Subject: [Diffserv] A question on PHB-PDB relationship

From: demir <[email-masked]>
Date: Mon, 26 Feb 2001 14:47:20 -0800 (PST)

Can a PDB definition overload a PHB definition? To be more specific, Can
someone define a PDB where he/she overloads a PHB with additional
rules? i.e. Foo PDB: Based on AF PHB, but wants to achieve the goals of a
PDB based on EF PHB, i.e. VW (virtual wire) and has rules such as:
MaxThreshold=MinThreshold=AFQueueLength, mark only using one DSCP,
additional delay and rate constraints defined in the new EF draft, etc...
Let's not discuss if Foo PDB makes sense or not to choose such a way. My
aim is not to ask if it is possible to achieve EF-based PDB using AF-based
PDB. I am also aware of that, if one needs a PHB to define a PDB, he/she
could define a new PHB.

Alper K. Demir

_______________________________________________
diffserv mailing list
[email-masked]
http://www1.ietf.org/mailman/listinfo/diffserv
Archive: http://www2.ietf.org/mail-archive/working-groups/diffserv/current/maillist.html

---

From: Kathleen Nichols <[email-masked]>
Date: Mon, 26 Feb 2001 17:19:37 -0800

Yes, of course. Just make the additional rules clear. This is somewhat
the approach that Brian and I took with Bulk Handling and CS01.

---

From: Brian E Carpenter <[email-masked]>
Date: Mon, 26 Feb 2001 19:35:01 -0600

It seems perfectly reasonable for a PDB definition to constrain the
parameters of the PHB it is using (I wouldn't use the word overload).
Actually the BH PDB does exactly that to the class selector, which
is why Kathie and I don't see the need for an LE PHB.

   Brian

---

From: demir <[email-masked]>
Date: Tue, 27 Feb 2001 15:14:45 -0800 (PST)

Brian,
> is why Kathie and I don't see the need for an LE PHB.

I assume the choice is kind of an "end-to-end argument". One might make an
extereme argument such that only one PHB is enough /Or We don't need PHBs
at all; PDBs can take care of that. Is there a fine-line /Or is there  
system design guidelines (tradeoffs defining a PDB with existing ones or
defining a new PHB) that Diffserv suggests?

Alper K. Demir

---

From: Brian E Carpenter <[email-masked]>
Date: Wed, 28 Feb 2001 07:38:32 -0600

Some of us believe that the set of PHBs already defined (default,
class selectors, AF, EF) is rich enough to keep us busy for many
years - i.e. they give us enough flexibility to define a rich set
of PDBs. 

  Brian

---

From: Brian E Carpenter <[email-masked]>
Date: Wed, 28 Feb 2001 07:38:32 -0600

Brian

---

From: Roland Bless <[email-masked]>
Date: Wed, 28 Feb 2001 18:22:05 +0100

> years - i.e. they give us enough flexibility to define a rich set

One can apply the same argument to EF PHB: it can also be realized by
using CSC PHB 8 and definition of a PDB that expresses the necessary
constraints. However, I suppose nobody doubts that we need to specify EF
by RFC2598(bis). Therefore, I think that it is sensible to define PHBs
that are more specific than the existing generic PHBs (which can
possibly also be used to achieve the newly defined behavior if configured
appropriately), but only if the more specific PHB describes the behavior
of a single DS node. Otherwise, instead of defining an EF PHB, the 
description of a VW PDB that uses CSC PHB 8 in a specific configuration 
would be sufficient.

Regards,
 Roland

---

From: demir <[email-masked]>
Date: Wed, 28 Feb 2001 19:15:36 -0800 (PST)

Brian,
Then what's wrong with defining a "Expedited Virtual Wire" PDB based on AF
PHB instead of defining a EF PHB purely. It seems that only AF PHB is
enough with some loose definitions (meaning intead of MUSTs, MAYs,
etc...). The rest is to define "right" PDBs (p.s. I am not sure about
class selectors :) 

Alper K. Demir