Question

So for our first assignment we made a basic ftp program using TCP, now we have to modify it to use UDP, also sending it to a router program (that we cannot modify, but have the code to look at) that will randomly drop and delay packets and handle it with a simple stop and wait protocol. But that’s not the problem.

I modified the Client and Server to use UDP using the notes from my lab teacher (http://www.cs.concordia.ca/~ste_mors/comp445/Assign2tutorial.ppt) and all I’m doing is sending a packet and when I receive it on the other end print a line of text. I followed the instructions in the slides, running it on localhost (have no other machines to test with) and it sends, and the router confirms it receives and forwards the packet, but the server never prints the line of text. Knowing that UDP drops packets a lot I made a while(true) loop that sends packets forever, the server still does nothing.

Here’s the code so far:
Client: http://pastebin.com/XdbxuJ9R
Server: http://pastebin.com/iN5j2Ku3
Unmodifiable Router given to us: http://pastebin.com/QwMAc0MW

For the client i left in everything after the connection starts from the old one, the send line is 175, in server I commented out everything in the run loop except the receive part which is at line 181

I’m going absolutely crazy trying to fix this. I had to cancel plans and ruin my entire day because I can’t get this one thing working. 🙁

Answer 1

From what i can tell you’re using the wrong ports. Here’s what the router.h defines:

// router.h
#define ROUTER_PORT1 7000 //router port number 1
#define ROUTER_PORT2 7001 //router port number 2
#define PEER_PORT1 5000   //port number of peer host 1
#define PEER_PORT2 5001   //port number of peer host 2

And here’s what you’re defining:

// client.cpp
#define REQUEST_PORT 0x5000 // hexadecimal, that's port 20480

and

// server.cpp
#define REQUEST_PORT 0x5001 // hexadecimal, that's port 20481

I didn’t check the rest of the code, but the server appeared to receive something after correcting the port numbers (as in removing the 0x prefix)

Maybe this will help illustrate how the router works:

// the router does (pseudocode):
recvfrom(7000), sendto(PEER2:5001)
recvfrom(7001), sendto(PEER1:5000)