Subject: FW: [mpls] One week last-last call on Soft Preemption

From: "Balaji, Hemanth" <[email-masked]>
Date: Tue, 21 Jun 2005 14:54:27 +0530

Hi,

Please Excuse me. There still seemed to have been some alignment
problem. 

-Hemanth.

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
On Behalf Of Balaji, Hemanth
Sent: Tuesday, June 21, 2005 11:03 AM
To: Adrian Farrel; George Swallow; [email-masked]
Subject: RE: [mpls] One week last-last call on Soft Preemption

Hi,

 Can anyone explain, how the following situation is handled ( be it
needed to ) by the soft-preemption draft.

Topology:

                   +---------------- R2
                   |
R0 --------------- R1
                   |
                   +---------------- R4
Reservable link Bandwidth( BW)  for all links = 1000

LSP1 :

R0 ----------------- R1 ---------------- R4

BW = 500
Priority(Hold): 7

LSP2 :

R2 ----------------- R1 ---------------- R4

BW = 600
Priority(Setup): 6

1) Initially LSP1 is UP. Soft preemption desired flag is set.

2) Now R1 gets a new resquest for LSP2. ( which requires LSP1 to be
preempted, softpreempted in this case)

3) Let us assume the following situation.

   > Before R1 notifies R0 about the preemption.
   > R0 changes its BW Req to 400 and sends out its first new path
     message.
   > The first Resv msg from R1 that R0 receives has (will have-due to 
     step 2) the preemption pending flag set.

Now, what will the behavior be in this case, will this situation make
any difference?

Ideally, R0 should not attempt a make before break and look for an
allternate path, since the new BW requirement ( 400(7) + 600(6) )
can be satisfied along the same path ( R0-R1-R4).

Regards,
Hemanth.

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---

From: JP Vasseur <[email-masked]>
Date: Tue, 21 Jun 2005 08:26:41 -0400

Hi,

> can be satisfied along the same path ( R0-R1-R4).

Looks like your question is not really related to soft preemption but  
the head-end reroute engine to find a new path for a (soft) preempted  
TE LSP. The head-end should avoid this path indeed. That said, even  
if it retries the same path (in your example), the LSP setup will not  
complete ...

JP.