Subject: Re: [mpls-tp] MPLS-TP Sections vs PSTs

From: <[email-masked]>
Date: Fri, 7 May 2010 08:56:17 +0100

re-sending snipped as got a 'too big' response - my apologies

________________________________

	From: Harrison,N,Neil,DKQ7 R 
	Sent: 07 May 2010 08:54
	To: 'Sprecher, Nurit (NSN - IL/Hod HaSharon)';
[email-masked]; [email-masked]
	Cc: [email-masked]
	Subject: RE: [mpls-tp] MPLS-TP Sections vs PSTs

	Nurit,
	 
	CC is not a good idea.  It comes from ATM I.610 OAM....and there
is more than simply CC wrong with this OAM standard. 
	 
	A break is one thing but a misconnectivity event (ie connection
A and B swapped) or mismerging event (eg unintended replication of
connection A traffic units into connection B....connection A may see no
effect) is a much more serious thing for the affected client.
	 
	I coined the term CV because I wanted to differentiate it from
the flawed CC.  I have no idea why some folks still talk about CC.
	 
	You have some misconceptions below.....see in-line:

________________________________

		From: Sprecher, Nurit (NSN - IL/Hod HaSharon)
[mailto:[email-masked]] 
		Sent: 06 May 2010 16:15
		To: Harrison,N,Neil,DKQ7 R; [email-masked];
[email-masked]
		Cc: [email-masked]
		Subject: RE: [mpls-tp] MPLS-TP Sections vs PSTs

		In principle, CC check breaks. I thought misconnectivity
can be avoided as you claims by CP or MP means, before the connection is
placed.  

		NH=> You have clearly not understood what is going on
here.....the CP/MP checking for DP loops before placing a connection is
a very different thing to the *DP* itself checking it has correct
connectivity *after* the connection is instantiated.  I am surprised you
confuse these.  If you consider the 2 exmaples I mentioned above about
swapped and mismerged connections you should see that the DP/CP will
*not* see any looping at all but once the DP OAM is established (and
this MUST be sync'd to connection set-up/tear-down please note)   then
the *DP* will detect the serious misconnectivity/mismerging defects.

		But as you say it is needed for all of which can happen
at any time after a connection has been placed.............this is
correct and I agree........so why TTL is not needed as well?  

		NH=> Ask yourself why FR, ATM, X.25, SDH VC4, etc, etc
co-ps/co-cs mode technologies do not use TTL.....I think the ('its not
needed') answer is rather obvious. 

		 It can be used as additional mechanism to prevent
endless loops, and other cases as well, also when CV is not used! 

		NH=> You cannot substitute TTL for CV.  I am a little
worried you don't seem to understand this.  TTL is important in cl-ps
technologies that use directed routing (as opposed to brute force
topology pruning to connectivity=1, eg original Ethernet) because we
don't have a parent connection.  TTL is not required at all in co-cs and
co-ps mode technologies.....which is why it has never been specified for
such.  Please do not confuse MPLS with properly specified co-ps mode
technologies....though to be strictly accurate it is only the LDP form
of MPLS that creates this (and other) problems here.

		regards, neil