RE: I-D ACTION:draft-ash-mpls-dste-bcmodel-max-alloc-resv-00.txt

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

Francois,

> Thanks for your answer. I get a better idea. But I am still
> struggling to understand the two tables in the I-D. 
> Can you (or someone else who understand MAR) help me out:
> 	- what's the relationship between "Link Load States" and
> "Allowed Load State Thresholds"? Is the idea that I first determine the
> "Link Load State" (which is CTi independent) to tell me whether I can
> consider a link at all or not. And then assuming I can consider the link
> (i.e. it is not in BNA state? ) I use Table 1 to tell me what thresholds
> to apply?
> 	- how do I read Table 1: is it "if I am in state of first column
> and in priority of first row, then here is the formula to 
> apply"  OR is
> it "if I am in priority of first row and the condition of formula
> applies, then I am in state of first column"???
> 	- I think a worked example (like you started below but showing
> how the table 1 and 2 come into play) would be really helpful.

As you suggested, below I've expanded the example to give some illustration of the use of Table 1 and Table 2 in http://www.ietf.org/internet-drafts/draft-ash-mpls-dste-bcmodel-max-alloc-resv-00.txt.

I hope this helps.

Thanks,
Jerry

Further additions to the prior example:

We have 3 CTs: CT0, CT1, CT2, all with 'normal' priority.
We have a particular link with capacity = 100. 
MAR allocates CT bandwidth for the normal traffic loads, and in this example the BWalloc values on the given link are as follows:

BWalloc for CT0 = BWalloc0 = 30
BWalloc for CT1 = BWalloc1 = 20
BWalloc for CT2 = BWalloc2 = 20
 
This leaves 100 - 70 = 30 units of spare bandwidth on the link under normal loading.  With MAR, any of the CTs is allowed to exceed its BWalloc as long a there is at least RBWk (reserved bandwidth on the link) units of spare bandwidth remaining.

Let's say RBW = 10.  So under overload, if 

CT0 has taken 50 units of bandwidth (bandwidth-in-progress for CT0 = BWIP0 = 50),
CT1 has taken 30 units of bandwidth (bandwidth-in-progress for CT1 = BWIP1 = 30),
CT2 has taken 10 units of bandwidth (bandwidth-in-progress for CT2 = BWIP2 = 10),

Therefore, for this loading,
Idle link bandwidth (ILBW) = 100 - 50 - 30 - 10 = 10

Let's say a flow arrives for CT0 needing 5 units of bandwidth (i.e., DBW = 5).  We need to decide based on Table 2 and Table 1 whether to admit this flow or not.

The link load state is determined from Table 2:

Since ILBW - RBW < DBW (i.e., 10 - 10 < 5), Table 2 says the link is in the RBW (reserved bandwidth) state.

The allowed load state is determined from Table 1 (the allowed load state is the minimum level of bandwidth that must be available on a link to admit the flow):

Since for CT0 (normal priority) BWalloc0 < BWIP0 (30 < 50), Table 2 says the allowed load state is ABW (available bandwidth).

Hence since the link has less bandwidth (RBW state) than the allowed load state level of bandwidth required to admit the flow (ABW), the flow is rejected/blocked.

Now let's say a flow arrives for CT2 needing 5 units of bandwidth (i.e., DBW = 5).  We need to decide based on Table 2 and Table 1 whether to admit this flow or not.

The link load state is determined from Table 2:

Since ILBW - RBW < DBW (i.e., 10 - 10 < 5), Table 2 says the link is in the RBW (reserved bandwidth) state.

The allowed load state is determined from Table 1 (the allowed load state is the minimum level of bandwidth that must be available on a link to admit the flow):

Since for CT2 (normal priority) BWIP2 < BWalloc2 (10 < 20), Table 2 says the allowed load state is RBW (reserved bandwidth).

Hence since the link has sufficient bandwidth (RBW state) compared to the allowed load state level of bandwidth required to admit the flow (also RBW), the flow is admitted.

Hence, in the above example, in the current state of the link and the current CT loading, CT0 and CT1 can no longer increase their bandwidth on the link, since they are above their BWalloc values and there is only RBW=10 units of spare bandwidth left on the link.  

But CT2 can take the additional bandwidth (up to 10 units) if the demand arrives, since it is below its BWalloc value.