Lab 2. Questions 3,4 and 5

Tiara Barias
Lab 2
February 5, 2014

# 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? Repeat this question for a 2m long link with 10bps transmission rate. Assume that the propagation speed is equal to the speed of light.

length of transmission= 36,000m

speed of transmission= 1 Gbps

propagation= 3.0*10^8 m/s which equals 299,792,458 m/s

Propagation Delay formula,also represented by (D) formula as shown in the video notes: length/ speed of light also represented by (C)

D= 36,000/299.792,458 m/s

  =0.12 m/s

transmission delay formula: M/R + D

M= bits

R= rate

rate= 1 Gbps= 10^9=84 ms

Transmission delay: 10*2^20*8/10^9=84 ms

Latency formula= transmission delay + propagation delay

Latency= 0.12+84= 84.12 ms

Part two of same question:

length of transmission= 2m

speed of transmission= 10bps

propagation speed of light= 3.0*10^8 m/s which equals 299,792,458 m/s

Propagation Delay formula,also represented by (D) formula as shown in the video notes: length/ speed of light also represented by (C)

D=2/299,792,458 ms

  =6.67*10^6 ms

transmission delay= 10*2^20*8/10= 8.4*10^9 ms

latency= 6.67*10^-6+8.4*10^9= 8.4*10^9ms

#4) We will start working on a group project that implements “Interprocess communication using pipes”. Pipes is one of the ways to implement IPC. Write a blog that explains the functions needed to implement IPC using pipes and also those needed for communication using shared memory.

popen() : this begins another to send and receive data

pclose() : this ends the file stream that was opened

fread() : this is used to read data from the file opened by the popen

fwrite() : this is used to write data to the file

shmget() :  this allows us to accesses memory that is shared

shmctl() : this alters characteristics and permissions of a shared memory

shmat() :  this connects memory portions

shmdt() : this breaks memory portions

#5) fread and fwrite are C functions that can read bytes (instead of lines, or strings, char etc) from a file. Describe these functions and also write short programs that demonstrate them. 

fread: is used to read data from the file opened

fwrite: is used to write data to a file.

basically they do opposite jobs.

fread function: 

size_p fread(void *ptr, size_p size, size_p nmemb, FILE *stream);

fwrite function:

size_p fwrite(const void *ptr, size_p size, size_p nmemb, FILE *stream);