Subject: RE: [NSIS] Re: QoS NSLP: ACK flag has no effect?

From: "Geib, Ruediger" <[email-masked]>
Date: Wed, 8 Feb 2006 15:07:51 +0100

Hello Roland,

|There is the MA-Hello mechanism in GIST which also allows to detect
|a failed messaging association (though this is not the main intention
|of MA Hellos, right?). The MA-Hold-Time is indicated
|to a peer during the setup phase. Thus, one is basically able to react
|faster than TCP would detect a dead peer if the NoHello 
|Timeout is small enough.

My point was whether GIST would detect a loss of connectivity if the 
reliable transport below it is broken, but not aware that it is broken.

The LDP example I mentioned was caused by such a problem. 

Would NSLP detect that the GIST layer below it is dead if GIST in that 
situation is not aware that it is dead? If yes, the above ack mechanism 
will indicate the problem on NSLP level.

The idea behind the proposed ACK mechanism on NSLP level despite reliable 
transport is a "lesson learned". Always make sure that a communication 
layer in itself is able to detect a broken communication, if that is 
relevant for the service offered.

The result of that lesson for LDP was the specification of MPLS OAM 
(MPLS PING, MPLS Traceroute). NSLP PING would be another possibility to 
achieve what I mean. It is reactive (you do that after discovering an 
issue), while an ACK mechanism could be used for pro-active problem 
detection (log or alert if RESV wasn't acked after beeing resent n times).

Regards,

Rüdiger

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From: Roland Bless <[email-masked]>
Date: Wed, 08 Feb 2006 15:26:46 +0100

Hi Ruediger,

> will indicate the problem on NSLP level.

Ok, if the point is to detect a dead GIST, then the ACK feature
may be useful indeed.

> detection (log or alert if RESV wasn't acked after beeing resent n times).

Ok, thanks for the motivation.

Regards,
 Roland