Subject: Re: Resource reservation during RSVP Path message forwarding?

From: Amir Birjandi <[email-masked]>
Date: Thu, 19 Apr 2001 15:52:30 -0400

>REASONS FOR NOT RESERVING RESOURCES UNTIL RESV PROCESSING
>
>1: There will be no data flow along the LSP until the Resv message
>   arrives, but the resources will be reserved.  These resources won't
>   be available for other purposes (perhaps other LSPs or non-MPLS
>   circuits.)
>

Can you explain what you mean by non-MPLS circuits? and why do you see a
problem?

Based on my understanding the reseravation starts at R4. 

A.

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From: Rajiv Papneja <[email-masked]>
Date: Thu, 19 Apr 2001 19:04:10 -0400 (EDT)

> Based on my understanding the reseravation starts at R4. 
 Hi Amir,
 
 The LSPs can be established using the extensions to RSVP without even
reserving any resources. Such LSPs can be used to carry the best effort
traffic and also can be used for other purposes such as recovery policies. 
 
 For TE applications path message could be used as a means to verify the
resource availability along the path before preempting the
lower priority traffic. If the path message is allowed to progress when
there are no resources, then it might preempt the lower priority tunnels
unnecessarily. 

 Regards,
  -Rajiv

********************************
Rajiv Papneja (GRA)
Advanced Internet Laboratory
George Mason University,
G10, Johnson Center,
Fairfax, VA 22030-4444
Tel: 703.993.4703
email: [email-masked]
********************************

---

From: David Charlap <[email-masked]>
Date: Thu, 19 Apr 2001 19:18:29 -0400

Amir Birjandi wrote:
>>    arrives, but the resources will be reserved.  These resources
>>    won't be available for other purposes (perhaps other LSPs or
>>    non-MPLS circuits.)
> 
> Can you explain what you mean by non-MPLS circuits? and why do you
> see a problem?

For instance, on an ATM/MPLS switch running a "ships in the night"
scenario, resources consumed by an LSP will not be available for an ATM
VC and vice versa.

> Based on my understanding the reseravation starts at R4.

The Resv message originates there.  But the other routers can
pre-reserve resources in advance, in order to avoid having to do so
later.

In MPLS, under most circumstances, the amount of resources reserved in
the Resv will be the same amount that was requested in the Path
message.  So resources can theoretically be reserved at Path processing
time, even though a label won't be available until after the Resv
arrives.

-- David