and dirservers are better for non-clique situations

svn:r668

doc/tor-design.tex

@@ -679,11 +679,14 @@ the shared directory is straightforward, and is described in the Tor
 specification \cite{tor-spec}.
 % we should, uh, add this to the spec. oh, and write it. -RD
 
-Because the directories are signed, they can be cached at all the other
-onion routers (or even elsewhere). Thus directory servers are not a
-performance bottleneck when we have many users, and also they won't
-aid traffic analysis by forcing clients to periodically announce their
-existence to any central point.
+Using directory servers rather than flooding approaches provides
+simplicity and flexibility. For example, they don't complicate
+the analysis when we start experimenting with non-clique network
+topologies. And because the directories are signed, they can be cached at
+all the other onion routers (or even elsewhere). Thus directory servers
+are not a performance bottleneck when we have many users, and also they
+won't aid traffic analysis by forcing clients to periodically announce
+their existence to any central point.
 
 \Section{Rendezvous points: location privacy}
 \label{sec:rendezvous}