The MPLS WG Archive

["Feng, Mark" <m_feng@trillium.com>]

IMO, the exact behavior depends on the implementation, though the end result
should be the same.

In one behavior, when B receives the PTear, it would remove the reference to
sender1 in PSB and RSB; but leave the allocation unchanged (i.e. 20 units).
When C receives the PTear, it would generate a new Flowspec of 10 units,
since sender1 is removed. When the new Resv message has been propagated back
to Ingress, the desired allocation is in place.

B could try to guess what the new allocation is, based on the Tspec, before
receiving the new Flowspec. IMO, that's entirely up to the implementation.

Hope this helps.

- Mark

> -----Original Message-----
> From: Gopalkrishna Panicker [mailto:gopanicker@yahoo.com]
> Sent: Thursday, May 23, 2002 11:29 AM
> To: mpls@UU.NET
> Subject: RSVP-TE : bandwidth decrease
> 
> 
> Hello,
> 
> Consider the following topology
> 
> 
>    A-----------B----------C
> 
> Let us say
> 1. we are using make-before-break and therefore
>    using SE style.
> 2. LSP1 with Sender1 has been signalled with a  
>    bandwidth of 20 units. A is the ingress and C is
>    the egress.
> 
>  Now A decides to reduce the bandwidth to 10 units.
>  A ceates a new sender template (Sender2) and 
>  Tspec. A then sends the path message towards C. 
> 
>  After receiving the path message, C computes the
>  bandwidth to be allocated. Since SE style is being 
>  used, the merged flowspec sent in the resv message
>  from C to B will  continue to say a bandwidth of 
>  20 units. 
>  The only reason the resv  makes it back
>  to A is because of the new filterspec (Sender2).
> 
>  I assuming this is correct.
> 
>   Now A issues a path tear for sender1. B will
>   delete the path state associated with sender1. 
>   B will also delete the corresponding filter spec
>   from the resv state. 
>  
>   Now to my question. How does B know that it has
>   to delete the 10 units of bandwidth reservation ?
>   
>   If my understanding is correct, the resv message
>   from C had carried a merged flowspec and set of
>   filterspecs (Sender1, Sender2). How does B 
>   determine the orginal flowspec associated with
>   the filterspec (in this case Sender1) ?
>   
>   Should B on rely on the tspec stored in the PSB ? 
> 
> 
>  Obviously I am missing something.
> 
>  Thanks
> 
>  Cheers
>  Gopal
> 
> 
> 
> 
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