Scalability Considerations for Network Resource Partition
draft-dong-teas-nrp-scalability-01
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
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|---|---|---|---|
| Authors | Jie Dong , Zhenbin Li , Liyan Gong , Guangming Yang , Jim Guichard , Gyan Mishra , Fengwei Qin , Tarek Saad , Vishnu Pavan Beeram | ||
| Last updated | 2022-02-07 (Latest revision 2021-12-17) | ||
| Replaces | draft-dong-teas-enhanced-vpn-vtn-scalability | ||
| Replaced by | draft-ietf-teas-nrp-scalability | ||
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draft-dong-teas-nrp-scalability-01
TEAS Working Group J. Dong
Internet-Draft Z. Li
Intended status: Informational Huawei Technologies
Expires: 11 August 2022 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
7 February 2022
Scalability Considerations for Network Resource Partition
draft-dong-teas-nrp-scalability-01
Abstract
The IETF Network Slice service aims to meet the connectivity demands
of 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 traffic and meet the required SLOs and SLEs.
One or multiple IETF Network Slice services can be mapped to one NRP.
As the demand for IETF Network Slice services increases, scalability
would become an important factor for the large scale 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,
there are concerns about the scalability of NRPs. This document
describes the scalability considerations about NRPs in the network
control plane and data plane, and some optimization mechanisms are
proposed.
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 . . . . . 3
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 . . . . . . . . . . . . . . . . . 6
3.3. Gap Analysis of the Existing Mechanism . . . . . . . . . 7
4. Proposed Scalability Optimizations . . . . . . . . . . . . . 8
4.1. Control Plane Optimizations . . . . . . . . . . . . . . . 8
4.1.1. Distributed Control Plane Optimizations . . . . . . . 8
4.1.2. Centralized Control Plane Optimization . . . . . . . 10
4.2. Data Plane Optimizations . . . . . . . . . . . . . . . . 10
5. Solution Evolution for Improved Scalability . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 13
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
10.1. Normative References . . . . . . . . . . . . . . . . . . 13
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10.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
The IETF Network Slice service aims to meet the connectivity demands
of 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 Slice services, a concept called Network
Resource Partition (NRP) is introduced, which refers to a set of
network resources that are available in the underlay network to
ensure the requested SLOs and SLEs of IETF Network Slices can be met.
[I-D.ietf-teas-enhanced-vpn] describes the layered framework and
candidate technologies for delivering enhanced VPN (VPN+) services.
VPN+ aims to meet the needs of customers or applications, including
the applications that are associated with 5G, 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 built
with a set of network resources. The VPN+ framework and technologies
could be used for the realization of IETF Network Slice services.
NRP could be used as the underlay network construct to support the
VPN+ services.
As the demand for IETF Network Slice services increases, scalability
would become an important factor for the large scale 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,
there are concerns about the scalability of NRPs. This document
describes the scalability considerations about NRPs in the network
control plane and data plane, and some optimization mechanisms are
proposed.
2. Network Resource Partition Scalability Requirements
As described in [I-D.ietf-teas-ietf-network-slices], IETF Network
Slices may be grouped together according to characteristics
(including SLOs and SLEs). This grouping allows an operator to host
a number of slices on a particular set of resources to reduce the
amount of state information needed in the network. This can help to
avoid the maintenance of per IETF Network Slice state in the underlay
network.
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With the development and evolution of 5G and other services, it is
expected that an increasing number of IETF Network Slices will be
deployed. The number of network slices required depends on how IETF
Network Slices will be used, and the progress of network slicing for
the vertical industrial services. The potential number of IETF
Network Slice services and NRPs is analyzed by classifying the
network slice deployment into three typical scenarios:
1. IETF Network Slices can be used by a network operator for
different types of service. For example, in a converged multi-
service network, different IETF Network Slices can be created to
carry mobile transport services, fixed broadband services and
enterprise services respectively: each type of service could be
managed by a separate department or management team. Some
service types, such as multicast services may also be deployed in
a dedicated NRP. In this case, a separate NRP may need to be
created for each service type. It is also possible that a
network infrastructure operator provides IETF Network Slices to
other network operators as a wholesale service, and a NRP may
also be needed for each wholesale service customer. In this
scenario, the number of NRPs in a network could be relatively
small, such as in the order of 10 or so. This could be one of
the typical cases in the beginning of IETF Network Slice
deployment.
2. IETF Network Slices can be requested by customers of industrial
verticals, where the assurance of SLOs and the fulfilment of SLEs
are quite important. At the early stage of the vertical
industrial services, a few top customers in some industries will
begin to use IETF Network Slices to provide performance assurance
to their business, such as smart grid, manufacturing, public
safety, on-line gaming, etc. The realization of such IETF
Network Slices typically requires the provision of different NRPs
for different industries, and some top customers can require
dedicated NRPs for strict service performance guarantees.
Considering the number of vertical industries, and the number of
top customers in each industry, the number of NRPs needed may be
in the order of 100.
3. With the evolution of 5G and cloud networks, IETF Network Slices
could be widely used by various vertical industrial customers and
enterprise customers who require guaranteed or predictable
service performance. The total amount of IETF Network Slices may
increase to thousands or more, although it is expected that the
number of IETF Network Slices would still be less than the number
of traditional VPN services in the network. Accordingly, the
number of NRPs needed may be in the order of 1000.
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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 are 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, and the
required NRPs may increase as well.
Thus, there may be large numbers of IETF Network Slices in some
scenarios and the realization of IETF Network Slices needs to meet
the scalability requirements. Mapping multiple IETF Network Slices
to the same NRP presents a significant scaling benefit, but there can
still be a requirement for a large number of NRPs which presents its
own scalability challenges.
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 hybrid of a centralized controller and a distributed control
plane. The subsections that follow consider the scalability of these
two approaches: the resultant scalability of the control plane will
depend on how the hybrid is constructed.
3.1.1. Distributed Control Plane
It is necessary to create multiple NRPs for the delivery of IETF
network slice services. Each NRP can be associated with a customized
logical topology. The network resource attributes and the associated
logical 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
considered in the following aspects:
* The number of control protocol instances maintained on each node
* The number of protocol sessions maintained on each link
* The number of routes advertised by each node
* The amount of attributes associated with each route
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* The number of route computations (i.e., SPF computation) executed
by each node
As the number of NRPs increases, it is expected that 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 separated control protocol instances (e.g., IGP
instances) for different NRPs is considered higher than maintaining
the information of separate 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 the information exchange of
multiple NRPs. To meet the requirements of the increasing number of
NRPs, it is suggested to choose a control plane mechanism which could
improve the scalability while still provide the required
functionality.
3.1.2. Centralized Control Plane
By introducing a centralized network controller, the Software Defined
Network (SDN) approach 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
centralized controller, thus the scalability of the controller also
needs to be considered.
To provide global optimization for the Traffic Engineered (TE) paths
in different NRPs, the controller needs to keep the topology and
resource information of all the NRPs up-to-date. To achieve this,
the controller may need to maintain a communication channel with each
network node in the network. When there is significant change in the
network, or multiple NRPs require global optimization concurrently,
there may be a heavy processing burden at the controller, and a heavy
load in the network surrounding the controller for the distribution
of the updated network state and the TE paths.
3.2. Data Plane Scalability
To provide different IETF Network Slice services with the required
SLOs and SLEs, it is necessary to allocate different subsets of
network resources as different NRPs to avoid or reduce the unexpected
interference from other services in the network. As the number of
NRPs increases, it is required that the underlying network can
provide fine-granular network resource partitioning, which means the
amount of state about the partitioned network resources to be
maintained on the network nodes will also increase.
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In packet forwarding, IETF Network Slice service traffic needs to be
processed according to the topology and 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
either directly or implicitly. Different approaches of encapsulating
the NRP information in data packet can have different scalability
implications.
One practical approach is to reuse some of the existing fields in the
data packet to additionally identify the NRP the packet belongs to.
For example, the destination IP addresses or the MPLS forwarding
labels may be reused to further identify the NRP. This can avoid the
cost of introducing new fields in the data packet, while since it
introduces additional semantics to the existing fields, the
processing of the existing fields in packet forwarding may need to be
changed. Moreover, introducing resource semantics to existing
identifiers in the packet (e.g., IP addresses, MPLS forwarding
labels, etc.) may result in the increase of the amount of the
existing IDs in proportion to the number of the NRPs, which may cause
scalability problem in networks where a relatively large number of
NRPs is needed.
An alternative approach is to introduce a new dedicated field in the
data packet for identifying the NRP. This could avoid the impacts to
the existing fields in the packet. And if this new field carries a
globally-significant identifier of the NRP, it could be used together
with the existing fields to determine the packet forwarding behavior.
The potential issue with this approach is the difficulty in
introducing a new field in some of the data plane technologies.
In addition, the introduction of NRP specific packet forwarding has
an impact on the scalability of the forwarding entries on network
nodes, as a network node may need to maintain separate forwarding
entries for each NRP it participates in.
3.3. Gap Analysis of the Existing Mechanism
This section provides a gap analysis for an existing mechanism to
perform NRP identification in the data plane and the related
information distribution in the control plane.
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 distribute the resource
attributes and the associated logical topology information in the
control plane using mechanisms based on Multi-topology
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[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 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 needed 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. As 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.
3. The maximum number of logical topologies supported by OSPF
[RFC4915] is 128, and the maximum number of Flexible Algorithms
[I-D.ietf-lsr-flex-algo] is 128, which may not meet the required
number of NRPs in some network scenarios.
4. Proposed Scalability Optimizations
4.1. Control Plane Optimizations
4.1.1. Distributed Control Plane Optimizations
Several optimizations can be considered to reduce the distributed
control plane overhead and improve its scalability.
The first optimization mechanism is to reduce the amount of control
plane sessions used for the establishment and maintenance of the
NRPs. For multiple NRPs which have the same connection relationship
between two adjacent network nodes, it is proposed that one single
control protocol session is used for each such group of NRPs. The
information of different NRPs can be exchanged over the same session,
with necessary identification information to distinguish the NRPs in
the control message. This could reduce the overhead of maintaining a
large number of separate control protocol sessions for each NRP, and
could also reduce the amount of control plane messages flooded in the
network.
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The second optimization mechanism is to decouple the NRP information
from the associated logical topology information in the control
plane, so that the resource attributes and the topology attributes
can be advertised and processed separately. In a network, it is
possible that multiple NRPs associate with the same logical topology,
and multiple NRPs may share the same set of network resources on a
subset of network nodes and links. Then it is more efficient if only
one copy of the topology information is advertised, and multiple NRPs
sharing the same topology could refer to this topology information.
More importantly, with this approach, the result of topology-based
route computation could be shared by multiple NRPs, so that the
overhead of per NRP route computation could be avoided. Similarly,
information of a subset of network resources reserved on a particular
network node or link could be advertised once and may be referred to
by multiple NRPs which share the same set of resources.
O#####O#####O O*****O*****O
# # # * * *
# # # * * *
O#####O#####O O*****O*****O
NRP-1 NRP-2
O-----O-----O
| | |
| | |
O-----O-----O
Shared 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 which share the same logical
topology. As shown in the figure, NRP-1 and NRP-2 are associated
with the same topology, while the resource attributes of each NRP are
different. In this case, only one copy of the network topology
information needs to be advertised, and the topology-based route
computation result can be shared by the two NRPs to generate the
corresponding routing and forwarding tables.
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O#####O#####O O----O#####O
# # # \/ # #
# # # /\ # #
O#####O#####O O----O#####O
NRP-1 NRP-2
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 share the same set
of network resources on some of the links. In this case, information
about the resources allocated on each link only needs to be
advertised once, then both NRP-1 and NRP-2 could refer to the
reserved 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
mechanism to the distributed control plane rather than a replacement,
so that the workload for NRP specific path computation in control
plane could be shared by both the centralized controller and the
network nodes, and the scalability of both systems could be improved.
In addition, the centralized controller may be realized with multiple
network entities, each is responsible for one subset or region of the
network. This is the typical approach for scale out of the
centralized control plane.
4.2. Data Plane Optimizations
To support more IETF Network Slice services while keeping the amount
of data plane state at a reasonable scale, one typical approach is to
classify a set of IETF Network Slice services which have similar
service characteristics and performance requirements into a group,
and such groups of IETF Network Slice services are mapped to one NRP,
which is allocated with an aggregated set of network resources and
the union of the required logical topologies to meet the service
requirement of the whole group of IETF Network Slice services.
Different groups of IETF Network Slice services can be mapped to
different NRPs with different set of network resources allocated from
the underlay network. With appropriate grouping of IETF Network
Slice services, a reasonable number of NRPs with network resources
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reservation and aggregation could still meet the IETF Network Slice
service requirements.
Another optimization in the data plane is to decouple the identifiers
used for topology-based forwarding and the identifier used for the
resource-specific processing introduced by NRP. One possible
mechanism is to introduce a dedicated network-wide NRP Identifier
(NRP-ID) in the packet header to uniquely identify the set of network
resources allocated to a NRP on each involved network node and link
for the processing and forwarding of the data packets mapped to the
NRP. Then the existing identifiers in the packet header used for
topology based forwarding (e.g., the 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 global NRP-ID field
will be used together with other existing fields to determine the
packet forwarding behavior, this may require network nodes to support
a hierarchical forwarding table in data plane. Figure 3 shows the
concept of using different data plane identifiers for topology-
specific and resource-specific packet forwarding and processing
respectively.
+--------------------------+
| Packet Header |
| |
| +----------------------+ |
| | Topology-specific IDs| |
| +----------------------+ |
| |
| +----------------------+ |
| | Global NRP-ID | |
| +----------------------+ |
+--------------------------+
Figure 3. Decoupled Topology and Resource Identifiers in data packet
In an IPv6 [RFC8200] based network, this could be achieved by
introducing a dedicated field in either the IPv6 fixed 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.dong-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.
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In an MPLS [RFC3032] based network, this may be achieved by
introducing a dedicated NRP-ID either in the MPLS label stack or
following the MPLS label stack. This way, the existing MPLS
forwarding labels are used for topology-specific packet forwarding
towards the destination node, 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 be 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 data plane are under discussion as part of the work in MPLS
Open Design Team and is out of the scope of this document.
5. Solution Evolution for Improved Scalability
Based on the analysis in this document, the control plane 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.
At the first step, by introducing resource-awareness to segment
routing SIDs [I-D.ietf-spring-resource-aware-segments], and using
Multi-Topology or Flex-Algo as the control plane mechanism to define
the logical topology, it could provide a solution for building a
limited number of NRPs in the network, and can meet the requirements
of 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 attribute from the resource
attribute, so that multiple NRPs could share the same topology or
resource attribute to reduce the control plane and data plane
overhead. The data plane can still be based 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].
When 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, this could help to reduce the number of IP addresses or
SR SIDs needed to support a large number of NRPs. This mechanism is
called the NRP-ID based mechanism.
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6. Security Considerations
This document describes the scalability considerations about the
network control plane and data plane of NRPs in the realization of
IETF Network Slice services, and proposes the 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.
7. IANA Considerations
This document makes no request of IANA.
8. Contributors
Zhibo Hu
Email: huzhibo@huawei.com
Hongjie Yang
Email: hongjie.yang@huawei.com
9. Acknowledgments
The authors would like to thank Adrian Farrel for the review and
discussion of this document.
10. References
10.1. 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+)
Services", Work in Progress, Internet-Draft, draft-ietf-
teas-enhanced-vpn-09, 25 October 2021,
<https://www.ietf.org/archive/id/draft-ietf-teas-enhanced-
vpn-09.txt>.
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[I-D.ietf-teas-ietf-network-slices]
Farrel, A., Gray, E., 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-05, 25
October 2021, <https://www.ietf.org/archive/id/draft-ietf-
teas-ietf-network-slices-05.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>.
10.2. Informative References
[I-D.dong-6man-enhanced-vpn-vtn-id]
Dong, J., Li, Z., Xie, C., Ma, C., and G. Mishra,
"Carrying Virtual Transport Network (VTN) Identifier in
IPv6 Extension Header", Work in Progress, Internet-Draft,
draft-dong-6man-enhanced-vpn-vtn-id-06, 24 October 2021,
<https://www.ietf.org/archive/id/draft-dong-6man-enhanced-
vpn-vtn-id-06.txt>.
[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-18, 25 October
2021, <https://www.ietf.org/archive/id/draft-ietf-lsr-
flex-algo-18.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-02, 13 January 2022,
<https://www.ietf.org/archive/id/draft-ietf-lsr-isis-sr-
vtn-mt-02.txt>.
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[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-03, 12 July 2021,
<https://www.ietf.org/archive/id/draft-ietf-spring-
resource-aware-segments-03.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-01,
12 July 2021, <https://www.ietf.org/archive/id/draft-ietf-
spring-sr-for-enhanced-vpn-01.txt>.
[I-D.zhu-lsr-isis-sr-vtn-flexalgo]
Zhu, Y., Dong, J., and Z. Hu, "Using Flex-Algo for Segment
Routing based VTN", Work in Progress, Internet-Draft,
draft-zhu-lsr-isis-sr-vtn-flexalgo-03, 11 July 2021,
<https://www.ietf.org/archive/id/draft-zhu-lsr-isis-sr-
vtn-flexalgo-03.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>.
[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
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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
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
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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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