The MPLS WG Archive

["Vishal Sharma" <v.sharma@ieee.org>]

Anna, Shahram,

> -----Original Message-----
> From: owner-mpls@UU.NET [mailto:owner-mpls@UU.NET]On Behalf Of Anna
> Charny
> Sent: Thursday, August 15, 2002 5:35 PM
> To: Shahram Davari
> Cc: 'mpls@UU.net'
> Subject: Re: Comments on Backup-Computation draft
>
>
<<snip>


> >8) Section 6.2.1 suggests finding the backup pool, by subtracting the
> >global reservable BW from the link BW. How does a node know the
> link BW to
> >do this computation?
>
> Here is an example with OSPF (link TLV of the TE opaque LSA):
>
> Sub-TLV 6 - Maximum Bandwidth
>
>     The Maximum Bandwidth sub-TLV specifies the maximum bandwidth that
>     can be used on this link in this direction (from the system
>     originating the LSA to its neighbor), in IEEE floating point format.
>     This is the true link capacity.
>
> Sub-TLV 7 - Maximum Reservable Bandwidth
>
>     The Maximum Reservable Bandwidth sub-TLV specifies the maximum
>     bandwidth that may be reserved on this link in this direction, in
>     IEEE floating point format
>
> Maximum bandwidth - Maximum Reservable Bandwidth = Backup bandwidth pool.
>

I seem to recall that the maximum reservable bandwidth can, in fact, be
set to be _larger_ than the link capacity to allow for admitting
traffic/LSPs
whose cumulative b/w exceeds the maximum bandwidth, in those cases where
link oversubscription is allowed or desired.

As a result, the backup bandwidth pool may not be directly derivable from
the simple calculation above, unless there an assumption of a network-wide
policy of
using no oversubscription.

-Vishal