omnet++ 示例13練習題

Exercise: you’ll notice that this simple “routing” is not very efficient: often the packet keeps bouncing between two nodes for a while before it is sent to a different direction. This can be improved somewhat if nodes don’t send the packet back to the sender. Implement this. Hints: cMessage::getArrivalGate(), cGate::getIndex(). Note that if the message didn’t arrive via a gate but was a self-message, then getArrivalGate() returns NULL. 。

原有例子中存在消息在兩個節點間來回“bouncing”（跳），使得消息到達目的節點的路由過程低效。示例要求改進原有路由政策，即避免将消息傳給發送者。這裡有有兩個注意的地方：

1. 會出現getSize=1的情況，即消息所在的節點隻有一個連接配接節點，那麼此時消息隻能原路傳回
2. 示例中提到的self-message情況，此時的arrivalgate=NULL

forwardMessage函數的代碼如下：

void Txc1::forwardMessage(cMessage *msg)
{
    int n = gateSize("out");
    EV << "The number of gates:" << n << "\n";
    int k = intuniform(, n-);
    cGate *arrivalGate = msg->getArrivalGate();
    if((arrivalGate == NULL)||(n==))
    {
        EV << "Forwarding message " << msg << " on port out[" << k << "]\n";
        send(msg, "out", k);
    }
    else{
        int arrivalGateIndex = arrivalGate->getIndex();
        EV << "arrivalGateIndex: " << arrivalGateIndex << ".\n";
        while(k == arrivalGateIndex)
                k = intuniform(, n-);
        EV << "Forwarding message " << msg << " on port out[" << k << "]\n";
        send(msg, "out", k);
    }
}
           

結果圖：