RE: [GD-General] UDP questions

[Jaek S. <smi...@cs...>]

> >   - It may be corrupt
> 
> This I'm not sure about -- isn't a CRC check part of the UDP and TCP
> protocols, or is this something that every application is expected to
> implement?  I know that some application protocols do CRC (e.g. Quake)
> but I was under the impression this was more to stop cheating, not to
> verify that the data wasn't corrupted.

TCP definately is guarenteed data-wise, order-wise, etc.

UDP, however, uses only a quick CheckSum - which, I believe, can be turned off.

With a quick search, here's a quote:

  "the Internet checksum is not foolproof ... it is still
  possible that there are undetected errors in the segment.
  For this reason, a number of protocols use more
  sophisticated error detection techniques than simple
  checksumming."
  ( http://www-net.cs.umass.edu/kurose/transport/UDP.html )

Also, another quote (from the same page):

  "Although UDP provides error checking, it does not
  do anything to recover from an error. Some implementations
  of UDP simply discard the damaged segment; others pass the
  damaged segment to the application with a warning. "
  ( http://www-net.cs.umass.edu/kurose/transport/UDP.html )

I can't guarentee the quality of the above information.  However, it matches my understanding from when I studied the TCP/IP protocol several years ago.  (If only my memory weren't volatile I could guarentee my answers also, heh).

About a year ago I found out about a protocol being developed (that I think was being build on top of IP - same layer as TCP and UDP) that did guarenteed messaging.  I can't remember the name - should see if I can find some info / status.  Streams are just so wrong in the world of software data communications. :P

Later for now
--Jaek