backbone routers' priority settings for ICMP & UDP

["Marko B." <mrako () notwork net>]

Greetings,

In my travels I have heard numerous times that it is a popular practice to
give ICMP and even UDP traffic a lower priority on backbone routers in
times of congestion. 

Are there any providers that document this policy? How is this policy
carried out on the actual hardware? Any pointers would be appreciated.

Thanks.

-Marko