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

[Mach Chen <[e-mail]>]

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
> >     > >
> >     > > _______________________________________________
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> >     >
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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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