RE: Dropping the Local Overbooking Multiplier (LOM) method from DS-TE specs?

["Ash, Gerald R (Jerry), ALABS" <gash@att.com>]

Sanjay, All,

> DSTE-REQ already states that the per-CT overbooking
> is an optional feature and does not require the vendors
> to implement it.
> 
> We already discussed the overbooking/underbooking issues
> quite some time back. I don't think we, should change
> requirement [DSTE-REQ] at this stage (past last call),
> unless there is a real problem or limitation.

The DSTE-REQ say:

" The DS-TE solution MUST also allow overbooking and MUST effectively 
   allow different overbooking ratios to be enforced for different CTs. 
    
   The DS-TE solution SHOULD optionally allow the effective overbooking 
   ratio of a given CT to be tweaked differently in different parts of 
   the network."

This does not exactly *require* LOM.  As we've discussed, by using Link Size Overbooking Multipliers (LSOM) and LSP Size overbooking multipliers (LSPOM), we can achieve some degree of per-CT overbooking that is tweaked differently in different parts of the network.  

For example, by setting
LSOM0 = 1 on link 0,
LSOM1 = 1.5 on link 1,
LSPOM0 = 2 for LSPs on CT0,
LSPOM1 = 1 for LSPs on CT1,
we could overbook CT0 by 2 on link 0 and 3 on link 1 (LSPOM0 * LSOM1 = 2 * 1.5 = 3),
while overbooking CT1 by 1 on link 0 and 1.5 on link 1.

However, for the example Francois gave:
"CT0 is overbooked by factor 2 on link 0 and overbooked by factor 3 on link 1, while CT1 is not overbooked on link0 nor on link1. This could NOT be achieved just by combination of "LSP Size overbooking" and "Link Size Overbooking"; it could only be achieved via the use of the LOM method. But, as being discussed, it is not obvious that the need for this justifies the extra complexity."

I agree that this example requires LOM, but I also agree that the need for this is not obvious.  Can anyone explain why such a capability would be needed?

It is also not obvious that the above flexibility (i.e., need for LOM) is *required* by DSTE-REQ.
 
> If we are trying to change the requirement because the 
> LOM concept is difficult, let's take steps to clarify
> the concept by necessary editorial changes (and examples).

I'm not sure we are trying to change the requirement, however I agree that we need good examples of how/why LOM is absolutely needed to achieve the requirements.

Thanks,
Jerry