TEAS Working Group J. Dong
Internet-Draft Z. Li
Intended status: Informational Huawei Technologies
Expires: 27 April 2023 L. Gong
China Mobile
G. Yang
China Telecom
J. Guichard
Futurewei Technologies
G. Mishra
Verizon Inc.
F. Qin
China Mobile
T. Saad
V. Beeram
Juniper Networks
24 October 2022
Scalability Considerations for Network Resource Partition
draft-ietf-teas-nrp-scalability-01
Abstract
The IETF Network Slice aims to offer a connectivity service to a
network slice customer with specific Service Level Objectives (SLOs)
and Service Level Expectations (SLEs) over a common underlay network.
A Network Resource Partition (NRP) is a set of network resources that
are allocated from the underlay network to carry a specific set of
network slice service traffic and meet specific SLOs and SLEs.
As the demand for IETF Network Slice increases, scalability would
become an important factor for the deployment of IETF Network Slices.
Although the scalability of IETF Network Slices can be improved by
mapping a group of IETF Network Slices to one NRP, that design may
not be suitable or possible for all deployments, thus there are
concerns about the scalability of NRPs.
This document discusses some scalability considerations about NRPs in
the network control and data plane. It also investigates a set of
optimization mechanisms.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Network Resource Partition Scalability Requirements . . . . . 4
3. Network Resource Partition Scalability Considerations . . . . 5
3.1. Control Plane Scalability . . . . . . . . . . . . . . . . 5
3.1.1. Distributed Control Plane . . . . . . . . . . . . . . 5
3.1.2. Centralized Control Plane . . . . . . . . . . . . . . 6
3.2. Data Plane Scalability . . . . . . . . . . . . . . . . . 7
3.3. Gap Analysis of Existing Mechanisms . . . . . . . . . . . 8
4. Proposed Scalability Optimizations . . . . . . . . . . . . . 9
4.1. Control Plane Optimization . . . . . . . . . . . . . . . 9
4.1.1. Distributed Control Plane Optimization . . . . . . . 9
4.1.2. Centralized Control Plane Optimization . . . . . . . 11
4.2. Data Plane Optimization . . . . . . . . . . . . . . . . . 12
5. Solution Evolution Perspectives . . . . . . . . . . . . . . . 13
6. Operational Considerations . . . . . . . . . . . . . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 14
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
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11.1. Normative References . . . . . . . . . . . . . . . . . . 15
11.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
The IETF Network Slice aims to offer a connectivity service to a
network slice customer with specific Service Level Objectives (SLOs)
and Service Level Expectations (SLEs) over a common underlay network.
[I-D.ietf-teas-ietf-network-slices] defines the terminologies and the
characteristics of IETF Network Slices. It also discusses the
general framework, the components and interfaces for requesting and
operating IETF Network Slices. For the realization of IETF Network
Slices, the concept called Network Resource Partition (NRP) is
introduced by [I-D.ietf-teas-ietf-network-slices]. An NRP is a
collection of network resources in the underlay network, which can be
used to ensure the requested SLOs and SLEs of IETF Network Slices
services are met.
[I-D.ietf-teas-enhanced-vpn] describes a layered architecture and the
candidate technologies in different layers for delivering enhanced
VPN (VPN+) services. VPN+ aims to meet the needs of customers or
applications which require connectivity services with advanced
characteristics, such as the assurance of Service Level Objectives
(SLOs) and specific Service Level Expectations (SLEs). VPN+ services
can be delivered by mapping one or a group of overlay VPNs to a
virtual underlay network which is allocated with a set of network
resources. The VPN+ architecture and technologies could be used for
the realization of IETF Network Slices. And in the context of
network slicing, NRP could be used to instantiate the virtual
underlay network construct in VPN+.
As the demand for IETF Network Slice services increases, scalability
(the number of network slices a network can support) would become an
important factor for the deployment of IETF Network Slices in
specific networks. Although the scalability of IETF Network Slices
can be improved by mapping a group of IETF Network Slices to one NRP,
that design may not be suitable or possible for all deployments, thus
there are concerns about the scalability of NRPs.
This document discusses some scalability considerations about NRPs in
the network control and data plane. It also investigates a set of
optimization mechanisms.
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2. Network Resource Partition Scalability Requirements
As described in [I-D.ietf-teas-ietf-network-slices], the connectivity
constructs of IETF Network Slices may be grouped together according
to their characteristics (including SLOs and SLEs) and mapped to a
given NRP. The grouping and mapping of IETF Network Slices are
policy-based and under the control of operator. For example, a
policy can be considered by an operator to host a large number of
IETF Network Slices into a relatively small number of NRPs to reduce
the amount of state information to be maintained in the network.
This can help to avoid the maintenance of per IETF Network Slice
state in the underlay network, which is equivalent to the one-to-one
mapping between IETF Network Slices and NRPs.
With the introduction of various services which require enhanced
connectivity, it is expected that the number of IETF Network Slices
will increase. The potential number of IETF Network Slices and the
underlying NRPs are estimated by classifying the network slice
deployment into three typical scenarios:
1. IETF Network Slices can be used by a network operator to deliver
different types of services. For example, in a multi-service
network, different IETF Network Slices can be created to carry,
e.g., mobile transport services, fixed broadband services, and
enterprise services respectively: each type of service could be
managed by a separate team. Some other type of services, such as
multicast services, may also be deployed in a separate virtual
underlay network. Then a separate NRP may be created for each
service type. It is also possible that a network infrastructure
operator provides IETF Network Slice services to other network
operators as wholesale services, and an NRP may also be needed
for each wholesale service operator. In this scenario, the
number of NRPs in a network could be relatively small, such as in
the order of 10 or so.
2. IETF Network Slice services can be requested by customers of
industrial verticals, where the assurance of SLOs and the
fulfilment of SLEs are contractually defined between the customer
and the slice service provider, possibly including financial
penalties in case the service provider fails to honor the
contract (SLO or SLE). At the early stage of the vertical
industrial deployment, a few customers in some industries will
start using IETF Network Slices to address the connectivity
requirements and performance assurance raised by their business,
such as smart grid, manufacturing, public safety, on-line gaming,
etc. The realization of such IETF Network Slices may require the
provision of different NRPs for different industries, and some
customers may require dedicated NRPs for strict service
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performance guarantees. Considering the number of vertical
industries and the number of customers in each industry, the
number of NRPs needed may be in the order of 100.
3. With the advent of 5G and cloud networks, IETF Network Slices
services could be widely used by customer of various vertical
industries and enterprises who require guaranteed or predictable
network service performance. The amount of IETF Network Slices
may increase to the order of thousands or more. Accordingly, the
number of NRPs needed may be in the order of 1000.
In [TS23501], the 3GPP defines a 32-bit identifier for a 5G network
slice with an 8-bit Slice/Service Type (SST) and a 24-bit Slice
Differentiator (SD). This allows mobile networks (the RAN and mobile
core networks) to potentially support a large number of 5G network
slices. It is likely that multiple 5G network slices may be mapped
to the same IETF Network Slice, but in some cases (for example, for
specific SST or SD) the mapping may be closer to one-to-one. This
may require increasing number of IETF Network Slices, the number of
required NRPs may increase as well.
Thus the question of scalable IETF network slice services arises.
Mapping multiple IETF Network Slices to the same NRP presents a
significant scaling benefit, while a large number of NRPs may also be
required, which raises scalability challenges too.
3. Network Resource Partition Scalability Considerations
This section analyses the scalability of NRPs in the control plane
and data plane to understand the possible gaps in meeting the
scalability requirements of IETF Network Slices.
3.1. Control Plane Scalability
The control plane for establishing and managing NRPs could be based
on the combination of a centralized controller and a distributed
control plane. The following subsections consider the scalability
property of both the distributed and centralized control plane in
such design.
3.1.1. Distributed Control Plane
In some networks, multiple NRPs may need to be created for the
delivery of IETF Network Slice services. Each NRP is associated with
a logical topology. The network resource attributes and the
associated topology information of each NRP may need to be exchanged
among the network nodes. The scalability of the distributed control
plane used for the distribution of NRP information needs to be
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considered from the following aspects:
* The number of control protocol instances maintained on each node
* The number of control protocol sessions maintained on each link
* The number of control messages advertised by each node
* The amount of attributes associated with each message
* The number of computations (e.g., SPF computation) executed by
each node
As the number of NRPs increases, it is expected that at least in some
of the above aspects, the overhead in the control plane may increase
in proportion to the number of the NRPs. For example, the overhead
of maintaining separate control protocol instances (e.g., IGP
instances) for each NRP is considered higher than maintaining the
information of multiple NRPs in the same control protocol instance
with appropriate separation, and the overhead of maintaining separate
protocol sessions for different NRPs is considered higher than using
a shared protocol session for exchanging the information of multiple
NRPs. To meet the scalability and performance requirements with
increasing number of NRPs, it is suggested to select the control
plane mechanisms which have better scalability while can still
provide the required functionality, isolation and security for the
NRPs.
3.1.2. Centralized Control Plane
The use of centralized network controllers may help to reduce the
amount of computation overhead in the distributed control plane,
while it may also transfer some of the scalability concerns from
network nodes to the network controllers, thus the scalability of the
controller also needs to be considered.
A centralized controller can have a global view of the network, and
is usually used for Traffic Engineering (TE) path computation with
various constraints, or the global optimization of TE paths in the
network. To provide TE paths computation and optimization for
multiple NRPs, the controller needs to keep the topology and resource
information of all the NRPs up-to-date. And for some events such as
link or node failures, the resulting updates to the NRPs may need to
be distributed to the controller in real time, and may affect the
planning and operation of some NRPs. When there is a significant
change in the network which impacts multiple NRPs, or multiple NRPs
require global optimization concurrently, there may be a heavy
processing burden at the controllers, and a large amount of signaling
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traffic to be exchanged between the controller and corresponding NRP
components. These need to be taken into consideration from a
scalability and performance standpoints.
3.2. Data Plane Scalability
To provide different IETF Network Slice services with the required
SLOs and SLEs, it is important to allocate as many different subsets
of network resources as there are different NRPs to avoid or reduce
the risk of interference both between different IETF network slice
services and between slice services and other services in the
network. With both the use cases and the number of NRPs increases,
it is required that the underlay network can provide a finer
granularity of network resource partitioning for more IETF network
slice services, which means the amount of state about the partitioned
network resources to be maintained on the network nodes is likely to
increase.
IETF Network Slice service traffic needs to be processed and
forwarded by network nodes according to a forwarding policy that is
associated with the topology and the resource attributes of the NRP
it is mapped to, this means that some fields in the data packet need
to be used to identify the NRP and its associated topology and
resources either directly or implicitly. Different approaches for
encapsulating the NRP information in data packets may have different
scalability implications.
One practical approach is to reuse some of the existing fields in the
data packet to additionally indicate the NRP the packet belongs to.
For example, destination IP address or MPLS forwarding label may be
reused to identify the NRP. This avoids the complexity of
introducing new fields in the data packet, while the additional
semantics introduced to the existing fields may require additional
processing. Moreover, introducing NRP-specific semantics to existing
identifiers in the packet may result in the amount of the existing
identifiers increasing in proportion to the number of the NRPs. For
example, if IP address is reused to further identify an NRP, for a
node which pariticipate in M NRPs, the amount of IP addresses needed
for reaching this node in different NRPs would increase from 1 to M.
This may cause scalability problems in networks where a relatively
large number of NRPs is in operation.
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An alternative approach is to introduce a new dedicated field in the
data packet for identifying an NRP. And if this new field carries a
network wide unique NRP identifier (NRP ID), it could be used
together with the existing fields to determine the packet forwarding
behavior. The potential issue with this approach lies in the
difficulty of introducing a new field in some of data plane
technologies.
In addition, the introduction of NRP-specific packet forwarding
impacts the number of the forwarding entries maintained by the
network nodes.
3.3. Gap Analysis of Existing Mechanisms
This section provides gap analysis of existing mechanisms which may
be used to provide NRP identification in the data plane and the
distribution of NRP related information using control plane
protocols.
One existing mechanism of building NRPs is to use resource-aware
Segment Identifiers (either SR-MPLS or SRv6)
[I-D.ietf-spring-resource-aware-segments] to identify the allocated
network resources in the data plane based on the mechanisms described
in [I-D.ietf-spring-sr-for-enhanced-vpn], and then distribute the
resource attributes and the associated logical topology information
in the control plane using mechanisms based on Multi-topology
[I-D.ietf-lsr-isis-sr-vtn-mt] or Flex-Algo
[I-D.zhu-lsr-isis-sr-vtn-flexalgo]. This mechanism is suitable for
networks where a relatively small number of NRPs are needed. As the
number of NRPs increases, there may be several scalability challenges
with this approach:
1. The number of SR SIDs will increase in proportion to the number
of NRPs in the network, which will bring challenges both to the
distribution of SR SIDs and the related information in the
control plane, and to the installation of forwarding entries for
resource-aware SIDs in the data plane.
2. If each NRP is associated with an independent logical topology or
algorithm, the number of route computations (e.g., SPF
computations) will increase in proportion to the number of NRPs
in the network, which may introduce significant overhead to the
control plane of network nodes.
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3. The maximum number of logical topologies supported by OSPF
[RFC4915] is 128, the maximum number of logical topologies
supported by IS-IS [RFC5120] is 4096, and the maximum number of
Flexible Algorithms [I-D.ietf-lsr-flex-algo] is 128. Some of
these technologies may not meet the required number of NRPs in
some network scenarios.
4. Proposed Scalability Optimizations
To support more IETF Network Slice services while keeping the amount
of network state at a reasonable scale, one basic approach is to
classify a set of IETF Network Slice services (e.g., services which
have similar service characteristics and performance requirements)
into a group, and such group of IETF Network Slice services are
mapped to one NRP, which is allocated with an aggregated set of
network resources and the combination of the required logical
topologies to meet the service requirements of the whole group of
IETF Network Slice services. Different groups of IETF Network Slice
services may be mapped to different NRPs, each of which is allocated
with different set of network resources from the underlay network.
According to operator's deployment policy, appropriate grouping of
IETF Network Slice services and mapping them to a set of NRPs with
proper network resource allocation could still meet the IETF Network
Slice service requirements. However, in some network scenarios, such
aggregation mechanism may not be applicable. The following sub-
sections proposes further optimization in control plane and data
plane respectively.
4.1. Control Plane Optimization
4.1.1. Distributed Control Plane Optimization
Several optimization mechanisms can be considered to reduce the
distributed control plane overhead and improve its scalability.
The first control plane optimization consists in reducing the amount
of control plane sessions used for the establishment and maintenance
of the NRPs. When multiple NRPs have the same connection
relationship between two adjacent network nodes, it is proposed that
one single control protocol session is used for these NRPs. The
information specific to the different NRPs can be exchanged over the
same control protocol session, with necessary identification
information to distinguish the information of different NRPs in the
control message. This could reduce the overhead of node in creating
and maintaining a separate control protocol session for each NRP, and
could also reduce the amount of control plane messages.
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The second control plane optimization is to decouple the resource
information of the NRP from the associated logical topology
information, so that the resource attributes and the topology
attributes of the NRP can be advertised and processed separately. In
a network, it is possible that multiple NRPs are associated with the
same logical topology, or multiple NRPs may share the same set of
network resources hosted by a specific set of network nodes and
links. With topology sharing, it is more efficient to advertise only
one copy of the topology information, and multiple NRPs deployed over
the very same topology could exploit such topology information. More
importantly, with this approach, the result of topology-based route
computation could also be shared by multiple NRPs, so that the
overhead of per NRP route computation could be avoided. Similarly,
for the resource sharing case, information about a set of network
resources allocated on a particular network node or link could be
advertised in the control plane only once and then be referred to by
multiple NRPs which share that set of resource.
# O #### O #### O * O **** O **** O
# # # # * * * *
O # # # O * * *
# # # # * * * *
# O #### O #### O * O **** O **** O
NRP-1 NRP-2
^^ ^^
|| O-----O-----O ||
<<<< / | \ / | | >>>>
O | X | |
\ | / \ | |
O-----O-----O
Underlay Network Topology
Legend
O Virtual node
### Virtual links with a set of reserved resources
*** Virtual links with another set of reserved resources
Figure 1. Topology Sharing between NRPs
Figure 1 gives an example of two NRPs that share the same logical
topology. NRP-1 and NRP-2 are associated with the same logical
topology, while the resource attributes of each NRP are different.
In this case, the information of the shared network topology can be
advertised using either MT or Flex-Algo, then the two NRPs can be
associated with the same MT or Flex-Algo, and the outcomes of
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topology-based route computation can be shared by the two NRPs for
further generating the corresponding NRP-specific routing and
forwarding entries.
# O #### O #### O * O ***** O #### O
# # # # * * * # #
O # # # O * # #
# # # # * * * # #
# O #### O #### O * O ***** O #### O
NRP-1 NRP-2
^^ ^^
|| O-----O-----O ||
<<<< / | \ / | | >>>>
O | X | |
\ | / \ | |
O-----O-----O
Underlay Network Topology
Legend
O Virtual node
### Virtual links with a set of reserved resource
*** Virtual links with another set of reserved resource
Figure 2. Resource Sharing between NRPs
Figure 2 gives another example of two NRPs which have different
logical topologies, while they share the same set of network
resources on a subset of the links. In this case, the information
about the shared resources allocated on the those links needs to be
advertised only once, then both NRP-1 and NRP-2 can refer to the
common set of allocated link resource for constraint based path
computation.
4.1.2. Centralized Control Plane Optimization
For the optimization of the centralized control plane, it is
suggested that the centralized controller is used as a complementary
computational facility to the distributed control plane rather than a
replacement, so that the workload for NRP-specific path computation
can be shared by both the centralized controller and the network
nodes. In addition, the centralized controller may be realized with
multiple network entities, each of which is responsible for one
subset or region of the network. This is the typical approach for
scale out of the centralized controller.
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4.2. Data Plane Optimization
One optimization in the data plane consists in decoupling the
identifiers used for topology-based forwarding from the identifier
used for the NRP-inferred resource-specific processing. One possible
mechanism is to introduce a dedicated network-wide NRP Identifier
(NRP ID) in the packet header to uniquely identify the set of local
network resources allocated to an NRP on each participating network
node and link for the processing of packets. Then the existing
identifiers in the packet header used for topology based forwarding
(e.g., destination IP address, MPLS forwarding labels) are kept
unchanged. The benefit is the amount of the existing topology-
specific identifiers will not be impacted by the increasing number of
NRPs. Since this new NRP ID field will be used together with other
existing fields of the packet to determine the packet forwarding
behavior, this may require network nodes to maintain a hierarchical
forwarding table in data plane. Figure 3 shows the concept of using
separate data plane identifiers for topology-specific and resource-
specific packet forwarding and processing purposes.
+--------------------------+
| Packet Header |
| |
| +----------------------+ |
| | Topology-specific IDs| |
| +----------------------+ |
| |
| +----------------------+ |
| | Global NRP-ID | |
| +----------------------+ |
+--------------------------+
Figure 3. Decoupled Topology and Resource Identifiers in data packet
In an IPv6 [RFC8200] network, this could be achieved by introducing a
dedicated field in either the IPv6 base header or the extension
headers to carry the NRP ID for the resource-specific forwarding,
while keeping the destination IP address field used for routing
towards the destination prefix in the corresponding topology. Note
that the NRP ID needs to be parsed by every node along the path which
is capable of NRP-aware forwarding.
[I-D.ietf-6man-enhanced-vpn-vtn-id] introduces the mechanism of
carrying the VTN resource ID (which is equivalent to NRP ID in the
context of network slicing) in IPv6 Hop-by-Hop extension header.
In an MPLS [RFC3032] network, this may be achieved by inserting a
dedicated NRP ID either in the MPLS label stack or a specific field
that follows the MPLS label stack. Thus the existing MPLS forwarding
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labels are used for topology-specific packet forwarding purposes, and
the NRP ID is used to determine the set of network resources for
packet processing. This requires that both the forwarding label and
the NRP ID are parsed by nodes along the forwarding path of the
packet, and the forwarding behavior may depend on the position of the
NRP ID in the packet. The detailed extensions to MPLS is currently
under discussion as part of the work conducted by the MPLS Open
Design Team, and is out of the scope of this document.
5. Solution Evolution Perspectives
Based on the analysis provided by this document, the control and data
plane for NRP need to evolve to support the increasing number of IETF
Network Slice services and the increasing number of NRPs in the
network. This section describes the foreseeable solution evolution
taking the SR-based NRP solutions as an example, while the analysis
and optimization in this document are generic and not specific to SR.
First, by introducing resource-awareness with specific SR SIDs
[I-D.ietf-spring-resource-aware-segments], and using Multi-Topology
or Flex-Algo mechanisms to define the logical topology of the NRP,
providing a limited number of NRPs in the network is possible, and
can meet the requirements for a relatively small number of IETF
Network Slice services. This mechanism is called the "basic SR-based
NRP".
As the required number of IETF Network Slice services increases, more
NRPs may be needed, then the control plane scalability could be
improved by decoupling the topology attributes from the resource
attributes, so that multiple NRPs could share the same topology or
resource attributes to reduce the overhead. The data plane can still
rely on the resource-aware SIDs. This mechanism is called the
"scalable SR-based NRP". Both the basic and the scalable SR-based
NRP mechanisms are described in
[I-D.ietf-spring-sr-for-enhanced-vpn].
Whenever the data plane scalability becomes a concern, a dedicated
NRP ID can be introduced in the data packet to decouple the resource-
specific identifiers from the topology-specific identifiers in the
data plane, so as to reduce the number of IP addresses or SR SIDs
needed in supporting a large number of NRPs. This is called the NRP-
ID-based mechanism.
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6. Operational Considerations
The instantiation of NRPs require NRP-specific configurations of the
participating network nodes and links. There can also be cases where
the topology or the set of network resources allocated to an existing
NRP needs to be modified. Of course, the amount of configurations
for NRP instantiation and modification will increase with the number
of NRPs.
For the management and operation of NRPs and the optimization of
paths within the NRPs, the status of NRPs needs to be monitored and
reported to the network controller. The increasing number of NRPs
would require additional NRP status information to be monitored.
7. Security Considerations
This document discusses scalability considerations about the network
control plane and data plane of NRPs in the realization of IETF
Network Slice services, and investigates some mechanisms for
scalability optimization. As the number of NRPs supported in the
data plane and control plane of the network can be limited, this may
be exploited as an attack vector by requesting a large number of
network slices, which then result in the creation of a large number
of NRPs.
One protection against this is to improve the scalability of the
system to support more NRPs. Another possible solution is to make
the network slice controller aware of the scaling constraints of the
system and dampen the arrival rate of new network slices and NRPs
request, and raise alarms when the thresholds are crossed.
The security considerations in [I-D.ietf-teas-ietf-network-slices]
and [I-D.ietf-teas-enhanced-vpn] also apply to this document.
8. IANA Considerations
This document makes no request of IANA.
9. Contributors
Zhibo Hu
Email: huzhibo@huawei.com
Hongjie Yang
Email: hongjie.yang@huawei.com
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10. Acknowledgments
The authors would like to thank Adrian Farrel, Dhruv Dhody, Donald
Eastlake, Kenichi Ogaki, Mohamed Boucadair, Christian Jacquenet and
Kiran Makhijani for their review and valuable comments to this
document.
11. References
11.1. Normative References
[I-D.ietf-teas-enhanced-vpn]
Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
Framework for Enhanced Virtual Private Network (VPN+)",
Work in Progress, Internet-Draft, draft-ietf-teas-
enhanced-vpn-11, 19 September 2022,
<https://www.ietf.org/archive/id/draft-ietf-teas-enhanced-
vpn-11.txt>.
[I-D.ietf-teas-ietf-network-slices]
Farrel, A., Drake, J., Rokui, R., Homma, S., Makhijani,
K., Contreras, L. M., and J. Tantsura, "Framework for IETF
Network Slices", Work in Progress, Internet-Draft, draft-
ietf-teas-ietf-network-slices-15, 21 October 2022,
<https://www.ietf.org/archive/id/draft-ietf-teas-ietf-
network-slices-15.txt>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
11.2. Informative References
[I-D.ietf-6man-enhanced-vpn-vtn-id]
Dong, J., Li, Z., Xie, C., Ma, C., and G. Mishra,
"Carrying Virtual Transport Network (VTN) Information in
IPv6 Extension Header", Work in Progress, Internet-Draft,
draft-ietf-6man-enhanced-vpn-vtn-id-01, 11 July 2022,
<https://www.ietf.org/archive/id/draft-ietf-6man-enhanced-
vpn-vtn-id-01.txt>.
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[I-D.ietf-lsr-flex-algo]
Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
A. Gulko, "IGP Flexible Algorithm", Work in Progress,
Internet-Draft, draft-ietf-lsr-flex-algo-26, 17 October
2022, <https://www.ietf.org/archive/id/draft-ietf-lsr-
flex-algo-26.txt>.
[I-D.ietf-lsr-isis-sr-vtn-mt]
Xie, C., Ma, C., Dong, J., and Z. Li, "Using IS-IS Multi-
Topology (MT) for Segment Routing based Virtual Transport
Network", Work in Progress, Internet-Draft, draft-ietf-
lsr-isis-sr-vtn-mt-03, 10 July 2022,
<https://www.ietf.org/archive/id/draft-ietf-lsr-isis-sr-
vtn-mt-03.txt>.
[I-D.ietf-spring-resource-aware-segments]
Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li,
Z., and F. Clad, "Introducing Resource Awareness to SR
Segments", Work in Progress, Internet-Draft, draft-ietf-
spring-resource-aware-segments-06, 11 October 2022,
<https://www.ietf.org/archive/id/draft-ietf-spring-
resource-aware-segments-06.txt>.
[I-D.ietf-spring-sr-for-enhanced-vpn]
Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li,
Z., and F. Clad, "Segment Routing based Virtual Transport
Network (VTN) for Enhanced VPN", Work in Progress,
Internet-Draft, draft-ietf-spring-sr-for-enhanced-vpn-04,
11 October 2022, <https://www.ietf.org/archive/id/draft-
ietf-spring-sr-for-enhanced-vpn-04.txt>.
[I-D.zhu-lsr-isis-sr-vtn-flexalgo]
Zhu, Y., Dong, J., and Z. Hu, "Using Flex-Algo for Segment
Routing (SR) based Virtual Transport Network (VTN)", Work
in Progress, Internet-Draft, draft-zhu-lsr-isis-sr-vtn-
flexalgo-05, 11 July 2022,
<https://www.ietf.org/archive/id/draft-zhu-lsr-isis-sr-
vtn-flexalgo-05.txt>.
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, DOI 10.17487/RFC4915, June 2007,
<https://www.rfc-editor.org/info/rfc4915>.
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[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120,
DOI 10.17487/RFC5120, February 2008,
<https://www.rfc-editor.org/info/rfc5120>.
[TS23501] "3GPP TS23.501", 2016,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3144>.
Authors' Addresses
Jie Dong
Huawei Technologies
Huawei Campus, No. 156 Beiqing Road
Beijing
100095
China
Email: jie.dong@huawei.com
Zhenbin Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Road
Beijing
100095
China
Email: lizhenbin@huawei.com
Liyan Gong
China Mobile
No. 32 Xuanwumenxi Ave., Xicheng District
Beijing
China
Email: gongliyan@chinamobile.com
Guangming Yang
China Telecom
No.109 West Zhongshan Ave., Tianhe District
Guangzhou
China
Email: yangguangm@chinatelecom.cn
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James N Guichard
Futurewei Technologies
2330 Central Express Way
Santa Clara,
United States of America
Email: james.n.guichard@futurewei.com
Gyan Mishra
Verizon Inc.
Email: gyan.s.mishra@verizon.com
Fengwei Qin
China Mobile
No. 32 Xuanwumenxi Ave., Xicheng District
Beijing
China
Email: qinfengwei@chinamobile.com
Tarek Saad
Juniper Networks
Email: tsaad@juniper.net
Vishnu Pavan Beeram
Juniper Networks
Email: vbeeram@juniper.net
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