In order to make interaction between the nodes, there should be some kind of protocol to communicate. So I implement stop-and-wait protocol in this network.

And for that, there should be some timer and ack signals. Acorrding to Official Guide, I use

• simtime_t timeout; // timeout
• cMessage *timeoutEvent; // holds pointer to the timeout self-message

These two signals are designed to record the time when to send the message, and send the time-out message to the sender. The core function in this experiment is handleMessage(cMessage *msg);

• initialize()

  initialize the signals simtime_t timeout; and cMessage *timeoutEvent;, and generate the message, make msg_ to record that.

• sendACK(sdn_message *msg)

  use the method to get the sender and send ack to it.

• handleMessage(cMessage *msg)

  • if it is a msg message, then it should have a choice
    • if this is the destination, then finish this message and start a new one
    • else forward this message
  • if it is a ack message, then delete the timer
  • if it is a timeOut message, then retransfer the message

• generateMessage(char *a)

  generate the kind of a message and return it

  this method also set the source and destination for the message

• forwardMessage(sdn_message *msg)

  send the message to next random port

1. How to reply to the message in OMNet++?
2. use default method like setName() and getName() regularly for cMessage*
3. getVectorSize() will return the total gates in network, while gateSize("gate") will only return the number of nodes attached to this node.