Re: [PWE3] CW usage in opposite directions for static PWs

Lizhong Jin<lizhong.jin@zte.com.cn> Tue, 10 April 2012 15:34 UTC

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To: Yaakov Stein <yaakov_s@rad.com>
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Subject: Re: [PWE3] CW usage in opposite directions for static PWs
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Hi Yaakov,
The use case below may work, but does not mean asymmetric CW for PW would 
work in all cases. One example is, when CW is used for packet 
fragmentation, if asymmetric CW is used, packet fragmentation may not be 
achieved in one direction, and lead to pack loss. Other examples would be 
OAM tools for PW. IMO, we could consider asymmetric CW as a special 
implemenation case.

Lizhong
 
------------------------
Yaakov Stein <yaakov_s@rad.com> wrote 2012/04/10 16:14:03:

> Sasha
> 
> The only scenario I can think of where it is really useful, is the 
> asymmetric bandwidth and usage case.
> 
> Consider a bandwidth constrained upstream sending very small packets
> (ack's and control signaling) where the CW may be significant overhead,
> and a wide bandwidth downstream sending very large packets (e.g., 
video),
> where the CW would be useful.
> 
> The mixed static-signaled MS-PW case is not really a constraint.
> If the end-end MS-PW uses (or doesn't) the CW,
> then the configuration of the static segment(s) would need to 
> enforce that behavior,
> along with all other parameters.
> This has little to do with the general question of enforcing 
> duplexing behavior.
> 
> Y(J)S
> 
> 
> From: Alexander Vainshtein [mailto:Alexander.Vainshtein@ecitele.com] 
> Sent: Tuesday, April 10, 2012 11:05
> To: Yaakov Stein
> Cc: Lizhong Jin; pwe3@ietf.org
> Subject: RE: [PWE3] CW usage in opposite directions for static PWs
> 
> Yaakov, and all,
> My reading of RFC 4447 is that in the case of a signaled PW the CW 
> is either used or not used bi-directionally by a PW endpoint.
> Further, as per RFC 6073, S-PEs in multi-segment PWs cannot strip, 
> insert or manipulate the CW in any way.
> Hence I think that the asymmetric usage of the CW must be prohibited
> in static PWs in order to assure interoperability of MS-PWs 
> comprised of static and dynamic segments.
> 
> (On top of that, I do not see any advantage in allowing asymmetric 
> usage of the CW, but this is a different story.)
> 
> Regards,
>      Sasha
> 
> From: pwe3-bounces@ietf.org [mailto:pwe3-bounces@ietf.org] On Behalf Of 
> Yaakov Stein
> Sent: Tuesday, April 10, 2012 10:39 AM
> To: Lizhong Jin; pwe3@ietf.org
> Subject: Re: [PWE3] CW usage in opposite directions for static PWs
> 
> Lizhong
> 
> OK, maybe I agree. But my point was that this requirement was not 
> fully discussed.
> 
> Perhaps a statically configured PW should be able to use the CW in 
> one direction while not using it in the other.
> 
> Y(J)S
> 
> From: pwe3-bounces@ietf.org [mailto:pwe3-bounces@ietf.org] On Behalf Of 
> Lizhong Jin
> Sent: Monday, April 09, 2012 10:18
> To: pwe3@ietf.org; Yaakov Stein
> Subject: Re: [PWE3] CW usage in opposite directions for static PWs
> 
> 
> Hi Yaakov, 
> Sorry, word mistake. It should not be OR, but AND operation. If one 
> side support and the other side not, then CW will not be used. Then 
> the result will be aligned with RFC4447. 
> 
> Regards 
> Lizhong 
> 
> > ----------------------------------------------------------------------
> > 
> > Message: 1
> > Date: Sun, 8 Apr 2012 15:28:52 +0000
> > From: Yaakov Stein <yaakov_s@rad.com>
> > To: Lizhong Jin <lizho.jin@gmail.com>
> > Cc: "pwe3@ietf.org" <pwe3@ietf.org>
> > Subject: Re: [PWE3] CW usage in opposite directions for static PWs
> > Message-ID:
> >    <07F7D7DED63154409F13298786A2ADC904363878@EXRAD5.ad.rad.co.il>
> > Content-Type: text/plain; charset="us-ascii"
> > 
> > Lizhong
> > 
> > Of course each side needs to KNOW if the other side is using a CW or 
not;
> > but, that does not mean they can not be asymmetric.
> > 
> > What do you mean by OR - that if either CAN use a CW then both MUST 
use?
> > This is the opposite of 4447.
> > 
> > 
> > Y(J)S
> > 
> > From: Lizhong Jin [mailto:lizho.jin@gmail.com]
> > Sent: Saturday, April 07, 2012 05:58
> > To: Yaakov Stein
> > Cc: pwe3@ietf.org
> > Subject: Re: [PWE3] CW usage in opposite directions for static PWs
> > 
> > Hi Yaakov,
> > Thanks for the comments during the session of PWE3.
> > For the static PW, the CW usage should be consisted, otherwise the 
> > packet processing would be wrong. The CW nibble is not enough to 
> > identify a ACH, and "PW label + CW nibble" is used to identify ACH. 
> > IMO, the static PW CW capability could be got by "OR" operation of 
> > both local and remote CW parameters.
> > 
> > Thanks
> > Lizhong
> > 
> > ------------------------------
> > 
> > Date: Sun, 1 Apr 2012 12:44:56 +0000
> > From: Yaakov Stein <yaakov_s@rad.com<mailto:yaakov_s@rad.com>>
> > To: "pwe3@ietf.org<mailto:pwe3@ietf.org>" <pwe3@ietf.org<mailto:
> pwe3@ietf.org
> > >>
> > Subject: [PWE3] CW usage in opposite directions for static PWs
> > Message-ID:
> >        <07F7D7DED63154409F13298786A2ADC904332092@EXRAD5.ad.rad.co.il<
> > mailto:07F7D7DED63154409F13298786A2ADC904332092@EXRAD5.ad.rad.co.il>>
> > Content-Type: text/plain; charset="us-ascii"
> > 
> > At the meeting I promised to check when this issue in the subject 
> > line was last discussed.
> > 
> > It was only a short while ago in Prague (see http://www.ietf.
> > org/proceedings/80/slides/pwe3-3.pdf slides 9 - 11<http://www.ietf.
> > org/proceedings/80/slides/pwe3-3.pdf%20slides%209%20-%2011>).
> > 
> > I recall a lively discussion after the presentation,
> > but the minutes do not show resolution of the issue of whether a CW 
> > MUST be used or not used
> > in both directions for PWs not set up using the PWE3 control protocol.
> > 
> > Y(J)S
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