Questions on draft-ietf-ccamp-gmpls-recovery-analysis-05.txt

["Adrian Farrel" <olddog@clara.co.uk>]

Hi, 

Posting this question on behalf of Lei Lei who has had some difficulty 
subscribing to the list. 

Thanks,
Adrian
===
The section 8.4.1 of draft-ietf-ccamp-gmpls-recovery-analysis-05.txt 
discusses how to realize recovery resource sharing using GMPLS protocols.
It draws the conclusion that no further extensions of GMPLS routing 
protocols are needed to perform this task, since the use of Maximum 
Reservable Bandiwidth, the Unreserved Bandwidth and the Maximum LSP 
Bandwidth is sufficient for the purpose. However, I do not quite follow this 
idea. 

I've read the [KODIALAM1],  [KODIALAM2] and [GLI] papers, which is referred 
to in the draft, even before I read this draft. I have no problem in 
understanding the ideas described in those papers, In those papers, the 
Maximum TE Link Bandwidth is divided into three parts: the capacity 
committed for working LSPs, and capacity reserved for backup LSPs, and the 
unallocated capacity. The Partial  Information routing algorithm needs to 
know the above three values in order to compute the optimal path. The Full 
Information routing algorithm in [GLI] needs still more information. 
However, section 8.4.1 of draft-ietf-ccamp-gmpls-recovery-analysis-05.txt
claims that only the value of Maximum Reservable Bandiwidth, the Unreserved 
Bandwidth and the Maximum LSP Bandwidth need to be avaiable for recovery 
resource sharing, as shown in the figure below. But I do not understand how. 

1. I do not understand the relationships between the  Max Reservable
 Bandwidth, Maximum LSP Bandwidth and the Unreserved Bandwidth.
  1.a Why should the difference between Max Reservable Bandwidth and the
      Maximum LSP Bandwidth be the Maximum Shareable Bandwidth?
  1.b Why should  the difference between the Max Reservable Bandwidth and
      the Maximum TE Link Bandwidth be the amount of bandwidth currently
      allocated for shared recovery?
      The Max Reservable Bandwidth should be  larger than the Maximum TE
      Link Bandwidth, then how to set the exact value of Max Reservable
      Bandwidth?
      Is it decided by policy or can be calculated by some equations?
      Is it a constant value during network operation or change over time?
  1.c Why should the difference between the Maximum TE Link Bandwidth and
      the Maximum LSP Bandwidth be the actual bandwidth committed for
      shared recovery instead of the sum of the bandwidth committed for
      working LSPs and the actual bandwidth committed for shared recovery? 

2. What is the routing algorithm supposed to be used in this method?
 I suppose the working LSP can be calculated with SPF algorithm on the
 network topology where the links whose Maximum LSP Bandwidth smaller
 than the request bandwidth are pruned? But how to calculate the optimum
 backup path? Is it similar with the Partial Information approach? If it
 is, I fail to see how this could be done. 

                               - ---------- Max Reservable Bandwidth
                              |  -----  ^
                              |R -----  |
                              |  -----  |
                               - -----  |max_R
                                 -----  |
 --------  TE link Capacity    - ------ | - Maximum TE Link Bandwidth
 -----                        |r -----  v
 -----     <------ b ------>   - ---------- Maximum LSP Bandwidth
 -----                           -----
 -----                           -----
 -----                           -----
 -----                           -----
 -----                           ----- <--- Minimum LSP Bandwidth
 -------- 0                      ---------- 0 


Best regards 

Lei Lei