RE: Reflecting new-MAM/SAM definition in diff-te drafts

["Francois Le Faucheur (flefauch)" <flefauch@cisco.com>]

Hello Dimitry,

>> -----Original Message-----
>> From: Dimitry Haskin [mailto:dhaskin@axiowave.com] 
>> Sent: 25 April 2003 22:28
>> To: 'Ash, Gerald R (Jerry), ALABS'; Francois Le Faucheur (flefauch)
>> Cc: te-wg@ops.ietf.org
>> Subject: RE: Reflecting new-MAM/SAM definition in diff-te drafts
>> 
>> 
>> Gerald,
>> 
>> > 3. The 'maximum link bandwidth' parameter is a physical 
>> > constraint and serves to limit the assignable sum of link 
>> > bandwidth across class types.  In the recent discussion, this 
>> > constraint has sometimes been referred to as an 'implicit max 
>> > link BW constraint'.  However there is nothing 'implicit' 
>> > about this constraint/parameter, it is an existing link 
>> > parameter and a physical constraint on assignable link bandwidth.
>> > 4. Given comment #3, we don't need to use the 'max reservable 
>> > link bandwidth' parameter instead of the 'maximum link 
>> > bandwidth' parameter, as you have proposed.
>> 
>> The 'maximum link bandwidth' as defined is the actual link 
>> capacity and not
>> meant to be used as a reservation constraint. The 'max 
>> reservable link
>> bandwidth' was originally defined for this purpose. The 
>> amount of confusion
>> around these definitions puzzles me.
>>

After some investigation, here's my understanding:

1) At the time where "Max Link Bandwidth" was specified, (at least some
of) the folks involved were intending it as a constraint on the single
size of an LSP. Now, this didn't actually quite make it in the text of
the OSPF/ISIS specs, yet arguably the text doesn't either completely
exclude this interpretation. I suspect this may be (part of) the
explanation for the confusion around this. But that doesn't matter too
much...I guess.

2) Anyway, today, it seems that using "Max Link Bandwidth" to limit the
size of an individual LSP is not supported by all implementations, and
where supported, is not commonly used by SPs.
Based on this, I propose to follow Dimitry's suggestion and remove the
2nd check in the CAC formulas.
ie remove the following check:
"> >>        B <= Max Link Bandwidth "
(for memory, B is the size of the LSP being admitted)

Cheers

Francois

 
>> Dimitry
>> 
>> P.S. Excerpts from draft-katz-yeung-ospf-traffic-09.txt:
>> 
>> 
>>  2.5.6. 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.  The units are bytes per second.
>> 
>>    The Maximum Bandwidth sub-TLV is TLV type 6, and is four octets in
>>    length.
>> 
>>  2.5.7. 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.  Note that this may be 
>> greater than the
>>    maximum bandwidth (in which case the link may be oversubscribed).
>>    This SHOULD be user-configurable; the default value should be the
>>    Maximum Bandwidth.  The units are bytes per second.
>> 
>>    The Maximum Reservable Bandwidth sub-TLV is TLV type 7, 
>> and is four
>>    octets in length.
>>