WiMax security in mesh mode

Hi, I've been reading about the security features of 802.16-2004 (or
802.16d) in mesh mode, but there is something I don't quite
understand.

When a node wants to be authorized in mesh mode, it finds a sponsor
node that securely tunnels traffic towards the BS. The last message in
the authorization procedure contains both an Operator Shared Secret
(OSS) that and an Authorization Key (AK). The AK is sent encrypted
with the joining node's public key, but for the OSS no encryption is
mentioned. In mesh mode the OSS is used instead of the AK to grant the
joining node access. Is the OSS really sent from the sponsor node to
the joining node without being encrypted?


Espen