Subject: Bandwidth reservation per PSC

From: "Darek Skalecki" <[email-masked]>
Date: Fri, 16 Jun 2000 12:24:45 -0400

Hi,

I have a question with regard to bandwidth availability per PSC and TE
extensions to OSPF/ISIS.

Draft "draft-ietf-mpls-diff-ext-05.txt" talks in APPENDIX B Scenario 2
about constraint based routing being
performed separately for each PSC  where one of the constraints is
availability of bandwidth from the bandwidth
allocated to the relevant PSC.

My question is how TE extensions to OSPF/ISIS support advertizing
bandwidth availability per PSC. The only way I can
think this can be achieved is by assigning different colors/resource
classes to different PSCs thus advertizing bandwidth
availability per PSC simply as bandwidth availability per color/resource
class. Is this correct?.

If it is correct then how serious is the scaling/operational issue at
least within OSPF since N  TE LSAs are needed for  N
PSCs  for every link, implying lots of LSA traffic not to mention
storage within LSDB (which I gather can only store
65536 TE LSAs).

Thanks,

Darek Skalecki
Nortel Networks

---

From: Francois Le Faucheur <[email-masked]>
Date: Mon, 19 Jun 2000 11:31:03 +0200

Darek,

>storage within LSDB (which I gather can only store

First, of course , in some environments, Constraint Based Routing may be performed "off-line"/"in a Centralised Manner". In these situations, per-PSC bandwidth availability can be determined by the centralised tool without relying on extensions to OSPF/ISIS.

Where Constraint Based Routing is performed "on-line"/"in a Distributed Manner", then yes, OSPF/ISIS are required to propagate all necessary bandwidth information. This could be achieved in a number of ways:
	- one approach would be to advertise bandwidth information for every PSC. As you are pointing out above, this may lead to scaling/operational issues earlier than desired.  
	- another approach would be to advertise bandwidth information only for each "family/class" of PSCs. A family/class of PSC would comprise all the PSCs which share the same bandwidth constraints. It is likely that multiple PSCs can share the same bandwidth constraints (eg "max-reservable-bandwidth"). For instance, multiple Premium/Non-real-time PSCs may share the same "max-reservable-bandwidth". In that case, you have traded a little bit of fine-grain control (you can't enforce bandwidth constraints which are different for absolutely every PSC), but you have significantly gained in scalability of OSPF/ISIS by "only" advertising 2/3 available bandwidth information. 

You will find some text on the second approach in section "6.7 Traffic Engineering in Diffserv Environments" of <draft-ietf-tewg-framework-01.txt>:

   "Instead of having per-class parameters being configured and
   propagated on each LSR interface, per-class parameters can be
   aggregated into per-class-type parameters. The main motivation for
   grouping a set of classes into a class-type is to improve the
   scalability of IGP link state advertisements by propagating
   information on a per-class-type basis instead of on a per-class
   basis, and also to allow better bandwidth sharing between  classes in
   the same class-type..."

Francois

>Nortel Networks

_________________________________________________________________
Francois Le Faucheur   
Development Engineer, IOS Layer 3 Services 
Cisco Systems 
Office Phone:   	+33 4 92 96 75 64
Home Office Phone:     +33 4 92 94 00 78
Mobile :               +33 6 89 108 159
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Fax:                   +33 4 92 96 79 08
Email:          	[email-masked]
_________________________________________________________________
Petra B - Les Lucioles - 291, rue Albert Caquot - 06560 Valbonne - France
_________________________________________________________________

---

From: "Darek Skalecki" <[email-masked]>
Date: Tue, 20 Jun 2000 14:51:27 -0400

Thanks Francois,

My question was indeed related to the distributed model. What I am still not sure about is how bandwidth availability within OSPF/ISIS is advertized  per PSC or per family  of TE related PSCs when the TE extensions only imply advertizement per priority. Are colors assigned to different PSCs or families of TE related PSCs and bandwidth availability advertized per color?.

Thanks,

Darek

---

From: "Angela Chiu" <[email-masked]>
Date: Tue, 20 Jun 2000 15:06:41 -0400

Darek,

These are additional requirements for IGP extensions, as stated in TE
Framework draft
http://www.ietf.org/internet-drafts/draft-ietf-tewg-framework-01.txt
"In order to perform constraint-based routing on a per-class basis for LSPs,
the conventional IGPs (e.g., IS-IS and OSPF) should provide extensions to
propagate per-class resource information."
Then the draft states that "per-class parameters can be aggregated into
per-class-type parameters" for scalability improvements.

Regards,

Angela

-----Original Message-----
From: Darek Skalecki [mailto:[email-masked]]
Sent: Tuesday, June 20, 2000 2:51 PM
To: Francois Le Faucheur
Cc: [email-masked]; [email-masked]
Subject: Re: Bandwidth reservation per PSC

Thanks Francois,

My question was indeed related to the distributed model. What I am still not
sure about is how bandwidth availability within OSPF/ISIS is advertized  per
PSC or per family  of TE related PSCs when the TE extensions only imply
advertizement per priority. Are colors assigned to different PSCs or
families of TE related PSCs and bandwidth availability advertized per
color?.

Thanks,

Darek

Francois Le Faucheur wrote:

> First, of course , in some environments, Constraint Based Routing may be
performed "off-line"/"in a Centralised Manner". In these situations, per-PSC
bandwidth availability can be determined by the centralised tool without
relying on extensions to OSPF/ISIS.
>
> Where Constraint Based Routing is performed "on-line"/"in a Distributed
Manner", then yes, OSPF/ISIS are required to propagate all necessary
bandwidth information. This could be achieved in a number of ways:
>         - one approach would be to advertise bandwidth information for
every PSC. As you are pointing out above, this may lead to
scaling/operational issues earlier than desired.
>         - another approach would be to advertise bandwidth information
only for each "family/class" of PSCs. A family/class of PSC would comprise
all the PSCs which share the same bandwidth constraints. It is likely that
multiple PSCs can share the same bandwidth constraints (eg
"max-reservable-bandwidth"). For instance, multiple Premium/Non-real-time
PSCs may share the same "max-reservable-bandwidth". In that case, you have
traded a little bit of fine-grain control (you can't enforce bandwidth
constraints which are different for absolutely every PSC), but you have
significantly gained in scalability of OSPF/ISIS by "only" advertising 2/3
available bandwidth information.
>
> You will find some text on the second approach in section "6.7 Traffic

---

From: "Darek Skalecki" <[email-masked]>
Date: Tue, 20 Jun 2000 16:06:05 -0400

Thanks Angela,

Are these extensions currently defined for OSPF and ISIS?. If yes then please
provide me with a reference, and if not then is anyone working on them ?. I can
only find extensions related to advertizing bandwidth availability per priority
not resource class.

Thanks,

Darek

---

From: "Angela Chiu" <[email-masked]>
Date: Tue, 20 Jun 2000 17:41:43 -0400

Darek,

I don't think it is currently included in the OSPF and ISIS TE extensions. I
am not aware of anyone who is working on it. But I could be wrong since
there are so many activities around MPLS, hard to keep track of all of them.

Angela

-----Original Message-----
From: Darek Skalecki [mailto:[email-masked]]
Sent: Tuesday, June 20, 2000 4:06 PM
To: alchiu
Cc: mpls; 'Francois Le Faucheur'
Subject: Re: Bandwidth reservation per PSC

Thanks Angela,

Are these extensions currently defined for OSPF and ISIS?. If yes then
please
provide me with a reference, and if not then is anyone working on them ?. I
can
only find extensions related to advertizing bandwidth availability per
priority
not resource class.

Thanks,

Darek

---

From: Francois Le Faucheur <[email-masked]>
Date: Wed, 21 Jun 2000 17:48:27 +0200

Darek, 
I am hoping to submit something on extensions to IGPs for support of "Class-types". Let me know if you're interested in working on this.
Francois