Re: [Detnet] Regarding the model for Active OAM packet

[Mach Chen <[e-mail]>]

Hi Loa,

Can you clarify how a new ACH-type can address the problem?

Best regards,
Mach

> -----Original Message-----
> From: Loa Andersson [mailto:[e-mail]]
> Sent: Thursday, September 20, 2018 6:14 PM
> To: Mach Chen <[e-mail]>; Greg Mirsky
> <[e-mail]>
> Cc: DetNet WG <[e-mail]>; János Farkas
> <[e-mail]>; [e-mail]
> Subject: Re: [Detnet] Regarding the model for Active OAM packet
> 
> Mach,
> 
> I'd like Stewart or Matthew to look at this, but as I understand it it is possible
> to define a new ACH-type that can do exactly what you want.
> 
> /Loa
> 
> On 2018-09-20 17:58, Mach Chen wrote:
> > Loa,
> >
> > GAL is just an OAM indicator, the problem here is that when do DetNet
> OAM, the d-CW will replaced by ACH or by GAL+ACH. No matter which way is
> used, to support the replication or elimination, there has to be a sequence
> number filed. But ACH (as its current defined) does not have such a field.
> >
> > My suggestion is to use the reserved field of ACH to carry sequence
> number of OAM packet,  and for those replication or elimination nodes, they
> do not have to differentiate whether a packet is OAM packet or a normal
> packet, they could just treat the right 28 bits of the ACH as the sequence
> number ( or treat the ACH as the d-CW), then both OAM and
> replication/elimination can be supported.
> >
> > Best regards,
> > Mach
> >
> >> -----Original Message-----
> >> From: detnet [mailto:[e-mail]] On Behalf Of Loa
> >> Andersson
> >> Sent: Thursday, September 20, 2018 3:21 PM
> >> To: Mach Chen <[e-mail]>; Greg Mirsky
> >> <[e-mail]>
> >> Cc: DetNet WG <[e-mail]>; János Farkas
> >> <[e-mail]>; [e-mail]
> >> Subject: Re: [Detnet] Regarding the model for Active OAM packet
> >>
> >> Mach,
> >>
> >> If I understand you correctly this is for an LSP in an MPLS network,
> >> can you help me understand why GAL does not enough. Given that there
> >> might be some minor extensions to GAL because of replication and
> elimination.
> >>
> >> /Loa
> >>
> >> On 2018-09-19 14:31, Mach Chen wrote:
> >>> Hi Greg,
> >>>
> >>> Indeed, there is no DetNet Associated Channel defined in
> >>> draft-ietf-detnet-dp-sol-mpls for now, I think there should be.  I
> >>> also assume that PW ACH will be used for DetNet OAM.
> >>>
> >>> Assume that PW ACH will be used for DetNet OAM and the reserved
> >>> filed of the PW ACH will be used to carry sequence number for OAM
> packet.
> >>> But
> >>>    for PREF, a tricky way is to treat the “Version”+ “Reserved” +
> >>> ”Channel type” as the Sequence number, the replication or
> >>> elimination nodes do not need to differentiate whether it is a d-CW or  a
> PW ACH .
> >>> This way, OAM can be supported without additional processing and
> states.
> >>>
> >>>          0                   1                   2
> >>> 3
> >>>
> >>>          0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
> >>> 0
> >>> 1
> >>>
> >>>
> >>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >>>
> >>>         |0 0 0 1|Verion |    Reserved   |         Channel Type
> >>> |
> >>>
> >>>
> >>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> >>>
> >>> Regarding sequence number, there are two ways to generate the
> >> sequence
> >>> number IMHO:  1) generated by the edge node, but it may need to
> >>> configure the start number, or 2) copied from the application-flow
> >>> (if there is). If the WG agree with this, the model can be updated
> >>> reflect this.
> >>>
> >>> Best regards,
> >>>
> >>> Mach
> >>>
> >>> *From:*Greg Mirsky [mailto:[e-mail]]
> >>> *Sent:* Wednesday, September 19, 2018 11:29 AM
> >>> *To:* Mach Chen <[e-mail]>
> >>> *Cc:* János Farkas <[e-mail]>; DetNet WG
> >>> <[e-mail]>; [e-mail]
> >>> *Subject:* Re: Regarding the model for Active OAM packet
> >>>
> >>> Hi Mach,
> >>>
> >>> thank you for your attention to my comment and the most expedient
> >> response.
> >>>
> >>> I don't find the DetNet Associated Channel defined in
> >>> draft-ietf-detnet-dp-sol-mpls and thus I assumed that OAM packets
> >>> that follow the data packet encapsulation defined in that draft use
> >>> PW ACH as defined in section 5 RFC 4385: True, it includes 8
> >>> bits-long Reserved field that may be defined as OAM Sequence Number
> >>> but that
> >> had
> >>> not been discussed. One is certain, existing nodes do not check the
> >>> Reserved field. And without a field to hold the sequence number,
> >>> PREF will not handle the OAM packets. Another question, additional
> >>> processing and amount of state introduced in the fast path by the
> >>> fact that OAM's Sequence Number will have different length and
> >>> location in d-CW (differentiating cases by the first nibble).
> >>>
> >>> Now, if we step back from DetnNet in MPLS data plane encapsulation,
> >>> why the control-word, as I understand, is configurable? I think that
> >>> the Sequence Number is not configurable, nor the first nibble. What
> >>> do you think?
> >>>
> >>> Regards,
> >>>
> >>> Greg
> >>>
> >>> On Tue, Sep 18, 2018 at 7:48 PM Mach Chen <[e-mail]
> >>> <mailto:[e-mail]>> wrote:
> >>>
> >>>      Hi Greg,
> >>>
> >>>      The MPLS DetNet header is defined as below:
> >>>
> >>>      grouping mpls-detnet-header {
> >>>           description
> >>>               "The MPLS DetNet encapsulation header information.";
> >>>           leaf service-label {
> >>>             type uint32;
> >>>             mandatory true;
> >>>             description
> >>>               "The service label of the DetNet header.";
> >>>           }
> >>>           leaf control-word {
> >>>             type uint32;
> >>>             mandatory true;
> >>>             description
> >>>               "The control word of the DetNet header.";
> >>>           }
> >>>         }
> >>>
> >>>      Although do not consider Active OAM when design the above
> >>>      mpls-denet-header,  seems that it can cover Active OAM case as well.
> >>>      No matter a normal DetNet packet or an Active OAM packet, there
> >>>      should be a CW field, just as defined above.
> >>>
> >>>      For normal DetNet packets, the CW is the d-CW as defined in the
> >>>      draft-ietf-detnet-dp-sol-mpls.
> >>>
> >>>      For OAM packets, the CW is the "DetNet Associated Channel".
> >>>
> >>>      Best regards,
> >>>      Mach
> >>>
> >>>
> >>>      > -----Original Message-----
> >>>      > From: detnet [mailto:[e-mail] <mailto:detnet-
> >> [e-mail]>] On Behalf
> >>>      Of Greg Mirsky
> >>>      > Sent: Wednesday, September 19, 2018 3:17 AM
> >>>      > To: János Farkas <[e-mail]
> >> <mailto:[e-mail]>>
> >>>      > Cc: DetNet WG <[e-mail] <mailto:[e-mail]>>;
> >>> detnet-
> >> [e-mail]
> >>>      <mailto:[e-mail]>
> >>>      > Subject: Re: [Detnet] WG adoption poll draft-geng-detnet-conf-
> yang
> >>>      >
> >>>      > Hi Janos, et. al,
> >>>      > the mpls-detnet-header container is based on the solution
> described in
> >>>      > draft-ietf-detnet-dp-sol-mpls. Analysis of active SFC OAM in
> >>> the
> >> proposed
> >>>      > MPLS data plane solution in draft-mirsky-detnet-oam points to
> >>> the
> >> potential
> >>>      > problem as result the fact that OAM packet doesn't include
> >>> d-CW. I
> >> believe
> >>>      > that this question should be discussed and, if we agree on the
> problem
> >>>      > statement, properly resolved. Until then, I do not support
> >>> the adoption
> >> of
> >>>      > the model that may not be capable to support active OAM.
> >>>      >
> >>>      > Regards,
> >>>      > Greg
> >>>      > On Tue, Sep 18, 2018 at 12:03 PM Janos Farkas
> >> <[e-mail] <mailto:[e-mail]>>
> >>>      > wrote:
> >>>      > >
> >>>      > > Dear all,
> >>>      > >
> >>>      > > This is start of a two week poll on making
> >>>      > > draft-geng-detnet-conf-yang-04 a working group document.
> >>> Please
> >> send
> >>>      > > email to the list indicating "yes/support" or "no/do not
> support".  If
> >>>      > > indicating no, please state your reservations with the
> document.  If
> >>>      > > yes, please also feel free to provide comments you'd like to see
> >>>      > > addressed once the document is a WG document.
> >>>      > >
> >>>      > > The poll ends Oct 3.
> >>>      > >
> >>>      > > Thanks,
> >>>      > > János and Lou
> >>>      > >
> >>>      > > _______________________________________________
> >>>      > > detnet mailing list
> >>>      > > [e-mail] <mailto:[e-mail]>
> >>>      > > https://www.ietf.org/mailman/listinfo/detnet
> >>>      >
> >>>      > _______________________________________________
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> >>>
> >>>
> >>>
> >>> _______________________________________________
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> >>>
> >>
> >> --
> >>
> >>
> >> Loa Andersson                        email: [e-mail]
> >> Senior MPLS Expert
> >> Bronze Dragon Consulting             phone: [phone]
> >>
> >> _______________________________________________
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> >
> 
> --
> 
> 
> Loa Andersson                        email: [e-mail]
> Senior MPLS Expert
> Bronze Dragon Consulting             phone: [phone]