UDP and IP fragmentation

[Philip Lavine <source_route () yahoo com>]

To all,

I am running a Windows based high performance computing application that uses "reliable" multicast (29West) on a 
gigabit LAN. All systems are logically on the same VLAN and even on the same physical switch The application is set to 
use an 8k buffer and therefore results in IP fragmentation when datagrams are transmitted. The application is sensitive 
to any latency or data loss (of course) and uses a proprietary mechanism to create TCP-like retransmissions in case 
there is any actual data loss. Unfortunately, becasue of the fragmentation during the retransmission window all ip 
fragments must be resent even though only one may have been lost.

If the buffer size is tweeked to the ~1460 this may fix the fragmentation but will the side effects be less throughput 
and possibly more latency. Is there a sweet spot for UDP on an ethernet segment? 

Philip