Network Working Group Y. Ma Internet-Draft R. Luo Intended status: Informational China Telecom Expires: 12 January 2023 A. Chan B. Suen China Mobile Hong Kong J. Dong Huawei Technologies Y. Liu China Unicom H. Allahoum Algeria Telecom 11 July 2022 IETF Network Slice Deployment Status and Considerations draft-ma-teas-ietf-network-slice-deployment-01 Abstract Network Slicing is considered as an important approach to provide different services and customers with the required network connectivity, network resources and performance characteristics over a shared network. Operators have started the deployment of network slices in their networks for different purposes. This document introduces several deployment cases of IETF network slices in operator networks. Some considerations collected from these IETF network slice deployments are also provided. 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/. Ma, et al. Expires 12 January 2023 [Page 1] Internet-Draft IETF Network Slice Deployment July 2022 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 12 January 2023. Copyright Notice Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. IETF Network Slice Deployment Status . . . . . . . . . . . . 3 2.1. China Telecom Ningxia . . . . . . . . . . . . . . . . . . 3 2.2. China Mobile Hong Kong . . . . . . . . . . . . . . . . . 4 2.3. China Unicom Hebei . . . . . . . . . . . . . . . . . . . 4 2.4. Algeria Telecom . . . . . . . . . . . . . . . . . . . . . 4 3. IETF Network Slice Deployment Cases . . . . . . . . . . . . . 4 3.1. Network Slicing for Multi-Industrial Network . . . . . . 4 3.2. Network Slicing for Fixed-Mobile Convergence . . . . . . 6 3.3. Network Slicing for Government Affairs Separation . . . . 8 3.4. Network Slicing for Live Video Service . . . . . . . . . 9 4. Network Slice Deployment Considerations . . . . . . . . . . . 11 4.1. Isolation . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2. Topology and Connection Types . . . . . . . . . . . . . . 12 4.3. Scalability . . . . . . . . . . . . . . . . . . . . . . . 12 4.3.1. Data Plane Scalability . . . . . . . . . . . . . . . 12 4.4. Automation . . . . . . . . . . . . . . . . . . . . . . . 13 4.5. Hierarchical Network Slicing . . . . . . . . . . . . . . 13 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 13 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 9.1. Normative References . . . . . . . . . . . . . . . . . . 14 9.2. Informative References . . . . . . . . . . . . . . . . . 15 Ma, et al. Expires 12 January 2023 [Page 2] Internet-Draft IETF Network Slice Deployment July 2022 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 1. Introduction Network Slicing is considered as an important mechanism to provide different services and customers with the required network connectivity, resources and performance characteristics over a shared network. [I-D.ietf-teas-ietf-network-slices] describes network slicing in the context of networks built from IETF technologies, and discusses the general framework of IETF network slices. [I-D.ietf-teas-ietf-network-slices] also introduces the concept Network Resource Partition (NRP) as a set of network resources that are available to carry traffic and meet the SLOs and SLEs. [I-D.ietf-teas-enhanced-vpn] describes the framework and candidate component technologies for providing enhanced VPN services, by utilizing an approach that is based on existing VPN and Traffic Engineering (TE) technologies and adds characteristics that specific services or customers require above traditional overlay VPNs. VPN+ is delivered using a VPN overlay and an underlying Virtual Transport Network (VTN) which has a set of dedicated or shared resources and is associated with a customized logical network topology in the underlay network. A centralized network controller can be used for the creation and operation of the VTNs, and the mapping of the enhanced VPN services to the appropriate VTNs. The enhanced VPN (VPN+) mechanism can be used for the realization of IETF network slices. VTN and NRP are considered as similar concepts, and NRP can be seen as an instantiation of VTN in the context of network slicing. Although the concept of network slicing is firstly introduced for the 5G, the use cases of IETF network slices are not limited to 5G. Operators have started the deployment of IETF network slices based on VPN+ in their networks for different service scenarios. This document introduces several deployment cases of IETF network slices in operator networks. Some considerations about the IETF network slice deployments are also collected. 2. IETF Network Slice Deployment Status 2.1. China Telecom Ningxia Service scenario: Multiple industrial services Resource partitioning: Virtual sub-interface with dedicated bandwidth Data Plane: SRv6 Ma, et al. Expires 12 January 2023 [Page 3] Internet-Draft IETF Network Slice Deployment July 2022 Control plane: SR Policy with link affinity 2.2. China Mobile Hong Kong Service scenario: Fixed-Mobile convergence services Resource partitioning: Flexible Ethernet interface and virtual sub- interface with dedicated bandwidth Data plane: SR-MPLS Control Plane: SR Policy with link affinity 2.3. China Unicom Hebei Service scenario: Multiple type of services Resource partitioning: Flexible Ethernet interface Data Plane: SRv6 Control Plane: SR Policy with link affinity 2.4. Algeria Telecom Service scenario: Live Video and other services Data Plane: SRv6 with NRP-ID Control plane: SR Policy with NRP-ID 3. IETF Network Slice Deployment Cases 3.1. Network Slicing for Multi-Industrial Network China Telecom has deployed a dedicated SRv6 based network in Ningxia to carry multiple industrial services. The three major types of service in the network are: Healthcare service, Education service and Broadband services, and the operator plans to migrate a set of industrial and governmental services from dedicated private networks or Multi-Service Transport Platform (MSTP) networks to this IP based multi-industrial network. With the help of network slicing, services of different industries can be isolated from each other, so that the performance of each service can be guaranteed, and the cost of maintaining and expanding the dedicated private networks for each industry can be reduced. Ma, et al. Expires 12 January 2023 [Page 4] Internet-Draft IETF Network Slice Deployment July 2022 In order to provide the required resource and security isolation between the health care, education and broadband services, three NRPs are created in the network. All the NRPs share the same IGP instance, while each NRP is defined with a logical topology using different link administrative groups (i.e. color), and is allocated with a set of dedicated bandwidth resources on each involved physical link using the virtual sub-interface mechanism. In an NRP, each link is assigned with a SRv6 End.X SID to identify the sub-interface used for packet forwarding. With more industrial and governmental customers migrate to this network, more NRPs with dedicated network resources will be created. Multiple L3VPNs belonging to the same industry are provisioned in the corresponding NRP. For example, the NRP created for the health care services is used to support the VPNs for the connection between hospitals belonging to the medical consortium, and the VPNs for connecting the hospitals and the insurance systems in the healthcare cloud. The VPN traffic mapped to a NRP is steered into the set of virtual sub-interfaces of the NRP based on the corresponding SRv6 End.X SIDs. A centralized network controller is responsible for the management of the NRP and the VPNs. This includes the topology and resource planning of NRP, the NRP creation, the mapping of VPN services to the NRP, and the computation of SRv6 TE paths based on the service constraints and the topology and resource attributes of the NRP. The controller also collects the traffic statistics and performance information of the NRPs and the VPN services to enable the network slice services visualization and ensure the service SLAs are always met. Ma, et al. Expires 12 January 2023 [Page 5] Internet-Draft IETF Network Slice Deployment July 2022 +-------------------+ Centralized | Network Controller| Control & Management +-------------------+ /\ || \/ ________________________ VPN-1 o----/ o----o----o----o----o /----o VPN-2 o----/ / / / /----o NRP-1 VPN-3 o----/ o----o----o----o----o /----o Healthcare /_______________________/ ________________________ VPN-4 o----/ o----o----o----o----o /----o / / / / / NRP-2 VPN-5 o----/ o----o----o----o----o /----o Education /_______________________/ _________________________ VPN-6 o----/ o----o----o----o----o /----o VPN-7 o----/ / / / /----o NRP-3 VPN-8 o----/ o----o----o----o----o /----o Broadband /________________________/ .... _________________________ VPN-m o----/ ... /----o NRP-n /________________________/ Vertical Figure 1. IETF network slice deployment in China Telecom Ningxia 3.2. Network Slicing for Fixed-Mobile Convergence China Mobile Hong Kong (CMHK) has deployed network slices in their SR-MPLS based Fixed-Mobile Convergence (FMC) network, which is used to carry the mobile services, the enterprise private line services and the residential broadband services together. Each type of service has different traffic characteristics and performance requirements, thus independent network planning and operation for each service type is required. Ma, et al. Expires 12 January 2023 [Page 6] Internet-Draft IETF Network Slice Deployment July 2022 Currently three NRPs are created for mobile service, enterprise service and the residential service respectively. Depends on the new service requirement of 5G, More NRPs may be created for 5G critical services in the future. According to the operator's network planning, each NRP is allocated with a set of dedicated bandwidth resources using either virtual sub-interface or Flexible Ethernet (FlexE) interface mechanism. All the NRPs share the same IGP instance, while the links belonging to different NRPs are assigned with different link administrative groups (i.e. color). In a NRP, each link is assigned with an SR-MPLS Adj-SID to identify the sub- interface or FlexE interface used for packet forwarding. Multiple VPNs (EVPN, L3VPN and L2VPN) belonging to the one of the three major service types are mapped to the corresponding NRP. For example, the NRP created for the enterprise private line services is used to support the VPNs of a group of enterprise customers. The VPN traffic mapped to a NRP is steered into the set of virtual sub- interfaces or FlexE interfaces allocated to the NRP based on the corresponding SR-MPLS Adj-SIDs. A centralized network controller is responsible for the management of the NRP and the VPNs. This includes the topology and resource planning of NRP, the NRP creation, the mapping of VPN services to the NRP, and the computation of SRv6 TE paths based on the service constraints together with the topology and resource attributes of the NRP. The controller also collects the traffic statistics and performance information of the NRPs and the VPN services to enable the network slice services visualization and ensure the service SLAs are always met. Ma, et al. Expires 12 January 2023 [Page 7] Internet-Draft IETF Network Slice Deployment July 2022 +-------------------+ Centralized | Network Controller| Control & Management +-------------------+ /\ || \/ ________________________ VPN-1 o----/ o----o----o----o----o /----o VPN-2 o----/ / / / /----o NRP-1 VPN-3 o----/ o----o----o----o----o /----o Mobile /_______________________/ ________________________ VPN-4 o----/ o----o----o----o----o /----o VPN-5 o----/ / / / /----o NRP-2 VPN-6 o----/ o----o----o----o----o /----o Enterprise /_______________________/ __________________________ VPN-7 o----/ o----o----o----o----o /----o VPN-8 o----/ / / / /----o NRP-3 VPN-9 o----/ o----o----o----o----o /----o Residential /________________________/ Figure 2. IETF network slice deployment in CMHK 3.3. Network Slicing for Government Affairs Separation China Unicom has deployed an SRv6 based cloud network in Hebei for the transport of multiple types of services, including 5G mobile services, government affair service, business private line services and broadband service. In order to meet the performance and isolation requirement of different type of services, four NRPs are provisioned in the network. All the NRPs share the same IGP instance, while each NRP is defined with a logical topology using different link administrative groups (i.e. color), and is allocated with a set of dedicated bandwidth resources on each involved physical link using FlexE. In an NRP, each FlexE client interface is assigned with a SRv6 End.X SID to steer packets to the set of link resources allocated to the NRP. Ma, et al. Expires 12 January 2023 [Page 8] Internet-Draft IETF Network Slice Deployment July 2022 According to the service requirement, one or multiple EVPN instances are provisioned for each type of service, and are mapped to the corresponding NRP. For example, an NRP created for the government affair service is used to support the VPNs for the connection between government institution in different cities and towns, and the VPNs for connecting the government institution with the government affair cloud. Based on SRv6 Policy, VPN traffic is steered into a SRv6 TE path which comprises of the FlexE client interfaces of the NRP according to the corresponding SRv6 SID list. +-------------------+ Centralized | Network Controller| Control & Management +-------------------+ /\ || \/ ________________________ VPN-1 o----/ o----o----o----o----o /----o NRP-1 VPN-2 o----/ / / / /----o Government VPN-3 o----/ o----o----o----o----o /----o affairs /_______________________/ ________________________ VPN-4 o----/ o----o----o----o----o /----o / / / / / NRP-2 VPN-5 o----/ o----o----o----o----o /----o 5G mobile /_______________________/ _________________________ VPN-6 o----/ o----o----o----o----o /----o NRP-3 VPN-7 o----/ / / / /----o Business VPN-8 o----/ o----o----o----o----o /----o private lines /________________________/ .... _________________________ VPN-m o----/ ... /----o NRP-0 /________________________/ Broadband Figure 3. IETF network slice deployment in China Unicom Hebei 3.4. Network Slicing for Live Video Service Algeria Telecom has deployed an SRv6 based metro network. The recent requirement is to deliver live video broadcast service for sports games, and the related intranet services and internet services together happening on the same sites, the SLA requirement of each type of service is different. There are also existing services which need to coexist with these three types of services. Ma, et al. Expires 12 January 2023 [Page 9] Internet-Draft IETF Network Slice Deployment July 2022 In order to meet the performance and isolation requirement of these type of services, four NRPs are provisioned in the network: * NRP-1 for live video services * NRP-2 for intranet services * NRP-3 for internet services * NRP-0 for other services +-------------------+ Centralized | Network Controller| Control & Management +-------------------+ /\ || \/ ________________________ o----/ o----o----o----o----o /----o VPN-1 o----/ / / / /----o NRP-1 o----/ o----o----o----o----o /----o Video /_______________________/ ________________________ o----/ o----o----o----o----o /----o VPN-2 / / / / / NRP-2 o----/ o----o----o----o----o /----o Intranet /_______________________/ _________________________ o----/ o----o----o----o----o /----o NRP-3 VPN-3 o----/ / / / /----o Internet o----/ o----o----o----o----o /----o /________________________/ .... _________________________ VPN-m o----/ o----o----o----o----o /----o NRP-0 ... o----/ / / / /----o Default VPN-n o----/ o----o----o----o----o /----o /________________________/ Figure 4. IETF network slice deployment in Algeria Telecom All these NRPs share the same IGP instance, while each NRP is allocated with a subset of dedicated network resources. On each physical link which participates in an NRP, a set of link bandwidth is allocated using FlexE, and the FlexE client interface is associated with the NRP-ID. Ma, et al. Expires 12 January 2023 [Page 10] Internet-Draft IETF Network Slice Deployment July 2022 According to the service requirement, one or multiple L2 or L3 EVPN instances are provisioned for each type of service, and are mapped to the corresponding NRP. For example, an NRP created for the live video broadcast service is used to support the EVPNs for the connection between the stadiums and the video broadcasting center. A network controller performs the path computation using the topology and resources of the NRP as constraints, and SRv6 Policy is used to provision the SRv6 TE paths associated with each NRP to the ingress nodes, using the mechanism defined in [I-D.dong-idr-sr-policy-nrp]. SRv6 Policy is also used to steer the VPN service traffic to SRv6 paths which could meet the service requirement, For VPN traffic which is steered into an SRv6 Policy in an NRP, in addition to encapsulating the SRv6 SID list, the packet is also encapsulated with the global unique NRP-ID in the IPv6 HBH extension header based on the mechanism defined in [I-D.ietf-6man-enhanced-vpn-vtn-id], and the NRP-ID is used to determine the FlexE client interfaces which are used to forward the traffic mapped to the NRP. 4. Network Slice Deployment Considerations Based on the network slice deployment cases collected in section 2, this section describes some of the operators' considerations about network slice deployment. 4.1. Isolation Network slicing is introduced to operators' network to meet the connectivity and performance requirements of different services or customers. Since many services or customers are migrated from their own dedicated networks to network slices, it is expected that services or customers carried by a network slice will not be affected by any other traffic in the network, thus the resource, policy and security isolation from other services becomes a typical requirement. Operators have considered the usage of several forwarding plane mechanisms, such as FlexE interface or virtual sub-interfaces to allocate different set of network resources for the NRPs used for different services or customers. The services or customers which do not have specific requirement on resource or security isolation may be provisioned as separated VPNs, while these VPNs can be aggregated and mapped to a shared NRP with a set of aggregated network resources. Ma, et al. Expires 12 January 2023 [Page 11] Internet-Draft IETF Network Slice Deployment July 2022 4.2. Topology and Connection Types According to the deployment scenarios of network slices, there can be different requirements on the topology and connection type of the network slices. When a network slice is provided for a particular service type or for a particular industry, the network slice usually covers a network scope similar to the scope of the physical network, and there are usually a large number of end points attached to the network slice, which requires meshed multipoint-to-multipoint connectivity between them. When a network slice is provided for a specific private line service customer, the network slice could have a customized topology covering a portion of the physical network, and usually has a small number of end points attached, in this case the network slice may be expressed as a set of point-to-point connections. The suitable mechanisms to define the topology of the NRP and build the connectivity needed by network slice service streams. For example, the administrative groups (i.e. color) can be used by a centralized controller to specify the topology of a NRP and compute the constraint paths for network slice services in the NRP. The Distributed control plane based mechanism for topology definition and the constraint path computation may be used for network slices which require meshed connectivity between a large number of end points. 4.3. Scalability As shown in several IETF network slice deployments, the number of NRPs at the initial stage can be small (e.g. less than 10). While there are also cases in which hundreds of network slices are needed for industrial and premium private line customers. It is expected that the number of NRPs required in the future could be at the hundreds or even thousands level. Thus the scalability considerations and optimization mechanisms as described in [I-D.dong-teas-nrp-scalability] need to be considered to allow the deployment of a larger number of network slices in the network in future. 4.3.1. Data Plane Scalability The current deployment of network slices are mainly based on SR-MPLS or SRv6 data plane, with which each NRP is allocated with a separate group of SR SIDs, and the SIDs are associated with a group of dedicated network resources [I-D.ietf-spring-resource-aware-segments]. This provides a practical approach to deliver IETF network slices to meet the requirements in the early stage. While with the number of the required NRPs increases, the increasing amount of SR SIDs will bring challenges Ma, et al. Expires 12 January 2023 [Page 12] Internet-Draft IETF Network Slice Deployment July 2022 both to the forwarding tables and to the network management and operation. It is expected that the mechanisms with dedicated NRP-ID encapsulation as defined in [I-D.ietf-6man-enhanced-vpn-vtn-id] could help to reduce the number of SR SIDs needed, and simplify the large scale network slice provisioning and management. 4.4. Automation The centralized network controller plays an important role in the life cycle management of network slices. With the number of network slices increases, it is necessary that the planning, creation, monitoring and the optimization of IETF network slices can be automated to reduce the burden in the network slice management and operation. For example, in a network where multiple IETF network slices are deployed, when the bandwidth utilization of one NRP reaches a specific threshold, there are two possible approaches for the NRP capacity expansion. The first approach is to expand the capacity of the physical network, which usually can take a long time. The second approach is to adjust the resource allocation of different NRPs based on the utilization ratio. The network controller can provide the monitoring and visualization of the resource utilization of the NRPs and VPNs, and gives recommendations about the optimal resource adjustment strategy to the network operation. 4.5. Hierarchical Network Slicing In the beginning of the network slice deployment, a group of network slice services are provisioned in the same NRP for a particular industry or service type, such as an NRP for all the business private line services. While some of customers within an industry or service type may require to have a set of dedicated network resources allocated within the industry or service type based NRP. This brings the requirement of hierarchical network slicing to the operators. Thus it is expected that the deployed network slices can evolve to support hierarchical network slices according to the service demand. 5. IANA Considerations This document makes no request of IANA. 6. Security Considerations TBD 7. Contributors Ma, et al. Expires 12 January 2023 [Page 13] Internet-Draft IETF Network Slice Deployment July 2022 Terence Ho Email: terenceho@hk.chinamobile.com Jimmy Tu Email: jimmytu@hk.chinamobile.com Jonathan Chung Email: jonathanchung@hk.chinamobile.com Kristy Li Email: kristyli@hk.chinamobile.com Tommy Zou: Email:tommyzou@hk.chinamobile.com Zhenbin Li Email: lizhenbin@huawei.com Zhibo Hu Email: huzhibo@huawei.com 8. Acknowledgements The authors would like to thank XXX for his valuable comments. 9. References 9.1. 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-10, 6 March 2022, . [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-12, 30 June 2022, . Ma, et al. Expires 12 January 2023 [Page 14] Internet-Draft IETF Network Slice Deployment July 2022 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . 9.2. Informative References [I-D.dong-idr-sr-policy-nrp] Dong, J., Hu, Z., and R. Pang, "BGP SR Policy Extensions for Network Resource Partition", Work in Progress, Internet-Draft, draft-dong-idr-sr-policy-nrp-00, 3 March 2022, . [I-D.dong-teas-nrp-scalability] Dong, J., Li, Z., Gong, L., Yang, G., Guichard, J. N., Mishra, G., Qin, F., Saad, T., and V. P. Beeram, "Scalability Considerations for Network Resource Partition", Work in Progress, Internet-Draft, draft-dong- teas-nrp-scalability-02, 16 May 2022, . [I-D.ietf-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-ietf-6man-enhanced-vpn-vtn-id-00, 5 March 2022, . [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-04, 5 March 2022, . [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-02, 5 March 2022, . Ma, et al. Expires 12 January 2023 [Page 15] Internet-Draft IETF Network Slice Deployment July 2022 Authors' Addresses Yusong Ma China Telecom Email: mayusong.nx@chinatelecom.cn Rui Luo China Telecom Email: luorui.nx@chinatelecom.cn Alex Chan China Mobile Hong Kong Email: alexckchan@hk.chinamobile.com Ben Suen China Mobile Hong Kong Email: bensuen@hk.chinamobile.com Jie Dong Huawei Technologies Email: jie.dong@huawei.com Yang Liu China Unicom Email: liuyang118@chinaunicom.cn Houcine Allahoum Algeria Telecom Email: allahoum@algerietelecom.dz Ma, et al. Expires 12 January 2023 [Page 16]