NETMOD Working Group M. Wang Internet-Draft Q. Wu Intended status: Standards Track Huawei Expires: April 3, 2019 C. Xie China Telecom September 30, 2018 A YANG Data model for Event Management draft-wwx-netmod-event-yang-00 Abstract This document defines an YANG data model for event management [RFC7950]. The Event YANG provides the ability to monitor state change on the local system or on a remote system and take simple action when a trigger condition on system state is met. 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 April 3, 2019. Copyright Notice Copyright (c) 2018 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 Simplified BSD License text as described in Section 4.e of Wang, et al. Expires April 3, 2019 [Page 1] Internet-Draft Event YANG September 2018 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions used in this document . . . . . . . . . . . . . . 2 2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2 2.2. Tree Diagrams . . . . . . . . . . . . . . . . . . . . . . 3 3. Objectives . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Relationship to YANG PUSH . . . . . . . . . . . . . . . . . . 3 5. Relationship to EVENT MIB . . . . . . . . . . . . . . . . . . 4 6. Model Overview . . . . . . . . . . . . . . . . . . . . . . . 5 7. EVENT YANG Module . . . . . . . . . . . . . . . . . . . . . . 8 8. Security Considerations . . . . . . . . . . . . . . . . . . . 19 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 10. Normative References . . . . . . . . . . . . . . . . . . . . 20 Appendix A. Example of Event . . . . . . . . . . . . . . . . . . 21 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 1. Introduction This document defines an Event YANG data model [RFC7950]. The Event YANG provides the ability to monitor state changes on the local system or on a remote system and take simple action when a trigger condition on system state is met. The data model in this document is designed to be compliant with the Network Management Datastore Architecture (NMDA) [RFC8342]. 2. Conventions used in this document 2.1. Terminology 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 [RFC2119]. In this document, these words will appear with that interpretation only when in ALL CAPS. Lower case uses of these words are not to be interpreted as carrying [RFC2119] significance. This document uses the following terms: Error A deviation of a system from normal operation [RFC3877]. Fault Lasting error or warning condition [RFC3877]. Wang, et al. Expires April 3, 2019 [Page 2] Internet-Draft Event YANG September 2018 Event Something that happens which may be of interest or trigger the invocation of the rule. A fault, an alarm, a change in network state, network security threat, hardware malfunction, buffer untilization crossing a threshold, network connection setup, an external input to the system, for example [RFC3877]. 2.2. Tree Diagrams Tree diagrams used in this document follow the notation defined in [RFC8340]. 3. Objectives This section describes some of the design objectives for the Event Data Model: The Event YANG should provide the ability to monitor yang instance on a local or remote system using the NETCONF/RESTCONF, and initiates simple actions whenever a trigger condition is met. For example, a NETCONF subscribed notification can be generated when an instance value exceeds the threshold. Clear and precise identification of Event types and instances. Allow the server to inform the client that certain Events are related to other Events. Allow one event to be able to trigger another external event or generate derived events. The event data model defined in this document can be implemented on a system that also implements EVENT-MIB; thus, the mapping between the event data model and ENTITY-MIB should be clear. 4. Relationship to YANG PUSH YANG-push mechanism provides a subscription service for updates from a datastore. And it support two types of subscriptions which are distinguished by how updates are triggered: periodic and on-change. The On-change PUSH allow receivers to receive updates whenever changes to targeted objects occur. This document specifies a mechanism that provides three trigger conditions: o Existence: When a specific yang instance appears, the trigger fires. E.g. Reserved ports are configured. Wang, et al. Expires April 3, 2019 [Page 3] Internet-Draft Event YANG September 2018 o Boolean: If the test result is true the trigger fires. The trigger will not fire again until the value has become false and come back to true. And the user can set the type of boolean comparison (e.g. unequal, equal, less, less-or-equal, greater, greater-or-equal, etc), so for example if the boolean comparison type is 'less' the trigger will be fired if the value of YANG Instance is less than the value of Boolean Value. o Threshold: The event that may be triggered when a YANG instance at data-instance list is found. If the first sample after this instance becomes active is greater than or equal to 'rising-value' and the 'startup' is equal to 'rising' then one threshold rising event is triggered for that instance. And if the first sample after this instance becomes active is less than or equal to 'falling-value' and the 'startup' is equal to 'falling' then one threshold falling event is triggered for that instance. And the YANG PUSH mechanism more focus on the remote mirroring and monitoring of configuration and operational state. For example, for on change method, the subscriber will receive a notification if the changes appears. The model defines in this document provides a method which allow automatic setting the value of the corresponding instance node when some event is triggered. It esbalishes connection between network service monitoring and network service provision and can use output generated by network service monitoring as input of network service provision and thereby provide automated network management. The details of the usage example is described in Appendix A. 5. Relationship to EVENT MIB If the device implements the EVENT-MIB [RFC2981], each entry in the "/events/event/trigger" list is mapped to MteTriggerEntry,MteTriggerE xistenceEntry,MteTriggerBooleanEntry,MteTriggerThresholdEntry,MteObje ctsEntry,MteEventEntry,MteEventSetEntry. respectively. The following table lists the YANG data nodes with corresponding objects in the EVENT-MIB [RFC2981]. Wang, et al. Expires April 3, 2019 [Page 4] Internet-Draft Event YANG September 2018 +------------------------------|---------------------------------+ | | | | YANG data node in | EVENT-MIB Objects | | ietf-event.yang | (RFC2981) | | | | +----------------------------------------------------------------+ | | | | evt-smp-min | mteResourceSampleMinimum | | | | | evt-smp-instance-max | mteResourceSampleInstanceMaximum| | | | | traget | mteObjectsName | | | | | event-name | mteEventName | | | | | event-description | mteEventComment | | | | | value | mteEventSetValue | | | | | events/event/trigger/name | mteTriggerName | | | | | trigger-description | mteTriggerComment | | | | | frequency | mteTriggerFrequency | | | | | comparison | mteTriggerBooleanComparison | | | | | value | mteTriggerBooleanValue | | | | | rising-event | mteTriggerThresholdRising | | | | | falling-event | mteTriggerThresholdFalling | | | | | delta-rising-event | mteTriggerThresholdDeltaRising | | | | | threshold/startup | mteTriggerThresholdStartup | | | | | existence/enable | mteTriggerExistenceStartup | | | | | boolean/enable | mteTriggerBooleanStartup | | | | -------------------------------|---------------------------------| 6. Model Overview The event yang has four lists: trigger, target, event, and action. Triggers define the targets meeting some conditions that lead to events. Events trigger corresponding actions. Wang, et al. Expires April 3, 2019 [Page 5] Internet-Draft Event YANG September 2018 The trigger list defines what managed objects or targets are to be monitored and how and relates each trigger to an event. In this model, the trigger list provides three trigger conditions: o Existence: When a specific yang instance appears, the trigger fires. o Boolean: If the test result is true the trigger fires. o Threshold: The event that may be triggered when a YANG instance at data-instance list is met the threshold. Each trigger can be seen as a logical test that, if satisfied or evaluated to be true, cause the action to be carried out. The target list defines managed objects that can be added to notifications based or be set to a new value on the trigger, the trigger test type, or the event that resulted in the actions. The event list defines what happens when an event is triggered, i.e., trigger corresponding action, e.g.,sending a notification, setting a value to the managed object or both. The action list consists of updates or innvcations on local managed object attributes and defines a set of actions which will be performed (e.g. notification, set, another event, etc) when corresponding event be triggered. The value to be set can use many variations on rule structure. This document defines the YANG module "ietf-event", which has the following structure: module: ietf-event +--rw events +--rw evt-smp-min? uint32 +--rw evt-smp-instance-max? uint32 +--rw event* [event-name type] +--rw event-name string +--rw type identityref +--rw event-description? string +--rw target* target +--rw clear? boolean +--rw related-event* [event-name type] | +--rw event-name string | +--rw type identityref +--rw trigger* [name] | +--rw name string | +--rw type? enumeration Wang, et al. Expires April 3, 2019 [Page 6] Internet-Draft Event YANG September 2018 | +--rw trigger-description? string | +--rw frequency | | +--rw type? identityref | | +--rw periodic | | | +--rw interval uint32 | | | +--rw start? yang:date-and-time | | | +--rw end? yang:date-and-time | | +--rw scheduling | | | +--rw month* string | | | +--rw day-of-month* uint8 | | | +--rw day-of-week* uint8 | | | +--rw hour* uint8 | | | +--rw minute* uint8 | | | +--rw second* uint8 | | | +--rw start? yang:date-and-time | | | +--rw end? yang:date-and-time | | +--rw immediate | | +--rw immediate empty | +--rw (test)? | +--:(existences) | | +--rw existences | | +--rw target* -> /events/event/target | | +--rw enable? boolean | +--:(boolean) | | +--rw boolean | | +--rw comparison? enumeration | | +--rw value? match-value | | +--rw target* -> /events/event/target | | +--rw enable? boolean | +--:(threshold) | +--rw threshold | +--rw rising-value? match-value | +--rw rising-target* -> /events/event/target | +--rw falling-value? match-value | +--rw falling-target* -> /events/event/target | +--rw delta-rising-value? match-value | +--rw delta-rising-target* -> /events/event/target | +--rw startup? enumeration +--rw action* [action-name] +--rw action-name string +---n event-notification | +---- event-name? -> /events/event/event-name | +---- type? -> /events/event/type | +---- target* target +---x set | +---w input | +---w target* target | +---w value? Wang, et al. Expires April 3, 2019 [Page 7] Internet-Draft Event YANG September 2018 +--rw trigger-event* -> ../../event-name The relation between Event, Trigger, Target and Action is described as follows: +-------------------------------+ | Event | | +-------+ | | |Target | | | +---|---+ | +-------------------------------+ | | | | Event | | +----V---+ +--------+ | | +-------+ | | |Trigger |------->| Action |-------->|Target | | | +--------+ +--------+ | | +---|---+ | +-------------------------------+ | | | | +----|---+ +--------+ | | |Trigger |------- | Action | | | +--------+ +--------+ | +-------------------------------+ One event may trigger another event, but if it does not trigger another event, the right part of above figure should be ignored. 7. EVENT YANG Module file "ietf-event@2018-09-18.yang" module ietf-event { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-event"; prefix evt; import ietf-yang-types { prefix yang; } organization "IETF xxx Working Group"; contact "Zitao Wang: wangzitao@huawei.com Qin Wu: bill.wu@huawei.com"; description "This module defines a model for the service topology."; revision 2018-09-18 { description "Initial revision."; reference "foo"; Wang, et al. Expires April 3, 2019 [Page 8] Internet-Draft Event YANG September 2018 } identity event-type { description "Base identity for event type"; } identity frequency { description "Base identity for frequency"; } identity periodic { base frequency; description "Identity for periodic trigger"; } identity scheduling { base frequency; description "Identity for scheduling trigger"; } identity immediate { base frequency; description "Identity for immediate trigger"; } typedef match-value { type union { type yang:xpath1.0; type yang:object-identifier; type string; } description "This type is used to match resources of type 'target'. Since the type 'target' is a union of different types, the 'match-value' type is also a union of corresponding types."; } typedef target { type union { type instance-identifier; type yang:object-identifier; type yang:uuid; Wang, et al. Expires April 3, 2019 [Page 9] Internet-Draft Event YANG September 2018 type string; } description "If the target is modelled in YANG, this type will be an instance-identifier. If the target is an SNMP object, the type will be an object-identifier. If the target is anything else, for example a distinguished name or a CIM path, this type will be a string. If the target is identified by a UUID use the uuid type. If the server supports several models, the presedence should be in the order as given in the union definition."; } grouping start-end-grouping { description "A grouping that provides start and end times for Event objects."; leaf start { type yang:date-and-time; description "The date and time when the Event object starts to create triggers."; } leaf end { type yang:date-and-time; description "The date and time when the Event object stops to create triggers. It is generally a good idea to always configure an end time and to refresh the end time as needed to ensure that agents that lose connectivity to their Controller do not continue executing Schedules forever."; } } container events { leaf evt-smp-min { type uint32; description "Sets the minimum value for data instance sampling"; } leaf evt-smp-instance-max { type uint32; description "Sets the maximum value for data instance instance sampling."; Wang, et al. Expires April 3, 2019 [Page 10] Internet-Draft Event YANG September 2018 } list event { key "event-name type"; leaf event-name { type string; description "Event name"; } leaf type { type identityref { base event-type; } description "Type of event"; } leaf event-description { type string; description "Event description"; } leaf-list target { type target; description "targeted objects"; } leaf clear { type boolean; default "false"; description "A flag indicate whether the event be closed"; } list related-event { key "event-name type"; leaf event-name { type string; description "Event name"; } leaf type { type identityref { base event-type; } description "Type of event"; } description "List for related events"; } Wang, et al. Expires April 3, 2019 [Page 11] Internet-Draft Event YANG September 2018 list trigger { key "name"; leaf name { type string; description "Trigger name"; } leaf type { type enumeration { enum "existence" { description "Indicates that the trigger type is 'existence'. For 'existence', the specific test is as selected. When an object appears, vanishes or changes value, the trigger fires."; } enum "boolean" { description "Indicates that the trigger type is 'boolean'. If the test result is true the trigger fires. The trigger will not fire again until the value has become false and come back to true."; } enum "threshold" { description "Indicates that the trigger type is 'threshold'. The event that may be triggered when a YANG instance at data-instance list is found. If the first sample after this instance becomes active is greater than or equal to 'rising-value' and the 'startup' is equal to 'rising' then one threshold rising event is triggered for that instance."; } } description "Trigger type"; } leaf trigger-description { type string; description "Trigger description"; } container frequency { leaf type { type identityref { base frequency; } description "Type of trigger frequency"; Wang, et al. Expires April 3, 2019 [Page 12] Internet-Draft Event YANG September 2018 } container periodic { when "derived-from-or-self(../type, 'periodic')"; description "A periodic timing object triggers periodically according to a regular interval."; leaf interval { type uint32 { range "1..max"; } units "seconds"; mandatory true; description "The number of seconds between two triggers generated by this periodic timing object."; } uses start-end-grouping; } container scheduling { when "derived-from-or-self(../type, 'scheduling')"; description "A scheduling timing object triggers."; leaf-list month { type string; description "A set of months at which this scheduling timing will trigger."; } leaf-list day-of-month { type uint8 { range "0..59"; } description "A set of days of the month at which this scheduling timing will trigger."; } leaf-list day-of-week { type uint8 { range "0..59"; } description "A set of weekdays at which this scheduling timing will trigger."; } leaf-list hour { type uint8 { range "0..59"; } Wang, et al. Expires April 3, 2019 [Page 13] Internet-Draft Event YANG September 2018 description "A set of hours at which the scheduling timing will trigger."; } leaf-list minute { type uint8 { range "0..59"; } description "A set of minutes at which this scheduling timing will trigger."; } leaf-list second { type uint8 { range "0..59"; } description "A set of seconds at which this calendar timing will trigger."; } uses start-end-grouping; } container immediate { when "derived-from-or-self(../type, 'immediate')"; leaf immediate { type empty; mandatory true; description "This immediate Event object triggers immediately when it is configured."; } description "This immediate Event object triggers immediately when it is configured."; } description "Container for frequency"; } choice test { description "Choice test"; container existences { leaf-list target { type leafref { path "/events/event/target"; } description "List for target objects"; Wang, et al. Expires April 3, 2019 [Page 14] Internet-Draft Event YANG September 2018 } leaf enable { type boolean; description "Startup"; } description "Container for existence"; } container boolean { leaf comparison { type enumeration { enum "unequal" { description "Indicates that the comparision type is 'unequal'."; } enum "equal" { description "Indicates that the comparision type is 'equal'."; } enum "leass" { description "Indicates that the comparision type is 'less'."; } enum "less-or-equal" { description "Indicates that the comparision type is 'less or equal'."; } enum "greater" { description "Indicates that the comparision type is 'greater'."; } enum "greater-or-equal" { description "Indicates that the comparision type is 'greater or equal'."; } } description "Comparison type"; } leaf value { type match-value; description "Compartion value"; } leaf-list target { type leafref { path "/events/event/target"; Wang, et al. Expires April 3, 2019 [Page 15] Internet-Draft Event YANG September 2018 } description "List for target objects"; } leaf enable { type boolean; description "Startup"; } description "Container for boolean test"; } container threshold { leaf rising-value { type match-value; description "Sets the rising threshold to the specified value, ] When the current sampled value is greater than or equal to this threshold, and the value at the last sampling interval was less than this threshold, the event is triggered. "; } leaf-list rising-target { type leafref { path "/events/event/target"; } description "List for target objects"; } leaf falling-value { type match-value; description "Sets the falling threshold to the specified value"; } leaf-list falling-target { type leafref { path "/events/event/target"; } description "List for target objects"; } leaf delta-rising-value { type match-value; description "Sets the delta rising threshold to the specified value"; } leaf-list delta-rising-target { type leafref { path "/events/event/target"; Wang, et al. Expires April 3, 2019 [Page 16] Internet-Draft Event YANG September 2018 } description "List for target objects"; } leaf startup { type enumeration { enum "rising" { description "If the first sample after this instance becomes active is greater than or equal to 'rising-value' and the 'startup' is equal to 'rising' then one threshold rising event is triggered for that instance."; } enum "falling" { description "If the first sample after this instance becomes active is less than or equal to 'falling-value' and the 'startup' is equal to 'falling' then one threshold falling event is triggered for that instance."; } enum "rising-or-falling" { description "That event is also triggered if the first sample after this entry becomes active is less than or equal or rising than to this threshold and 'startup' is equal to 'rising-or-falling'."; } } description "Startup"; } description "Container for threshold"; } } description "List for trigger"; } list action { key "action-name"; leaf action-name { type string; description "Action name"; } notification event-notification { leaf event-name { type leafref { Wang, et al. Expires April 3, 2019 [Page 17] Internet-Draft Event YANG September 2018 path "/events/event/event-name"; } description "Report the event name"; } leaf type { type leafref { path "/events/event/type"; } description "Report the event type"; } leaf-list target { type target; description "Report the target objects"; } description "This notification is used to report that an operator acted upon an Event."; } action set { input { leaf-list target { type target; description "Report the target objects"; } anydata value { description "Inline set content."; } } } leaf-list trigger-event { type leafref { path "../../event-name"; } description "This action trigger another event"; } description "List for Actions"; } description "List for Events"; } description Wang, et al. Expires April 3, 2019 [Page 18] Internet-Draft Event YANG September 2018 "YANG data module for defining event triggers and actions for network management purposes"; } } 8. Security Considerations The YANG modules defined in this document MAY be accessed via the RESTCONF protocol [RFC8040] or NETCONF protocol ([RFC6241]). The lowest RESTCONF or NETCONF layer requires that the transport-layer protocol provides both data integrity and confidentiality, see Section 2 in [RFC8040] and [RFC6241]. The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH)[RFC6242] . The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS [RFC5246]. The NETCONF access control model [RFC6536] provides the means to restrict access for particular NETCONF or RESTCONF users to a preconfigured subset of all available NETCONF or RESTCONF protocol operations and content. There are a number of data nodes defined in this YANG module that are writable/creatable/deletable (i.e., config true, which is the default). These data nodes may be considered sensitive or vulnerable in some network environments. Write operations (e.g., edit-config) to these data nodes without proper protection can have a negative effect on network operations. These are the subtrees and data nodes and their sensitivity/vulnerability: o /events/event/event-name o /events/event/target o /events/action/set/target o /events/event/trigger/name 9. IANA Considerations This document registers a URI in the IETF XML registry [RFC3688]. Following the format in [RFC3688], the following registration is requested to be made: Wang, et al. Expires April 3, 2019 [Page 19] Internet-Draft Event YANG September 2018 --------------------------------------------------------------------- URI: urn:ietf:params:xml:ns:yang:ietf-event Registrant Contact: The IESG. XML: N/A, the requested URI is an XML namespace. --------------------------------------------------------------------- This document registers a YANG module in the YANG Module Names registry [RFC6020]. --------------------------------------------------------------------- Name: ietf-event Namespace: urn:ietf:params:xml:ns:yang:ietf-event Prefix: evt Reference: RFC xxxx --------------------------------------------------------------------- 10. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", March 1997. [RFC2981] Kavasseri, R., Ed., "Event MIB", RFC 2981, DOI 10.17487/RFC2981, October 2000, . [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, . [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, . [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, . [RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011, . [RFC6370] Bocci, M., Swallow, G., and E. Gray, "MPLS Transport Profile (MPLS-TP) Identifiers", RFC 6370, DOI 10.17487/RFC6370, September 2011, . Wang, et al. Expires April 3, 2019 [Page 20] Internet-Draft Event YANG September 2018 [RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration Protocol (NETCONF) Access Control Model", RFC 6536, DOI 10.17487/RFC6536, March 2012, . [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, . [RFC7952] Lhotka, L., "Defining and Using Metadata with YANG", RFC 7952, DOI 10.17487/RFC7952, August 2016, . Appendix A. Example of Event For example, some service requires to monitoring the "in-errors" state of the interface, and if the value of "in-errors" exceeds the threshold, the event should reset the interface's enabled value to false: Wang, et al. Expires April 3, 2019 [Page 21] Internet-Draft Event YANG September 2018 interface-state-exception interface-exception /if:interfaces/if:interface[if:name='eth1'] /if:interfaces/if:interface[if:name='eth2'] /if:interfaces/if:interface[if:name='eth3'] evaluate-in-errors evaluate the number of the packets that contained errors 10m threshold rising 100 /if:interfaces/if:interface[if:name='eth1'] /if:statistic/if:in-errors /if:interfaces/if:interface[if:name='eth2'] /if:statistic/if:in-errors interface-exception interface-state-exception interface-exception /if:interfaces/if:interface[if:name='eth1'] /if:interfaces/if:interface[if:name='eth1'] eth1 false Wang, et al. Expires April 3, 2019 [Page 22] Internet-Draft Event YANG September 2018 Authors' Addresses Michael Wang Huawei Technologies,Co.,Ltd 101 Software Avenue, Yuhua District Nanjing 210012 China Email: wangzitao@huawei.com Qin Wu Huawei 101 Software Avenue, Yuhua District Nanjing, Jiangsu 210012 China Email: bill.wu@huawei.com Chongfeng Xie China Telecom Email: xiechf@ctbri.com.cn Wang, et al. Expires April 3, 2019 [Page 23]