Lab 2 by Shahzaman Akbar

Question 3:

Consider a transmission link that is 36000m long and uses 1Gbps transmission speed.

 How long will it take to transmit a 10MB file along this link?

Answer:

Length of transmission link = 36000 m

Speed of transmission = 1Gbps

Propagation speed of light = 3.0 x 10^8 m/s (which is equal to 299,792,458 metres per second).

Formula for Propagation Delay (D) = Length / speed of light (C)

By plugging in the value we get  

             D = 36000 / 299792458 we will get approximately .00012seconds which is 0.12ms.

Formula for transmission delay = M(bits)/ Rate (bits/sec) = M/R seconds

M = length of message

R = transmission speed

Rate(bits/sec) = 1 gbps = 10^9 bits 

M(bits): 10MB

By plugging the values we get

T-delay = 10*2^20*8 / 10^9 = approximately 84ms

 Formula for Latency (L) = T-delay + propagation delay (D)

L = .12 + 84  = 84.12ms

Question 3b.

For a 2m long link with 10bps transmission rate. Assume that the propagation speed is equal to the speed of light.

Answer:

Length of transmission link = 2m

Speed of transmission = 10bps

Propagation speed of light = 3.0 x 10^8 m/s (which is equal to 299,792,458 metres per second).

Formula for Propagation Delay (D) = Length / speed of light (C)

By plugging in the value we get  

             D = 2 / 299792458 we will get approximately 6.67 * 10^6 ms.

Formula for transmission delay = M(bits)/ Rate (bits/sec) = M/R seconds

M = length of message

R = transmission speed

By plugging the values we get

T-delay = 10*2^20*8 / 10 = approximately 8.4 * 10^9ms

 Formula for Latency (L) = T-delay + propagation delay (D)

L = .6.67 * 10^-6 +8.4 * 10^9  = 8.4 * 10^9 ms

Question 4:

PIPES:

A pipe is a serial communication device (i.e., the data is read in the order in which it was written). The data written to end is read back from the other end.

The pipe is mainly used to communicate between two threads in a single process or between parent and child process. Pipes can only connect the related process. In shell, the symbol | can be used to create a pipe.


Pipes Functions: pipe()
Pipe functions are used for passing data between two programs and also allows to read and write the data.
#include<unistd.h>
  int pipe(int file_descriptor[2]);

Ø  pipe()function is passed with an array of file descriptors. It will fill the array with new file descriptors and returns zero. On error, returns -1 and sets the error to indicate the reason of failure.

Ø  The file descriptors are connected in a way that is data written to file_ descriptor[1] can be read back from the file_descriptor[0].

Popen() and Pclose() functions.

Popen();

FILE *Popen(const char *type ,  const char *open-mode);

(Note)       On failure Popen() will returns a NULL pointer.

Pclose();

                         int Pclose(FILE *stream_close);

                       (Note)       By using Pclose(), we can close the filestream associated with Popen().

                       

Shared memory:

A process can allocate a shared memory by using shmget() function.

                                       #include<sys/shm.h>
                                         int shmget(key_K key,size_K size,int shmflg);

Ø  The first parameter is the integer key that specifies which segment to create.

Ø  The second parameter specifies the number of bytes in the segment. 

Ø  The third parameter is the flag values, which specifies the options to shmget().

shmat():

shmat() function is used to attached to the address space of a process.

void *shmat(int shmid, const void *shmaddr, int shmflg);

Ø  The first parameter is the shm_id,identifier returned by the shmget().

Ø  The second parameter is the address at which the segment is to be attached to the current process.

Ø  The third parameter is the flag value.

shmctl();

The shmctl()will return the information about a shared memory segment and it can also be modified.

int shmctl(int shmid, int cmd, struct shmid_ds *buf);

shmdt():

The shmdt function will detach the shared memory from the current process.

shmdt(const void *shmaddr);

It takes the pointer to the address returned by the shmget as the parameter.   On success it returns 0,and -1 on error.



QUESTION 5:

#include <stdio.h>

#include <string.h>

int main()

{

               int i, j, k;

               FILE *fd, *fr;

               char buff[100];

               memset(buff, 0, sizeof(buff));

               fd = fopen("text.c", "rw+");

               if(fd == NULL)

               {

                               printf("Error: fopen()");

                               return 0;

               }

               i = fread(buff, 1, 100, fd);

               if(i != 100)

               {

                               printf("Error: fread()");

                               return 0;

               }

               printf("File Content\n%s", buff);

               fr = fopen("test.txt", "rw+");

               if(fr == NULL)

               {

                               printf("FR:Error fopen()");

                               return 0;

               }

               i = fwrite(buff, 1, 100, fr);

               if(i != 100)

               {

                               printf("fr:Error fwrite()");

                               return 0;

               }

               fclose(fd);

               fclose(fr);

               return 0;

}