OS

 /* link.c */

#include <fcntl.h>
int main(int argc, char * argv[]) {
link(argv[1],argv[2]);
return 0;
}

/* mkdir.c */
#include <fcntl.h>
int main(int argc, char * argv[]) {
mkdir(argv[1],0700);
return 0;
}

/* unlink.c */
#include <fcntl.h>
int main(int argc, char * argv[]) {
unlink(argv[1]);
return 0;
}

/* myexec.c */ #include <stdio.h> main () { printf ("I'm process %d and I'm about to exec an ls -l\n",getpid ()); execl ("/bin/ls", "ls", "-l", NULL); /* Execute ls */ printf ("This line should never be executed\n"); }

NETWORK LAYERS

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Network Security

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Basic Security Concepts

Three basic security concepts important to information on the internet are confidentiality, integrity, and availability.

What Is Hacking?


Hacking is quite simply the attempt to gain access to a computer system without
authorization.

What is Network Security?

Activities designed to protect your network are referred to as network security

Two OO Design Principles

Cohesion and Coupling

Cohesion and Coupling deal with the quality of an OO design. Generally, good OO design calls for loose coupling and high cohesion. The goals of OO designs are to make the application

• Easy to Create
• Easy to Maintain
• Easy to Enhance

COUPLING:


Coupling is the degree to which one class knows about another class. Let us consider two classes class A and class B. If class A knows class B through its interface only i.e it interacts with class B through its API then class A and class B are said to be loosely coupled.
If on the other hand class A apart from interacting class B by means of its interface also interacts through the non-interface stuff of class B then they are said to be tightly coupled. Suppose the developer changes the class B‘s non-interface part i.e non API stuff then in case of loose coupling class A does not breakdown but tight coupling causes the class Ato break.
So its always a good OO design principle to use loose coupling between the classes i.e all interactions between the objects in OO system should use the APIs. An aspect of good class and API design is that classes should be well encapsulated.

COHESION:

Cohesion is used to indicate the degree to which a class has a single, well-focused purpose. Coupling is all about how classes interact with each other, on the other hand cohesion focuses on how single class is designed. Higher the cohesiveness of the class, better is the OO design.
Benefits of Higher Cohesion:

• Highly cohesive classes are much easier to maintain and less frequently changed.
• Such classes are more usable than others as they are designed with a well-focused purpose.

Computer Network Lab

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IPV4 TO IPV6

CN-VIDEO

http://www.youtube.com/watch?v=ETsfylK7kzM&feature=relmfu

J2EE

CN

1. What are the two types of transmission technology available?
       (i) Broadcast and (ii) point-to-point