Re: [Teas] network Slice Endpoint in draft-ietf-teas-ietf-network-slice-definition-00

Adrian Farrel <> Thu, 25 February 2021 10:52 UTC

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From: "Adrian Farrel" <>
To: "'Young Lee'" <>, "'Luis M. Contreras'" <>
Cc: "'Rokui, Reza \(Nokia - CA/Ottawa\)'" <>, <>, "'Eric Gray'" <>, "'John E Drake'" <>, "'Joel M. Halpern'" <>, <>
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Date: Thu, 25 Feb 2021 10:51:56 -0000
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Subject: Re: [Teas] network Slice Endpoint in draft-ietf-teas-ietf-network-slice-definition-00
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Hi all, 


Good thread, and really good to see the debate on the WG list.


I’m piling in in response to Young, mainly because that’s the email I happen to have open. But also because the perspective of Young and Luis should be valuable to us in this context.


While I think that the usage of “CE” and “PE” has a long history in packet networks, I don’t believe the concepts are firmly linked only to packet. They are pretty much what they call themselves: the PE is at the edge of the “provider” == “underlay” network, and the CE is at the edge of the “consumer” == “overlay” network. 


I find that, as the discussion continues, we are still missing a really clear figure to help us talk about what we are describing. But Reza’s [1] is a much better start than anything previous. Here I see the classic distinction between a CE-based VPN and a PE-based VPN [2], but we have to ask ourselves carefully whether we *really* want the CE-based approach in our network slicing:

*	What are the considerations for how much knowledge of the underlay network has to be shared to the CE?
*	What are the considerations for how an underlay distinguishes CE-originated slicing traffic?

These are pretty much the same questions that CE-based VPNs have to answer. Of course, the concept of a “provider-managed CE” muddies these waters somewhat.


Conversely, the port-based PE-based VPN has none of these problems, but does have to agree on the “Access Connection” encoding, and that is either payload-sensitive (like in PWE3) or technology-aware (like in L3VPN).


But my opinion of all of this is coloured by thinking about enhanced VPNs (VPN+) [3] and IETF network slices as the same thing.


I also think that Luis’ point about contiguous or stitched segments is important. There are, I think, two cases to be considered:

1.	The multi-domain IETF network slice. Here the problem is very much the same as the multi-AS L3VPN. We have to consider how the “service request” is mapped from one domain to another. But it may help to recall that, for all our dreaming, end-to-end multi-AS MPLS-TE tunnels are not much of a thing: domains don’t like sharing information about or control of their network resources. Thus the “E-NNI” between slice domains may be as much of a service interface as the “UNI” between consumer and provider.
2.	The 5G architecture considers stitching slices from different technology networks to provide an end-to-end slice. From a consumer’s point of view, this is exactly what happens, but it is not clear to me whether this is really what happens in a deployment. Surely there is aggregation as we go down the technology layers and into the “transport” networks. That is, there may be very, very many micro slices in the RAN, but as this moves onto the IP transport, it is likely that the slicing is aggregated. That means that the stitching of slices actually follows a hierarchical model with recursion. The interface between slice domains is the “UNI”.


Net-net, I like John’s original proposal. I hope we can take that as our base point and factor in further discussions.






[2] RFC 4026

[3] draft-ietf-teas-enhanced-vpn


From: Teas <> On Behalf Of Young Lee
Sent: 24 February 2021 10:22
To: Luis M. Contreras <>
Cc: Rokui, Reza (Nokia - CA/Ottawa) <>om>;; Eric Gray <>om>; John E Drake <>rg>; Joel M. Halpern <>om>;
Subject: Re: [Teas] network Slice Endpoint in draft-ietf-teas-ietf-network-slice-definition-00




This is an interesting discussion. I am now in the mobile side and reconginize that there are a number of scenarios that may need transport network slices (which is now called IETF network slices). For instance, possibly slices may be needed in the fronthaul, midhaul and backhaul as well as within DC networks that host the functions. Other than backhaul networks, the terms CE and PE may not be adequate because for the aforementioned transport networks except the backhaul, CE and PE terminology would not easily apply. For each of the aforementioned transport subnetworks, I think using slice endpoints makes more sense. 


In other words, I agree with Luis on this point. 


My two cents,



2021년 2월 24일 (수) 오후 7:00, Luis M. Contreras < <> >님이 작성:

Thanks Med and Joel for the answers.


Noting what you said, and assuming that we are covering not only IP/MPLS technologies, probably we need to associate the same idea of CE and PE to technologies where those roles are not commonly associated, such as OTN, DWDM or wireless / microwave, since all of them can be potential targets of the IETF Network Slicing realization. Then, if we follow this same rationale and finally the WG decides to go in this direction, I guess we need to span the CE and PE conception also to those, maybe explaining this in the definitions draft. Am I right?


Med, when I was referring to IETF Network Slice of technology X or Y I was thinking on the realization. So my point here is that in case you have an IETF Network Slice let's say realized as IP/MPLS, and another one let's say realized on OTN or DWDM, where the IP/MPLS slice is supported by the OTN/DWDM slice, can we consider that the CE is IP/MPLS and the PE is OTN/DWDM? It sounds strange to me.


Best regards





El mié, 24 feb 2021 a las 7:16, < <> > escribió:

Hi Luis, 


Actually, this is all about recursion, service decomposition and manipulating customer/provider ROLES. In all cases, there are reference points delimiting the scope of the slice from both the customer view (we call them, customer edges) and provider view (provider edges).  


Nothing prevents that at the realization stage, two PEs can’t be connected. I’m thinking about the example where inter-AS VPN can be used to implement an IETF network slice.


BTW, can you please clarify what do you mean by a “IETF Network Slice of technology X or Y” as slice is technology-agnostic? Thank you.





De : Luis M. Contreras [ <> ] 
Envoyé : mardi 23 février 2021 23:46
À : Eric Gray < <> >
Cc : BOUCADAIR Mohamed TGI/OLN < <> >; Rokui, Reza (Nokia - CA/Ottawa) < <> >; John E Drake < <> >; <> ; Joel M. Halpern < <> >
Objet : Re: [Teas] network Slice Endpoint in draft-ietf-teas-ietf-network-slice-definition-00


Hi all,


Regarding the CE / PE discussion, I have doubts if this would apply to scenarios where we could have stitching of IETF Network Slices or in scenarios where an IETF Network Slice of technology X is supported on  IETF Network Slice of technology Y. While end-point can work in all the cases, I think that CE / PE don't become naturally applicable in all cases.


Respect to the discussion on IETF Network Slice Service, I think it is redundant since we are talking of consumer/customer and provider in the context of  IETF Network Slice, so being "Service" redundant there. Probably adds more confusion than clarification.


Best regards