IDR Working Group J. Dong
Internet-Draft Z. Hu
Intended status: Standards Track Huawei Technologies
Expires: May 7, 2020 November 4, 2019
BGP-LS Extensions for Segment Routing based Enhanced VPN
draft-dong-idr-bgpls-sr-enhanced-vpn-00
Abstract
Enhanced VPN (VPN+) is an enhancement to VPN services to support the
needs of new applications, particularly including the applications
that are associated with 5G services. These applications require
better isolation and have more stringent performance requirements
than that can be provided with traditional overlay VPNs. An enhanced
VPN may be used for 5G transport network slicing, and will also be of
use in more generic scenarios. This document specifies BGP-LS based
mechanism with necessary extensions to advertise the information of
Segment Routing (SR) based virtual networks. These virtual networks
could be used as the underlay of enhanced VPN service. The proposed
mechanism is applicable to both segment routing with MPLS data plane
(SR-MPLS) and segment routing with IPv6 data plane (SRv6).
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 7, 2020.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Advertisement of Transport Network Slice Definition . . . . . 3
2.1. Sub-TLVs of TNSD TLV . . . . . . . . . . . . . . . . . . 4
3. Advertisement of Network Topology and Resource Attributes . . 6
3.1. Intra-domain Network Topology Advertisement . . . . . . . 6
3.1.1. MTR based Topology Advertisement . . . . . . . . . . 6
3.1.2. Flex-Algo based Topology Advertisement . . . . . . . 7
3.2. Intra-domain Resource Information Advertisement . . . . . 8
3.3. Inter-Domain Topology and Resource Information
Advertisement . . . . . . . . . . . . . . . . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
Driven largely by needs arising from the 5G mobile network, the
concept of network slicing has gained traction
[NGMN-NS-Concept][TS23501][TS28530] . Network slicing requires to
partition the physical network to several pieces to provide each
network slice with the required networking, computing, and storage
resources and functions to meet the requirement of slice tenants. As
specified in [I-D.ietf-teas-enhanced-vpn], a transport network slice
is a virtual (logical) network with a particular network topology and
a set of shared or dedicated network resources, which are used to
provide the network slice consumer with the required connectivity,
appropriate isolation and specific Service Level Agreement (SLA).
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The enhanced VPN service (VPN+) [I-D.ietf-teas-enhanced-vpn] is
targeted at new applications which require better isolation from both
control plane and data plane's perspective and have more stringent
performance requirements than can be provided with existing overlay
VPNs. To meet the requirement of enhance VPN services, a number of
virtual networks need be created, each with a subset of the underlay
network topology and a set of network resources allocated to meet the
requirement of a specific enhanced VPN or a group of enhanced VPNs.
In the context of 5G, each virtual network can be considered as a
transport network slice.
[I-D.dong-spring-sr-for-enhanced-vpn] describes the mechanisms to
build Segment Routing (SR) based virtual networks, which could be
used to as the underlay of different enhanced VPN services.
[I-D.dong-lsr-sr-enhanced-vpn] specifies the IGP mechanism and
extensions to build a set of SR based virtual networks with
customized topology and resource attributes. When the virtual
networks span multiple areas or multiple Autonomous Systems(ASes),
BGP-LS is needed to advertise the virtual network information of each
IGP area or AS to the network controller to build the inter-area or
inter-AS SR based transport network slices.
This document describes BGP-LS [RFC7752] based mechanism with
necessary extensions to advertise the topology and resource
information of intra-domain and inter-domain Segment Routing (SR)
based transport network slices. The definition of transport network
slice is advertised as a node attribute using BGP-LS. The attributes
of network resources allocated to a transport network slice is
advertised as a link attribute using BGP-LS.
2. Advertisement of Transport Network Slice Definition
The definition of a transport network slice or virtual network
consists of the combination of a set of network attributes. The
topology attribute and resource attribute are two major types of
attributes of a transport network slice, and they can be decoupled in
the control plane advertisement and processing. Transport Network
Slice Definition (TNSD) TLV is a new TLV of the optional BGP-LS
Attribute which is associated with the node NLRI.
The format of TNSD TLV is as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transport Network Slice Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs |
~ ... ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
o Type: TBD
o Length: the length of the value field of the sub-TLV. It is
variable dependent on the included Sub-TLVs.
o Flags: 16-bit flags to indicate the attributes of the transport
network slice. All flags are reserved and MUST be set to zero on
transmission and ignored on reception.
o Reserved: this field is reserved for future use, MUST be set to
zero on transmission and ignored on reception.
o Transport Network Slice Identifier (TNSI): A 32-bit identifier
which is used to identify a transport network slice.
o Sub-TLVs: optional sub-TLVs to specify the attributes of a virtual
network.
2.1. Sub-TLVs of TNSD TLV
The sub-TLVs of the TNSD TLV is used to advertise the identifiers of
different types of attributes of the transport network slice. Two
sub-TLVs of the TNSD TLV are defined in this document: Network
Topology sub-TLV and Network Resource sub-TLV.
The format of the Network Topology sub-TLV is as below:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|A| Flags | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
o Type: 1
o Length: the length of the value field of the sub-TLV.
o Flags: 16-bit flags to indicate the attribute of the virtual
network topology. Where:
M flag: indicates the topology is determined by the MT-ID when
set.
A flag: indicates the topology is determined by the Algorithm
when set. In this case, the value of the Algorithm field
SHOULD be between 128 and 255.
o MT-ID: 16-bit identifier which indicates the multi-topology
identifier of the IGP topology.
o Algorithm: 8-bit identifier which indicates the algorithm which is
used within this network topology.
o Reserved: this field is reserved for future use, MUST be set to
zero on transmission and ignored on reception.
The format of the Network Resource sub-TLV is as below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Resource Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
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Type: 2
Length: 6 octets.
Flags: 16 bit flags. All the bits are reserved, which MUST be set
to 0 on transmission and ignored on receipt.
Reserved: this field is reserved for future use, MUST be set to
zero on transmission and ignored on reception.
Resource Identifier: A 32-bit identifier which is used to identify
the group of network resources allocated to a transport network
slice.
3. Advertisement of Network Topology and Resource Attributes
[I-D.dong-lsr-sr-enhanced-vpn] describes the candidate IGP mechanisms
to distribute the topology attributes of SR based transport network
slices. This section describes the BGP-LS mechanism to distribute
both the intra-domain and inter-domain topology and resource
attribute of SR based transport network slices.
3.1. Intra-domain Network Topology Advertisement
3.1.1. MTR based Topology Advertisement
In section 3.2.1.5 of [RFC7752], the Multi-Topology Identifier (MT-
ID) TLV is defined, which can contain one or more IS-IS or OSPF
Multi-Topology IDs. The MT-ID TLV MAY be present in a Link
Descriptor, a Prefix Descriptor, or the BGP-LS attribute of a Node
NLRI.
[I-D.ietf-idr-bgp-ls-segment-routing-ext] defines the BGP-LS
extensions to carry the segment routing information using TLVs of
BGP-LS Attribute. When MTR is used with SR-MPLS data plane,
topology-specific prefix SIDs and topology-specific adjacency SIDs
can be carried in the BGP-LS Attribute associated with the prefix
NLRI and link NLRI respectively, the MT-ID TLV is carried in the
prefix descriptor and link descriptor to identify the corresponding
topology of the SIDs.
[I-D.ietf-idr-bgpls-srv6-ext] defines the BGP-LS extensions to
advertise SRv6 segments along with their functions and attributes.
When MTR is used with SRv6 data plane, the SRv6 Locator TLV is
carried in the BGP-LS Attribute associated with the prefix-NLRI, the
MT-ID TLV can be carried in the prefix descriptor to identify the
corresponding topology of the SRv6 Locator. The SRv6 End.X SIDs are
carried in the BGP-LS Attribute associated with the link NLRI, the
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MT-ID TLV can be carried in the link descriptor to identify the
corresponding topology of the SIDs. The SRv6 SID NLRI is defined to
advertise other types of SRv6 SIDs, in which the SRv6 SID Descriptors
can include the MT-ID TLV so as to advertise topology-specific SRv6
SIDs.
[RFC7752] also defines the rules of the usage of MT-ID TLV:
"In a Link or Prefix Descriptor, only a single MT-ID TLV containing
the MT-ID of the topology where the link or the prefix is reachable
is allowed. In case one wants to advertise multiple topologies for a
given Link Descriptor or Prefix Descriptor, multiple NLRIs need to be
generated where each NLRI contains an unique MT-ID. In the BGP-LS
attribute of a Node NLRI, one MT-ID TLV containing the array of MT-
IDs of all topologies where the node is reachable is allowed."
This indicates that only one MT-ID is allowed to be carried the Link
or Prefix descriptors. When a link or prefix participates in
multiple topologies, multiple NLRIs needs to be generated to report
all the topologies a link or prefix participates in, together with
the topology-specific segment routing information. This would
increase the number of BGP Updates and may introduce additional
processing burden to both the sending BGP speaker and the receiving
network controller. When the number of topologies in a network is
not a small number, some optimization may be introduced for the
reporting of multi-topology information and the associated segment
routing information in BGP-LS. This will be elaborated in a future
version.
3.1.2. Flex-Algo based Topology Advertisement
As specified in [I-D.dong-lsr-sr-enhanced-vpn], Flex-Algo
[I-D.ietf-lsr-flex-algo] can also be used to advertise the
topological constraints of a virtual network. The BGP-LS extensions
for SR-MPLS [I-D.ietf-idr-bgp-ls-segment-routing-ext] and SRv6
[I-D.ietf-idr-bgpls-srv6-ext]provide the mechanisms to advertise the
Flex-Algo definition information and the algorithm-specific segment
routing information.
The Flex-Algo definition can be used to describe the topological
constraints for path computation. According to the network nodes'
participation of a Flex-Algo, and the rules of including or excluding
specific Admin Groups (colors), a network topology can be determined
by a Flex-Algo.
In[I-D.ietf-idr-bgp-ls-segment-routing-ext], algorithm-specific
prefix-SIDs can be advertised as Link attributes of the associated
Link NLRI. In [I-D.ietf-idr-bgpls-srv6-ext], algorithm-specific SRv6
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Locators can be advertised as Link attributes of the associated
prefix NLRI, and algorithm-specific End.X SIDs can be advertised as
Link attributes of the associated Link NLRI. Other types of SRv6
SIDs are advertised using SRv6 SID NLRI and can also be algorithm-
specific.
3.2. Intra-domain Resource Information Advertisement
[I-D.dong-lsr-sr-enhanced-vpn] specifies the mechanism to advertise
the resource information associated with each transport network
slice. It is based on the extensions to the advertisement of L2
bundle member links information. This section defines the
corresponding BGP-LS extensions.
In [I-D.ietf-idr-bgp-ls-segment-routing-ext], L2 bundle member
Attribute TLV is used to advertise the attributes of a member link of
a parent L3 link. Two new sub-TLVs are defined under the L2 bundle
member Attribute TLV.
The link attribute sub-TLV is use to carry the link characteristics
of a L2 member link. The format of the sub-TLV is as below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type: TBD
Length: 4 octets.
Flags: 16-bit flags. This field is consistent with the Flag field
in IS-IS Link Attribute sub-TLV in [RFC5029]. In addition to the
flags defined in [RFC5029], A new Flag V is defined in this
document. When the V flag is set, it indicates this link is a L2
virtual member link.
The Resource Identifier (ResID) sub-TLV is used to describe to which
resource group a particular member links belongs to.
A global-significant Resource Identifier (ResID) is introduced to
identify a resource group which is the collection of all the network
resources allocated to a transport network slice.
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The format of Resource Identifier sub-TLV is as below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Resource Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
o Type: TBD
o Length: 12 octets.
o Flags: 16 bit flags. All the bits are reserved, which MUST be set
to 0 on transmission and ignored on receipt.
o Reserved: this field is reserved for future use. MUST be set to 0
on transmission and ignored on receipt.
o Bundle Member Link Local Identifier: A 32-bit local identifier of
a member link. The link can be physical or virtual.
o Resource Identifier: A 32-bit global-significant identifier to
identify the resource group this member link belongs to.
3.3. Inter-Domain Topology and Resource Information Advertisement
[I-D.ietf-idr-bgpls-segment-routing-epe] defines the BGP-LS
extensions for advertisement of BGP Peering Segments and the peering
topology information between ASes. Such information could be used by
a network controller for the computation and instantiation of inter-
AS traffic engineering SR paths.
In some scenarios, transport network slices which spans multiple ASes
need to be created. The inter-domain network slices may have
different inter-domain connectivity, and may be associated with
different set of network resources in each domain and on the inter-
domain links. In order to build the inter-domain transport network
slices using segment routing, it is necessary to advertise the
topology and resource attribute of the inter-domain links and the
associated BGP Peering Segments.
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Depending on the requirement of inter-domain network slices,
different levels of isolation on the inter-domain connection can be
achieved:
o One EBGP session between two ASes can be established over several
underlying links. In this case, different underlying links can be
used for different inter-domain transport network slices which
requires hard isolation between each other. In another similar
case, the EBGP session is established over a single link, while
the resource on this link can be splited into several pieces, each
of which can be considered as a virtual member link. In both
cases, different BGP Peer-Adj-SIDs are allocated to each
underlying physical or virtual link, and the ASBRs SHOULD
advertise the transport network slice identifiers associated with
each BGP Peer-Adj-SID.
o For inter-domain connection between two ASes, multiple EBGP
sessions can be established between different peering ASBRs. It
is possible that some of these BGP sessions are used for one
inter-domain transport network slice, while some other BGP
sessions are used for another inter-domain transport network
slice. Different BGP peer-node-SIDs are allocated to each BGP
session, and ASBR SHOULD advertise the information of topology
identifiers associated with different BGP Peer-node-SIDs.
o Different inter-domain transport network slices can have different
inter-domain connectivity at the AS level. Different BGP Peer-
Set-SID can be allocated to represent the groups of BGP peers
which can be used for load-balancing in each transport network
slice.
The detailed protocol extensions for advertising the inter-domain
network slice information will be specified in a future version.
4. Security Considerations
This document introduces no additional security vulnerabilities to
BGP-LS.
The mechanism proposed in this document is subject to the same
vulnerabilities as any other protocol that relies on BGP-LS.
5. IANA Considerations
TBD
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6. Acknowledgments
The authors would like to thank Shunwan Zhuang for the review and
discussion of this document.
7. References
7.1. Normative References
[I-D.dong-lsr-sr-enhanced-vpn]
Dong, J. and S. Bryant, "IGP Extensions for Segment
Routing based Enhanced VPN", draft-dong-lsr-sr-enhanced-
vpn-01 (work in progress), October 2018.
[I-D.dong-spring-sr-for-enhanced-vpn]
Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., and
Z. Li, "Segment Routing for Enhanced VPN Service", draft-
dong-spring-sr-for-enhanced-vpn-05 (work in progress),
October 2019.
[I-D.ietf-idr-bgp-ls-segment-routing-ext]
Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
and M. Chen, "BGP Link-State extensions for Segment
Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16
(work in progress), June 2019.
[I-D.ietf-idr-bgpls-segment-routing-epe]
Previdi, S., Talaulikar, K., Filsfils, C., Patel, K., Ray,
S., and J. Dong, "BGP-LS extensions for Segment Routing
BGP Egress Peer Engineering", draft-ietf-idr-bgpls-
segment-routing-epe-19 (work in progress), May 2019.
[I-D.ietf-teas-enhanced-vpn]
Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
Framework for Enhanced Virtual Private Networks (VPN+)
Service", draft-ietf-teas-enhanced-vpn-03 (work in
progress), September 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5029] Vasseur, JP. and S. Previdi, "Definition of an IS-IS Link
Attribute Sub-TLV", RFC 5029, DOI 10.17487/RFC5029,
September 2007, <https://www.rfc-editor.org/info/rfc5029>.
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[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
7.2. Informative References
[I-D.ietf-idr-bgpls-srv6-ext]
Dawra, G., Filsfils, C., Talaulikar, K., Chen, M.,
daniel.bernier@bell.ca, d., and B. Decraene, "BGP Link
State Extensions for SRv6", draft-ietf-idr-bgpls-
srv6-ext-01 (work in progress), July 2019.
[I-D.ietf-lsr-flex-algo]
Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex-
algo-04 (work in progress), September 2019.
[I-D.ietf-lsr-isis-srv6-extensions]
Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
Z. Hu, "IS-IS Extension to Support Segment Routing over
IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-03
(work in progress), October 2019.
[NGMN-NS-Concept]
"NGMN NS Concept", 2016, <https://www.ngmn.org/fileadmin/u
ser_upload/161010_NGMN_Network_Slicing_framework_v1.0.8.pd
f>.
[TS23501] "3GPP TS23.501", 2016,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3144>.
[TS28530] "3GPP TS28.530", 2016,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3273>.
Authors' Addresses
Jie Dong
Huawei Technologies
Email: jie.dong@huawei.com
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Zhibo Hu
Huawei Technologies
Email: huzhibo@huawei.com
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