Subject Books for UGC NET Computer Science

Friends,

I found a comprehensive list of suggested books for preparing different subjects under computer Science. You may check it and even suggest me if you came across better books than I have mentioned here.

S.No.	Book Title	Author
1.	Matrices	AR Vasista
2.	Higher Engineering Maths	BS Grewal
3.	Probability and Statistics	Miller and Freund
4.	Discrete Mathematical Structures	JP Trembly and Manohar
5.	Discrete Maths	Schaum’s Series
6.	Discrete Mathematical Structures	Kolman, Busby and Ross
7.	Graph Theory	Narsingh Deo
8.	Numerical Methods	Golden Series
9.	Numerical Methods	BS Grewal
10.	Numerical Methods	SS Sastry
11.	Numerical Methods	Jain and Iyengar
12.	Discrete Mathematics	Mott, Kandel and Baker
13.	Automata	Ullman and Hopcroft
14.	Introduction to Computer Theory	Daniel Cohen 2nd Edition
15.	Theory of ComputerScience 2nd Edition	Chandrasekaran & Mishra
16.	Design Analysis of Comp. Algorithms	Aho, Hopcroft and Ullman
17.	Computer Algorithms	Horowitz and Sahni
18.	Introduction to Algorithms	Thomas Cormon, Charles Ronald
19.	Switching and Finite Automata Theory	Kohavi
20.	Digital Logic and Computer Design	Morris Mano
21.	Digital Principles and Applications	Leach and Malvino
22.	Computer System Architecture	Mano
23.	Computer Org. and Architecture	William Stallings
24.	Computer Organization	Hamacher, Vranesic &Zaky
25.	Computer Architecture and Organization	Hayes
26.	Programming Languages	Pratt and Zelkewitz
27.	Compilers	Aho, Ullman and Sethi
28.	Principles of Compiler Design	Aho and Ullman
29.	Fundamentals of Data Structures	Horowitz. Sahni
30.	Introduction to DS with Applications	Trembly and Sorenson
31.	Data Structures	Schaum Series
32.	DS and Programming in C	Kruse, Tondo and Leung
33.	C Programming	Venugopal
34.	C Programming Language	Kernighan and Ritchie
35.	System Programming	Donovan
36.	System Programming and OS	Dhamdhere
37.	Operating Systems	Dietel
38.	Operating Systems	William Stallings
39.	Operating Systems	Milan Milenkovic
40.	OS Concepts	Galvin and Silberschatz
41.	Computer Networks	Andrew Tanenbaum
42.	Data Communications	William Stallings
43.	Engg. Approach to Comp. Networks	S Keshav
44.	Introduction to Switching Theory & Logic Design	FJ Hill and Peterson
45.	Database Systems	Korth and Sudhershan
46.	Fundamentals of DBMS	Elmasri, Navathe
47.	An Introduction to DBMS	CJ Date
48.	DBMS 3rd Edition	Ramakrishnan, Gehrke
49.	An Introduction to DBMS	Bipin C Desai
50.	Multiple Choice Questions in Computer Science	Timothy J Williams

Software Testing Techniques

Here, we will discuss some important software testing techniques. In exams like UGC NET, questions are often asked from this topic.

There are four levels of software testing: Unit >> Integration >> System >> Acceptance.

Usually, Black Box Testing method is used in Acceptance Testing. Acceptance Testing is performed after System Testing and before making the system available for actual use.

Smoke Testing, also known as “Build Verification Testing", comprises of a non-exhaustive set of tests that aim at ensuring that the most important functions work, but none of them in depth. It helps in exposing integration and major problems early in the cycle.

Functional testing ensures that the requirements are properly satisfied by the application. During functional testing, Black Box Testing technique is used. It is performed during the levels of System Testing and Acceptance Testing. It has a high possibility of redundant testing.

Security Testing intends to uncover vulnerabilities of the system and determine that its data and resources are protected from possible intruders.
Example of a basic security test: Click the BACK button of the browser (Check if you are asked to log in again or if you are provided the logged-in application.)

Regression testing intends to ensure that changes (enhancements or defect fixes) to the software have not adversely affected it.Regression testing can be performed during any level of testing but it is mostly relevant during System Testing.

Unit Testing is performed by using the White Box Testing method. This type of testing is performed prior to Integration Testing, by software developers themselves or their peers.

Integration Testing: The purpose of this level of testing is to expose possible faults in the interaction between integrated units. Different approaches are:
Big Bang:  all or most of the units of the code are combined together and tested at one go. This approach is used when the testing team receives the entire software in a bundle. Big Bang Integration tests only the interactions between the units while System Testing tests the entire system.

Top Down: top level units are tested first and (step by step ) lower level units are tested later. This approach is followed with top down development. Test Stubs are needed to simulate lower level units which may not be available during the initial phases.

Bottom Up: bottom level units are tested first and upper level units step by step after that. This approach is used when bottom up development approach is followed. Test Drivers are needed to simulate higher level units which may not be available during the initial phases.

Sandwich/Hybrid: A combination of Top Down and Bottom Up approaches.

System Testing: A complete, integrated system/software is tested. The purpose is to evaluate the system’s compliance with the specified requirements. Usually, Black Box Testing method is used. independent Testers perform System Testing.

Acceptance Testing: This testing method does not usually follow a strict procedure and is not scripted but is rather ad-hoc. It is performed after System Testing and before making the system available for actual use.

Black Box Testing is also known as Behavioral Testing. There are some techniques that can be used for designing black box tests:

Equivalence partitioning: Involves dividing input values into valid and invalid partitions and selecting representative values from each partition as test data.

Boundary Value Analysis: Involves determination of boundaries for input values and selecting values that are at the boundaries and just inside/outside of the boundaries as test data.

Cause Effect Graphing: Identifies the cases (input conditions) and effects (output conditions), producing a Cause-Effect Graph, and generating test cases accordingly.

White Box Testing (Code-Based Testing or Structural Testing): The internal structure/design/implementation of the item being tested is known to the tester. It is mainly applied to Unit Testing.

Gray Box Testing: The internal structure is partially known. This involves having access to internal data structures and algorithms for purposes of designing the test cases, but testing at the user, or black-box level. it is primarily useful in Integration Testing.

Cracking NET: No Instant Recipe but Strategy

Dear Friends!

I have been sharing my views on strategy for succeeding in NET exam on this blog as well as in Facebook groups. Most of times, I am thrown the queries on "Instant Recipe" for success in NET....like:

"Do you have study material for NET exam?"

"How I can prepare in next 2-3 months so that I crack the next exam?"

I start wondering why people look for "Instant Formula" to get success in competitive exams like UGC NET? Perhaps the "successful" formulas used by them in academic exams of their degree made them to think the same way for UGC NET exam also, but sorry, it is not that easy.

Before the pattern of NET examination was changed to 100% objective, Paper-III was subjective. You were supposed to secure just passing marks (40%) in paper III and 50% in total of Paper I and Paper II. It means, there was no criteria of falling in top 15% of eligible candidates. Still, the rate of success in Computer Science was dismally low all over India.

Now, the pattern has been changed and the high ratio of successful candidates is an indicator that cracking NET is far easier now. But, still, there is no "Instant Recipe" for success in NET.

NET preparation takes planning as well as patience. Unless you are born genius and covered all important topics of NET exam with utmost sincerity as a student and started preparing while you were in 1st semester of Masters degree....it definitely takes time to qualify. How much of time? It all depends on 3 factors, which we will discuss at the end.

Previously I posted two articles: One-> Getting success in NET exam, Two-> Securing great marks. In this post, I am sharing some more ideas on planning for your goal to qualify the Exam. Your success depends much on the dedicated execution of these steps.

First:

Select the topics you can study and prepare well for the next NET exam. You better focus on only those subjects you know are important to cover and also, you are confident that you can understand and can study them in short time. One strategy to choose the topics is to select 7-8 old topics, means, the topics you have already studied in your Masters. Additionally, select one or two new topics which you have never studied but are important for NET exam. For example, I had never heard about Theory of Computation (TOC) while doing MCA. The questions from this subject are always asked in paper II and/or paper III. You will need to select around 10 subjects.
For your old subjects, make a list of books you need to study. Follow the standard and famous books.

For the new topics, it would be better either you watch tutorial videos on NPTEL website, Youtube or find a good book for beginners on such topic. In my case, to learn Automata, I started with the book by Ullman. But that was a mistake, since the language of this book is not suitable for beginners. So, I shifted to online Videos and other web-based tutorials.  I later came to know that books on Automata by Peter Linz and Mishra were better for beginners.

For now, in first step, Do not start reading/re-reading books. Do this after following the next step.

Second:

Now, download all previous UGC papers from cbsenet.nic.in as well as ugcnetonline.in. For saving your time, here are the URLs to old question papers:

1. December 2015
2. June 2015

3. December 2014

4. June 2009 to June 2014

Now take printout of all the papers if you prefer to study offline. In my case, I took printout of all question papers and binded all papers in order like an MCQ book. Study the questions of all 3 papers. Try to understand the pattern and the types of questions asked. (Right now, do not focus on solutions to the problems, just develop an understanding on the types of the questions). 

To do this exercise in a planned manner, select any one topic and study questions from that topic only - in all question papers. For example, if you choose to begin with OS, make a list of only OS related questions from previous papers. On average, you will find 5-6 questions on OS from each exam session. It means, you will have more than 60 questions in hand on OS. If you have just began to prepare for NET, it is for sure that you will find that more than 50% questions are challenging. Highlight such questions. Do the same for all other topics. (Right now, we are not focusing on the solutions to the questions, but simply developing understanding of the topics). Solve  the questions as mentioned in third step.

Third:

Now solve the questions (which you selected in previous step) in three ways:

1. Find the topics in the text book, for example Galvin, and read the text. Make notes of important concepts. If you are short of time, simply use highlighter to mark in the book itself (Don't do this in borrowed books :-)

2. If  you could not find useful information in the book, take help of Google to research these questions. You will find Tens of useful links to study.

3. Still, if you fail to find the solution, post your question if forums like Facebook groups you have joined, online blogs related to your topic etc. Someone will definitely post answer to your question in any of the forums.

Remember, solving each challenging question can take time. Sometimes, it may take even 2 hours just to find the right answer and concept behind the asked question. (DO NOT CRAM ANS KEYS GIVEN BY UGC. I too made this mistake. It consumes time but is least helpful.) Why I have asked to do this step? You are not supposed to remember the given answers, but study the concept behind each such question. If you get the concept right, you will find many other questions easy to answer which are based on the same concept. If later you read the same questions or other questions on the concept you learnt, you will realise that you can now understand the problem in a better manner before you covered the topics.

Fourth:

After covering most of previous NET questions, research more on MCQ from other resources (both offline and online). Start solving questions from MCQ book by authors like Timothy Williams and any other you consider as good book. 

You may also use web sites some of which I am listing below:

http://www.geeksforgeeks.org/

http://nptel.ac.in/course.php

http://www.indiabix.com/engineering/

Last thing! There are three factors which will decide the direction of your exam preparation:
#1. (Most Important) Your focus on your goal (means how much serious you are to crack the NET)

#2. Your previous academics, means how much and which subjects you have learnt good by the time you complete your masters.

#3. Your perseverance, means "Never Say Die" spirit even if it is taking longer than you thought to qualify the exam. I stressed on this attitude in one of my previous posts also.

These 3 factors will decide when and how you will succeed.

Readers! The only objective of this post is to make you realise that it is better to equip yourself with all necessary Armour for hitting the exam. Give yourself at least 6 months of dedicated preparation. After 6 months, you will be confident on the concepts as well as on how to solve MCQs.

Best of Luck for July 2016 exam!

7 Steps to success in UGC NET Exam

Hello Friends!

Cracking UGC NET examination, especially in a subject like Computer Science, is not a piece of cake. But at the same time, it is not an uphill task, which only selected few in the world can do.

Many of the candidates, after failing in 1-2 attempts, start thinking that it is not their cup of tea. I too failed to crack the exam, not just once or twice, but even after 7 attempts. However, my misery lasted only a few days. Every time the notification for UGC NET was out, I always decided to give it a shot. I must admit that every time I missed the sweet success, I felt low on confidence. Still I had a gut feeling that I was doing better than my last attempts and inch by inch, I was getting closer towards my goal.

Now, after qualifying UGC NET exam twice, I have gained more confidence in my teaching abilities. I have also realised that the way I planned and studied for getting success in NET exam was a kind of mixed bag. Means, if I had planned in a better manner and had devoted more time to practice, then it cannot take one more than 2 years to crack the exam!!

Here, I want to share with you my experience and my topsy-turvy journey towards this goal. If you do not want to spend 3-4 years to qualify this exam (like I did) and qualify the exam in less than two years, then, get ready to follow the steps (with determination) I am mentioning here:

Step 1:
Buy/procure the standard text books for different subjects plus one or two good MCQ books on computer Sci. (At the end, I will list names of some of good books). You need not to buy books on all subjects, focus on maximum 9-10 subjects, since you are not supposed to answer every question right and you are never expected to score 90% and above ;-)

Step 2:
Download all previous question papers (of all 3 papers) from the following website links of UGC:

http://ugcnetonline.in/news.php
http://www.cbsenet.nic.in
http://www.ugc.ac.in/net/oldqpyr.aspx?sub=87
http://www.ugc.ac.in/net/oldqpyr.aspx?sub=00

Also download all available answer keys of different exams (from June' 12 to June' 14, you will find ans keys of all 3 papers at UGCNetonline site, for NET exam December 2014 onward, please check CBSENET site).

DO TAKE PRINTOUT of all papers. It is better to use printed paper than reading it on your screen. However, to save your time and energy, better focus on question papers of last 4-5 years only and leave very old papers. For example, patter of question papers of 2004 and 2005 is very old and not many of the questions of the old pattern are asked nowadays.

Step 3:
Study the questions of previous papers thoroughly. Remember, this step is very important to understand where you stand now and how much time and preparation you will need. So, do this religiously and devote next 2-3 days in reading the questions and try to understand what is asked by the examiner. You will surely gain a good understanding about 3 things:

1. What are the subjects I must focus on
2. What are the subjects I can ignore or I can't study
3. What are the important topics of each subject from the point of view of NET exam

There are definitely some subjects of you will have a weak understanding. Rather than wasting your time and energy on these topics, better you focus on strengthening the subjects you have a flair as well as you can prepare. For example, I was not comfortable with Image Processing, Computer Graphics and ANN (Artificial Neural Network), so I left them out. For such topics, one would be tempted to not to miss them. I have a tip for these. For questions beyond your comprehension, just memorise their right answer. Who knows, the same question is asked in next exam :-)

Step 4:
Select one or two subjects (at max) to begin with and start reading their text book. For next 7-10 days, read only the books on the selected 1-2 topics. ALWAYS KEEP A HIGHLIGHTER OR A GOOD PENCIL with you. Any statement or concept which you may find important, then immediately highlight the points in the book itself. (You will be able to do this easily if you did step 3 right)

After finishing the book, go to
step 5. After step 5 is finished, come back to this step and follow the similar exercise for next 1-2 topics in the sequence.

Step 5:
Now, start solving the question papers you downloaded earlier. (Here, you need to solve only questions of the subject you studied in step 4). Eureka!! You will find that you are able to understand the question better now than previously-before reading the text book. (Still, there will be many questions you will not be able to solve). Mark your answers with a pencil then compare your answers with official ans. keys of UGC. For all the questions, you were not able to solve, go to step 6:

Step 6:
Research the tricky questions on Net (Internet dear, not UGC NET ;-) ). Take the help of Google Baba as well as your Facebook group of UGC to find the solution of the question. Stay determined to find the solution till you have not found the satisfactory explanation of the question). Who knows if the same question is asked in the exam itself, then you will be happy for your homework.

Step 7:
The final step is highly important-perseverance. Come what may, stay determined to get through your goal at any cost. Follow all 6 steps, especially step 5 and 6 in a loop, with all your determination. If you fail in one attempt, hold your emotions and bounce back to fight for the next exam.

After taking exam of one session, say June, do not sit idle and wait for the result. Continue with other subjects, solve the questions of your last exam. If you were not able to succeed, you will be left with lesser time to prepare for the exam of the next session. If you are already following your routine, nothing will be unexpected for you.

Stay focused, determined and relaxed also. Enjoy the feeling of putting your best foot forward. Pray to God to keep you on track. Nobody can stop you from achieving your share of success and joys in this world.

ALL THE BEST!!

UGC NET/SET Exam: Some Ideas for success

Friends,

I want to share some of my ideas on NET/SET preparation. I have done MCA and qualified UGC NET exam twice and SET(H.P.)-2013 exam.

The very first time I appeared in NET exam simply to know the pattern of the exam and I didn't prepare much. At that time, exam had subjective pattern. I was able to clear Paper I and Paper II but I could not clear paper III. Still, I was very happy that I cleared first 2 papers. Then, I appeared again, then again. In total 5 of my efforts, I was not able to clear Paper III. In my 4th and 5th attempt, pattern of the paper had become totally objective. Still, I was not able to clear paper III.

I had started losing my faith in myself and I decided to opt out of Dec' 13 NET Exam and preferred to sit in another exam on the same date. I believed that the same story will get repeated. But one good thing I did was that before Dec' 13 exam, Himachal Pradesh Public Service commission had announced SET/SLET exam for the state universities/colleges. I applied for the exam and had appeared in the exam on November 17, 2013. The result of the exam was announced on  March 14, 2014 and I was declared qualified! WOW!!

The success in SET gave me much needed high and faith in myself. The point here is, we throw seeds on the land without bothering about which seed will bore fruits and when. Our efforts in one direction may show result somewhere else. The time I devoted in preparation of NET helped me to crack SET exam. Further, the success in SET exam enthused me and started preparing in a more determined manner. SET is limited in scope and a bit easier than NET. But success in this exam rekindled my faith in myself that NET too is not far and can be cracked with some more planning.

And the result was that I was able to qualify December 2014 exam. For the first time, I Cracked the "hard NUT" called UGC NET.

If one is failing 3 or more times in NET, it is quite possible that one will get disappointed and will lose one's confidence. To uplift one's spirits, focusing on some other exam/objective (for time being) of your chosen career will help you to forget the stress you might have been facing due to rejection in NET. You may choose to focus on some other competition exams for computer teacher/lecturers like CTET, SET, KV schools exams etc. whichever is announced in the time frame. Believe me, these exams can be cracked more easily than NET.

Your sole objective may be NET only, but if you succeed in other exams I have mentioned, it will lift your morale and will give birth to an enthusiastic mindset which is very crucial for cracking exams like NET.

PLEASE post your ideas (If whatever I have mentioned is right or wrong)..

Useful Q & A on Networking - Part 1

Q 1. What happens at every layer of the OSI model when we type "www.google.com" in the browser? 

Ans. The following sequence of steps takes place every time we type the name of a website in a browser->
1) Your PC will need to resolve "www.google.com" to an IP address. It will therefore need to send a 
query to your DNS server ( usually your ISP's DNS).

2) The PC constructs a DNS query packet with a destination IP address equal to your DNS server 
and a destination MAC address of your router (gateway).

3) The DNS query process begins to resolve the IP address of the given URL.

4) Once your PC (web browser application) receives the IP address of the destination web server, it will construct a HTTP GET request and send it to Google's web server. (As per OSI model at application layer [layer 7] application software which is client web browser now know the IP address of google.com). After that it pass that information down to presentation layer.

5) Presentation layer[ layer 6] converts that HTTP request into a standard format which is HTTP format so that the other layers can understand.and pass that information down to session layer.

6) Session layer[ layer 5] at client side creates session for www.google.com which is HTTP session so that it can be separated from other sessions.and pass that information down to transport Layer.

7) Transport Layer[ layer 4]  at client side chooses TCP for every HTTP session which is reliable connection which creates virtual connection by using three way hand-shake before sending actual data [HTTP Request]. This layer also prepares segments by adding source and destination port number. Source port is chosen by upper layer which is random number range from 1024 to 65535  and destination port number is here 80, which is well known port number used for HTTP services.

Layer 4 assign source port number to distinguish the web browser application from every other program running on computer and it also used to identify which application should receive return traffic. The destination port number is used to make sure that messages coming from web browser gets and sent to web server program running on the server and is not grabbed by other program. After preparing segment, layer 4 at client side pass that information down to network layer.

8) Network Layer [ layer 3] at client side  prepares packet by adding source and destination IP address. It also check whether destination IP address is on local network or it is on remote network. If it is on local network it checks ARP cache to find mac address of local device. If cache is empty it sends ARP message to resolve IP address into MAC address. Here the device is on remote network so client PC sends ARP to find MAC address of default gate way [192.168.1.1]. Every devices on that network segment gets that ARP request because as it layer 2 broadcast message destined for all devices on that broadcast domain but only the default gateway, which is 192.168.1.1, replies with its MAC address. Then network layer passes this information down to data link layer.

9) Data link layer[ layer 2]  prepares frame by adding source and destination MAC address of default gate way[192.168.1.1]. It also rund CRC which simply checks the data and frame header bits and add that result in to frame check sequence (FCS) field. Then, passes this information down to Physical layer.

10) Physical layer[ layer 1]: converts all this information in 1's and 0's and sends it to destination device using Ethernet cable.

11) Google's Web server will reply and start sending your application the necessary data using TCP session.

12) The application will start to draw and present the website on your screen.

At the server side, i.e. Google:

1) At Physical layer, server receives the bits. Layer 2 of server builds frames and runs CRC and checks answer with FCS field. If answer didn't match then the frame is discarded. If it matches then the destination MAC address is checked. Here, destination MAC address is right, so it checks Ethernet type field to find the protocol used at network layer (which is IP). It retrieves the packet from the frame and gives to IP at network layer.

2) Network layer checks destination IP address and in our case it matches so it checks protocol type field to find the protocol used at Layer 4 (which is TCP). Now network layer of server sends all information up to TCP at layer 4.

3) At transport layer, destination port number is checked which is well know port number 80, which is destined to web server application running on that particular server i.e. in our case www.google.com. So it passes all those information up to google web server. Google web server sends acknowledgement message to client to ensure that it has received its request. Finally, it sends the web page in the form of packet by packet over the network to client. This information gives google web page to our client web browser.

Notes on Computer Networking:Part II

IP address classes:

Class	Leftmost bits	Start address	Finish address
A	0xxx	0.0.0.0	127.255.255.255
B	10xx	128.0.0.0	191.255.255.255
C	110x	192.0.0.0	223.255.255.255
D	1110	224.0.0.0	239.255.255.255
E	1111	240.0.0.0	255.255.255.255

IP address range for Intranets (Private Networks):

Class	Private start address	Private finish address
A	10.0.0.0	10.255.255.255
B	172.16.0.0	172.31.255.255
C	192.168.0.0	192.168.255.255

IP packets addressed by them cannot be transmitted onto the public Internet. If such a private network needs to connect to the Internet, it must use either a network address translator (NAT) gateway, or a proxy server.

Some good facts on IP V6:

In IPV6, The address block fc00::/7 has been reserved for private networks.

IP officially reserves the entire range from 127.0.0.0 through 127.255.255.255 for loopback purposes.

Very Imp: IPv6 does not use classes. IPv6 supports the following three IP address types: 

1. Unicast 

2. Multicast 

3. Anycast

IPv6 does not support broadcast. Multicast addresses in IPv6 start with 'FF' (255) just like IPv4 addresses. Unicast addresses have 3 defined scopes, including link-local, site-local and global; and multicast addresses have 14 scopes.

The number of IPv6 addresses is 10^28. There is no ARP in V6. Currently, DHCP, FTP, PPP, RIP, SNMP, VPN, L2TP and Telnet do not support IPv6.

IPv6 does not require NAT. NAT, too, doesn't support V6. Currently, IPv6 packets are not forwarded.

IPv6 reserves just two special addresses: 0:0:0:0:0:0:0:0 and 0:0:0:0:0:0:0:1. IPv6 uses 0:0:0:0:0:0:0:0 internal to the protocol implementation, so nodes cannot use it for their own communication purposes. IPv6 uses 0:0:0:0:0:0:0:1 as its loopback address, equivalent to 127.0.0.1 in IPv4. The minimum size of an IP datagram is 28 bytes, including 20 bytes of header.

Anycast is a network addressing and routing methodology in which datagrams from a single sender are routed to the topologically nearest node in a group of potential receivers, though it may be sent to several nodes, all identified by the same destination address. On the Internet, anycast is usually implemented by using BGP.

In denial-of-service attacks (DoS), a rogue network host may advertise itself as an anycast server for a vital network service, to provide false information or simply block service.

6to4 is an Internet transition mechanism for migrating from IPv4 to IPv6, a system that allows IPv6 packets to be transmitted over an IPv4 network. 6to4 does not facilitate interoperation between IPv4-only hosts and IPv6-only hosts, but simply a transparent mechanism used as a transport layer between IPv6 nodes.

The network requests supporting DNS lookups run over TCP and UDP, port 53 by default.

Some Questions-Answers with explanation

In a network of LANs connected by bridges, packets are sent from one LAN to another through intermediate bridges. Since more than one path may exist between two LANs, packets may have to be routed through multiple bridges. Why is the spanning tree algorithm used for bridge-routing? (GATE 2005)

(a) For shortest path routing between LANs         (b) For avoiding loops in the routing paths

(c) For fault tolerance                                      (d) For minimizing collisions

SOLUTION: Spanning tree is a protocol that allows the bridges to exchange information so that only one of them will handle a given message that is being sent between two computers within the network. This  protocol prevents the condition known as a BRIDGE LOOP. It is typical to add a second bridge between two network segments as a backup in case the primary bridge fails (both bridges need to have some way to understand which bridge is the primary one). To do this, they have a separate path connection just between the bridges in which they exchange information, using bridge protocol data units (BPDUs).

The program in each bridge that allows it to determine how to use the protocol is known as the spanning tree algorithm. The algorithm is specifically constructed to avoid bridge loops (for a bridge using only the most efficient path when faced with multiple paths). If the best path fails, the algorithm recalculates the network and finds the next best route.

How many 8-bit characters can be transmitted per second over a 9600 baud serial communication link using asynchronous mode of transmission with one start bit, eight data bits, two stop bits and one parity bit?
(1) 600         (2) 800         (3) 876           (4) 1200

For 9600 baud, 1 bit=1/9600=0.104mS. Each char would require 11 bits. That means, to transmit one char, it would take 1.144 mS. So, applying the formula 1000/1.144 (mS in one Sec/transmission time for one char)=approx 875. Nearest answer is (3)

The single stage network is also called

A) one sided network                             B) two sided network

C) recirculating network                      D) pipeline network

Single-Stage Network is a single stage of switching elements (SEs) existing between the inputs and the outputs of the network. Data is circulated a number of times around the network.

 If a class B network on the Internet has a subnet mask of 255.255.248.0, what is the maximum number of hosts per subnet?
(a) 1022 (b) 1023 (c) 2046 (d) 2047

Explanation: Convert the subnet mask into binary format.

255.255.248.0 = 11111111.11111111.11111000.00000000

Number of 1's in the subnet mask indicates the Network-ID and the Subnet-ID part. Number of 0's in the subnet mask indicates the Host-ID part. Maximum number of Hosts per subnet = 2¹¹ = 2048, where 11 = Number of 0's in the Subnet Mask. Out of 2048 values, 2 addresses are reserved, hence we remove them (2048-2 = 2046). Note: In the host part of the address:- all bits as 1 is reserved as broadcast address and all bits as 0 is used as network address of subnet.

Which of the following system calls results in the sending of SYN packets?
(a) socket (b) bind (c) listen (d) connect

The connect system call is normally called by the client process to connect to the server process. The socket system call creates a new socket and assigns the protocol and resources to the created socket descriptor. The bind system call associates a local network transport address with a socket. For a client process, it is not mandatory to issue a bind call. The kernel takes care of doing an implicit binding when the client process issues the connect system call. It is often necessary for a server process to issue an explicit bind request before it can accept connections or start communication with clients. The listen call indicates to the protocol that the server process is ready to accept any new incoming connections on the socket. There is a limit on the number of connections that can be queued up, after which any further connection requests are ignored.