fig-3-11.c

计算机网络第四版的实现源代码

/* Protocol 2 (stop-and-wait) also provides for a one-directional flow of data from
   sender to receiver. The communication channel is once again assumed to be error
   free, as in protocol 1. However, this time, the receiver has only a finite buffer
   capacity and a finite processing speed, so the protocol must explicitly prevent 
   the sender from flooding the receiver with data faster than it can be handled. */

typedef enum {frame_arrival} event_type;
#include "protocol.h"

void sender2(void)
{
  frame s;			/* buffer for an outbound frame */
  packet buffer;		/* buffer for an outbound packet */
  event_type event;		/* frame_arrival is the only possibility */

  while (true) {
        from_network_layer(&buffer); /* go get something to send */
        s.info = buffer;	/* copy it into s for transmission */
        to_physical_layer(&s);	/* bye-bye little frame */
        wait_for_event(&event);	/* do not proceed until given the go ahead */
  }
}

void receiver2(void)
{
  frame r, s;	/* buffers for frames */
  event_type event;		  /* frame_arrival is the only possibility */
  while (true) {
        wait_for_event(&event);	  /* only possibility is frame_arrival */
        from_physical_layer(&r);  /* go get the inbound frame */
        to_network_layer(&r.info);/* pass the data to the network layer */
        to_physical_layer(&s);	  /* send a dummy frame to awaken sender */
  }
}