Re: [mpls-tp] [PWE3] Proposal of using GAL for PW

[Greg Mirsky <[e-mail]>]

Dear Giles,
the problem is that the entropy label and the GAL both must be at the
bottom of stack as corresponding normative documents suggest.

Regards,
Greg

2010/7/1 Giles Heron <[e-mail]>om>:
> That wasn't what I said.  I said entropy labels are optional.  Most MPLS PWs
> don't have them.
>
> Presumably if we did GAL with a PWE it could come after the entropy label?
>
> Giles
>
>
> On 01/07/2010 19:35, "Shahram Davari" <[e-mail]> wrote:
>
> !mmm so if one used entropy then they can't have OAM?
>
> -SD
>
>
> From: Giles Heron [mailto:[e-mail]]
> Sent: Thursday, July 01, 2010 11:32 AM
> To: Shahram Davari; Tom Nadeau; Luca Martini; Andy Malis
> Cc: [e-mail]; [e-mail]; HUANG Feng F; [e-mail]
> Subject: Re: [mpls-tp] [PWE3] Proposal of using GAL for PW
>
> The entropy label is optional, surely?
>
> I've never seen one in the wild - but then maybe I'm behind the times...
>
> On 01/07/2010 19:29, "Shahram Davari" <[e-mail]> wrote:
> Giles,
>
> I don't want yet another VVCV type. If you are not using CW then just use
> RAL or TTL=1. Besides you proposal only works for MPLS-TP and not MPLS,
> where there is a Entropy label below PW label.
>
> Thx
> SD
>
>
> From: Giles Heron [mailto:[e-mail]]
> Sent: Thursday, July 01, 2010 11:10 AM
> To: Shahram Davari; Tom Nadeau; Luca Martini; Andy Malis
> Cc: [e-mail]; [e-mail]; HUANG Feng F; [e-mail]
> Subject: Re: [mpls-tp] [PWE3] Proposal of using GAL for PW
>
> Hi Shahram,
>
> I didn't say CW was only for identifying OAM messages - I said adding it
> just to enable occasional OAM messages was overkill.
>
> The CW has half a dozen uses (the first 3 of which were the "original"
> ones):
> 1) enabling small PWE payloads over Ethernet links
> 2) carrying L2 flags where the L2 header is stripped (e.g. FR)
> 3) sequence numbering
> 4) fragmentation (RFC4623).  Stole a couple of spare CW bits.
> 5) avoiding PWE packets aliasing IP where ECMP implementations "walk the
> stack" and then look at the first nibble after the stack (nice side effect)
> 6) OAM indicator for in-band VCCV.  Stole a spare CW bit.
>
> So let's consider the Ethernet PWE case over MPLS-TP
>
> 1) Ethernet PWE packets are by definition larger than the minimum Ethernet
> payload
> 2) There are no L2 flags in Ethernet
> 3) Sequence numbering is rarely used - and isn't needed in the MPLS-TP case
> 4) I'm not aware of anyone implementing fragmentation for Ethernet PWE
> 5) There's no ECMP when you're doing MPLS-TP
> 6) the only one that applies (hence my comment)
>
> As for the parsing thing that seems a bit odd to me.  Surely VCCV only tells
> you that the payload is a PWE rather than IP?  It doesn't tell you what sort
> of PWE it is.
>
> Sure, CW would help interop if everyone had one.  But with Ethernet PWE the
> history is that nobody ever used them so I'm not sure we make our lives any
> easier by mandating them now.
>
> As for 1588 (and anything else we might try to squeeze into VCCV) that's
> another question.  I'd think we're more likely to carry 1588 over Ethernet
> over PWE, or over VCCV (and VCCV can be carried by mechanisms other than the
> CW).
>
> So the key argument for mandating CW would seem to be ensuring that OAM
> traffic follows the same path as data traffic.  In the TP case I'd expect to
> see that behaviour anyway (as any intermediate hops will label switch
> without looking deep enough into the packet to spot the VCCV identifier -
> whether that identifier is CW, router alert, TTL, or GAL).
>
> Giles
>
> On 01/07/2010 18:13, "Shahram Davari" <[e-mail]> wrote:
> Giles,
>
> CW is not just for identifying OAM messages. It normalizes the packet format
> and makes the job of parsers much simpler. It allows you to identify the
> payload type without knowing the PW label context. It also improves
> interoperability and could also simplify many other applications such as
> 1588 over MPLS.
>
> Regards,
> Shahram
>
>
> From: [e-mail] [mailto:[e-mail]] On Behalf
> Of Giles Heron
> Sent: Thursday, July 01, 2010 6:22 AM
> To: Tom Nadeau; Luca Martini; Andy Malis
> Cc: [e-mail]; [e-mail]; HUANG Feng F; [e-mail]
> Subject: Re: [mpls-tp] [PWE3] Proposal of using GAL for PW
>
> Not sure I agree.
>
> Many CPs have deployed PWs with no CW.   Adding a CW to all packets just to
> enable occasional OAM messages seems like overkill.
>
> But the downside of adding GAL is that it's a fourth OAM mode for PWEs (back
> to your point about interoperability).  Too many options!
>
> Giles
>
> On 01/07/2010 12:14, "Tom Nadeau" <[e-mail]> wrote:
>
>     I  agree with Andy's assertion. This service provider's experience is
> that making the CW mandatory going forward (and hopefully retrofitting
> existing PW protocol specs) would improve implementation interoperability.
>
>     --Tom
>
>
>
> On 6/30/10 11:22 PM, "Luca Martini" <[e-mail]> wrote:
> Andy,
>
> I have to disagree that there was any consensus about this issue.
> If anything , there was consensus that there is no written statement that we
> must  to use the CW in MPLS-TP.
>
> At the end we needed more input from service providers that have deployed
> PWs.  The point is not whether there is hardware support for the CW, but
> whether we even want to use it in many cases where it adds absolutely no
> value. For example ATM PWs in cell mode , where it add almost 10% overhead
> with no benefit. Another case where the CW is not useful is the ethernet PW
> without network link load balancing, where we add 4 bytes to every packet
> just to occasionally send a status , or OAM message.
>
> I would like to propose update the rfc5586 to allow the use of the GAL in
> PWs without the CW.
>
> This makes the use of the GAL very symmetric among PWs and MPLS-TP LSPs.
> This makes it easy to process by hardware based implementations.
>
> Luca
>
>
> Andrew G. Malis wrote:
>
> Larry and Feng,
>
> This issue has previously been discussed at length by the working
> group, both at the Anaheim meeting and by email, for example in emails
> with the subject line "Possible Contradiction re use of GAL in
> pwe3-static-pw-status". There was rough consensus that for MPLS-TP
> applications and/or when PW OAM is desired, PW implementations are
> mature enough (it has been 10 years now, after all) that the time has
> come to require the implementation of the CW for all PWs, including
> Ethernet.
>
> Cheers,
> Andy
>
> On Wed, Jun 30, 2010 at 6:34 AM, HUANG Feng F
> <[e-mail]>
> <mailto:[e-mail]>  wrote:
>
>
>
> it is reasonable to support GAL in MPLS-TP PW OAM, it is more generic,
> because CW is an option RFC4448 for Ethernet over MPLS.
>
> 4.6.  The Control Word
>
> xxxx
>
>
> The features that the control word provides may not be needed for a
>   given Ethernet PW.  For example, ECMP may not be present or active on
>   a given MPLS network, strict frame sequencing may not be required,
>   etc.  If this is the case, the control word provides little value and
>   is therefore optional.  Early Ethernet PW implementations have been
>   deployed that do not include a control word or the ability to process
>   one if present.  To aid in backwards compatibility, future
>   implementations MUST be able to send and receive frames without the
>   control word present.
> xxxx
>
>
>
> B.R.
> Feng Huang
>
>
> -----Original Message-----
> From: [e-mail] [mailto:[e-mail]] On Behalf Of
> Larry
> Sent: 2010年6月30日 17:38
> To: [e-mail]; [e-mail]
> Cc: [e-mail]
> Subject: [PWE3] Proposal of using GAL for PW
>
> Dear all:
>
>     In section 4.2 in RFC5586, it is defined that GAL MUST NOT be used with
> PWs in MPLS-TP. The PWE3 control word [RFC4385] MUST be present when the ACH
> is used to realize the associated control channel.
>     In real application, a lot of MPLS and MPLS-TP equipments do not support
> control word. It is proposed to use the GAL to identify associated control
> channel in PW layer.
>
> Best regards,
>
>                 Han Li
>
> ********************************************************************
> Han Li, Ph.D
> China Mobile Research Institute
> Unit 2, 28 Xuanwumenxi Ave, Xuanwu District, Beijing 100053, China
> Fax: [phone]
> MOBILE: [phone]
> ********************************************************************
>
>
>
>
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