Subject: [NSIS] QoS NSLP -- 4.7. Reduced State or Stateless Interior Nodes

From: Hannes Tschofenig <[email-masked]>
Date: Thu, 09 Aug 2007 11:06:11 +0200

I do not quite understand how the stateless interior nodes work.

I understand that you do not store GIST state for reverse routing. I 
also understand that there is a desire not to install per-flow 
reservations.

But if there is no state stored at all, as mentioned in Section 4.7 of 
the QoS NSLP, then what's the point of signaling?

I also believe that Section 4.7 is missing an important point:

If a reservation request fails then the RESERVE message is forwarded 
until it hits the egress node. In standard QoS NSLP operation a RESPONSE 
message would be returned immediately when an error is detected.

Here is a figure:

         Please view in a fixed-width font such as Courier.

          QNE             QNE             QNE            QNE
        ingress         interior        interior        egress
    GIST stateful  GIST stateless  GIST stateless  GIST stateful
           |               A               B              |
   RESERVE |               |               |              |
  -------->| RESERVE       |               |              |
           +--------------------------------------------->|
           | RESERVE'      |               |              |
           +-------------->|               |              |
           |               | RESERVE'      |              |
           |               +-------------->|              |
           |               |               | RESERVE'     |
           |               |               +------------->|
           |               |               |  RESPONSE'   |
           |<---------------------------------------------+
           |               |               |              | RESERVE
           |               |               |              +-------->
           |               |               |              | RESPONSE
           |               |               |              |<--------
           |               |               |     RESPONSE |
           |<---------------------------------------------+
   RESPONSE|               |               |              |
  <--------|               |               |              |

Assume that the RESERVE' message fails at node A. Then, a RESPONSE 
cannot be sent back to the ingress but instead the message continues its 
way towards the egress node.

It is, however, necessary to mark the message in a way that subsequent 
nodes (in this case node B) does not attempt to make a reservation but 
just forwards the message as is.

When the egress node receives the message it then constructs a RESPONSE' 
message indicating the failure of the reservation attempt.

This procedure requires additional protocol mechanisms to support
a) marking a message as failed
b) allow the state machine to forward the message in this particular 
mode even though the reservation failed.

I don't see any of these things in the document. A bug or intention?

Ciao
Hannes

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