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

[Giles Heron <[e-mail]>]

Sure, but that could be changed I suspect.  Logically you'd want OAM  
under the entropy label so you can test all paths, right?

Sent from my iPhone

On 1 Jul 2010, at 21:25, Greg Mirsky <[e-mail]> wrote:

> 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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