The MPLS WG Archive

[Khuzema Pithewan <KhuzemaP@netbrahma.com>]

How would you make "Out of Order" check on Error Messages...

consider following scenario...

	L1---------L2--------L3

if L2 sends PATH message contains the messageID generated at L2  to L3. In
reponse of this message L3 sends a PATH Error message back to L2 which
contains the message ID generated at L3. Now at L2 how to check whether this
error message  is out of order or not.

RFC says....

"To determine ordering, the received
   Epoch value must match the value previously received from the message
   sender.  If the values differ then the receiver MUST NOT treat the
   message as out of order.  When the Epoch values match and the
   Message_Identifier value is less than the largest value previously
   received from the sender, then the receiver SHOULD check the value
   previously received for the state associated with the message.  "

Assume here messageID received in the error mesage is less than the largest
value received from L3 till now and we have not received RESV message from
L3 yet .. so how u will determine the "Out of order" message here??

Khuzema.


> ----------
> From: 	Suresh Katukam[SMTP:skatukam@cisco.com]
> Sent: 	Thursday, February 14, 2002 7:40 AM
> To: 	Sandeep B
> Cc: 	mpls@UU.NET
> Subject: 	Re: Doubt about Refresh reduction
> 
> 
> I think it is useful to have Message IDs for all messages. Even for 
> optical/SONET links too.
> If you have OF/OB, or IF/IB control channels, it is quite possible that
> you 
> wanted to send
> a refresh PATH message and then send a PATH TEAR. If you do not use
> message 
> ids,
> it is quite possible that PATH TEAR may come first and then the PATH 
> message at the
> other end. This would tear down and create the circuit at the other end of
> 
> the link.
> 
> In effect, to find out of order messages.
> 
> -- Suresh
> 
> At 03:48 PM 2/13/2002 -0800, Ping Pan wrote:
> >If I recall correctly, at one point, we were worried about the noisy 
> >links, where without some sort of ack, RSVP messages may get dropped. In 
> >this case, having msgids for teardown and error would be nice. Depending 
> >on where you want to apply refresh reduction, you have the option where
> to 
> >apply msgid's. On SONET/optial links, I am not sure it's useful to use 
> >msgid for error and teardown messages.
> >
> >2 cents,
> >
> >- Ping
> >
> >
> >Sandeep B wrote:
> >
> >>I have a more basic question.
> >>Ping -
> >>Why do we need to send PATHTEAR, RESVTEAR, PATHERR, RESVERR with Msgids.
> 
> >>These are all triggered messages and what purpose do they solve when we 
> >>send these packets with msgid.
> >>-Sandeep
> >>
> >>_________________________________________________________________
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> >
> >
>