Subject: Processing <S, G> prunes clarification.

From: "Shekhar, Ravi" <[email-masked]>
Date: Mon, 20 Sep 1999 15:07:59 -0400

Hi,
  I have a question on section 3.2.2 [prune part] point 2.(3) 
  [ 2. (c) in ps version ]. 

  It states:

>           3 If (*,G), or corresponding (*,*,RP), state exists, but
>             there is no (Sp,G) entry, an (Sp,G)RPT-bit entry is created
>             . The outgoing interface list is copied from the (*,G), or
>             (*,*,RP), entry, with the interface, I, on which the prune
>             was received, is deleted.  Packets from the pruned source,
>             Sp, match on this state and are not forwarded toward the
>             pruned receivers.

  Does "deleted" mean that the interface "I" be removed immediately from 
  the oif list for (Sp,G) entry?
  Or does it mean that its oif-timer is set to 1/3rd the holdtime in the 
  message and then removed on its expiration?
    If its deleted immediately, prune might get transmitted up before other 
  routers on the LAN get a chance to override the prune. 

  Same question for point 3.(b)  [ (*, *, RP) and (*, G) case ].

  Two unrelated very minor points:

  A) Section 3.2.2 point 3.(4)

>          4 The (Sj,G) entry's SPT bit is cleared until data comes
>             down the shortest path tree.
     
     Would it be appropriate to say that this is done only the first time
     SPT join is recvd i.e. only if RPT bit is set in (Sj, G) entry?

  B) Section 3.2.1.3 Fragmentation: 
           It states:

>						    However, if a Join/Prune
message
>   must be fragmented the complete prune list corresponding to a group G
>   must be included in the same Join/Prune message as the associated
>   RP-tree Join for G.

     Would it add value to state that all <*, G>prunes for given <*, *,
RP>join
     must also be included in the same Join/Prune message (or perhaps
G=224.0.0.0
     already implies it).

    Thanks.
    - Ravi Shekhar.

---

From: [email-masked] (Billy Ng)
Date: Thu, 23 Sep 1999 23:29:30 -0400

> From [email-masked] Mon Sep 20 15:12:44 1999
> 

Since no one seems to have answered this yet, let me try...

>   the oif list for (Sp,G) entry?

there is no interface I in the (Sp,G) to begin with since this entry is 
newly created.  The spec just means don't copy this "I" from the share
entry.

>   routers on the LAN get a chance to override the prune. 

if another downstream on the shared LAN sees this prune, it will immediately
trigger a join to override the prune.

>      SPT join is recvd i.e. only if RPT bit is set in (Sj, G) entry?

no, because what if the data has not come before you received the 2nd join?
so it is set only when data is received.

>      Would it add value to state that all <*, G>prunes for given <*, *,

It probably should since the next (*,*,RP) could graft some of the previous
(*,G)s back if they are not in the same packet.

--Billy

---

From: "Shekhar, Ravi" <[email-masked]>
Date: Fri, 24 Sep 1999 10:19:18 -0400

Thanks Billy.
Please see my comments embedded.

> trigger a join to override the prune.

  I guess thats my question. How long should the upstream wait to
  get the join-override before sending its prune up? 1 sec/2sec or 
  something else.
  Usual way of doing this is to decrease the join timer to 
  Oif-deletion-delay timer and spec specifically specifies that at all 
  other places. 
  Since in this case oif does not exist, should one be created and its
  deletion-delay be set to 1/3rd the holdtime in the J/P message itself?

> so it is set only when data is received.

  The point talks about "clearing" the bit (not setting it). Once 
  its cleared by first join, we need not clear it for second join. 
  But thats not a big deal. More importantly it should not be cleared
  each time a join is recvd after SPT-bit is set once. Doing that 
  would result in SPTBitClear-To-SPTBitSet switch every join interval 
 (although spec clarifies it not to be like that at other places). 
  But again, its nothing major. Just rewording "until data comes down 
  FOR THE FIRST TIME down the shortest path tree" would also do.  

  Regards.
  - Ravi Shekhar.