Question

Please type answer do not hand write. Thank you

Write a program that implements message flow from the top layer to the bottom layer
of the 7-layer protocol model. Your program should include a separate protocol function
for each layer. Protocol headers are sequence up to 64 characters. Each protocol
function has two parameters: a message passed from the higher layer protocol (a char
buffer) and the size of the message. This function attaches its header in front of the
message, prints the new message on the standard output, and then invokes the protocol
function of the lower-layer protocol. Program input is an application message (a sequence
of 80 characters or less).

Answer 1

Answer is as follows:

Code is as follows : Written in C language.

#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#include "assert.h"

void application_layer_send(char *buffer, int len);
void presentation_layer_send(char *buffer, int len);
void session_layer_send(char *buffer, int len);
void transport_layer_send(char *buffer, int len);
void network_layer_send(char *buffer, int len);
void datalink_layer_send(char *buffer, int len);
void physical_layer_send(char *buffer, int len);

char* attach_header(char *buffer, char *header, int *len2) {
int len = strlen(buffer);
int hlen = strlen(header);
*len2 = len + hlen;

char *buffer2 = (char*)malloc(*len2 + 1);
memcpy(buffer2, header, hlen);
memcpy(buffer2 + hlen, buffer, len);
buffer2[*len2] = '\0';

return buffer2;
}

void application_layer_send(char *buffer, int len) {
static char header[] = "application_layer_header;";
assert(strlen(buffer) == len);

int len2 = 0;
char *buffer2 = attach_header(buffer, header, &len2);
printf("%s\n", buffer2);

presentation_layer_send(buffer2, len2);
free(buffer2);
}

void presentation_layer_send(char *buffer, int len) {
char header[] = "presentation_layer_header;";
assert(strlen(buffer) == len);

int len2 = 0;
char *buffer2 = attach_header(buffer, header, &len2);
printf("%s\n", buffer2);

session_layer_send(buffer2, len2);
free(buffer2);
}

void session_layer_send(char *buffer, int len) {
char header[] = "session_layer_header;";
assert(strlen(buffer) == len);

int len2 = 0;
char *buffer2 = attach_header(buffer, header, &len2);
printf("%s\n", buffer2);

transport_layer_send(buffer2, len2);
free(buffer2);
}

void transport_layer_send(char *buffer, int len) {
char header[] = "transport_layer_header;";
assert(strlen(buffer) == len);

int len2 = 0;
char *buffer2 = attach_header(buffer, header, &len2);
printf("%s\n", buffer2);

network_layer_send(buffer2, len2);
free(buffer2);
}

void network_layer_send(char *buffer, int len) {
char header[] = "network_layer_header;";
assert(strlen(buffer) == len);

int len2 = 0;
char *buffer2 = attach_header(buffer, header, &len2);
printf("%s\n", buffer2);

datalink_layer_send(buffer2, len2);
free(buffer2);
}

void datalink_layer_send(char *buffer, int len) {
char header[] = "datalink_layer_header;";
assert(strlen(buffer) == len);

int len2 = 0;
char *buffer2 = attach_header(buffer, header, &len2);
printf("%s\n", buffer2);

physical_layer_send(buffer2, len2);
free(buffer2);
}

void physical_layer_send(char *buffer, int len) {
char header[] = "physical_layer_header;";
assert(strlen(buffer) == len);

int len2 = 0;
char *buffer2 = attach_header(buffer, header, &len2);
printf("%s\n", buffer2);

free(buffer2);
}

void application_routine() {
char message[] = "Hello World!";
application_layer_send(message, strlen(message));
}

int main(int argc, char *argv[]) {
application_routine();
return 0;
}

if there is any query please ask in comments...