Slow Start Backoff Algorithm for Ad-Hoc - GeeksforGeeks

17 Jan, 2022
If the receiver proclaims a large window-size, larger than what the network en-route can manage, then there will always be packet losses. So there will be re-transmissions as well. However, the sender can’t send all the packets for which ACK (Acknowledgement) has not been received. Because of this way, even more congestion in the network will be caused. Moreover, the sender cannot be sure about the packets that have been lost due to transmission. It might be that this is the only packet that has been lost. It will also be not know how many packets have been actually received and buffered by the receiver. In that case, the sender will have superfluously sent various packets.So the re-transmission of the packets also follows slow – start backoff mechanism. However, we do precisely need to keep an upper bound on the size of the packets as it gets increases in slow start, to prevent it from the increasing in unbounded and causing congestion. In slow – start backoff mechanism the threshold window size is half the value of the size of the congestion window.Prerequisite: Back-off Algorithm for CSMA/CD Algorithm of Slow-Start Mechanism:-  
repeat
 if ACK frame received then successful transmission
  if current backoff window size <= Wm then
   if current backoff window size = W0 then
    current backoff window size = W0
  else
  current backoff window size =  current backoff window size ÷ 2
 else
 current backoff window size = current backoff window size-W0
else
 if current backoff window size < Wm then
 current backoff window size = current backoff window size × 2
  else frame lost due to collision or interference
   if current backoff window size = Wn then
   current backoff window size = Wn
   else
 current backoff window size = current backoff window size +W0
until no more frame to transmit
end
Examples:  
This represents the successful transmission because Threshold window is lesser the current window. Input : Enter the Threshold value:–>512 Enter the Current backoff window size:–>64 Output : Backoff Window Size is:–>128 Backoff Window Size is:–>96 Successful transmission Backoff Window Size is:–>32 Successful transmission Backoff Window Size is:–>32 Backoff Window Size is:–>128 Backoff Window Size is:–>96 Successful transmission Backoff Window Size is:–>32This represents the unsuccessful transmission because the threshold window is greater the current window. Input : Enter the Threshold value:–>512 Enter the Current backoff window size:–>1024 Output : Frame lost due to collision or interferenceBackoff Window Size is:–>1056 Successful transmission Backoff Window Size is:–>512 Successful transmission Backoff Window Size is:–>512 Frame lost due to collision or interferenceBackoff Window Size is:–>1056 Successful transmission Backoff Window Size is:–>512  
Notations:- 
W0 -->  Initial backoff window size
Wm -->  Threshold
Wn -->  Maximum backoff window size
ACK --> Acknowledgement
Curr_BT --> Current  backoff window size
Implementation of the Slow-Start Mechanism:- 
CPP
#include <cstdlib>#include <iostream>#include <math.h>#include <random>#include <string>#include <time.h> using namespace std; void signal(int array_ACK[]){    srand(time_t(0));    for (int i = 0; i < 5; i++) {        array_ACK[i] = rand() % 2;    }} void Slow_Start_Backoff(int Wm, int Wo, int Wn,                        int Curr_BT, int array_ACK[]){    // Taking ACK Binary values in    // array by user one by one     // backoff_win_size defines    // backoff window size     int backoff_win_size = 0;     // Printing of backoff window size takes place     for (int j = 0; j < 5; j++) {        if (array_ACK[j] == 1) {            cout << "Successful transmission" << endl;            if (Curr_BT <= Wm) {                if (Curr_BT == Wo) {                    Curr_BT = Wo;                    cout << "Backoff Window Size is:-->"                            << Curr_BT << endl;                }                else {                    Curr_B= Curr_BT / 2;                    cout << "Backoff Window Size is:-->"                            << Curr_BT << endl;                }            }            else {                Curr_BT = Curr_BT - Wo;                cout << "Backoff Window Size is:-->"                        << Curr_BT << endl;            }        }        else {            if (Curr_BT < Wm) {                Curr_BT = Curr_BT * 2;                cout << "Backoff Window Size is:-->"                        << Curr_BT << endl;            }            else {                cout << "Frame lost due to collision"                        <<" or interference";            }            if (Curr_BT == Wn) {                Curr_BT = Wn;                cout << "Backoff Window Size is:-->"                        << Curr_BT << endl                            << endl;            }            else {                Curr_BT = Curr_BT + Wo;                cout << "Backoff Window Size is:-->"                        << Curr_BT << endl;            }        }    }} // Driver Codeint main(){    int Wm, Wo, Wn, Curr_BT;    int array_ACK[5];     Wo = 32; // Initial backoff window size    Wn = 1024; // Maximum backoff window size     // Curr_BT defines the current backoff window size     cout << "Enter the Threshold value:-->";    cin >> Wm; // Threshold backoff window size    cout << "Enter the Current backoff window size:-->";    cin >> Curr_BT;    signal(array_ACK);    Slow_Start_Backoff(Wm, Wo, Wn, Curr_BT, array_ACK);     return 0;}
How the data sent in the form of packets through the network:-Any type of data gets converted into the binary format and this binary format contains 0’s and 1’s bytes which gets divided into the small binary bit sequences called packets.Now, we are implementing code in which the random matrix of 0’s and 1’s generates and suppose the binary file bit sequence arranged in the matrix row-wise in fixed-length (Taking a Length 10). Then each row of the matrix represents a single data packet that is going to be transmitted.Implementation of the Random Matrix Generator:-
CPP
// C++ program to construct the// Random Matrix Generator.#include <iostream>#include <iterator>#include <list>#include <random>#include <string>using namespace std; void showlist(list<string> l1){    list<string>::iterator it;    cout << "list of frame packets are "            <<"show as below :-> " << endl;    cout << endl;         for (it = l1.begin(); it != l1.end(); ++it)        cout << *it << endl;    cout << '\n';} // Driver Codeint main(){    int x, y, k = 1;    string s, s1, s2;         list<string> l1;         srand(time_t(0));         cout << "Rows: " << endl;    cin >> x;         cout << "Columns: " << endl;    cin >> y;         int randomNums[x][y];    std::string temp[x];         int random;         for (int i = 0; i < x; i++) {             // This loop is for the row        for (int p = 0; p < y; p++) {                         // Here you would randomize each            // element for the array.            random = rand() % 2;            randomNums[i][p] = random;        }    }     for (int i = 0; i < x; i++) {                 // This loop is for the row        for (int p = 0; p < y; p++) {                         // Here you would randomize each            // element for the array.            cout << randomNums[i][p] << "\t";        }                 cout << endl;    }    cout << endl;         // concatenation of the bits in the matrix row    // to form a single data packet    for (int i = 0; i < x; i++) {                 temp[i] = to_string(randomNums[i][0]);                 for (int j = 0; j < y; ++j) {                         s1 = temp[i];            s2 = to_string(randomNums[i][j]);             s = s1 + s2;             temp[i] = s;            k++;        }                 temp[i].erase(temp[i].begin() + 1);        l1.push_back(temp[i]);    }     showlist(l1);    return 0;}
Example:  
Input: Rows: 10 Columns: 10 Output: 0 1 1 0 1 1 0 1 0 1 0 0 0 0 0 0 1 1 0 0 0 1 1 0 1 1 0 1 1 1 0 1 0 0 0 0 1 0 0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 0 1 0 1 1 1 0 0 0 1 1 0 0 1 1 0 1 1 1 0 0 1 1 0 0 0 1 1 1 0 0 1 0 1 1 1 1 0 1 0 1 1 0 0 1 1 1 list of frame packets are show as below :-> 0110110101 0000001100 0110110111 0100001000 0011001000 0000101110 0011001101 1100110001 1100101111 0101100111  
Reference: Slow Start Backoff Algorithm for Ad-Hoc Wireless Networks
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