Joel,
Thank you for your comments.
From the pespective of an operator, new services need more support from 
underlay network, such as network resource and connection support. Considering 
the limition of MPLS-TE, we think that new mechanisms should be introduced into 
underlay network to meet the requirements of services.

Best regards
Chongfeng



中国电信股份有限公司研究院 
+86-10-50902116


 
From: Joel M. Halpern
Date: 2020-03-26 21:35
To: [email protected]; lsr
Subject: Re: [Lsr] Using IS-IS Multi-Topology (MT) for Segment Routing based 
Virtual Transport Network
In once sense, the statement is inherently true.  A VPN technology 
without underlay support would seem to have significant difficulty in 
consistently meeting an SLA.  Having said that much, the rest does not 
seem to follow.
 
Yours,
Joel
 
On 3/26/2020 1:40 AM, [email protected] wrote:
> 
> Hi, Joel,
> 
> The statement is that pure overlay VPNs cannot meet the requirement of 
> some new services, and it would require integration between the underlay 
> and the overlay networks.
> 
> As mentioned in this document, there is existing technology in the 
> underlay to support enhanced VPNs , such as using a set of MPLS-TE based 
> resource reserved point-to-point paths, while it scalability is the 
> concern of many operators.
> 
> Thus VTN is introduced to provide the required topology and resource 
> attribute in the underlay in a scalable manner. This is described in the 
> introduction section.
> 
> Hope this helps.
> 
> 
> Chongfeng
> 
> 
>     *From:* Joel M. Halpern <mailto:[email protected]>
>     *Date:* 2020-03-25 21:52
>     *To:* [email protected] <mailto:[email protected]>; lsr
>     <mailto:[email protected]>
>     *Subject:* Re: [Lsr] Using IS-IS Multi-Topology (MT) for Segment
>     Routing based Virtual Transport Network
>     This drafts starts by asserting that there are limitations on what can
>     be done with the existing technology.  As the description is quite
>     vague, I can not be certain.  But I do not know of any difficulty in
>     providing the described capabilities with current technology, without
>     introducing a new, undescribed, construct called a VTN.
>     Yours,
>     Joel
>     On 3/25/2020 9:44 AM, [email protected] wrote:
>      >
>      > Hello, folks,
>      >
>      > we have submitted a new draft of
>      >   https://tools.ietf.org/html/draft-xie-lsr-isis-sr-vtn-mt-00 .
>      >
>      > It is about Using IS-IS Multi-Topology (MT) for Segment Routing
>     based
>      > Virtual Transport Network. Enhanced VPN (VPN+) as defined in
>      > I-D.ietf-teas-enhanced-vpn aims to provide enhanced VPN service to
>      > support some applications's needs of enhanced isolation and
>     stringent
>      > performance requirements.  VPN+ requries integration between the
>     overlay
>      > VPN and the underlay network.  A Virtual Transport Network (VTN)
>     is a
>      > virtual network which consists of a subset of the network toplogy
>     and
>      > network resources allocated from the underlay network.  A VTN
>     could be
>      > used as the underlay for one or a group of VPN+ services.. This
>     document
>      > describes a simplified mechanism to build the SR based VTNs using
>     IGP
>      > multi- topology together with other well-defined IS-IS extensions.
>      >
>      > Comments and suggestions are highly appreciated.
>      >
>      > Chongfeng Xie
>      >
>      >
>      >
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