The MPLS WG Archive

["Daniel N. Bauer" <dnb@zurich.ibm.com>]

> The examples I have in mind are based on the naive understanding of the
> "weighted" per E-LSP admission rules.
> Example 1: Bandwidth on the link is pre-allocated like you have said (i.e.,5
> MBit/s for EF, 10 Mbit/s for AF1 etc.).  However, "all" the  5 Mbit/s of the
> EF traffic in this node as well as, say 1 Mbit/s of AF1 and  1 Mbit/s of AF3
> go to the same destination. Such a flow could be satisfied by a 7 Mbit/s
> E-LSP with appropriate admission rules - but these rules cannot, to the best
> of my understanding,  be derived from the overall distribution of capacity
> of the egress link.

Of course, there are other (and maybe better) ways to conduct admission control
for E-LSPs. If you have another solution that works for both L-LSPs and E-LSPs,
then I'm really eager to know how it works.
However, I still think that my proposal makes some sense. The distribution of
pre-allocated resources reflects the distribution of the total expected
traffic. It is therefore also reasonable to request that the distribution
of traffic inside an E-LSP corresponds to this global distribution. The system
would then work as follows:
1.) For each PSC, the amount of reservable bandwidth is maintained.
2.) If an L-LSP is admitted, only a single PSC applies and admission control
    is easy. There must be some sort of policing at the edge of the network,
    such that no more than the requested bandwidth is used. This might means a
    re-mapping of the DiffServ Code Point.
3.) If an E-LSP is admitted, multiple PSC apply. Admission control uses the
    global distribution, as described earlier, to compute the requested bandwidth
    per OA and thus can check whether enough bandwidth for the corresponding PSC
    is available. Also, there must be some sort of policing at the edge of the
    network. In fact, the same global distribution is used to break down the
    total reserved amount of bandwidth. Policing of E-LSP traffic is then
    be carried out per OA.

To come back to your example: Given the global distribution and the 7 Mbit/s
of total bandwidth for that E-LSP, then policing will kick in. The distribution:
EF - 5, AF1 - 1, AF3 -1 would not be possible. If such a distribution is required,
then three L-LSPs need to be set up.

> Example 2: Two 25 Mbit/s E-LSPs are requested, one carrying EF and AF3, the
> other one carrying EF and AF4. According to the "relative weights" logic, up
> to 5 Mbit/s would be admitted to each of the two E-LSPs, with the total
> exceeding the overall 5% limit on EF.

Since admission control does not work in parallel, the following would happen.
Global distribution: EF gets 5%, AF1.x gets 10%, AF2.x gets 20%, AF3.x gets 20%,
AF4.x gets 20%. Total link capacity: 100Mbit/s. Reservable bw for EF: 5 Mbit/s.
First E-LSP: 25 Mbit/s -> 5 Mbit/s for EF, 20 Mbit/s for AF3. This can be admitted.
Now, there is no reservable bandwidth for EF left.
Second E-LSP: 25 Mbit/s -> 5 Mbit/s for EF,20 Mbit/s for AF4. Since no bw is left
for EF, the second E-LSP will not get admitted.

Best regards,

-Daniel