CCAMP Working Group X. Zhang, Ed. Internet-Draft Huawei Technologies Intended status: Informational A. Sharma, Ed. Expires: January 08, 2017 Infinera S. Belotti Nokia T. Cummings Ericsson July 07, 2016 YANG Models for the Northbound Interface of a Transport Network Controller: Requirements and Gap Analysis draft-zhang-ccamp-transport-yang-gap-analysis-00 Abstract A transport network is a lower-layer network designed to provide connectivity services for a higher-layer network to carry the traffic opaquely across the lower-layer network resources. A transport network may be constructed from equipment utilizing any of a number of different transport technologies such as the evolving optical transport infrastructure (Synchronous Optical Networking (SONET) / Synchronous Digital Hierarchy (SDH) and Optical Transport Network (OTN)) or packet transport as epitomized by the MPLS Transport Profile (MPLS-TP). All transport networks have high benchmarks for reliability and operational simplicity. This suggests a common, technology- independent management/control paradigm that can be extended to represent and configure specific technology attributes. This document describes the high-level requirements facing transport networks in order to provide open interfaces for resource programmability and control/management automation. Furtheremore, gap analysis against existing models are also provided so that it can used as the guidance to separate efforts/drafts proposing new models or augmentation models based on existing models. 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 http://datatracker.ietf.org/drafts/current/. Zhang, et al. Expires January 8, 2017 [Page 1] Internet-Draft Transport NBI Gap Analysis July 2016 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 January 8, 2017. Copyright Notice Copyright (c) 2016 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 (http://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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. High-level Modeling Requirements . . . . . . . . . . . . . . 5 3.1. Generic Requirements . . . . . . . . . . . . . . . . . . 5 3.2. Transport Network and TE Topology Requirements . . . . . 5 3.2.1. Topological Link Requirements . . . . . . . . . . . . 6 3.2.2. Topology Node Requirements . . . . . . . . . . . . . 6 3.2.3. Termination Point Requirements . . . . . . . . . . . 6 3.3. Transport Service Requirements . . . . . . . . . . . . . 6 3.4. Tunnel/LSP Requirements . . . . . . . . . . . . . . . . . 7 4. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.1. Single-domain Scenario . . . . . . . . . . . . . . . . . 7 4.2. Multi-domain Scenario . . . . . . . . . . . . . . . . . . 9 4.3. Multi-layer Scenario . . . . . . . . . . . . . . . . . . 11 4.4. Function Summary and Related YANG Models . . . . . . . . 11 5. Function Gap Analysis on YANG Model Level . . . . . . . . . . 12 5.1. Topology Related Functions . . . . . . . . . . . . . . . 12 5.1.1. Obtaining Access Point Info . . . . . . . . . . . . . 13 5.1.2. Obtaining Topology . . . . . . . . . . . . . . . . . 13 5.1.3. Virtual Network Operations . . . . . . . . . . . . . 13 5.2. Tunnel Operations . . . . . . . . . . . . . . . . . . . . 13 5.3. Service Requests . . . . . . . . . . . . . . . . . . . . 14 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 7. Security Considerations . . . . . . . . . . . . . . . . . . . 14 Zhang, et al. Expires January 8, 2017 [Page 2] Internet-Draft Transport NBI Gap Analysis July 2016 8. Manageability Considerations . . . . . . . . . . . . . . . . 15 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 10. Contributing Authors . . . . . . . . . . . . . . . . . . . . 15 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 11.1. Normative References . . . . . . . . . . . . . . . . . . 16 11.2. Informative References . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 1. Introduction A transport network is a server-layer network designed to provide connectivity services, or more advanced services like Virtual Private Networks (VPN) for a client-layer network to carry the client traffic opaquely across the server-layer network resources. It acts as a pipe provider for upper-layer networks, such as IP network and mobile networks. Transport networks, such as Synchronous Optical Networking (SONET) / Synchronous Digital Hierarchy (SDH), Optical Transport Network (OTN), Wavelength Division Multiplexing (WDM), and flexi-grid networks, are often built using equipment from a single vendor and are managed using proprietary interfaces to dedicated Element Management Systems (EMS) / Network Management Systems (NMS). All transport networks have high benchmarks for reliability and operational simplicity. This suggests a common, technology-independent management/control paradigm that is extended to represent and configure specific technology attributes. Network providers need a common way to manage multi-vendor and multi- domain transport networks (where each domain is an island of equipment from a single supplier) and this requirement has been further stressed by the expansion in network size. At the same time, applications such as data center interconnection require larger and more dynamic connectivities. Therefore, transport networks face new challenges going beyond automatic provisioning of tunnel setup enabled by GMPLS (Generalized Multi-Protocol Label Switching) protocols to achieve automatic service provisioning, as well as address opportunities enabled by partitioning the transport network through the process of resource slicing. With a reduction in operational expenditure (OPEX) and capital expenditure (CAPEX) as the usual objectives, a common interface to transport network controllers are considered by network providers as a way to meet the requirements. The concept of Software Defined Networking (SDN) leverages these ideas. The YANG language [RFC6020] is currently the data modeling language of choice within the IETF and has been adopted by a number of industry-wide open management and control initiatives. YANG may be Zhang, et al. Expires January 8, 2017 [Page 3] Internet-Draft Transport NBI Gap Analysis July 2016 used to model both configuration and operational states; it is vendor-neutral and supports extensible APIs for control and management of elements. This document first specifies the scope and provides high-level requirements for transport network open interface modelling. Furthermore, detailed gap analysis of the typical scenarios with the existing model are provided. Thus, this document can used as a reference of existing models, and provides information of the missing ones which suggest further work. 2. Scope For this draft, we use the domain controller as the reference point, with South Bound Interface (SBI) to the transport devices and North Bound Interface (NBI) to the orchestrator. Transport networks have been evolving and deploying for decades, making them very heterogeneous. New and legacy transport devices support many of interface protocols like Path Computation Element Protocol (PCEP), TL1, SNMP, CLI, XML, NETCONF, Openflow etc. Domain controllers interfacing with transport devices need to support these protocols on its SBI, making the southbound fragmented. Domain controllers abstract the fragmented southbound view for its northbound clients by normalizing the NBI across various technologies, protocols, and vendors. The focus of this document is not to go into various southbound protocols to interface with the transport devices. Instead, this document focuses on the models that can be used by the domain controller and the orchestrator for various use cases identified in later sections of this document. This document analyzes IETF models for various use cases, such as single- domain network, multi-domain network, multi-layer network, etc. to identify any modeling gaps. YANG models are currently developed not only in IETF, but also in other Standard Development Organizations (SDO) such as ONF and MEF, which can be used on the interfaces of a domain controller and an orchestrator. Each domain controller and orchestrator can use models developed by different SDOs. Therefore it is important to ensure that deployment use cases and related funcionalities are supported by all models to allow a seamless translation/mediation between systems using different models. If the Abstraction and Control of Traffic-Engineered Networks (ACTN) defined in [I-D.ceccarelli-teas-actn-framework] is used as a reference architcture, then the focus is equivalent to MPI (MDSC-PNC Interface) and CMI (CNC-MDSC Interface). Zhang, et al. Expires January 8, 2017 [Page 4] Internet-Draft Transport NBI Gap Analysis July 2016 3. High-level Modeling Requirements This section covers various high-level modeling requirements for transport networks. 3.1. Generic Requirements The following are generic requirements for Transport models: o User Intent: Transport models should maintain separation between high level user intent and the operational state of the network. For e.g., maintain separation between user service request, including all constraints, and the actual service and connection state in the network. o State Management: Network and service objects should support the following states: administrative state, operational state, and lifecycle state. Administrative state and operational states are well understood. Lifecycle state is defined in the ONF to model the following entity lifecylce states: planned state, potential state, installed state, in conflict state, and pending removal state. o Identifiers: Network and service objects should support the following identifier: * ID: A unique entity ID provided by the controller. The identifier SHOULD be chosen such that the same entity in a real network topology will always be identified through the same ID, even if the model is instantiated in separate datastores. Controller may choose to capture semantics in the identifier, for example to indicate the type of entity and/or the type of the parent identity. * Name: A unique name provided by the client for the entity. The name can be modified, if required, by the client. * User Labels: A list of freeform strings that can be used as alias for the entity by the client. Multiple user labels are permitted for the entity, and client can edit these user labels. User labels do not need to be unique. 3.2. Transport Network and TE Topology Requirements Zhang, et al. Expires January 8, 2017 [Page 5] Internet-Draft Transport NBI Gap Analysis July 2016 3.2.1. Topological Link Requirements The model should support the following Topological Links: o Physical Links o Abstract Links [I-D.ietf-teas-interconnected-te-info-exchange] o Compound Link which are are internally aggregated lower level links o Access Links which connect the router port to the client port of the transport system o Transitional Links which provide adaptation capability between layers within a network element The Link should support various link related attributes like cost, latency, capacity, risk characteristics (including shared risk). The model should provide clear association between Link and its topology (including virtual topology), nodes and termination points. The model should provide association between the Link and any underlay circuit / service supporting the Link. 3.2.2. Topology Node Requirements The model should support the following Topology Node: o Physical Node o Abstract Node o Chassis / Forwarding Domain [Editors' note: more details will be added later.] 3.2.3. Termination Point Requirements [Editors' note: this will be added later.] 3.3. Transport Service Requirements [Editors' note: this will be added later.] Zhang, et al. Expires January 8, 2017 [Page 6] Internet-Draft Transport NBI Gap Analysis July 2016 3.4. Tunnel/LSP Requirements [Editors' note: this will be added later.] 4. Scenarios There are several scenarios (a.k.a., use cases) where an open interface via domain controller to access server-layer (transport) network resources would be useful. Three scenarios are provided and can be used for model instantiation exercise to identify missing pieces of existing models. 4.1. Single-domain Scenario The first scenario is depicted as below (Figure 1 ): Zhang, et al. Expires January 8, 2017 [Page 7] Internet-Draft Transport NBI Gap Analysis July 2016 /--\ +------+ +------+ /--\ | 1 ~~~| A +------------------| B |~~~~~ 3 | \--/ +-----++ +--+---+ \--/ | | | | | | ++-----+ +---+--+ | F +------------+ C | ++-----+ +--+---+ | | | | | | | | | | +---+-+ +---+-+ /---\ | E +---------------+ D |~~~~ 4 | /--\~~~~~+-----+ +-----+ \---/ | 2 | \--/ +----+ /--\ | | Transport NE | | DC +----+ \--/ ----- Transport Link ~~~ Transport-DC link (a) Data Centers interconnected via a transport network +---------------------+ | Data Center Network | | Controller | +---------+-----------+ | | | | Open Interface | | +---------+-----------+ | Transport Network | | Controller | +---------------------+ (b) The controller architecture for data center interconnection Figure 1: Scenario 1: Data centers interconnected via a transport network and the controller architecture Zhang, et al. Expires January 8, 2017 [Page 8] Internet-Draft Transport NBI Gap Analysis July 2016 For the data center operator, as a client of the transport network, assuming the objective is to trigger the transport network to provide connectivity on demand, the following capabilities, at a minimum, would be required on the common interface between the two controllers illustrated in Figure 1: o The ability to obtain information about a set of access points of the transport network, including information such as access point identifiers, capabilities, etc.; for instance, transport-network- side end point identifiers related to the access link between DC1 and Transport NE A. o The capability to send a request for a service using the aforementioned access point information, as well as the ability to retrieve a list of service requests and their statuses. In this request, it should at least be possible to include source node, destination node, and requested bandwidth to request the transport network to set up tunnels/paths so as to provide the requested connectivitiy for the service request. o Note that in this case, the acquisition of the topology, be it physical or logical, of the transport network is not a compulsory requirement, but it may indeed be able to give data center providers more control over the transport resource usage. Furtheremore, the client controller can impose a virtual network of its own choice by requesting a slice of network resource with its choice of network parameters (such as network topology type, bandwidth etc.). 4.2. Multi-domain Scenario The second scenario, more complicated than the first, is depicted as below (Figure 2). In this example, we focus on the management and control via common interfaces for multi-domain networks with homogeneous technologies (such as OTN), but it can be extended further to multi-domain networks with heterogeneous technologies with higher complexity. Zhang, et al. Expires January 8, 2017 [Page 9] Internet-Draft Transport NBI Gap Analysis July 2016 +-------------------------------------------------+ | Orchestrator/Coordinator | +---------+--------------+-------------------+----+ | | | | | | +------------+--+ | +----------+----------+ | Controller 1 | | | Controller 2 | +---------+-----+ | +-------+-------------+ # +----------------+ # #Qx | Controller 3 | # # +----------------+ #TL1 # # # ----+----- # ----+----- ____/ \____ # ____/ \____ | | # | | | | # | | | Network Domain +***********+ Network Domain | | 1 | # | 2 | |____ ___| # |____ ___| \ / #PCEP \ / ----------- # *---------- * * # * * * * # * * * * # * * * * # * * * * # * * * * # * * * *----+-----* * * ____/ \____ * *| |* | | | Network Domain | | 3 | |____ ___| \ / ---------- ***** inter-domain links ----- Open Interfaces ##### Controller-device interfaces Figure 2: Scenario 2: Multi-domain network control and management For the second scenario, the orchestrator controls and manages three distinct network domains, each controlled/managed by their domain controller. This scenario is of interest not only to transport-only Zhang, et al. Expires January 8, 2017 [Page 10] Internet-Draft Transport NBI Gap Analysis July 2016 networks, but also to heretegenous network orchestration such as coordinating the transport, the radio (5G) and packet core domains. But to keep the functions explanation later accurate, only transport- only multi-domain networks are considered. In order to orchestrate across domains/layers, besides the capabilities mentioned for the first scenario, the orchestrator needs its interface between domain controllers to be equipped with the following additional functions: o Access to the topologies reported by each domain controller, including cross-domain links for the purpose of planning and requesting the paths of end-to-end tunnels. Multiple technologies within a domain (i.e., a multi-layer network), this might be reflected in the reported topology. Depending on the abstraction level of the reported topology, the orchestrator has different control granularities. o Alterntively, the capability for the orchestrator to request "path computation" to a domain controller in order to create an end-to- end tunnel stitched together by different connection contribution obtained by consulting to each domain controller. o The ability to set up, delete and modify tunnels, be it within one domain or across multiple domains. Furthermore, it should have the abilty to view the tunnels created within each domain as well as those that cross domains as reported by each domain controller. 4.3. Multi-layer Scenario [Editors' note: to be added later.] 4.4. Function Summary and Related YANG Models For the common interface of a transport controller towards a northbound client, five functions are derived from the scenarios explained in the last section. They are summarized in the table below and we also match these functions with YANG models that are being developed in existing drafts. Zhang, et al. Expires January 8, 2017 [Page 11] Internet-Draft Transport NBI Gap Analysis July 2016 +-------------+-----------------------+-----------------------+ | Functions | Description | Related Existing | | | | YANG Models | |-------------+-----------------------+-----------------------+ | Obtaining |Getting the necessary | | | Access |access points info | [TE-Topo] | | Point Info | | | +-------------+-----------------------+-----------------------+ | Obtaining |Getting the topology |[TE-Topo], [WDM-Topo] | | Topology |info |[ODU-Topo] | +-------------+-----------------------+-----------------------+ | Tunnel |Tunnel Setup, Deletion | | | Operations |Modification and Info | [TE-Tunnel] | | |Retrieval | | +-------------+-----------------------+-----------------------+ | Service |Requesting connectivity| | | Request |service and retrieval | NONE | | |the list of service | | | |request | | +-------------+-----------------------+-----------------------+ |Path Comp. | Path Computation pre | | | | service provisioning | NONE | +-------------+-----------------------+-----------------------+ | Virtual |Requesting a virtual | | | Network |network and related |[TE-Topo], [WDM topo] | | Operations |control operations, |[ODU-Topo] | | |(e.g.,update, deletion)| | +-------------+-----------------------+-----------------------+ Analysis and descriptions of whether and how these functions are supported by the YANG models are provided in more detail in Section 5. 5. Function Gap Analysis on YANG Model Level 5.1. Topology Related Functions As shown in the previous section, the functions of obtaining access point information, obtaining topology, and imposing virtual network operations can take advantages of the same set of topology YANG models. These functions are briefly explained further in the following sub-sections. Zhang, et al. Expires January 8, 2017 [Page 12] Internet-Draft Transport NBI Gap Analysis July 2016 5.1.1. Obtaining Access Point Info For cases such as scenario 1, a client may have no interest in directly controlling network resources, but might want an automated common control interface for initiating service requests. In this case, a transport domain controller may provide the access point information. This information can then be used in service request sent over the common interface. The TE Topology YANG model provided in [TE-topo] [I-D.ietf-teas-yang-te-topo] can be used to provide a list of links. If the remote node and termination point information is unknown, it is omitted from the reported information. If the client-side node and termination point information is obtained via configuration or a distributed discovery mechanism, then it can also be added into the reported information. Technology-specific details might also be needed to further express the constraints/attributes associated with the access points. Note that all of this information is usually read only. 5.1.2. Obtaining Topology Refer to [I-D.ietf-teas-yang-te-topo] for explanations and examples on how to obtain the topology. For technology specific topology information, other models such as those provided in [WDM-Topo] [I-D.ietf-ccamp-wson-yang] and [ODU-Topo] [I-D.zhang-ccamp-l1-topo-yang] may be used. 5.1.3. Virtual Network Operations There are two ways to request the creation of a virtual network. One is to define the topology explicitly using the model provided in the topology YANG drafts listed in previous section. The other way is to provide an estimated traffic information (a traffic matrix) and ask for a domain controller of the provider network to provide a virtual network that can fulfill the demand. This second approach does not have a supporting model and need further work. 5.2. Tunnel Operations The current [TE-Tunnel] [I-D.ietf-teas-yang-te] provides a technology agnostic Traffic-Engineered (TE) device tunnel. The model included in that draft is currently being developed to make it generic for both controller and device usage. In the latest version, it already provides such a generic TE tunnel model that can cater to the base requirementss for tunnel operations but it may need to be augmented to support controller-specific operations. Zhang, et al. Expires January 8, 2017 [Page 13] Internet-Draft Transport NBI Gap Analysis July 2016 Furthermore, technology-specific augmentations of the base generic TE tunnel models are needed. For example, for Optical Channel (OCh) (note: ITU is updating this term as OTSi.) tunnels in WDM networks, information such as the lambda resource usage is needed. Similarly, for ODU tunnels, information such as ODU-specific client signal, tributary slot information etc. is needed. 5.3. Service Requests The service model is an important model that enables automated operations between a client controller or an orchestrator and a domain controller. The transport connectivity service model is different from the model of a tunnel since the transport connectivity service model hides technical details from a client. 6. IANA Considerations This document requests no IANA actions. 7. Security Considerations Clearly modifying server-layer resources will have a significant impact on network infrastructure. More specifically they will provide the services and applications running across client-layers, which the server-layer is supporting. Therefore, security must be an important consideration when implementing the architecture, models and protocol mechanisms discussed in this document. Communicating service and network information (including access point identifiers, capabilities, topologies, etc.) across external interfaces represents a security risk. Thus, mechanisms to encrypt or preserve the domain topology confidentiality should be used. A key consideration are the external protocols (those shown as entering or leaving the orchestrator and controllers shown in Figure 2 (Scenario 2: Multi-domain network control and management)) which must be appropriately secured. This security should include authentication and authorization to control access to different functions that the orchestrator may perform to modify or create state in the server-layer, and the establishment and management of the orchestrator to controller relationship. The orchestrator will contain significant data about the network domains, the services carried by each domain, and customer type information. Therefore, access to information held in the orchestrator must be secured. Since such access will be largely through external mechanisms, it may be pertinent to apply policy- based controls to restrict access and functions. Zhang, et al. Expires January 8, 2017 [Page 14] Internet-Draft Transport NBI Gap Analysis July 2016 8. Manageability Considerations The core objectives of this document are to assist in the deployment and operation of transport services across server-layer network infrastructure. The model-driven management/control principles, which are vendor-neutral and supported by extensible APIs, should be utilized. The open models described in this document are based on YANG [RFC6020] and the RESTCONF [RESTCONF] messaging protocol, a REST-like protocol running over HTTP for accessing data defined in YANG, may also be used. 9. Acknowledgements We would like to thank Young Lee, Igor Bryskin and Aihua Guo for their comments and discussions. 10. Contributing Authors The following people all contributed to this document and are listed below: Ruiquan Jing China Telecom Email: jingrq@ctbri.com.cn Yan Shi China Unicom Email: shiyan49@chinaunicom.cn Jeong-dong Ryoo ETRI Email: ryoo@etri.re.kr Yunbin Xu CAICT Email: xuyunbin@ritt.cn Daniel King Lancaster University Email: d.king@lancaster.ac.uk 11. References Zhang, et al. Expires January 8, 2017 [Page 15] Internet-Draft Transport NBI Gap Analysis July 2016 11.1. Normative References [I-D.ietf-netconf-restconf] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", draft-ietf-netconf-restconf-13 (work in progress), April 2016. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, . 11.2. Informative References [I-D.ceccarelli-teas-actn-framework] Ceccarelli, D. and Y. Lee, "Framework for Abstraction and Control of Traffic Engineered Networks", draft-ceccarelli- teas-actn-framework-02 (work in progress), April 2016. [I-D.ietf-ccamp-wson-yang] Lee, Y., Dhody, D., Zhang, X., Guo, A., Lopezalvarez, V., King, D., and B. Yoon, "A Yang Data Model for WSON Optical Networks", draft-ietf-ccamp-wson-yang-01 (work in progress), April 2016. [I-D.ietf-teas-interconnected-te-info-exchange] Farrel, A., Drake, J., Bitar, N., Swallow, G., Ceccarelli, D., and X. Zhang, "Problem Statement and Architecture for Information Exchange Between Interconnected Traffic Engineered Networks", draft-ietf-teas-interconnected-te- info-exchange-07 (work in progress), May 2016. [I-D.ietf-teas-yang-te] Saad, T., Gandhi, R., Liu, X., Beeram, V., Shah, H., Chen, X., Jones, R., and B. Wen, "A YANG Data Model for Traffic Engineering Tunnels and Interfaces", draft-ietf-teas-yang- te-02 (work in progress), October 2015. [I-D.ietf-teas-yang-te-topo] Liu, X., Bryskin, I., Beeram, V., Saad, T., Shah, H., and O. Dios, "YANG Data Model for TE Topologies", draft-ietf- teas-yang-te-topo-04 (work in progress), March 2016. Zhang, et al. Expires January 8, 2017 [Page 16] Internet-Draft Transport NBI Gap Analysis July 2016 [I-D.zhang-ccamp-l1-topo-yang] Zhang, X., Rao, B., and X. Liu, "A YANG Data Model for Layer 1 Network Topology", draft-zhang-ccamp-l1-topo- yang-01 (work in progress), December 2015. Authors' Addresses Xian Zhang (editor) Huawei Technologies F3-5-B R&D Center, Huawei Industrial Base, Bantian, Longgang District Shenzhen, Guangdong 518129 P.R.China Email: zhang.xian@huawei.com Anurag Sharma (editor) Infinera US Email: ansharma@infinera.com Sergio Belotti Nokia Italy Email: sergio.belotti@nokia.com Tara Cummings Ericsson Email: tara.cummings@ericsson.com Zhang, et al. Expires January 8, 2017 [Page 17]