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

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

Hello Jerry,

>> -----Original Message-----
>> From: Ash, Gerald R (Jerry), ALABS [mailto:gash@att.com] 
>> Sent: 20 May 2003 23:58
>> To: Francois Le Faucheur (flefauch)
>> Cc: Ash, Gerald R (Jerry), ALABS; te-wg@ops.ietf.org; Lai, 
>> Wai S (Waisum), ALABS; Dimitry Haskin
>> Subject: RE: Reflecting new-MAM/SAM definition in diff-te drafts
>> 
>> 
>> Francois, All,
>> 
>> > I've been using "Reserved" and "Normalised" as per their 
>> definitions in
>> > the proto draft, the RDM draft and the MAM draft.
>> > 
>> > Quoting from these drafts:
>> > 
>> > ==================================
>> > - "Reserved(CTc)": For a given Class-Type CTc ( 0 <= c <= 
>> MaxCT ) ,let
>> > us define "Reserved(CTc)" as the sum of the bandwidth 
>> reserved by all
>> > established LSPs which belong to CTc. 
>> > - Normalised(CTc) : let us define "Normalised(CTc)" as
>> > "Reserved(CTc)/LOM(c)", where LOM (c) is the Local Overbooking
>> > Multiplier for CTc defined in [DSTE-PROTO].
>> > =====================================
>> > 
>> > What that means is that "Reserved(CTc)" does factor in the 
>> overbooking
>> > method which is referred to as "LSP/link size overbooking" 
>> method and is
>> > the overbooking method commonly used in TE networks. 
>> However, it does
>> > NOT factor in the optional "Local Overbooking Multiplier" method.
>> > 
>> > "Normalised(CTc)"  factors-in both the "LSP/link size 
>> overbooking" and
>> > the optional "Local Overbooking Multiplier" method.
>> 
>> Thank you for reviewing this.  
>> 
>> I had not appreciated that 'Reserved(CTc)' is actually a 
>> normalized quantity, normalized by the 'LSP/link size 
>> overbooking multiplier' (LSOM).
>> 
>> Just to further clarify, in terms of the actual bandwidth 
>> requested, I suppose this relationship must hold:
>> 
>> Reserved(CTc) = Bandwidth-Requested(CTc)/LSOM
>> 
>> where
>> 
>> Bandwidth-Requested(CTc): For a given Class-Type CTc ( 0 <= 
>> c <= MaxCT ), define "Bandwidth-Requested(CTc)" as the sum 
>> of the bandwidth requested by all established LSPs which 
>> belong to CTc. 
>> 
>> Is that correct?  If so, then 'Reserved(CTc)' is also a 
>> 'normalized' quantity, but this time it is normalized by the 
>> LSOM, right?
>>

Yes, I do agree with your statement that "Reserved(CTc)" is also
normalised in the sense that it reflects the LSP/link size overbooking.

This is analogous to what happens today with regular TE. The bandwidth
that is configured as the LSP size may reflect some over/underbooking
factor. Similarly the Max Reservable bandwidth may reflect some
over/underbooking ratio.
The good thing is that from TE's perspective, the only thing we have to
worry about are these "normalised" bandwidth (reflecting LSP/link size
Overbooking).
If an LSP bandwidth is configured/signaled as 100, it is irrelevant (for
TE) whether the SP expects a peak load of 200 on that LSP and applied an
LSP overbooking of 2, or whether the SP actually expects a peak load of
100 and applied no overbooking.
Similarly, the relevant constraint is the Max Reservable Bandwidth
(which can be configured smaller or larger than real link capacity). For
TE, what matters is that the Max Reservable Bw is set to, say, 1000. It
doesn't really matter whether the link is actually indeed of 1000 or
whether it is actually a link of 500 with an link overbooking of 2.
Basically, TE will establish 10 LSPs of configured bandwidth 100 on that
link of 1000. That's it.
This is why, in regular TE, only the LSP bandwidth is the one considered
(and is indeed a normalised bandwidth factoring LSP Size Overbooking)
and only Max Reservable is considered (which is also a normalised value
factoring in the link size overbooking). 
One interesting point is that TE does not explicitely need the concept
of LSP size Overbooking *Multiplier" and the Link Size Overbooking
*Multiplier". They are effectively transparent to TE which works only on
normalised bandwidth. 

The DS-TE approach is the same with respect to LSP/link Size Overbooking
ie the only "bandwidth" we are concerned about is the actual LSP size,
which factors in the LSP Size Overbooking (ie which is normalised , as
you stated) and the BCs [+ Max Reservable Bw (as proposed)].
For DS-TE, like for TE, I think we don't need to explicitely define in
the drafts the concepts of LSP/Link Size overbooking Multipliers (LSOMs)
nor formulas using them because we operate directly/exclusively on
"normalised" values. But I think we  agree in spirit in what those would
be anyway, based on our discussion.

Thanks

Francois


PS: of course, as mentioned earlier, "Reserved(CTc)" factors LSOMs but
does not factor the LOMs. "Normalised(CTc)" does factor both.


 
>> Thanks for the clarifications,
>> Jerry
>>