[expert] Fine tuning my PPP?

[vern]

Hello All!
On modifying my options on the
PPP service to work with my raggedy
old 24K intermittent phone lines.
I've set my MTU, and MRU to 296
to minimize the packet fragmentation.
(I hope) I ran across the "noipx" command
an wondered what "IPX" stood for, do I
need it? And why should I care??   Every
single packet is precious and I need every
clock cycle I can latch on to!
Thanks for any help!
Vern