Ad-Hoc的慢启动退避算法

如果接收器宣称有一个大的窗口大小，大于网络途中可以管理的大小，那么总会有数据包丢失。因此也会有重新传输。但是，发送方无法发送尚未收到ACK(确认)的所有数据包。由于这种方式，将在网络中引起更多的拥塞。而且，发送者不能确定由于传输而丢失的分组。可能这是唯一丢失的数据包。也将不知道接收器实际已经接收和缓冲了多少个分组。在这种情况下，发送方将多余地发送各种数据包。
因此，数据包的重传也遵循缓慢的–启动退避机制。但是，我们确实需要在缓慢启动时增加数据包大小的上限，以防止数据包无限制增长并导致拥塞。慢速启动机制
阈值窗口大小是拥塞窗口大小的一半。
先决条件： CSMA / CD的退避算法
慢启动机制算法：-

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

例子：

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:–>32
This represents the unsuccessful transmission because Tthe hreshold 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 
 

表示法：-

W0 -->  Initial backoff window size
Wm -->  Threshold
Wn -->  Maximum backoff window size
ACK --> Acknowledgement
Curr_BT --> Current  backoff window size

慢启动机制的实现：

CPP

#include 
#include 
#include 
#include 
#include 
#include 
 
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 Code
int 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;
}

数据如何以分组形式通过网络发送：-
任何类型的数据都将转换为二进制格式，并且此二进制格式包含0和1的字节
它被分成一些小的二进制位序列，称为数据包。
现在，我们正在实现其中生成0和1的随机矩阵的代码，并假设二进制文件位序列以固定长度(以长度10计)按行排列。然后，矩阵的每一行代表将要发送的单个数据包。
随机矩阵生成器的实现：

CPP

// C++ program to construct the
// Random Matrix Generator.
#include 
#include 
#include 
#include 
#include 
using namespace std;
 
void showlist(list l1)
{
    list::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 Code
int main()
{
    int x, y, k = 1;
    string s, s1, s2;
     
    list 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;
}

例子：

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 
 

参考： Ad-Hoc无线网络的慢速启动退避算法