Re: [Teas] Definitions of VTN and Slice Aggregate in the drafts

Adrian Farrel <> Thu, 11 March 2021 13:43 UTC

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From: Adrian Farrel <>
To: "'Dongjie (Jimmy)'" <>, "'Belotti, Sergio (Nokia - IT/Vimercate)'" <>
Cc:, 'Daniele Ceccarelli' <>,
References: <> <> <>
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Date: Thu, 11 Mar 2021 13:41:51 -0000
Organization: Old Dog Consulting
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Subject: Re: [Teas] Definitions of VTN and Slice Aggregate in the drafts
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The line that stand out from this conversation for me is:


> As for the VN concept defined in RFC 8453, to me the concept of VN and VTN
looks similar, while they are introduced for different purposes.


>From my perspective, a VN (ACTN) is a topology carved out of the network and
presented to the ACTN consumer, while a VTN (VPN+) is a topology carved out
of the network for its own use in delivering enhanced VPNs. That looks
pretty much what Jie said: same concept but for different purposes.


FWIW, in draft-king-teas-applicability-actn-slicing we saw ACTN as a
tool/mechanism that could be used to realise a network slice or an enhanced
VPN. That is, it can build the virtual topology that underpins a network



I think a number of concepts are converging within TEAS. This should be
cause for celebration, although it is not always easy to get full


What we found when writing draft-king-teas-applicability-actn-slicing was
that the terminology was not consistent. That, sadly, led us to have to
define some of our own terms. I fully expect that as time progresses we will
see continued convergence on terminology that will cause a number of us to
have to update our drafts.





From: Teas <> On Behalf Of Dongjie (Jimmy)
Sent: 11 March 2021 09:57
To: Belotti, Sergio (Nokia - IT/Vimercate) <>
Cc:; Daniele Ceccarelli
Subject: Re: [Teas] Definitions of VTN and Slice Aggregate in the drafts


Hi Sergio, 


Thanks for your support on the terminology clarification. It is important to
have consistent understanding about the terminology before we could
understand the relationship between different proposals.


As for the VN concept defined in RFC 8453, to me the concept of VN and VTN
looks similar, while they are introduced for different purposes.


VN in RFC 8453 is to provide the customer with an abstracted view of the
network based on YANG models. There are two modes to provide such view to
customer: abstracted as a set of edge-to-edge links, or abstracted as a
topology or virtual nodes and virtual links. 


While the term VTN was introduced to refer to the virtual underlay network
in the layered architecture as described in draft-ietf-teas-enhanced-vpn, it
is used to organize a subset of the network nodes and links, and allocate a
set of network resources on these nodes and links to build a customized
underlay network. Operator can instantiate multiple VTNs to carry different
types of services, or the traffic of different customers. The customers does
not necessarily need to be provided with the information of VTN.


Another consideration was that the term VN is generic (not only defined in
RFC 8453), thus could mean different things in different context. Thus we
choose to use a dedicated term for the virtual underlay network. 


Hope this helps. 


Best regards,



From: Belotti, Sergio (Nokia - IT/Vimercate)
Sent: Wednesday, March 10, 2021 5:18 PM
To: Dongjie (Jimmy) <>
Cc:; Daniele Ceccarelli <>;
Subject: RE: Definitions of VTN and Slice Aggregate in the drafts


Hi Jie,

Clarification on terminology is always a good effort to do  thanks for that.

On the other hand I'd like to understand , about "VTN", what is the
difference in your VTN concept with respect what already defined in RFC 8453
in section 2.1? 

In that section there is a description also of the two types of VN ,
customer can manage.

A parallel effort with draft-ietf-teas-actn-vn-yang permits to "create" VN
of the desired type. 

So my question is : what in your "new" VTN is different with respect what
already defined related to VN to force using another term ? 









From: Teas < <> > On Behalf
Of Dongjie (Jimmy)
Sent: Tuesday, March 9, 2021 7:38 PM
To: <> 
Subject: [Teas] Definitions of VTN and Slice Aggregate in the drafts


Hi all, 


In today's meeting, some people raised comments about the confusions caused
by the multiple terms. To help the understanding with the term "VTN" and
"Slice Aggregate", I reread the text about their definitions and
descriptions in each draft. 


Although the terminologies are described in different ways, IMO the
essential information behind is the same: a logical network construct
consists of the topology attribute and the network resources attributes.


Some effort to resolve the terminology overlap could help to reduce the
confusions and provide a consistent view on the framework and technologies
for network slice realization.



Here are the text about the terms quoted from each draft:


- VTN (in draft-ietf-teas-enhanced-vpn-07): 


VPN+ is built from a VPN overlay and an underlying Virtual Transport Network
(VTN) which has a customized network topology and a set of dedicated or
shared resources in the underlay network.


A VTN is a virtual underlay network that connects customer edge points. The
VTN has the capability to deliver the performance characteristics required
by an enhanced VPN customer and to provide isolation between separate VPN+



- Slice Aggregate (in draft-bestbar-teas-ns-packet-02)


This document introduces the notion of a slice aggregate which comprises of
one of more IETF network slice traffic streams. It describes how a slice
policy can be used to realize a slice aggregate by instantiating specific
control and data plane behaviors on select topological elements in IP/MPLS


When logical networks representing slice aggregates are realized on top of a
shared physical network infrastructure, it is important to steer traffic on
the specific network resources allocated for the slice aggregate.


Slice aggregate: a collection of packets that match a slice policy selection
criteria and are given the same forwarding treatment; a slice aggregate
comprises of one or more IETF network slice traffic streams; the mapping of
one or more IETF network slices to a slice aggregate is maintained by the
IETF Network Slice Controller.



- Slice policy (in draft-bestbar-teas-ns-packet-02, to help the
understanding of Slice Aggregate)


Slice policy: a policy construct that enables instantiation of mechanisms in
support of IETF network slice specific control and data plane behaviors on
select topological elements; the enforcement of a slice policy results in
the creation of a slice aggregate.


A slice policy topology may include all or a sub-set of the physical nodes
and links of an IP/MPLS network; it may be comprised of dedicated and/or
shared network resources (e.g., in terms of processing power, storage, and


Best regards,