Subject: [Manet-dt] Proposed New Dymo Text - Judging Information Usefulness

From: "Ian Chakeres" <[email-masked]>
Date: Mon, 28 Aug 2006 09:01:31 -0700

Please let me know what you think of this text.

Ian

Note: that broken is kind of like invalid. I'm still experimenting
with the term.

5.2.1.  Judging Routing Information's Usefulness

   Given a routing table entry (Route.SeqNum, Route.HopCnt, and
   Route.Broken) and new routing information for a particular node in a
   RM (Node.SeqNum, Node.HopCnt, and RM message type - RREQ/RREP), the
   quality of the new routing information is evaluated to determine its
   usefulness.  The following comparisons are performed in order:

   1. Fresh
      If Node.SeqNum - Route.SeqNum > 0 (using signed 16-bit arithmetic)
      the information is fresh.  This information is newer than that
      known and should be used to update the routing table.

   2. Stale
      If Node.SeqNum - Route.SeqNum < 0 (using signed 16-bit arithmetic)
      the information is stale.  Using stale routing information is not
      allowed, since doing so might result in routing loops.

   3. Loop-possible
      If Node.SeqNum == Route.SeqNum the information may cause loops if
      used, in this case additional information must be examined.  If
      Route.HopCnt is unknown or set to zero (0), then the routing
      information is loop-possible.  Likewise, if Node.HopCnt is unknown
      or set to zero (0), then the routing information is loop-possible.
      If Node.HopCnt > Route.HopCnt + 1, then the routing information is
      loop-possible.  Using loop-possible routing information is not
      allowed, since doing so might result in routing loops.

   4. Inferior
      If Node.SeqNum == Route.SeqNum the information may be inferior,
      additional information must be examined.  If the Node.HopCnt ==
      Route.HopCnt + 1 or Route.HopCnt, the current route is not Broken
      and the message is a RREQ, then the new information is inferior.
      Inferior routes will not cause routing loops if introduced, but
      should not be used since better information is already available.

   5. Superior
      Routing information that does not match any of the above criteria
      is loop-free and better than the information existing in the
      routing table.  This type of information is used to update the
      routing table.  For completeness, the following other cases are
      possible:

         Node.HopCnt == Route.HopCnt + 1 or Route.HopCnt and the route
         is Broken.

         Node.HopCnt == Route.HopCnt + 1 or Route.HopCnt and the route
         is not Broken and the message is a RREP,

         Node.HopCnt < Route.HopCnt.

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