chan request = [0] of { byte };
chan reply = [0] of { byte };

active [2] proctype Server() {
  byte num;
end:
  do
    :: request ? num -> 
       printf("Client %d processed by server %d\n",
	      num, _pid);
       reply ! _pid
  od
}

active [2] proctype Client() {
  byte server;
  request ! _pid;
  reply ? server;
  printf("Reply received from server %d by client %d\n",
	 server, _pid)
}