Re: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much does it really save?

Andrew Qu <> Fri, 24 July 2015 15:46 UTC

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From: Andrew Qu <>
To: Eric C Rosen <>, Loa Andersson <>, Alexander Vainshtein <>, Stewart Bryant <>, "Andrew G. Malis" <>, "S. Davari" <>
Thread-Topic: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much does it really save?
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Date: Fri, 24 Jul 2015 15:45:55 +0000
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Subject: Re: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much does it really save?
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-----Original Message-----
From: Eric C Rosen [] 
Sent: Friday, July 24, 2015 5:10 PM
To: Andrew Qu; Loa Andersson; Alexander Vainshtein; Stewart Bryant; Andrew G. Malis; S. Davari
Subject: Re: [mpls] draft-fang-mpls-label-forwarding-no-swap - how much does it really save?

> When standard defines a "no-swap" operation,  ASIC engineer would 
> implement such operation completely differently

Well, this is where we came in.  

[Andrew]  That is right, we are supposed to do some bridging works.  But when RFC is better written, 
	You may be "called" in less and we can spend more time to do greater good.

The RFCs do not dictate how the ASICs should be designed, and your ASIC designers are free to design in whatever way best meets the needs of the systems that are going to use those ASICs.  You can put in any optimizations you think are warranted. 

  If you expect the ASICs to be used in products that will never need to swap label values, never need to push labels, never need to pop labels, then you are free to design the ASICs without any of these features.  If you think that these operations are needed, but that "don't change the label value or the stack size" are the most common operations, you can certainly optimize your design for that case.

But if you think you can get the ASICs designed properly simply by handing the RFCs to the ASIC designers, you may be in for an unpleasant surprise.

[Andrew] I don't know where did you get this idea from,  it is funny that how can you concluded that when I am asking
	better written doc implies that I will simply hand off the work completely.

> Since the label is to be "swap"ed with a new LABEL stack, then the 
> design of SWAPPING need to consider TTL handling such as 1) just 
> decrement of original TTL or 2) using a brand new TTL, such as using 
> local new register stored value to Fill the sawp'ed new label stack.

The TTL handling is exactly the same for both cases.  If you have been telling your ASIC designers something different, you most definitely are in for an unpleasant surprise.

[Andrew] I am using this case to indicate better written doc might help to reduce confusion.  
	This is the human thought process when people read "swap" and "no_swap" and consider how to implement
	Them.  Hence my point of no_swap may be defined to differentiate "swap".  



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