Subject: RE: question about the traffic engineering extensions to OSPF

From: Feihong Chen <[email-masked]>
Date: Wed, 22 Aug 2001 16:54:41 -0400

Still a little bit confuse here. What's the difference if ERO 
is calculated online or offline in terms of the information
database that CSPF refer to? 

If all of the sub-TLVs are mandatory, TED has enough information 
for CSPF to calculate a TE path and return a ERO list. Also, 
TED can be implemented independently from the traditional LSDB 
that OSPF currently uses. 

But, if only Link Type and Link ID are mandatory, unless CSPF is 
designed to be able to access TED as well as traditional LSDB, I am
wondering how CSPF can return a ERO (if local/remote ip addresses 
are not advertised) even for a simple path request to an egress LSR 
without any color or bandwidth constrains. 

Actually, it's back to my original question, shouldn't we put some or
all of the link sub-TLVs as mandatory since the extension to OSPF is for
traffic engineering. 

Thanks,
Feihong 

-----Original Message-----
From: Eric Osborne [mailto:[email-masked]]
Sent: Wednesday, August 22, 2001 4:01 PM
To: Feihong Chen
Cc: [email-masked]; [email-masked]; [email-masked]
Subject: Re: question about the traffic engineering extensions to OSPF

Not having this info makes online path calculation of an ERO more
difficult, but an offline tool can certainly calculate paths and give
them to a LSR, which just dumbly signals what it's told.

eric

On Wed, Aug 22, 2001 at 12:12:41PM -0400, Feihong Chen wrote:
> Hi, 
> 
> I just realized that the new version of the "Traffic Engineering
Extensions
> to OSPF (draft-katz-yeung-ospf-traffic-05.txt)" made some changes on the
> Sec2.4.2 (Link TLV). Unlike the previous version of the draft, this
version
> proposed that "The Link Type and Link ID sub-TLVs are mandatory, i.e.,
must
> appear exactly once. All other sub-TLVs defined here may occur at most
> once." (Note, other sub-TLVs includes traffic engineering metric,
> local/remote interface ip address, bandwidth information, class/color).
> 
> The question that I have here is, if the LSA only advertise the Link Type
> and Link ID as mandatory, then I don't see the capability of OSPF being a
> "traffic engineering helper" because the Traffic Engineering Database
build
> from these two information ( which is the worst case ) simply is not able
to
> calculate the ERO (i.e. the list of ip addresses), nor the bandwidth for
an
> attempted LSP. 
> 
> In another word, if the proposed extensions to OSPF is mainly for traffic
> engineering, shouldn't some or all of  "other sub-TLVs" (e.g. bandwidth,
ip
> address, color) be necessarily advertised besides the Link Type and Link
ID?
> Otherwise, it will end up the traditional OSPF not for TE purpose? 
> 
> Maybe I miss something here, looking forward to a clarify to better
> understand the purpose of this updated changes.
> 
> Thanks a lot,
> Feihong Chen
> 
>

---

From: "Amir Hermelin" <[email-masked]>
Date: Sun, 26 Aug 2001 14:12:59 +0300

Feihong,

It's enough to have one reason not to make a certain parameter
mandatory, in order to leave it optional. I'm sure there are other
reasons as well, but here are some:
* unreserved bw:  suppose your domain is only interested in Diffserv-TE
(whatever will come of it), and DS-TE advertises unres bw in different
TLVs. Then, there's no need to prevent turning (BE) unres-bw off.
* max bw and max reservable bw:  same as above.
* te metric:  suppose you don't want to use it (as some implementations
don't).
* color:  if a color hasn't been configured, there might not be a need
to advertise it.
* local and remote ip:  these can be inferred in other ways (although in
IS-IS the situation might be different).

So, in general, leaving them optional is really providing flexibility
(for the future, as well). I do agree, that advertising only LinkID and
LinkType TLVs (or, in the IS-IS case, advertising nothing) is useless to
TE (whether offline, online, or on the moon...).

Hope this helps...

--
Amir Hermelin                  <mailto:[email-masked]>
Charlotte's Web Networks Inc.   <http://www.cwnt.com>

-----Original Message-----
From: Feihong Chen [mailto:[email-masked]]
Sent: Wednesday, August 22, 2001 7:13 PM
To: [email-masked]; [email-masked]
Cc: [email-masked]
Subject: question about the traffic engineering extensions to OSPF

Hi, 

The question that I have here is, if the LSA only advertise the Link
Type
and Link ID as mandatory, then I don't see the capability of OSPF being
a
"traffic engineering helper" because the Traffic Engineering Database
build
from these two information ( which is the worst case ) simply is not
able to
calculate the ERO (i.e. the list of ip addresses), nor the bandwidth for
an
attempted LSP. 

In another word, if the proposed extensions to OSPF is mainly for
traffic
engineering, shouldn't some or all of  "other sub-TLVs" (e.g. bandwidth,
ip
address, color) be necessarily advertised besides the Link Type and Link
ID?
Otherwise, it will end up the traditional OSPF not for TE purpose? 

Thanks a lot,
Feihong Chen