Subject: [Ospf-manet] Active Overlapping Relays

From: "Spagnolo, Phillip A" <[email-masked]>
Date: Tue, 22 Nov 2005 12:52:55 -0800

Alavro,

At the OSPF meeting, you stated that active overlapping relays (OR)s are
selected in "zero" time.  I objected to this statement because
algorithms do not run in "zero" time.  These statements indicate that we
had some miscommunication.

After the meeting, you further explained that all neighbors of a node
are active ORs by default so upon initialization of a neighbor the
selection takes "zero" time (as you stated).  The delay will be seen
during the time it takes to deselect the active ORs, so they become
non-active ORs.  Additionally, I will state that this scenario is only
relevant during initialization of a neighbor.

Do you agree with these statements, or do we still have some
miscommunication?

Can you point me to the location in your draft that explains the
deselect?  I read through the draft again, and I can't find the
deselect.  I see (as we stated at the meeting) that all routers are
non-active overlapping relays by default, but I am missing the active
ORs initial state.

Thanks,

Phil Spagnolo 
Network Technology Engineer 
The Boeing Company 
Phone:  (425) 865-6723

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From: Alvaro Retana <[email-masked]>
Date: Wed, 23 Nov 2005 13:39:43 -0500

On 11/22/2005 3:52 PM, Spagnolo, Phillip A wrote:

> Do you agree with these statements, or do we still have some

Yes, we're in sync now. :-)

Just one nit to be clear.  The impact of the "deselecting" delay is that 
(during the time that it takes to figure out and communicate which nodes 
should be active) all nodes will flood the LSAs resulting in more 
overhead, but not preventing the flooding from happening.  In other 
words, a node can flood information as soon as it discovers a new peer 
-- it doesn't have to wait to learn the 2-hop neighborhood and make a 
decision.

> non-active overlapping relays by default, but I am missing the active

I went to read the draft myself and you're right, it isn't really clear 
about that initial state.  In fact, I only found a few hints as to the 
intended operation:

3.4.1  Operation Overview

    ...

    A speaker receives router LSAs from its adjacent neighbors.  A
    speaker's router LSA conveys the list of the adjacent speakers of the
    originator ("neighbor list").  The local speaker can compare the
    neighbor list reported by each speaker to its own neighbor list.  If
    the local neighbor list contains adjacent speakers that the
    originator cannot reach directly (i.e. those speakers that are not in
    the originator's neighbor list), then these speakers are locally
    known as non-overlapping neighbors for the originator.

    The local speaker should relay any routing information to non-
    overlapping neighbors of the sender based on the algorithm outlined
    in the Flooding and Relay Decisions section.  Because more than one
    such speaker may exist, the mechanism is called "overlapping relays."
    The algorithm, however, does select the set of overlapping relays
    that should transmit first.  This set is known as the active set of
    overlapping relays for a speaker.

    ...

    The set of active overlapping relays for a speaker is the minimum set
    of direct neighbors such that every node in the two-hop neighborhood
    of the speaker is a neighbor of a least one overlapping relay in the
    active set.  Each speaker SHOULD select a set of active overlapping
    relays based on a selection algorithm...

The hints are very subtle, and something we'll need to explicitly 
mention next time we refresh the draft.  In short, the designation of 
active relays is not mandatory (SHOULD, not MUST)...if not done, then 
the node assumes the default OSPF behavior.

Alvaro.