DetNet                                                         G. Mirsky
Internet-Draft                                                 ZTE Corp.
Intended status: Informational                              F. Theoleyre
Expires: 20 November 2021                                           CNRS
                                                       G.Z. Papadopoulos
                                                          IMT Atlantique
                                                           CJ. Bernardos
                                                             19 May 2021

   Framework of Operations, Administration and Maintenance (OAM) for
                   Deterministic Networking (DetNet)


   Deterministic Networking (DetNet), as defined in RFC 8655, is aimed
   to provide a bounded end-to-end latency on top of the network
   infrastructure, comprising both Layer 2 bridged and Layer 3 routed
   segments.  This document's primary purpose is to detail the specific
   requirements of the Operation, Administration, and Maintenance (OAM)
   recommended to maintain a deterministic network.  With the
   implementation of the OAM framework in DetNet, an operator will have
   a real-time view of the network infrastructure regarding the
   network's ability to respect the Service Level Objective, such as
   packet delay, delay variation, and packet loss ratio, assigned to
   each data flow.

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
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   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
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   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 20 November 2021.

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Copyright Notice

   Copyright (c) 2021 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 (
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.3.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  Role of OAM in DetNet . . . . . . . . . . . . . . . . . . . .   4
   3.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Information Collection  . . . . . . . . . . . . . . . . .   5
     3.2.  Continuity Check  . . . . . . . . . . . . . . . . . . . .   6
     3.3.  Connectivity Verification . . . . . . . . . . . . . . . .   6
     3.4.  Route Tracing . . . . . . . . . . . . . . . . . . . . . .   6
     3.5.  Fault Verification/detection  . . . . . . . . . . . . . .   6
     3.6.  Fault Localization and Characterization . . . . . . . . .   7
     3.7.  Use of Hybrid OAM in DetNet . . . . . . . . . . . . . . .   7
   4.  Administration  . . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Collection of metrics . . . . . . . . . . . . . . . . . .   8
     4.2.  Worst-case metrics  . . . . . . . . . . . . . . . . . . .   8
   5.  Maintenance . . . . . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  Replication / Elimination . . . . . . . . . . . . . . . .   9
     5.2.  Resource Reservation  . . . . . . . . . . . . . . . . . .   9
     5.3.  Soft transition after reconfiguration . . . . . . . . . .  10
   6.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  11
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     10.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

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1.  Introduction

   Deterministic Networking (DetNet) [RFC8655] has proposed to provide a
   bounded end-to-end latency on top of the network infrastructure,
   comprising both Layer 2 bridged and Layer 3 routed segments.  That
   work encompasses the data plane, OAM, time synchronization,
   management, control, and security aspects.

   Operations, Administration, and Maintenance (OAM) Tools are of
   primary importance for IP networks [RFC7276].  DetNet OAM should
   provide a toolset for fault detection, localization, and performance

   This document's primary purpose is to detail the specific
   requirements of the OAM features recommended to maintain a
   deterministic/reliable network.  Specifically, it investigates the
   requirements for a deterministic network, supporting critical flows.

   In this document, the term OAM will be used according to its
   definition specified in [RFC6291].  DetNet expects to implement an
   OAM framework to maintain a real-time view of the network
   infrastructure, and its ability to respect the Service Level
   Objectives (SLO), such as packet delay, delay variation, and packet
   loss ratio, assigned to each data flow.

   This document lists the functional requirements toward OAM for DetNet
   domain.  The list can further be used for gap analysis of available
   OAM tools to identify possible enhancements of existing or whether
   new OAM tools are required to support proactive and on-demand path
   monitoring and service validation.

1.1.  Terminology

   The following terms are used throughout this document as defined

   *  OAM entity: a data flow to be monitored for defects and/or its
      performance metrics measured.

   *  Maintenance End Point (MEP): OAM systems traversed by a data flow
      when entering/exiting the network.  In DetNet, it corresponds with
      the source and destination of a data flow.  OAM messages can be
      exchanged between two MEPs.

   *  Maintenance Intermediate endPoint (MIP): an OAM system along the
      flow; a MIP MAY respond to an OAM message generated by the MEP.

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   *  Control and management plane: the control and management planes
      are used to configure and control the network (long-term).
      Relative to a data flow, the control and/or management plane can
      be out-of-band.

   *  Active measurement methods (as defined in [RFC7799]) modify a
      normal data flow by inserting novel fields, injecting specially
      constructed test packets [RFC2544]).

   *  Passive measurement methods [RFC7799] infer information by
      observing unmodified existing flows.

   *  Hybrid measurement methods [RFC7799] is the combination of
      elements of both active and passive measurement methods.

1.2.  Acronyms

   OAM: Operations, Administration, and Maintenance

   DetNet: Deterministic Networking

   SLO: Service Level Objective

   SNMP: Simple Network Management Protocol

   SDN: Software Defined Network

   <TODO> we need here an exhaustive list, to be completed after the
   document has evolved.

1.3.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Role of OAM in DetNet

   DetNet networks expect to provide communications with predictable low
   packet delay and packet loss.  Most critical applications will define
   an SLO to be required for the data flows it generates.

   To respect strict guarantees, DetNet can use an orchestrator able to
   monitor and maintain the network.  Typically, a Software-Defined
   Network (SDN) controller places DetNet flows in the deployed network
   based on their SLO.  Thus, resources have to be provisioned a priori

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   for the regular operation of the network.  Because OAM is an
   essential element of the network operation, resources, necessary for
   OAM, need to be accounted for in addition to DetNet flows.

   Fault-tolerance also assumes that multiple paths could be provisioned
   so that an end-to-end circuit is maintained by adapting to the
   existing conditions.  The central controller/orchestrator typically
   controls the Packet Replication, Elimination, and Ordering Functions
   (PREOF) on a node.  OAM is expected to support monitoring and
   troubleshooting PREOF on a particular node and within the domain.

   Note that PREOF can also be controlled by a set of distributed
   controllers, in those scenarios where DetNet solutions involve more
   than one single central controller.

3.  Operation

   OAM features will enable DetNet with robust operation both for
   forwarding and routing purposes.

   It is worth noting that the test and data packets MUST follow the
   same path, i.e., the connectivity verification has to be conducted
   in-band without impacting the data traffic.  Test packets MUST share
   fate with the monitored data traffic without introducing congestion
   in normal network conditions.

3.1.  Information Collection

   Information about the state of the network can be collected using
   several mechanisms.  Some protocols, e.g., Simple Network Management
   Protocol (SNMP), send queries.  Others, e.g., YANG-based data models,
   generate notifications based on the publish-subscribe method.  In
   either way, information is collected and sent to the controller.

   Also, we can characterize methods of transporting OAM information
   relative to the path of data.  For instance, OAM information may be
   transported in-band or out-of-band with the data flow.  In case of
   the former, the telemetry information uses resources allocated for
   the monitored DetNet flow.  If an in-band method of transporting
   telemetry is used, the amount of generated information needs to be
   carefully analyzed, and additional resources must be reserved.
   [I-D.ietf-ippm-ioam-data] defines the in-band transport mechanism
   where telemetry information is collected in the data packet on which
   information is generated.  Two tracing methods are described - end-
   to-end, i.e., from the ingress and egress nodes, and hop-by-hop,
   i.e., like end-to-end with additional information from transit nodes.
   [I-D.ietf-ippm-ioam-direct-export] and
   [I-D.mirsky-ippm-hybrid-two-step] are examples of out-of-band

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   telemetry transport.  In the former case, information is transported
   by each node traversed by the data packet of the monitored DetNet
   flow in a specially constructed packet.  In the latter, information
   is collected in a sequence of follow-up packets that traverse the
   same path as the data packet of the monitored DetNet flow.  In both
   methods, transport of the telemetry can avoid using resources
   allocated for the DetNet domain.

3.2.  Continuity Check

   Continuity check is used to monitor the continuity of a path, i.e.,
   that there exists a way to deliver the packets between two endpoints
   A and B.

3.3.  Connectivity Verification

   In addition to the Continuity Check, DetNet solutions have to verify
   the connectivity.  This verification considers additional
   constraints, i.e., the absence of misconnection.  The misconnection
   error state is entered after several consecutive test packets from
   other DetNet flows are received.  The definition of the conditions of
   entry and exit for misconnection error state is outside the scope of
   this document.

3.4.  Route Tracing

   Ping and traceroute are two ubiquitous tools that help localize and
   characterize a failure in the network.  They help to identify a
   subset of the list of routers in the route.  However, to be
   predictable, resources are reserved per flow in DetNet.  Thus, DetNet
   needs to define route tracing tools able to track the route for a
   specific flow.  Also, tracing can be used for the discovery of the
   Path Maximum Transmission Unit or location of elements of PREOF for
   the particular route in the DetNet domain.

   DetNet with IP data plane is NOT RECOMMENDED to use multiple paths or
   links, i.e., Equal-Cost Multipath (ECMP) [RFC8939].  As the result,
   OAM in IP ECMP environment is outside the scope of this document.

3.5.  Fault Verification/detection

   DetNet expects to operate fault-tolerant networks.  Thus, mechanisms
   able to detect faults before they impact the network performance are

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   The network has to detect when a fault occurred, i.e., the network
   has deviated from its expected behavior.  While the network must
   report an alarm, the cause may not be identified precisely.  For
   instance, the end-to-end reliability has decreased significantly, or
   a buffer overflow occurs.

   DetNet OAM mechanisms SHOULD allow a fault detection in real time.
   They MAY, when possible, predict faults based on current network
   conditions.  They MAY also identify and report the cause of the
   actual/predicted network failure.

3.6.  Fault Localization and Characterization

   An ability to localize the network defect and provide its
   characterization are necessary elements of network operation.

      Fault localization, a process of deducing the location of a
      network failure from a set of observed failure indications, might
      be achieved, for example, by tracing the route of the DetNet flow
      in which the network failure was detected.  Another method of
      fault localization can correlate reports of failures from a set of
      interleaving sessions monitoring path continuity.

      Fault characterization is a process of identifying the root cause
      of the problem.  For instance, misconfiguration or malfunction of
      PREOF elements can be the cause of erroneous packet replication or
      extra packets being flooded in the DetNet domain.

3.7.  Use of Hybrid OAM in DetNet

   Hybrid OAM methods are used in performance monitoring and defined in
   [RFC7799] as:

      Hybrid Methods are Methods of Measurement that use a combination
      of Active Methods and Passive Methods.

   A hybrid measurement method may produce metrics as close to passive,
   but it still alters something in a data packet even if that is the
   value of a designated field in the packet encapsulation.  One example
   of such a hybrid measurement method is the Alternate Marking method
   (AMM) described in [RFC8321].  As with all on-path telemetry methods,
   AMM in a DetNet domain with the IP data plane is natively in-band in
   respect to the monitored DetNet flow.  Because the marking is applied
   to a data flow, measured metrics are directly applicable to the
   DetNet flow.  AMM minimizes the additional load on the DetNet domain
   by using nodal collection and computation of performance metrics in
   combination with optionally using out-of-band telemetry collection
   for further network analysis.

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4.  Administration

   The network SHOULD expose a collection of metrics to support an
   operator making proper decisions, including:

   *  Queuing Delay: the time elapsed between a packet enqueued and its
      transmission to the next hop.

   *  Buffer occupancy: the number of packets present in the buffer, for
      each of the existing flows.

   The following metrics SHOULD be collected:

   *  per virtual circuit to measure the end-to-end performance for a
      given flow.  Each of the paths has to be isolated in multipath
      routing strategies.

   *  per path to detect misbehaving path when multiple paths are

   *  per device to detect misbehaving node, when it relays the packets
      of several flows.

4.1.  Collection of metrics

   DetNet OAM SHOULD optimize the number of statistics / measurements to
   collected, frequency of collecting.  Distributed and centralized
   mechanisms MAY be used in combination.  Periodic and event-triggered
   collection information characterizing the state of a network MAY be

4.2.  Worst-case metrics

   DetNet aims to enable real-time communications on top of a
   heterogeneous multi-hop architecture.  To make correct decisions, the
   controller needs to know the distribution of packet losses/delays for
   each flow, and each hop of the paths.  In other words, the average
   end-to-end statistics are not enough.  The collected information must
   be sufficient to allow the controller to predict the worst-case.

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5.  Maintenance

   In the face of events that impact the network operation (e.g., link
   up/down, node crash/reboot, flows starting and ending), the DetNet
   Controller need to perform repair and re-optimization actions in
   order to permanently ensure the SLO of all active flows with minimal
   waste of resources The controller MUST be able to continuously
   retrieve the state of the network, to evaluate conditions and trends
   about the relevance of a reconfiguration, quantifying:

      the cost of the sub-optimality: resources may not be used
      optimally (e.g., a better path exists).

      the reconfiguration cost: the controller needs to trigger some
      reconfigurations.  For this transient period, resources may be
      twice reserved, and control packets have to be transmitted.

   Thus, reconfiguration may only be triggered if the gain is

5.1.  Replication / Elimination

   When multiple paths are reserved between two maintenance endpoints,
   packet replication may be used to introduce redundancy and alleviate
   transmission errors and collisions.  For instance, in Figure 1, the
   source node S is transmitting the packet to both parents, nodes A and
   B.  Each maintenance endpoint will decide to trigger the packet
   replication, elimination or the ordering process when a set of
   metrics passes a threshold value.

                          ===> (A) => (C) => (E) ===
                        //        \\//   \\//       \\
              source (S)          //\\   //\\         (R) (root)
                        \\       //  \\ //  \\      //
                          ===> (B) => (D) => (F) ===

       Figure 1: Packet Replication: S transmits twice the same data
                        packet, to DP(A) and AP (B).

5.2.  Resource Reservation

   Because the quality of service criteria associated with a path may
   degrade, the network has to provision additional resources along the
   path.  We need to provide mechanisms to patch the network

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5.3.  Soft transition after reconfiguration

   Since DetNet expects to support real-time flows, DetNet OAM MUST
   support soft-reconfiguration, where the novel resources are reserved
   before the ancient ones are released.  Some mechanisms have to be
   proposed so that packets are forwarded through the novel track only
   when the resources are ready to be used, while maintaining the global
   state consistent (no packet reordering, duplication, etc.)

6.  Requirements

   This section lists requirements for OAM in DetNet domain:

   1.   It MUST be possible to initiate DetNet OAM session from any
        DetNet node towards another DetNet node(s) within given domain.

   2.   It MUST be possible to initialize DetNet OAM session from a
        centralized controller.

   3.   DetNet OAM MUST support proactive and on-demand OAM monitoring
        and measurement methods.

   4.   DetNet OAM packets MUST be in-band, i.e., follow precisely the
        same path as DetNet data plane traffic.

   5.   DetNet OAM MUST support unidirectional OAM methods, continuity
        check, connectivity verification, and performance measurement.

   6.   DetNet OAM MUST support bi-directional OAM methods.  Such OAM
        methods MAY combine in-band monitoring or measurement in the
        forward direction and out-of-bound notification in the reverse
        direction, i.e., from egress to ingress end point of the OAM
        test session.

   7.   DetNet OAM MUST support proactive monitoring of a DetNet node
        availability in the given DetNet domain.

   8.   DetNet OAM MUST support Path Maximum Transmission Unit

   9.   DetNet OAM MUST support the discovery of PREOF along a route in
        the given DetNet domain.

   10.  DetNet OAM MUST support Remote Defect Indication (RDI)
        notification to the DetNet node performing continuity checking.

   11.  DetNet OAM MUST support performance measurement methods.

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   12.  DetNet OAM MAY support hybrid performance measurement methods.

   13.  DetNet OAM MUST support unidirectional performance measurement
        methods.  Calculated performance metrics MUST include but are
        not limited to throughput, packet loss, delay and delay
        variation metrics.  [RFC6374] provides detailed information on
        performance measurement and performance metrics.

   14.  DetNet OAM MUST support defect notification mechanism, like
        Alarm Indication Signal.  Any DetNet node in the given DetNet
        domain MAY originate a defect notification addressed to any
        subset of nodes within the domain.

   15.  DetNet OAM MUST support methods to enable survivability of the
        DetNet domain.  These recovery methods MAY use protection
        switching and restoration.

   16.  DetNet OAM MUST support the discovery of Packet Replication,
        Elimination, and Order preservation sub-functions locations in
        the domain.

   17.  DetNet OAM MUST support testing of Packet Replication,
        Elimination, and Order preservation sub-functions in the domain.

   18.  DetNet OAM MUST support monitoring levels of resources allocated
        for the particular DetNet flow.  Such resources include but not
        limited to buffer utilization, scheduler transmission calendar.

   19.  DetNet OAM MUST support monitoring any sub-set of paths
        traversed through the DetNet domain by the DetNet flow.

7.  IANA Considerations

   This document has no actionable requirements for IANA.  This section
   can be removed before the publication.

8.  Security Considerations

   This document lists the OAM requirements for a DetNet domain and does
   not raise any security concerns or issues in addition to ones common
   to networking and those specific to a DetNet discussed in

9.  Acknowledgments

   The authors express their appreciation and gratitude to Pascal
   Thubert for the review, insightful questions, and helpful comments.

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10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

10.2.  Informative References

              Grossman, E., Mizrahi, T., and A. J. Hacker,
              "Deterministic Networking (DetNet) Security
              Considerations", Work in Progress, Internet-Draft, draft-
              ietf-detnet-security-16, 2 March 2021,

              Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields
              for In-situ OAM", Work in Progress, Internet-Draft, draft-
              ietf-ippm-ioam-data-12, 21 February 2021,

              Song, H., Gafni, B., Zhou, T., Li, Z., Brockners, F.,
              Bhandari, S., Sivakolundu, R., and T. Mizrahi, "In-situ
              OAM Direct Exporting", Work in Progress, Internet-Draft,
              draft-ietf-ippm-ioam-direct-export-03, 17 February 2021,

              Mirsky, G., Lingqiang, W., Zhui, G., and H. Song, "Hybrid
              Two-Step Performance Measurement Method", Work in
              Progress, Internet-Draft, draft-mirsky-ippm-hybrid-two-
              step-10, 17 May 2021, <

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   [RFC2544]  Bradner, S. and J. McQuaid, "Benchmarking Methodology for
              Network Interconnect Devices", RFC 2544,
              DOI 10.17487/RFC2544, March 1999,

   [RFC6291]  Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
              D., and S. Mansfield, "Guidelines for the Use of the "OAM"
              Acronym in the IETF", BCP 161, RFC 6291,
              DOI 10.17487/RFC6291, June 2011,

   [RFC6374]  Frost, D. and S. Bryant, "Packet Loss and Delay
              Measurement for MPLS Networks", RFC 6374,
              DOI 10.17487/RFC6374, September 2011,

   [RFC7276]  Mizrahi, T., Sprecher, N., Bellagamba, E., and Y.
              Weingarten, "An Overview of Operations, Administration,
              and Maintenance (OAM) Tools", RFC 7276,
              DOI 10.17487/RFC7276, June 2014,

   [RFC7799]  Morton, A., "Active and Passive Metrics and Methods (with
              Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
              May 2016, <>.

   [RFC8321]  Fioccola, G., Ed., Capello, A., Cociglio, M., Castaldelli,
              L., Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi,
              "Alternate-Marking Method for Passive and Hybrid
              Performance Monitoring", RFC 8321, DOI 10.17487/RFC8321,
              January 2018, <>.

   [RFC8655]  Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", RFC 8655,
              DOI 10.17487/RFC8655, October 2019,

   [RFC8939]  Varga, B., Ed., Farkas, J., Berger, L., Fedyk, D., and S.
              Bryant, "Deterministic Networking (DetNet) Data Plane:
              IP", RFC 8939, DOI 10.17487/RFC8939, November 2020,

Authors' Addresses

   Greg Mirsky
   ZTE Corp.


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   Fabrice Theoleyre
   300 boulevard Sebastien Brant - CS 10413
   67400 Illkirch - Strasbourg

   Phone: +33 368 85 45 33

   Georgios Z. Papadopoulos
   IMT Atlantique
   Office B00 - 102A
   2 Rue de la Châtaigneraie
   35510 Cesson-Sévigné - Rennes

   Phone: +33 299 12 70 04

   Carlos J. Bernardos
   Universidad Carlos III de Madrid
   Av. Universidad, 30
   28911 Leganes, Madrid

   Phone: +34 91624 6236

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