Re: [CCAMP] I-D Action: draft-ietf-ccamp-flexible-grid-ospf-ext-01.txt

[Rajan Rao <[e-mail]>]

Ramon,

It is a matter of how much finer control you want to provide in your network.   Don’t you think having  [Min, Max & Available bandwidth] per priority in one place gives a better control of resources?   Think of a network with  mix of C.S.  I can segregate the spectrum whichever way I want with the above 3 parameters.   This was the intent in our draft.

I am fine if WG wants to use RFC4203 as precedence and move on without priority for Minimum LSP bandwidth field.  We can jump to Adrian’s questions to see if there is any interest to pursue generalization.

Thx
Rajan


From: Ramon Casellas [mailto:[e-mail]]
Sent: Wednesday, March 04, 2015 1:30 AM
To: Rajan Rao; [e-mail]; 'Zhangxian (Xian)'; 'CCAMP'
Cc: Iftekhar Hussain
Subject: Re: [CCAMP] I-D Action: draft-ietf-ccamp-flexible-grid-ospf-ext-01.txt

El 04/03/2015 a las 2:11, Rajan Rao escribió:
Adrian,


Looks like there is different interpretation of RFC 4202 text.  RFC 4202 text in sections 2.4.2 & 2.4.3  says

“…..an LSP at priority
  p could reserve any bandwidth between the Minimum LSP Bandwidth and
   the Maximum LSP Bandwidth at priority p, provided that the bandwidth…..”

Having only the Maximum LSP bandwidth field priority based & not the Minimum LSP bandwidth field doesn’t seem right.  It is a simplification for sure.  What is the correct interpretation of above text?  Will be good to know.

Rajan, all

It is a good question, and in my humble opinion, there are different things (echoing Adrian's questions):

i) Whether RFC4202 text could imply that Minimum LSP bandwidth is a function of priority (p)

ii) The need for a priority-dependent Minimum LSP bandwidth (and, in particular, for flexi-grid networks) in view of the requirements of preemption, resource usage, etc. This is to me the most important point.

iii) The actual encoding (in terms of "m" or Hz, in the ISCD SCSI ...)

For ii) it would be good to clearly agree on the requirement (let's stick to current in-force grid definitions). Personally, I see that higher priorities are allowed higher values of Max LSP bandwidth, but when would you need that a lower priority LSP is allowed a lower minimum value (or, similiarly, why would I constraint high priority LSPs to not use lower LSP bandwidths?). I have no objection to work on iii) if ii) is clear.


Although IMHO not critical, for i) It is my understanding that the minimum LSP bandwidth is unique across priorities, and only the Maximum LSP bandwidth depends on the priority. RFC4202
- An interface may have more than one Interface Switching Capability Descriptor.  This is used to handle interfaces that support multiple switching capabilities, for interfaces that have Max LSP Bandwidth  values that differ by priority level, and for interfaces that support  discrete bandwidths. // Only Max is mentioned
- For a simple (unbundled) link, the Maximum LSP Bandwidth at priority p is defined to be (...) // there is no such definition for minimum "at priority p".
- The Minimum LSP Bandwidth specifies the minimum bandwidth an LSP could reserve // it does not mention "at priority p" and is ISCD specific.
- an LSP at  priority p could reserve any bandwidth (...) by the Minimum LSP Bandwidth and the Maximum LSP Bandwidth at priority p. // It is my understanding that Minimum LSP Bandwidth refers to the actual definition in point 2, i.e., bw(p) = [min_lsp_bw, max_lsp_bw(p)]
- Actual OSPF-TE extensions (e.g. for PSC) where min_lsp_bw is unique.