RE: Example of LOM usage

[Dimitry Haskin <dhaskin@axiowave.com>]

Lai,

I understand that a provider may want different per CT overbooking ratios on
different links. However I still fail to understand why LOM would be
required to provide a good service in such a configuration. Can you clarify?

Thanks,
  Dimitry

> -----Original Message-----
> From: Lai, Wai S (Waisum), ALABS [mailto:wlai@att.com]
> Sent: Wednesday, June 04, 2003 4:56 PM
> To: te-wg@ops.ietf.org
> Cc: Ash, Gerald R (Jerry), ALABS
> Subject: Example of LOM usage
> 
> 
> This is a response to the request for an example of LOM usage by
> service providers in per-link per-CT overbooking.
> 
> Suppose link0 has 100 units (e.g., Mbps of link bandwidth), of which
> say 30 is allocated to CT0, and 70 to CT1.  Similarly, link1 has 500
> units, of which 150 is to CT0, and 350 to CT1.  That is, with 30%/70%
> allocation for both links, the bandwidth constraints are in the same
> proportion for both.  Then, in going from link0 to link1, CT0 sees an
> increase from 30 to 150, while CT1 sees an increase from 70 to 350.
> 
> To get a feel for the change in per-CT overbooking needed for the two
> links, at a very high level, we use the simple Erlang 
> formula, assuming
> 1% LSP blocking for both CT0 and CT1.  (Obviously, this is very very
> crude, without any consideration for sharing - but the idea is to
> see the scaling effect of link speeds, to be explained below.)
>  30 units support an offered load of  20.3 units (68% utilization)
> 150 units support an offered load of 131.6 units (88% utilization)
>  70 units support an offered load of  56.1 units (80% utilization)
> 350 units support an offered load of 326.2 units (93% utilization)
> 
> With only 30 units in link0, CT0 has a much smaller overbooking to
> start with.  Thus, CT0 should see a proportionally bigger increase
> in overbooking in link1, as the utilization increases by 20% from
> 68% to 88%.
> 
> OTOH, CT1 has 70 units in link0 and can work with a higher 
> overbooking.
> Thus, CT1 should see a proportionally smaller increase in overbooking
> in link1, as the utilization increase is much smaller, by 13% from 80%
> to 93%.
> 
> In summary, depending on the relative traffic size, per-CT overbooking
> may need to be proportionally different, even with LSPOM and LSOM in
> use.  This is because different CTs may see different scaling effects
> when link speeds change.  To support application scenarios like this,
> the use of LOM is needed.
> 
> Given that LOM is to be retained, I agree with Jerry that we should
> leave LOM as is and not progress it as a separate effort.  Thus, I
> would like to see some discussion on how LOM could be simplified:
> http://ops.ietf.org/lists/te-wg/te-wg.2003/msg00321.html
> This proposal is FULLY backward compatible with existing TE.
> 
> The formulation currently described in existing drafts is complicated
> with the use of different formulas in different components.  This will
> lead to operational complexity, as well as operational errors such as
> misconfigurations.  The above proposal does NOT call for a reinvention
> or redefinition of the overbooking model, rather, just a 
> simplification
> of what already exists by a more coherent and seamless integration.
> 
> Thanks, Wai Sum 
>