>I'm completely new to HiPPi, can you refer me to any document
>on HiPPi's architecture ? 

Check out:

GigaLabs -  www.gigalabs.com

Essential(Optical Data Solutions) - www.ods.com

There might be other vendors as well.  

>I'm most interested in learning how that 500 ns latency is 
>defined and achieved. Thanks.

In the most basic terms:  they throw money at it.  *8^)

Enjoy,
Paul