URN namespaces

[RikSaunderson]

Hi there,
I'm trying to understand the most modern implementations of gnutella, and, so far as I can see, none of the modern clients really pass files around using their filenames any more, they mostly use urn:sha1 hashes. (I've been using wireshark to capture transfers from Limewire, Frostwire, Gnutella-Turbo and Shareaza).

Having read the HUGE spec, it talks about the possibility of using several different urn namespaces in the format urn:namespace:info, it mentions the urn:bitprint namespace for one.

My question is, are there any urn namespaces other than sha1 in common use, and, if so, could you provide me with a specification for thier use?
Thanks,
Rik