draft-ietf-pim-bidir-03.txt

BCAST Implementation for NS2

     o On receipt of a Backoff message set the DF to be the originator
       of the message and record its metrics.










Handley/Kouvelas/Speakman/Vicisano           Section 3.5.3.5.  [Page 25]

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3.5.3.5.  Election State Transitions


                    +-----------------------------------+
                    | Figures omitted from text version |
                    +-----------------------------------+

            Figure 3: Designated Forwarder election state-machine


In tabular form, the state machine is:

+-------------++--------------------------------------------------------+
|             ||                         Event                          |
| Prev State  ++------------------+------------------+------------------+
|             || Recv better      |  Recv better     |  Recv better     |
|             || Pass / Win       |  Backoff         |  Offer           |
+-------------++------------------+------------------+------------------+
|             || -> Lose          |  -               |  -               |
| Offer       || DF = Sender or   |  DFT = BOperiod  |  DFT = OPhigh;   |
|             || Target; Stop     |  + OPlow; OC =   |  OC = 0          |
|             || DFT              |  0               |                  |
+-------------++------------------+------------------+------------------+
|             || -                |  -               |  -> Offer        |
| Lose        || DF = Sender or   |  DF = Sender     |  DFT = OPhigh;   |
|             || Target           |                  |  OC = 0          |
+-------------++------------------+------------------+------------------+
|             || -> Lose          |  -> Lose         |  -> Backoff      |
|             || DF = Sender or   |  DF = Sender;    |  Set Best to     |
| Win         || Target; Stop     |  Stop DFT        |  Sender; Send    |
|             || DFT              |                  |  Backoff; DFT =  |
|             ||                  |                  |  BOperiod        |
+-------------++------------------+------------------+------------------+
|             || -> Lose          |  -> Lose         |  -               |
|             || DF = Sender or   |  DF = Sender;    |  Set Best to     |
| Backoff     || Target; Stop     |  Stop DFT        |  Sender; Send    |
|             || DFT              |                  |  Backoff; DFT =  |
|             ||                  |                  |  BOperiod        |
+-------------++------------------+------------------+------------------+












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+-----------++----------------------------------------------------------+
|           ||                          Event                           |
|           ++-------------+--------------+--------------+--------------+
|Prev State ||Recv Backoff | Recv Pass    | Recv Worse   | Recv worse   |
|           ||for us       | for us       | Pass / Win / | Offer        |
|           ||             |              | Backoff      |              |
+-----------++-------------+--------------+--------------+--------------+
|           ||-            | -> Win       | -            | -            |
|           ||DFT =        | Stop DFT     | Set DF to    | DFT ?=       |
|Offer      ||BOperiod +   |              | Sender or    | OPlow; OC =  |
|           ||OPlow; OC =  |              | Target; DFT  | 0            |
|           ||0            |              | ?= OPlow; OC |              |
|           ||             |              | = 0          |              |
+-----------++-------------+--------------+--------------+--------------+
|           ||-> Offer     | -> Offer     | -> Offer     | -> Offer     |
|           ||DF = Sender; | DF = Sender; | DF = Sender  | DFT = OPlow; |
|Lose       ||DFT = OPlow; | DFT = OPlow; | or Target;   | OC = 0       |
|           ||OC = 0       | OC = 0       | DFT = OPlow; |              |
|           ||             |              | OC = 0       |              |
+-----------++-------------+--------------+--------------+--------------+
|           ||-> Offer     | -> Offer     | -> Offer     | -            |
|           ||DF = Sender; | DF = Sender; | DF = Sender  | Send Winner  |
|Win        ||DFT = OPlow; | DFT = OPlow; | or Target;   |              |
|           ||OC = 0       | OC = 0       | DFT = OPlow; |              |
|           ||             |              | OC = 0       |              |
+-----------++-------------+--------------+--------------+--------------+
|           ||-> Offer     | -> Offer     | -> Offer     | -> Win       |
|           ||DF = Sender; | DF = Sender; | DF = Sender  | Send Winner; |
|Backoff    ||DFT = OPlow; | DFT = OPlow; | or Target;   | Stop DFT     |
|           ||OC = 0       | OC = 0       | DFT = OPlow; |              |
|           ||             |              | OC = 0       |              |
+-----------++-------------+--------------+--------------+--------------+


+-----------------------------------------------------------------------+
|                            In Offer State                             |
+-----------------------+-----------------------+-----------------------+
| DFT Expires and OC    |  DFT Expires and OC   |   DFT Expires and OC  |
| is less than          |  is equal to          |   is equal to         |
| Robustness            |  Robustness and we    |   Robustness and      |
|                       |  have path to RP      |   there is no path    |
|                       |                       |   to RP               |
+-----------------------+-----------------------+-----------------------+
| -                     |  -> Win               |   -> Lose             |
| Send Offer; DFT =     |  Send Winner          |   Set DF to None      |
| OPlow; OC = OC + 1    |                       |                       |
+-----------------------+-----------------------+-----------------------+




Handley/Kouvelas/Speakman/Vicisano           Section 3.5.3.5.  [Page 27]

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+-----------------------------------------------------------------------+
|                            In Lose State                              |
+--------------------------------+--------------------------------------+
|     Detect DF Failure          |        Metric changes and now        |
|                                |        is better than DF             |
+--------------------------------+--------------------------------------+
|     -> Offer                   |        -> Offer                      |
|     DF = None; DFT =           |        DFT = OPlow_int; OC = 0       |
|     OPlow_int; OC = 0          |                                      |
+--------------------------------+--------------------------------------+


+-----------------------------------------------------------------------+
|                             In Win State                              |
+-----------------------+------------------------+----------------------+
| Metric changes and    |  Timer Expires and     |   No path to RP      |
| is now worse          |  Count is less than    |                      |
|                       |  Robustness            |                      |
+-----------------------+------------------------+----------------------+
| -                     |  -                     |   -> Offer           |
| DFT = OPlow; OC =     |  Send Winner; DFT =    |   Set DF to None;    |
| 0                     |  OPlow; OC = OC + 1    |   DFT = OPlow; OC =  |
|                       |                        |   0                  |
+-----------------------+------------------------+----------------------+


+-----------------------------------------------------------------------+
|                           In Backoff State                            |
+-----------------------------------+-----------------------------------+
|     Metric changes and is         |         Timer Expires             |
|     now better than Best          |                                   |
+-----------------------------------+-----------------------------------+
|     -> Win                        |         -> Lose                   |
|     Stop Timer                    |         Send Pass; Set DF to      |
|                                   |         stored Best               |
+-----------------------------------+-----------------------------------+

3.6.  Timers and Constants

BIDIR-PIM maintains the following timers, as discussed in section 3.1.
All timers are countdown timers - they are set to a value and count down
to zero, at which point they typically trigger an action.  Of course
they can just as easily be implemented as count-up timers, where the
absolute expiry time is stored and compared against a real-time clock,
but the language in this specification assumes that they count downwards
to zero.





Handley/Kouvelas/Speakman/Vicisano               Section 3.6.  [Page 28]

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Per Rendezvous-Point (RP):

     Per interface (I):

          DF Election Timer: DFT(RP,I)

Per Group (G):

     Upstream Join Timer: JT(G)

     Per interface (I):

          Join Expiry Timer: ET(G,I)

          PrunePending Timer: PPT(G,I)

When timers are started or restarted, they are set to default values.
This section summarizes those default values.

































Handley/Kouvelas/Speakman/Vicisano               Section 3.6.  [Page 29]

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Timer Name: DF Election Timer (DFT)


+--------------------+-------------------------+------------------------+
|  Value Name        |  Value                  |   Explanation          |
+--------------------+-------------------------+------------------------+
|  Offer_Period      |  100 ms                 |   Interval to wait     |
|                    |                         |   between repeated     |
|                    |                         |   Offer and Winner     |
|                    |                         |   messages.            |
+--------------------+-------------------------+------------------------+
|  Backoff_Period    |  1 sec                  |   Period that acting   |
|                    |                         |   DF waits between     |
|                    |                         |   receiving a better   |
|                    |                         |   Offer and sending    |
|                    |                         |   the Pass message     |
|                    |                         |   to transfer DF       |
|                    |                         |   responsibility.      |
+--------------------+-------------------------+------------------------+
|  OPLow             |  rand(0.5, 1) *         |   Range of actual      |
|                    |  Offer_Period           |   randomised value     |
|                    |                         |   used between         |
|                    |                         |   repeated messages.   |
+--------------------+-------------------------+------------------------+
|  OPHigh            |  Election_Robustness    |   Interval to wait     |
|                    |  * Offer_Period         |   in order to give a   |
|                    |                         |   chance to a router   |
|                    |                         |   with a better        |
|                    |                         |   Offer to become      |
|                    |                         |   the DF.              |
+--------------------+-------------------------+------------------------+

Timer Names: Join Expiry Timer (ET(G,I))


+----------------+----------------+-------------------------------------+
| Value Name     | Value          |  Explanation                        |
+----------------+----------------+-------------------------------------+
| J/P HoldTime   | from message   |  Hold Time from Join/Prune Message  |
+----------------+----------------+-------------------------------------+











Handley/Kouvelas/Speakman/Vicisano               Section 3.6.  [Page 30]

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Timer Names: Prune Pending Timer (PPT(G,I))


+--------------------------+--------------------+-----------------------+
| Value Name               |  Value             |   Explanation         |
+--------------------------+--------------------+-----------------------+
| J/P Override Interval    |  Default: 3 secs   |   Short period after  |
|                          |                    |   a join or prune to  |
|                          |                    |   allow other         |
|                          |                    |   routers on the LAN  |
|                          |                    |   to override the     |
|                          |                    |   join or prune       |
+--------------------------+--------------------+-----------------------+

Timer Names: Upstream Join Timer (JT(G))


+-------------+--------------------+------------------------------------+
|Value Name   |Value               |Explanation                         |
+-------------+--------------------+------------------------------------+
|t_periodic   |Default: 60 secs    |Period between Join/Prune Messages  |
+-------------+--------------------+------------------------------------+
|t_suppressed |rand(1.1 *          |Suppression period when someone     |
|             |t_periodic, 1.4 *   |else sends a J/P message so we      |
|             |t_periodic)         |don't need to do so.                |
+-------------+--------------------+------------------------------------+
|t_override   |rand(0, 0.9 * J/P   |Randomized delay to prevent         |
|             |Override Interval)  |response implosion when sending a   |
|             |                    |join message to override someone    |
|             |                    |else's prune message.               |
+-------------+--------------------+------------------------------------+

For more information about these values refer to the PIM-SM [9]
documentation.

Constant Name: DF Election Robustness


+--------------------------+-------------------+------------------------+
|  Constant Name           |    Value          |    Explanation         |
+--------------------------+-------------------+------------------------+
|  Election_Robustness     |    Default: 3     |    Minimum number of   |
|                          |                   |    election messages   |
|                          |                   |    that must be lost   |
|                          |                   |    in order for        |
|                          |