avoid mis-communication in all cases of packets being dropped. To understand this, consider the case when all ACKs are destroyed. If the receiving window is larger than half the maximum sequence number, some, possibly even all, of the packages that are resent after timeouts are duplicates that are not recognized as such. The sender moves its window for every packet that is acknowledged

 Video explanation :

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OSI Model - How an email passes through each layer

The Open Systems Interconnection model (OSI model) is a product of the Open Systems Interconnection effort at the International Organization for Standardization.

 

It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar communication functions are grouped into logical layers. An instance of a layer provides services to its upper layer instances while receiving services from the layer below.

This video explains the process of how an email passes from one machine to another while traversing through the 7 layers of the OSI  model. Very Interesting video and clearly mentions about what happens to the email at each layer. Next time someone asks you "How OSI model plays an important role in our day to day life" , share this video or explain it yourself.


A complete self-explanatory video on the 7 layers of OSI model and its real-time application. It's an interactive video , so make sure that you click on continue buttons once understand the description at each step.

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Go Back N Protocol (With Animation) - Computer Networks

Go-Back-N ARQ is a specific instance of the Automatic Repeat-reQuest (ARQ) Protocol, in which the sending process continues to send a number of frames specified by a window size even without receiving an ACK packet from the receiver. Learn this from this perfect animation.

The receiver process keeps track of sequence number of the next frame it expects to receive, and sends that number with every ACK it sends. The receiver will ignore any frame that does not have the exact sequence number it expects -- whether that frame is a "past" duplicate of a frame it has already ACK'ed, or whether that frame is a "future" frame past the lost packet it is waiting for. Once the sender has sent all of the frames in its window, it will detect that all of the frames since the first lost frame are outstanding, and will go back to sequence number of the last ACK it received from the receiver process and fill its window starting with that frame and continue the process over again.

Three cases are covered: 
1. All Packets reach the receiver and send acknowledgements back to the sender.
2. Some Packets a lost on their way to destination. 
3. Some Acknowledgements are lost on their way back to sender.

                View the animation to understand The Protocol

(Click the Play Button to start)

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Learn the TCP/IP model

      The TCP/IP model consists of two different protocols. The TCP is a protocol and the IP is an another protocol. TCP/IP is based on a four-layer reference model. All protocols that belong to the TCP/IP protocol suite are located in the top three layers of this model.

         As shown in the following illustration, each layer of the TCP/IP model corresponds to one or more layers of the seven-layer Open Systems Interconnection (OSI) reference model proposed by the International Standards Organization (ISO).

Application Layer :Defines TCP/IP application protocols and how host programs interface with transport layer services to use the network.

Protocols : HTTP, Telnet, FTP, TFTP, SNMP, DNS, SMTP, X Windows, other application protocols

Transport Layer : Provides communication session management between host computers. Defines the level of service and status of the connection used when transporting data.

Protocols - TCP, UDP, RTP

Internet Layer :  Packages data into IP datagrams, which contain source and destination address information that is used to forward the datagrams between hosts and across networks. Performs routing of IP datagrams.

Protocols :IP, ICMP, ARP, RARP

Network Interface Layer : Specifies details of how data is physically sent through the network, including how bits are electrically signaled by hardware devices that interface directly with a network medium, such as coaxial cable, optical fiber, or twisted-pair copper wire.

Protocols : Ethernet, Token Ring, FDDI, X.25, Frame Relay, RS-232, v.35

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TCP/IP utilities

To assist with the management of TCP/IP, there are three types of TCP/IP-based utilities:

• Connectivity utilities that you can use to interact with and use resources on a variety of Microsoft® and non-Microsoft hosts, such as UNIX systems.
  
• Diagnostic utilities that you can use to detect and resolve networking problems.
  
• TCP/IP server software that provides printing and publishing services to TCP/IP-based Microsoft Windows® clients.

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TCP (Transmission Control Protocol) Video Lecture

TCP/IP- Video Leccture (Part 1)

TCP/IP - Video Lecture (Part 2)

  

TCP/IP - Video Lecture (Part 3)

TCP/IP - I

TCP/IP - II

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Data Communication [Comp - Sem 5 ] [IT - Sem 4]

Introduction

         The subject Data Communication introduced in 4th semester of IT Engineering and 5th semester of Computer Engineering is a very important subject in the curriculum of Engineering. This subject lays the foundation of Networking in Engineering. This subject needs to be understood thoroughly as you will be learning Computer Networks in the next semester. The Engineering syllabus includes in all, 3 subjects in networking : viz Data Communication, Computer Networks and Advanced Computer Networks (Elective). All these are very important for an engineer who wants to establish a career in Networking. 'Networking' is a very vast field for education and has immense scope and applications in the  industry. The demand for Network Engineers keeps on increasing day by day.

       Now , one point I would precisely state is, syllabus of Data Communication is a bit different for both Computer and IT. Its not totally different, but definitely there is  a considerable amount of difference. Beginning a word with the OSI model, I now assume that you are aware of the OSI model. If not please refer this link.

     In the OSI model you have been introduced that there are seven layers in the model : i.e.  Physical layer, data link layer ..... Presentation Layer. Now from these seven layers : the bottom most 2 layers viz : physical layer and data link layer will be introduced in the subject Data Communication.

   Now the rest 5 layers namely.,Network layer on wards will  be covered in the subject Computer Networks along with a few other important networking topics.

Analysis

Unit  1 :  Layer models and Signals

The first unit gives you introduction and a brief idea about the different terminologies and concepts which are pre-requisites for any networking concepts. This unit is extremely lengthy and a bit boring. The concepts introduced here do not allow you to enjoy unlike other networking topics. This unit is relatively easy to learn even very vast. Normally, most of the questions asked in this subject have appeared in the previous university papers.

Unit  2 : Modulation and Multiplexing

Relatively short unit , when compared to the first unit but a little bit confusing. A few concepts introduced here have already been introduced to you in the subject 'Basic Electronics Engineering' [FE - Sem 2 ]. These concepts again appear as they are. people who find Electronics tough will have to invest relatively little more efforts in this unit.

Unit 3 : Transmission media and Switching

Introduces the basic Networking topics to you. A very simple and easy to learn unit. Concepts are really interesting and can be easily understood with a simple glance. Diagrams are an important part of this unit. Scoring unit and very interesting.

Unit 4 : Error control and Data link Control

A lengthy  unit , relatively tedious and very a  bit boring. You will understand many concepts of networking in this unit ....which you will be required to understand in the other unit. Not difficult , but a few sums make learning this unit a bit complicated, relatively time consuming. This unit will  definitely need multiple glances to understand the concepts well.

Unit 5 : Multiple Access and Ethernet

Very easy unit. I enjoyed learning the concepts introduced in this unit. Many new concepts a glance will give you a brief idea about the concepts. Really interesting, most of the questions from this unit can be easily predicted. Scoring, simple and very easy unit.

Unit 6 :  Devices , Backbone networks and SONETS

Lengthy unit,mainly covers 3 main topics.Devices, Backbone networks and SONETS , which are completely different from each other. Neat diagrams allow you to score in this unit. Simple but not as simple as 5th unit.

Books to Refer

     Among the local author's I would suggest only Techmax. The book is written by the well known author and publisher J. S. Katre. The book covers all the concepts mentioned in the syllabus. The book is complete in itself. Students, sometimes tend to avoid techmax and prefer Technical , since the Techmax books are huge in  size when compared to no of pages. Please, do not prefer Technical for D.C as many concepts are incomplete.

Among the foreign authors, I would suggest , the best one : Data Communication and Networking -Behrouz Forouzan. This book will help you to learn the concepts with simple diagrams and a lucid language.  

Verdict

    Data Communications a.k.a  D.C is a very lengthy  and a bit difficult for the beginners. The subject is very interesting as well as  a very important subject in the curriculum. Scoring is not that difficult...neat diagrams and quality answers will easily fetch you 65+ marks in this subject. Scoring 70+ will need good efforts and very precise answers . Totally theoretical  but very easy to learn and not that difficult.

Books for Download

Data Communication & Networking
Behrouz Forouzan


(Most Recommended)

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Understanding Data Communications

Gilbert Held

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Data and Computer Communications 

William Stallings

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