Not a lot is known about GRED. It looks like GRED with several internal queues, whereby the internal queue is chosen based on the Diffserv tcindex field. According to a slide found here, it contains the capabilities of Cisco's 'Distributed Weighted RED', as well as Dave Clark's RIO.
Each virtual queue can have its own Drop Parameters specified.
FIXME: get Jamal or Werner to tell us more
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