Subject: RE: E-LSP or L-LSP

From: Shahram Davari <[email-masked]>
Date: Thu, 23 Nov 2000 10:24:01 -0800

Hi Daniel,

You can do admission control for E-LSP too. But the admission control is done for the aggregate of all supported PHBs in that LSP.

Regards,
-Shahram

> -----Original Message-----
> From: Daniel N. Bauer [mailto:[email-masked]]
> Sent: Thursday, November 23, 2000 3:00 AM
> To: Simeone Mastropietro
> Cc: [email-masked]
> Subject: Re: E-LSP or L-LSP
> 
> 
> Here's one difference that might or might not be important:
> 
> Packets that are carried inside an E-LSP might belong to
> different PHB scheduling classes, whereas packets inside
> an L-LSP belong to the same PHB scheduling class.
> This difference is important in the case where admission control
> is required/wanted: For L-LSPs, admission control can be carried
> out since the traffic specification in the signaling matches a
> single PHB scheduling class. For E-LSPs, this is not true and
> consequently, no admission control can be carried out.
> 
> Regards,
> 
> -Daniel
> 
> 
> Simeone Mastropietro wrote:
> > 
> > Hi All,
> > I am a novel researcher on MPLS and TE for Co.Ri.Tel ( 
> Rome, Italy)...
> > Is there anyone that can help me to understand when E-LSPs or L-LSPs
> > actually should be used?
> > Thanks in advance
> > 
> > Simeone Mastropietro
>

---

From: Marcus Brunner <[email-masked]>
Date: Fri, 24 Nov 2000 11:21:06 +0100

Shahram,

In many scenarios, the admission control for a PBH scheduling classes is
already fuzzy, which means on a statistical level, you will run into
trouble if you want to do admission control for aggregates of different
PHB classes.

Marcus

-- 

Dr. Marcus Brunner
C&C Research Laboratories
NEC Europe Ltd.

E-Mail: [email-masked]
WWW:    http://www.ccrle.nec.de/
personal home page: http://www.tik.ee.ethz.ch/~brunner

Adenauerplatz 6
D-69115 Heidelberg
Germany

Phone: +49 (0)6221/ 9051129
Fax:   +49 (0)6221/ 9051155

---

From: "Daniel N. Bauer" <[email-masked]>
Date: Mon, 27 Nov 2000 09:48:43 +0100

Shahram, Marcus,

What about the following thought:

For an E-LSP, the aggregate bandwidth is known. This aggregate bandwidth
corresponds to the sum of bandwidths that are requested for each PHB class
that are carried inside the E-LSP. In case that the distribution of the
PHB classes is known, then admission control could be carried out.
In networks where resources are pre-allocated per PHB class
and where this is done consistently on all LSR, then the distribution
of the pre-allocated resources can be used to carry out admission control
per E-LSP.

For example, consider the following distribution:
EF gets 5%, AF1.x gets 10%, AF2.x gets 20%, AF3.x gets 20%, AF4.x gets 20%;
meaning that on a 100Mbit/s link, EF could reserve up to 5 Mbit/s, AF1.x up
to 10Mbit/s, etc. etc.

If now an E-LSP requests 7 Mbit/s and this E-LSP carries EF, AF1.x and AF3.x
traffic, then the 7 Mbit/s could be split up and assigned to the classes
as follows:
EF - 1 Mbit/s
AF1.x - 2 Mbit/s
AF3.x - 4 Mbit/s
according to the 'weights' of the resource distribution.
Then, admission control for each class could be done seperately. The E-LSP
could be admitted if all of the admission control checks succeed.

Does this sound reasonable?

Of course, the whole scheme does not work if the pre-allocated resource distribution
is not consistent amont all LSR routers.

Best regards,

-Daniel

---

From: "Sasha Vainshtein" <[email-masked]>
Date: Mon, 27 Nov 2000 11:41:35 +0200

______________________________________________
With best regards,
Sasha Vainshtein
mailto: [email-masked]
phone: +972-3-7659993 (office)
fax:      +972-3-6487779 (office)

>>From: [email-masked] [mailto:[email-masked]]On Behalf Of
>>Daniel N. Bauer
>>Sent: Monday, November 27, 2000 10:49 AM
>>To: [email-masked]; Shahram Davari
>>Cc: Simeone Mastropietro; [email-masked]
Sorry, to me it does not - please consider the case when you do not need any
more LSPs carrying EF traffic in this LSR.
>>> > You can do admission control for E-LSP too. But the admission
>>control is done for the aggregate of all supported PHBs in that LSP.
>>> >
>>> > Regards,
>>> > -Shahram
>>

---

From: "Daniel N. Bauer" <[email-masked]>
Date: Mon, 27 Nov 2000 11:03:45 +0100

> more LSPs carrying EF traffic in this LSR.

I don't understand what you mean here. Maybe you could give an example?

Thanks,

-Daniel

---

From: "Sasha Vainshtein" <[email-masked]>
Date: Mon, 27 Nov 2000 12:41:38 +0200

>>Sent: Monday, November 27, 2000 12:04 PM
>>To: Sasha Vainshtein
>>Cc: mpls@UU. NET

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.
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.
Hopefully these examples will be helpful.

---

From: "Daniel N. Bauer" <[email-masked]>
Date: Mon, 27 Nov 2000 14:47:04 +0100

> of my understanding,  be derived from the overall distribution of capacity

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.

> 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

---

From: "Sasha Vainshtein" <[email-masked]>
Date: Tue, 28 Nov 2000 14:21:13 +0200

>>From: [email-masked] [mailto:[email-masked]]
>>Sent: Monday, November 27, 2000 3:47 PM
>>To: Sasha Vainshtein
>>Cc: mpls@UU. NET
Of course 3 separate L-LSPs will solve the problem. The key underlying
problem (from my point of view) is:
Can we define meaningful applications for E-LSPs? And if yes, then what are
these applications?
The problem with implcit redistibution of bandwidth between several BAs
within the same E-LSP is exactly that: it is implicit.
That means that the network operator can obtain unexpected results and then
be stuck with them. Your interpretation of example 2 illustrates this
situation perfectly: the network operator has to guess (how? and based upon
which information) that the combination of two E-LSPs is illegal and to
choose anothre tool (e.g., L-LSP). From my point of view this means that the
bandwidth redistribution rules have to become part of the standard in order
to avoid interoperability problems and ambiguity.
My gut feeling (and I may be quite wrong, I have just started working in
this area) is that E-LSPs can be used for BAs which do not imply bandwidth
reservation, e.g., for the CS (say, with a trivial CS-->EXP mapping, you
happen to have exactly the right number of bits). I have strong doubts
regarding meaningful application of E-LSPs for combining BAs with
independent bandwidth reservation, like EF and AFx.
>>for EF, the second E-LSP will not get admitted.
The situation when the results depend upon the order of processing (i.e., if
we start with the 2nd LSP then the 1st one would not be admitted) look to me
highly suspicious.