Re: [CCAMP] Network Assigned Upstream Label - Draft Update

[Igor Bryskin <[e-mail]>]

Hi,
It is funny that we have to go through the same arguments again and again every 4 months :=)
One point that I made when I was 4 months younger is that Acceptable Label Set is an exceptionally bad idea in the context of overlay networks (UNI, ENNI, etc.). Consider the following scenario:

1.      Ingress UNI-C guesses upstream label for its LSP L to be X;

2.      Network made its own decision that the upstream label cannot be X - has to be Y. This decision is a function of many things: selected path, capabilities of network nodes along the path, capabilities of egress UNI-C. etc. *Only when the entire tail of client LSP is established the ingress UNI-N can definitively report the acceptable upstream label;* The point is that the signaled acceptable label set cannot contain more than one value.

3.      If label Y is not acceptable for ingress UNI-C, it will have no other choice other than to guess another upstream label Z, and start the process again;

4.      This can go on for quite a while until ingress UNI-C runs out of guesses and gives up.

Cheers,
Igor

From: CCAMP [mailto:[e-mail]] On Behalf Of Vishnu Pavan Beeram
Sent: Friday, February 28, 2014 9:16 AM
To: Giovanni Martinelli (giomarti)
Cc: [e-mail]
Subject: Re: [CCAMP] Network Assigned Upstream Label - Draft Update

Giovanni, Hi!

Can you please elaborate on why you think the LABEL_SET having good labels help in this context/argument? If the upstream-node doesn't guess right (when picking the upstream-label), you'll get a PATH-ERR back with the ACCEPTABLE_LABEL_SET. And this would happen for every setup request. Wouldn't you call this a compromised solution?

Regards,
-Pavan

On Fri, Feb 28, 2014 at 7:54 AM, Giovanni Martinelli (giomarti) <[e-mail]<mailto:[e-mail]>> wrote:
Hi Vishnu,

On 28 Feb 2014, at 13:26, Vishnu Pavan Beeram <[e-mail]<mailto:[e-mail]>> wrote:


(2) The use of Label-Set/Acceptable Label-Set was meant to be used for exceptions. Using it always for every setup request is a compromised solution.


At the time we discussed the wson signaling (http://tools.ietf.org/html/draft-ietf-ccamp-wson-signaling-06), the acceptable label set was considered good enough. Not sure it comes into play at every request since your label_set should have reasonably good labels.

Cheers
G