Showing posts with label Notes. Show all posts

Thursday, 28 November 2013

IT2042 Information Security - SDLC Notes

Software Development Life Cycle

SDLC stands for Software Development Life Cycle. SDLC is the process consisting of a series of planned activities to develop or alter the software products.

This tutorial will give you an overview of the SDLC basics, SDLC models available and their application in the industry. This tutorial also elaborates on the other related methodologies like Agile, RAD and Prototyping.

SDLC, Software Development Life Cycle is a process used by software industry to design, develop and test high quality softwares. The SDLC aims to produce a high quality software that meets or exceeds customer expectations, reaches completion within times and cost estimates.

SDLC is the acronym of Software Development Life Cycle.
It is also called as Software development process.
The software development life cycle (SDLC) is a framework defining tasks performed at each step in the software development process.
ISO/IEC 12207 is an international standard for software life-cycle processes. It aims to be the standard that defines all the tasks required for developing and maintaining software.

Friday, 15 November 2013

Microprocessor and Microcontroller - CS2252 - Notes By Experts

Notes for Microprocessor and Microcontroller by Leading Staff members

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Wednesday, 13 March 2013

IT2354 - Embedded System notes - "INTERRUPT"

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Interrupts

Basics

Busy-wait I/O is extremely inefficient—the CPU does nothing but test the device status

while the I/O transaction is in progress. In many cases, the CPU could do useful work in

parallel with the I/O transaction, such as:

ü

computation, as in determining the next output to send to the device or processing

the last input received, and

ü

control of other I/O devices. To allow parallelism,we need to introduce

new

The interrupt mechanism allows devices to signal the CPU and to force execution of a

particular piece of code. When an interrupt occurs, the program counter’s value is changed

to point to an interrupt handler routine (also commonly known as a device driver) that

takes care of the device: writing the next data, reading data that have just become ready,

and so on. The interrupt mechanism of course saves the value of the PC at the interruption

so that the CPU can return to the program that was interrupted. Interrupts therefore allow

the flow of control in the CPU to change easily between different contexts, such as a

foreground computation and multiple I/O devices. As shown in Figure, the interface

between the CPU and I/O device includes the following signals for interrupting:

ü the I/O device asserts the interrupt request signal when it wants service from the

CPU; and

ü the CPU asserts the interrupt acknowledge signal when it is ready to handle the I/O

device’s request.

The I/O device’s logic decides when to interrupt; for example, it may generate an

interrupt when its status register goes into the ready state. The CPU may not be able to

immediately service an interrupt request because it may be doing something else that must

be finished first—for example, a program that talks to both a high-speed disk drive and

a low-speed keyboard should be designed to finish a disk transaction before handling a

keyboard interrupt. Only when the CPU decides to acknowledge the interrupt does the

CPU change the program counter to point to the device’s handler. The interrupt handler

operates much like a subroutine, except that it is not called by the executing program.

The program that runs when no interrupt is being handled is often called the foreground

program; when the interrupt handler finishes, it returns to the foreground program,

wherever processing was interrupted.

The interrupt mechanism.

Ø Priorities and Vectors

Providing a practical interrupt system requires having more than a simple interrupt

request line. Most systems have more than one I/O device, so there must be some mechanism

for allowing multiple devices to interrupt.We also want to have flexibility in the locations of the

interrupt handling routines,the addresses for devices,and so on. There are two ways in which

interrupts can be generalized to handle multiple devices and to provide more flexible definitions

for the associated hardware and software:

ü interrupt priorities allow the CPU to recognize some interrupts as more important

than others, and

ü interrupt vectors allow the interrupting device to specify its handler.

Prioritized interrupts not only allow multiple devices to be connected to the interrupt

line but also allow the CPU to ignore less important interrupt requests while it handles more

important requests. As shown in Figure, the CPU provides several different interrupt request

signals, shown here as L1, L2, up to Ln. Typically, the lower-numbered interrupt lines are given

higher priority, so in this case, if devices 1, 2,and n all requested interrupts simultaneously, 1’s

request would be acknowledged because it is connected to the highest-priority interrupt line.

Rather than provide a separate interrupt acknowledge line for each device, most CPUs

use a set of signals that provide the priority number of the winning interrupt in binary form (so

that interrupt level 7 requires 3 bits rather than 7). A device knows that its interrupt request was

accepted by seeing its own priority number on the interrupt acknowledge lines.

Prioritized device interrupts.

How do we change the priority of a device?

Simply by connecting it to a different interrupt request line. This requires hardware

modification, so if priorities need to be changeable, removable cards, programmable switches, or

some other mechanism should be provided to make the change easy.

The priority mechanism must ensure that a lower-priority interrupt does not occur when

a higher-priority interrupt is being handled. The decision process is known as masking. When

an interrupt is acknowledged, the CPU stores in an internal register the priority level of that

interrupt. When a subsequent interrupt is received, its priority is checked against the priority

register; the new request is acknowledged only if it has higher priority than the currently pending

interrupt.

When the interrupt handler exits, the priority register must be reset. The need to reset the

priority register is one reason why most architectures introduce a specialized instruction to return

from interrupts rather than using the standard subroutine return instruction. The highest-priority

interrupt is normally called the non maskable interrupt (NMI).The NMI cannot be turned off

and is usually reserved for interrupts caused by power failures—a simple circuit can be used

to detect a dangerously low power supply, and the NMI interrupt handler can be used to save

critical state in nonvolatile memory, turn off I/O devices to eliminate spurious device operation

during power down, and so on.

Most CPUs provide a relatively small number of interrupt priority levels, such as eight.

While more priority levels can be added with external logic, they may not be necessary in all

cases. When several devices naturally assume the same priority (such as when you have several

identical keypads attached to a single CPU), you can combine polling with prioritized interrupts

to efficiently handle the devices.

Using polling to share an interrupt over several devices.

Vectors provide flexibility in a different dimension, namely, the ability to define the

interrupt handler that should service a request from a device. Figure shows the hardware

structure required to support interrupt vectors. In addition to the interrupt request and

acknowledge lines, additional interrupt vector lines run from the devices to the CPU. After a

device’s request is acknowledged, it sends its interrupt vector over those lines to the CPU. The

CPU then uses the vector number as an index in a table stored in memory as shown in Figure.

The location referenced in the interrupt vector table by the vector number gives the address of

the handler.

There are two important things to notice about the interrupt vector mechanism.

First, the device, not the CPU, stores its vector number. In this way, a device can be given

a new handler simply by changing the vector number it sends, without modifying the system

software. For example, vector numbers can be changed by programmable switches.

The second thing to notice is that there is no fixed relationship between vector numbers

and interrupt handlers. The interrupt vector table allows arbitrary relationships between devices

and handlers. The vector mechanism provides great flexibility in the coupling of hardware

devices and the software routines that service them.

Most modern CPUs implement both prioritized and vectored interrupts. Priorities

determine which device is serviced first, and vectors determine what routine is used to service

the interrupt. The combination of the two provides a rich interface between hardware and

software.

Saturday, 29 December 2012

CS2302 – COMPUTER NETWORKS - 16 Marks - Information Technology - Anna University, Chennai

PART-B (16 MARKS)

UNIT I

1. Explain the OSI-ISO model I of computer with neat diagram. (16)

2. Distinguish between Point to Point links and multi-point links with relevant diagram. (16)

3. (i) compare connection oriented and connection less service. (8)

(ii)What are the major component of an optical communication system discuss. (8)

4. Write shot notes on

a. Network Hierarchy (4)

b. Ethernet (4)

c. Token ring (4)

d. Ring topology (4)

5. Perform a comparative study between the ISO-OSI model and TCP/IP reference

model. (16)

Write notes on Issues in the data link layer (8)
Write notes on Hybrid multiple access techniques (10)

UNIT II

1. Write short notes on.

a. GO Back NARQ (8)

b. Selective Repeat ARQ (8)

2. (i) Explain Hamming code technique to correct single bit error with an example. (8)

(ii) Explain numbering of frames in GO Back NARQ, Selective Repeat ARQ protocols. (8)

3. (i) Explain MAC Ethernet protocol. (8)

(ii) Explain MAC sub layer protocol and frame structure of 802.16. (8)

4. Explain the following Inter connection devices also discuss their uses

a. Repeater (4)

b. Bridge (4)

c. Switch (4)

d. Gateway (4)

5. (i) Consider a 32- bit Block of data 11100111 11011101 00111001 10101001 that has been to be transmitted If longitudinal Redundancy check is used what is the transmitted bit stream? (8)

(ii) In the Hamming code for a data unit of ‘m’ bits how do you know compute the number of redundant bits “r’ needed? (8)

6. (i) Explain any one of the protocols used for flow control in noisy channels. (8)

(ii) Write short note on

a. sliding windows (4)

b. X-MODEM (4)

7.Explain about SONET (NOV/DEC 2007)

UNIT III

1. Find the class of each IP address given suitable explanation. (16)

a. 227.12.14.87

b. 193.14.56.22

c. 14.23.120.8

d. 252.5.15.111

e. 134.11.78.56

f. 000 000 00 1111 0000 11111111 00110011

g. 10000000 1111 0000 11111111 00110011

2. Discuss how DES Algorithm works. (16)

3. State the major difference between Vector Routing and link state routing. (16)

4. Discuss how these routing and link state routing techniques work. (16)

5. What is the subnet work address if the destination address is 200.45.34.56 and the subnet mask is 255.255.240.0. (16)

6. What are the limitations of distance vector routing. How are they addressed in link state routing? (16)

7. Explain routing of mobile hosting. (16)

8. Write notes on BGP and CIDR (10)

UNIT IV

1. i. Discuss how multiplexing and demultiplexing is done in the transport layer. (8)

ii. Explain in detail the mechanism in transport layer for controlling congestion. (8)

2. i) Explain choke packets methods of congestion control. (8)

ii) Explain classless inter domain running(CINR). (8)

3. i) Explain various problem and corresponding solution in establishing a connection at transport layer. (8)

ii) Explain the connection release process applied at transport layer. (4)

iii) Explain window management in TCP. (4)

4. i) Discuss about quality of services. (8) (MAY/JUNE 2009)

ii) Write short notes on integrated services. (8)

5.Explain the working of TCP using the state diagram(12)(MAY/JUNE 2009)

6.Discuss the operation of IntServ for providing QoS.(12)(MAY/JUNE 2009)

UNIT V

1.i) Explain in detail the title transfer protocol. (8)

ii) Describe the architecture of ISDN. (8)

2. i) Explain in detail a protocol for electronic mail. (8)

ii) Explain in detail any one ISDN protocol. (8)

3. i) what is HTTP protocol used for? (6)

ii) What is the default port number of HTTP protocol? (5)

iii) Discuss the features of HTTP and also discuss how HTTP works. (5)

4. Explain the importance of firewalls. (16)

5. Explain in detail the following

i) Fault management. (8)

ii) Security management. (8)

6. Write notes on Security protocols PGP & SSH (12)

7. Write notes on IMAP, POP3 (8)

8. Discuss the various commands used in FTP (12) (MAY/JUNE 2009)

9. Explain the salient features of the SMTP protocol (12) (MAY/JUNE 2009)

ALSO READ ..!

UNIT I NOTES
UNIT II NOTES
UNIT III NOTES
UNIT IV NOTES
UNIT V NOTES

CS 2302 CN - 16 MARKS

CLICK HERE TO OPEN 16 marks

CS2302 – COMPUTER NETWORKS (TWO MARKS) 2 marks - INFORMATION TECHNOLOGY , ANNA UNIVERSITY

CS2302 – COMPUTER NETWORKS

TWO MARKS

UNIT1- Network architecture – layers – Physical links – Channel access on links – Hybrid

multiple access techniques - Issues in the data link layer - Framing – Error correction

and detection – Link-level Flow Control

1. What are the three criteria necessary for an effective and efficient network?

The most important criteria are performance, reliability and security.

Performance of the network depends on number of users, type of transmission medium, and the capabilities of the connected h/w and the efficiency of the s/w.

Reliability is measured by frequency of failure, the time it takes a link to recover from the failure and the network’s robustness in a catastrophe.

Security issues include protecting data from unauthorized access and viruses.

2. Group the OSI layers by function?

The seven layers of the OSI model belonging to three subgroups.

Physical, data link and network layers are the network support layers; they deal with the physical aspects of moving data from one device to another.

Session, presentation and application layers are the user support layers; they allow interoperability among unrelated software systems.

The transport layer ensures end-to-end reliable data transmission.

3. What are header and trailers and how do they get added and removed?

Each layer in the sending machine adds its own information to the message it receives from the layer just above it and passes the whole package to the layer just below it. This information is added in the form of headers or trailers. Headers are added to the message at the layers 6,5,4,3, and 2. A trailer is added at layer2. At the receiving machine, the headers or trailers attached to the data unit at the corresponding sending layers are removed, and actions appropriate to that layer are taken.

4. What are the features provided by layering?

Two nice features:

· It decomposes the problem of building a network into more manageable components.

· It provides a more modular design.

5. Why are protocols needed?

In networks, communication occurs between the entities in different systems. Two entities cannot just send bit streams to each other and expect to be understood. For communication, the entities must agree on a protocol. A protocol is a set of rules that govern data communication.

6. What are the two interfaces provided by protocols?

· Service interface

· Peer interface

Service interface- defines the operations that local objects can perform on the protocol.

Peer interface- defines the form and meaning of messages exchanged between protocol peers to implement the communication service.

7. Mention the different physical media?

· Twisted pair(the wire that your phone connects to)

· Coaxial cable(the wire that your TV connects to)

· Optical fiber(the medium most commonly used for high-bandwidth, long-distance links)

· Space(the stuff that radio waves, microwaves and infra red beams propagate through)

8. Define Signals?

Signals are actually electromagnetic waves traveling at the speed of light. The speed of light is, however, medium dependent-electromagnetic waves traveling through copper and fiber do so at about two-thirds the speed of light in vacuum.

9. What is wave’s wavelength?

The distance between a pair of adjacent maxima or minima of a wave, typically measured in meters, is called wave’s wavelength.

10. Define Modulation?

Modulation -varying the frequency, amplitude or phase of the signal to effect the transmission of information. A simple example of modulation is to vary the power (amplitude) of a single wavelength.

11. Explain the two types of duplex?

· Full duplex-two bit streams can be simultaneously transmitted over the links at the same time, one going in each direction.

· Half duplex-it supports data flowing in only one direction at a time.

12. What is CODEC?

A device that encodes analog voice into a digital ISDN link is called a CODEC, for coder/decoder.

13. What is spread spectrum and explain the two types of spread spectrum?

Spread spectrum is to spread the signal over a wider frequency band than normal in such a way as to minimize the impact of interference from other devices.

· Frequency Hopping

· Direct sequence

14. What are the different encoding techniques?

· NRZ

· NRZI

· Manchester

· 4B/5B

15. How does NRZ-L differ from NRZ-I?

In the NRZ-L sequence, positive and negative voltages have specific meanings: positive for 0 and negative for 1. in the NRZ-I sequence, the voltages are meaningless.

Instead, the receiver looks for changes from one level to another as its basis for recognition of 1s.

16. What are the responsibilities of data link layer?

Specific responsibilities of data link layer include the following. a) Framing b) Physical addressing c) Flow control d) Error control e) Access control.

17. What are the ways to address the framing problem?

· Byte-Oriented Protocols(PPP)

· Bit-Oriented Protocols(HDLC)

· Clock-Based Framing(SONET)

18. Distinguish between peer-to-peer relationship and a primary-secondary relationship. peer -to- peer relationship?

All the devices share the link equally.

Primary-secondary relationship: One device controls traffic and the others must transmit through it.

19. Mention the types of errors and define the terms?

There are 2 types of errors

· Single-bit error.

· Burst-bit error.

Single bit error: The term single bit error means that only one bit of a given data unit (such as byte character/data unit or packet) is changed from 1 to 0 or from 0 to 1.

Burst error: Means that 2 or more bits in the data unit have changed from 1 to 0 from 0 to 1.

20. List out the available detection methods.

There are 4 types of redundancy checks are used in data communication.

· Vertical redundancy checks (VRC).

· Longitudinal redundancy checks (LRC).

· Cyclic redundancy checks (CRC).

· Checksum.

21. Write short notes on VRC.

The most common and least expensive mechanism for error detection is the vertical redundancy check (VRC) often called a parity check. In this technique a redundant bit called a parity bit, is appended to every data unit so, that the total number of 0’s in the unit (including the parity bit) becomes even.

22. Write short notes on LRC.

In longitudinal redundancy check (LRC), a block of bits is divided into rows and a redundant row of bits is added to the whole block.

23. Write short notes on CRC.

The third and most powerful of the redundancy checking techniques is the cyclic redundancy checks (CRC) CRC is based on binary division. Here a sequence of redundant bits, called the CRC remainder is appended to the end of data unit.

24. Write short notes on CRC checker.

A CRC checker functions exactly like a generator. After receiving the data appended with the CRC it does the same modulo-2 division. If the remainder is all 0’s the CRC is dropped and the data accepted. Otherwise, the received stream of bits is discarded and the dates are resent.

25. Define checksum.

The error detection method used by the higher layer protocol is called checksum. Checksum is based on the concept of redundancy.

26. What are the steps followed in checksum generator?

The sender follows these steps a) the units are divided into k sections each of n bits. b) All sections are added together using 2’s complement to get the sum. c) The sum is complemented and become the checksum. d) The checksum is sent with the data.

27. Mention the types of error correcting methods.

There are 2 error-correcting methods.

· Single bit error correction

· Burst error correction.

28. Write short notes on error correction?

It is the mechanism to correct the errors and it can be handled in 2 ways.

· When an error is discovered, the receiver can have the sender retransmit the entire data unit.

· A receiver can use an error correcting coder, which automatically corrects certain errors.

29. What is the purpose of hamming code?

A hamming code can be designed to correct burst errors of certain lengths. So the simple strategy used by the hamming code to correct single bit errors must be redesigned to be applicable for multiple bit correction.

30. What is redundancy?

It is the error detecting mechanism, which means a shorter group of bits or extra bits may be appended at the destination of each unit.

31. Define flow control?

Flow control refers to a set of procedures used to restrict the amount of data. The sender can send before waiting for acknowledgment.

32. Mention the categories of flow control?

There are 2 methods have been developed to control flow of data across communication links. a) Stop and wait- send one from at a time. b) Sliding window- send several frames at a time.

33. What is a buffer?

Each receiving device has a block of memory called a buffer, reserved for storing incoming data until they are processed.

34.What is the difference between a passive and an active hub?

An active hub contains a repeater that regenerates the received bit patterns before sending them out. A passive hub provides a simple physical connection between the attached devices.

35. For n devices in a network, what is the number of cable links required for a

mesh and ring topology?

· Mesh topology – n (n-1)/2

· Ring topology – n

36. Group the OSI layers by function. (MAY/JUNE2007)

The seven layers of the OSI model belonging to three subgroups. Physical, data link and network layers are the network support layers; they deal with the physical aspects of moving data from one device to another. Session, presentation and application layers are the user support layers; they allow interoperability among unrelated software systems. The transport layer ensures end-to-end reliable data transmission.

37.We have a channel with a 1 MHz bandwidth. The SNR for this channel is 63; what is the appropriate bit rate and signal level?

First, we use the Shannon formula to find our upper limit.

C = B log₂ (1 + SNR) = 10⁶ log₂ (1 + 63) = 10⁶ log₂ (64) = 6 Mbps

Then we use the Nyquist formula to find the

number of signal levels.

4 Mbps = 2 ´ 1 MHz ´ log₂ L è L = 4

= B log₂ (1) = B ´ 0 = 0

38.List the Channelization Protocols

n Frequency Division Multiple Access (FDMA)

n The total bandwidth is divided into channels.

n Time Division Multiple Access (TDMA)

n The band is divided into one channel that is time shared

n Code Division Multiple Access (CDMA)

n One channel carries all transmission simultaneously

39.What is protocol?What are its key elements?(NOV/DEC 2007)

Set of rules that govern the data communication is protocol. The key elements are

i)Syntax ii)Semantics iii)Timing

40.We have a channel with a 1 MHz bandwidth. The SNR for this channel is 63; what is the appropriate bit rate and signal level?