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

[Loa Andersson <[e-mail]>]

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:[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]>>; [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]>
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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]