What is the Difference between Windows ICMP.DLL and ICMP on HP-UNIX?

I am having trouble with our network dropping packets, when I run a traceroute from Windows it shows the dropped packets, but if I run a trace from a HP-Unix box at the same time the Unix Box doesn't show any drops. I know there is a problem because my Users who are accessing Unix across the network through a TNVT telnet session are experiencing their screens scrolling, pausing and just hanging. If I ping across the network it shows no dropped packets, not even one. Ping times run between 1ms to 14ms and nothing lost. Traceroute shows the drop on the outside IP Address of my routers. I ran traces in both directions and the drop is always on the outside of the routers. Thanks for any help on this!