Re: [Detnet-dp-dt] detnet LSPs and PWs

[Loa Andersson <[e-mail]>]

Folks,

Actually I think (except for the nomenclature, which I think we should
adopt) of what Stewart says is there in the new slides.

There are a few "if" that I don't agree to a design (maybe it may be
possible to collapse the design), e.g. assuming one single domain.

I think there are some design decision that need to be there.

- replication and elimination of packets at places/nodes that the
   operator can control, i.e. not every node should do it
- with an "S-detnet-PE" in the path (for replication/elimination) we
   need three levels of labels. The implication is that if we don't do
   replication/elimination other than at the T-detnet-PWs then we only
   need two layers.
- what we called "d-pw" is not a new pw, but a pw from the PWE3/PALS
   inventory

Now that last bullet is a problem, the sequence number is 16 bits in
PWE3/PALS and we know that is to small. Maybe we have to define a detnet
PW after all. A PW that carries sequence number + another PW.

I've been  thinking hard about the equivalence relationship, but is 
still not sure it will work in the generic case, equivalence
relationship tells node D that it should treat L1 from B and L2 from C
the same, which is fine, but it does still not tell us that the packet
came from A originally.

BTW - I think we need some type of sign-off from Stewart/Andy before we
commit to hard.

Also the problem of comparing sequence numbers arriving over
different physical interface seems to be a eal problem.

/Loa

On 2017-02-13 18:55, Stewart Bryant wrote:
> Hi,
>
> I was given some background information on your thoughts on detnet-PW,
> and pass on my thoughts in response.
>
> I think NSP issue  is a red herring. NSP can be NULL.
>
> An S-PE does no NSP, although in any case I suspect that you may need
> some processing function at the detnet-S-PE - see below.
>
> The underlying DETNET PW is an SS-PW in the diagram I was shown, in that
> the PW label is the same end to end, although of course it need not be,
> you could have an equivalence label set and run pure MS-PW. Indeed when
> you have multiple administrations you would like them to be different
> for administrative purposes (that is why we designed MS-PW like that).
>
> So if you create an equivalence relationship in the egress-PE, i.e. two
> entries in the global label table pointing to the same duplicate
> suppressor (sequencer), then you could use regular MS-PW for this.
>
> If the S-PEs are in the same administrative domain in both ingress and
> egress, you can also use a single label value on egress and on egress
> since you can give them the same label mappings, i.e. they have
> identical swap instructions programmed into the L-FIB.
>
> We don't have NSP at the S-PE's in the current PW architecture, in the
> data-plane it is essentially a simple MPLS LSR, swapping PW labels and
> forwarding the packet on a new LSP. What you will almost certainly want
> to do is to have the ability to replicate at nodes at the S-PEs, and
> that is new functionality.
>
> An approach I would look at is as follows:
>
> Create a new detnet-T-PE. On ingress this adds the sequence number,
> replicates and adds the PW label, which as I said above MAY be next hop
> detnet-S-PE dependent. Then it delivers the copies to the detnet-S-PEs
> over the LSPs. Now if you have an ECMP path between the detnet-T-PE and
> a detnet-S-PE, or you have SR or RSVP-TE available you can also deliver
> multiple copies to the detnet-S-PE and take advantage of the variability
> of transit time in the MPLS underlay.
>
> Now you create a new detnet-S-PE that operates as follows. On it's
> ingress side it looks for the first packet at a given sequence number on
> this PW (or PW set) and suppresses all future packets on that sequence
> number on that PW or PW-set. It then replicates the packet if required,
> swaps the PW label (note that it may also use multiple outgoing labels)
> and send the packet over the egress LSP set.
>
> At the egress T-PE it looks at the sequence number on this PW (or
> PW-set), trims all duplicates, applies any required egress processing
> and send the packet on it's way.
>
> In summary on ingress a detnet-T-PE replicates to multiple S-PEs using
> the PW label the detnet-S-PE expects and potentially sends the packet
> over multiple paths to the detnet-S-PEs. At egress a detnet-T-PE looks
> at the sequence numbers across the detnet-PW set and selects the first
> of the sequence number suppressing all others, and sends the underlying
> packet on its way. A detnet-S-PE is a back to back detnet-egress-T-PE
> and a detnet-ingress-T-PE with a PW label swap in the middle and no
> other PW processing.
>
> Now for the elephant in the corner of all of the schemes I have seen. If
> you have multiple paths to an X-PE, packets will likely arrive on
> different line cards. Sequence number co-ordination amongst different
> line cards, and at high speed even amongst different ports on the same
> line card is a hard problem. Indeed depending on the pipeline design on
> the line card, ANY sequence number processing can be hard. You could
> mitigate this (at the cost of availability) by requiring a common
> ingress port at any detnet X-PE. This would normally require an RSVP-TE
> or SR underlay.
>
> - Stewart
>
>
>
> On 13/02/2017 04:11, Andrew G. Malis wrote:
>> Loa et al,
>>
>> To be clear, there’s currently no definition of PWs encapsulated in
>> PWs, and while it might be conceptually possible, such as an Ethernet
>> PW carried within a SONET/SDH PW, I couldn’t imagine a use case for
>> doing it as it’s very inefficient, and I asked Loa if he had one. And
>> if you were to do so, each PW in the hierarchy would need NSP
>> functionality and real or emulated CE access circuits at the
>> endpoints. Also, thinking about it some more, you couldn’t have both
>> PWs in the same label stack, since a PW emulates a physical circuit.
>> So there would need to be a separate label stack (and MPLS LSP) inside
>> the emulated circuit for the outer PW. By definition, PW labels
>> terminate a label stack.
>>
>> As I haven’t been following Detnet at all, I don’t have the context
>> for what you’re trying to accomplish. That said, I’ll take a look at
>> the slides and let you know if I have any comments.
>>
>> Cheers,
>> Andy
>>
>>
>> On Sun, Feb 12, 2017 at 8:31 PM, Loa Andersson <[e-mail]
>> <mailto:[e-mail]>> wrote:
>>
>>     Folks,
>>
>>     The mail from Yuanlong mmade me go back and check the PW
>>     architecture and consult with Andy Malis and Stewart Bryant. So I
>>     have one more thing
>>     that we should discuss on "Tuesday".
>>
>>     What Yaunlong said was: "IMHO, multiple layers of PW is a break from
>>     the PWE3 architecture, and all DP/CP/MP things will become more
>>     complicated."
>>
>>     It is correct that multi-layer pw's is problematic, though Andy said
>>     that "if you have a good use case, you can do it".
>>
>>     The problem is that there is a native service processing (NSP) at
>>     the end of the PW. Multi-layer PWs will only do NSP at one level.
>>     I think
>>     we should replace the MS-PW with an LSP. I've added one slide (9) and
>>     change slide 8,9 and 11 in the earlier package. The other slides arere
>>     for reference
>>
>>     I want Andy and Stewart to have a chance to review this prior to that
>>     we commit too hard to it. Copied them.
>>
>>
>>     /Loa
>>     --
>>
>>
>>     Loa Andersson                        email: [e-mail]
>>     <mailto:[e-mail]>
>>     Senior MPLS Expert                          [e-mail]
>>     <mailto:[e-mail]>
>>     Huawei Technologies (consultant)     phone: [phone]
>>     <tel:%2B46%20739%2081%2021%2064>
>>
>>
>
>
>
> _______________________________________________
> Detnet-dp-dt mailing list
> [e-mail]
> https://www.ietf.org/mailman/listinfo/detnet-dp-dt
>

-- 


Loa Andersson                        email: [e-mail]
Senior MPLS Expert                          [e-mail]
Huawei Technologies (consultant)     phone: [phone]