TODO Working Group                                         P. Bellavista
Internet-Draft                                               L. Foschini
Intended status: Informational                                 L. Patera
Expires: 4 September 2022                          University of Bologna
                                                                M. Fogli
                                                            C. Giannelli
                                                           C. Stefanelli
                                                   University of Ferrara
                                                                D.Z. Lou
                                                                  Huawei
                                                            3 March 2022


  A Framework for QoS-Enabled Semantic Routing in Industrial Networks
                  draft-bellavista-semantic-sdn-mom-00

Abstract

   Industrial networks pose unique challenges in realizing a
   communication substrate on the shop floor.  Such challenges are due
   to strict Quality of Service (QoS) requirements, a wide range of
   protocols for data exchange, and highly heterogeneous network
   infrastructures.  In this regard, this document proposes a framework
   for QoS-enabled semantic routing in industrial networks.  Such a
   framework aims at providing loosely-coupled, asynchronous
   communications, fine-grained traffic management (delivery semantics
   and flow priorities), and in-network traffic optimization.

Discussion Venues

   This note is to be removed before publishing as an RFC.

   Source for this draft and an issue tracker can be found at
   https://github.com/fglmtt/draft-bellavista-semantic-sdn-mom.

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/.







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   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 4 September 2022.

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
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Target Scenario . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Principles and Design Guidelines  . . . . . . . . . . . . . .   7
   5.  Architecture  . . . . . . . . . . . . . . . . . . . . . . . .   9
   6.  Conventions and Definitions . . . . . . . . . . . . . . . . .  12
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   This Internet Draft defines a framework for Quality of Service (QoS)-
   enabled semantic routing in industrial networks.  The term "semantic
   routing" refers to a form of routing based on additional semantics
   other than mere IP addresses
   [I-D.draft-farrel-irtf-introduction-to-semantic-routing-03].  Along
   with the semantics carried in packet headers, such routing may also
   depend on policy coded in, configured at, or signaled to network
   devices.  A network device is an element that receives/transmits
   packets and performs network functions on them, such as forwarding,



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   dropping, filtering, and packet header (or payload) manipulation,
   among others.  Network devices may operate in, above, and below the
   network layer.

   The framework described in this draft uses the overlay networking to
   provide a semantic routing substrate that operates both at the
   application and network level.

   At the application level, the framework consists of Message-Oriented
   Middleware (MOM) and Application Gateways (AGWs).  The MOM allows
   decoupling senders and receivers, sorts messages in topics of
   interest, and provides delivery semantics (e.g., at most once, at
   least once, and exactly once).  The AGWs sit nearby industrial
   machines that are not natively compliant with the protocols the
   framework relies on.  For example, some legacy industrial machines
   may not even support IP-based communications.  It is worth mentioning
   that the typical lifetime of industrial equipment is 10 to 15 years
   (even longer sometimes), and in many cases, the software cannot be
   updated due to manufacturers' policy.  Accordingly, AGWs translate
   the plethora of (proprietary) protocols that coexist on the shop
   floor towards the one(s) used by the framework.

   At the network level, the framework combines two paradigms: Software-
   Defined Networking (SDN) [RFC7426] and In-Network Processing (INP)
   [ZILBERMAN2019], [PORTS2019].  Although the MOM enables critical
   features in message dispatching, it does not control how packets flow
   through network devices along routing paths.  This is where SDN comes
   in.  Specifically, the SDN controller computes optimal routes to meet
   the QoS requirements and configures network devices accordingly.  The
   term INP refers to executing end-host programs within network
   devices.  Such INP-enabled network devices operate at a line rate,
   processing packets as they traverse them without increasing the
   overall network load.  Given that the SDN controller holds a network-
   wide view, it also knows which network devices support INP and which
   do not.  The SDN controller may redirect flows towards target INP-
   enabled network devices based on the processing functions they
   provide.

   The objectives that the framework targets are the following:

   *  Loosely-coupled, asynchronous communications;

   *  Fine-grained traffic management (delivery semantics and flow
      priorities);

   *  In-network traffic optimization.





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   The remainder of this draft is structured as follows.  First,
   Section 2 details the target scenario.  Then, Section 3 provides the
   requirements of the target scenario.  Lastly, Section 4 presents the
   principles and design guidelines of the framework and Section 5
   depicts its architecture.

2.  Target Scenario

   Traditionally, a shop floor includes industrial machines,
   Programmable Logic Controllers (PLCs), and Human-Machine Interfaces
   (HMIs).  Typically, industrial machines are equipped with sensors and
   actuators, PLCs control manufacturing processes, and human operators
   interact with and receive feedback from industrial machines through
   HMIs.  In such legacy industrial networks, the message dispatching
   was primarily oriented to monitor operational- and safety-related
   machine parameters.

   Nowadays, the shop floor has become more articulated due to the
   advent of the Industrial Internet of Things (IIoT).  On the one hand,
   IIoT devices enable business-critical services (e.g., predictive
   maintenance) cost-effectively.  On the other hand, they dramatically
   increase overall network traffic volume, infrastructure
   heterogeneity, and cyber security threats.

   The heterogeneity is not only about the industrial equipment itself
   but also in how such equipment disseminates information.  The
   plethora of (proprietary) protocols that machines use to exchange
   data makes machine-to-machine communications challenging.

   Additionally, the shop floor may include dynamic industrial equipment
   (e.g., automated guided vehicles) that communicate on the move.  Such
   dynamic equipment may abruptly migrate communications across
   different access points according to the physical location at a given
   time.

   Therefore, modern industrial environments stress the network
   infrastructure more than traditional ones, where network traffic was
   fairly limited to mission-critical information generated by fixed
   network equipment.

   In fulfilling current industrial guidelines for cyber security (e.g.,
   IEC 62443 [IEC62443]), the industrial topology should consist of
   several shop floor subnets and a control room subnet.  Figure 1
   depicts an industrial topology compliant with such guidelines.







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    Control Room Subnet
   +---------------------------------------------------------------+
   |                                                               |
   |  +------------+ +------------+ +------------+ +------------+  |
   |  |    SDN     | |    AGW     | |    MOM     | |    INP     |  |
   |  | Controller | | Controller | | Controller | | Controller |  |
   |  +-----+------+ +-----+------+ +------+-----+ +------+-----+  |
   |        |              |               |              |        |
   |        +--------------+-------+-------+--------------+        |
   |                               |                               |
   |                           +---+---+                           |
   |                           |  SGW  |                           |
   +---------------------------+---+---+---------------------------+
                                   |
   ----------------+---------------+----------------+---------------
                   |                                |
   +-----------+---+---+----------+ +-----------+---+---+----------+
   |           |  SGW  |          | |           |  SGW  |          |
   |           +---+---+          | |           +---+---+          |
   |               |              | |               |              |
   |  +------------+-----------+  | |  +----------+ |              |
   |  |           AGW          |  | |  |   AGW    +-+--+------+    |
   |  +-+------+------+------+-+  | |  +-+------+-+    |      |    |
   |    |      |      |      |    | |    |      |      |      |    |
   |  +-+------+------+------+-+  | |  +-+------+-+  +-+------+-+  |
   |  |        Machines        |  | |  | Machines |  | Machines |  |
   |  +------------------------+  | |  +----------+  +----------+  |
   |                              | |                              |
   +------------------------------+ +------------------------------+
    Shop Floor Subnet 1              Shop Floor Subnet N

                     Figure 1: Target network topology

   Note that:

   *  With "Machines", we refer to any shop floor entity (e.g.,
      industrial machines, IIoT devices, PLCs, and so on) doing
      networking.  This document makes no distinction among shop floor
      entities because AGWs can normalize their outputs if needed;

   *  Each shop floor subnet may be provided with one or more AGWs,
      depending if machines support the protocols used by the framework;

   *  Each subnet is provided with a Subnet Gateway (SGW), which is a
      network device.  Additional network devices may be placed between
      different subnets as well as within subnets.





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   The network devices interconnecting the subnets form the industrial
   network backbone.  The outcome is a multihop multipath topology
   providing point-to-point connections with differentiated performance.

   The framework described in this document targets the scenario
   depicted in Figure 1.  The framework components (i.e., MOM, AGW, SDN,
   and INP controllers) run within the control room subnet.  Note that
   also other services may run in the control room subnet along with
   them.  Typical examples are the Manufacturing Execution System (MES)
   and the Enterprise Resource Planning (ERP).

3.  Requirements

   The transition from traditional to modern industrial environments
   raised critical communications challenges exposed in Section 2.  In
   this regard, it is worth remarking that industrial machines typically
   have long lifetimes (decades), high costs (millions of USD), and
   restrictive manufacturers' policies in place (e.g., to prevent
   firmware updates).  Accordingly, the communications substrate should
   face such challenges by fulfilling additional requirements.

   First, non-mission-critical and mission-critical traffic should be
   distinguished.  Typically, non-mission-critical flows (e.g.,
   monitoring of vibrations) are more massive than mission-critical ones
   (e.g., alerting human operators about dangerous events), thus the
   former may easily take network resources at the expense of the
   latter.  This requires per-flow traffic management, ranging from flow
   prioritization (mission-critical flows go first, then non-mission-
   critical ones) to data aggregation and filtering to reduce the
   traffic traversing the network.  Since the industrial control
   typically runs cyclically in millisecond level, the control traffic,
   especially the mission-critical traffic, demands high QoS in terms of
   latency, jitter, and extremely low packet loss ratio.

   Second, the industrial communication demands high reliability.  The
   telecommunication equipment deployed in the Internet typically
   guarantee the reliability to 99.99%. However, the industrial systems
   need to be much more reliable, from 99.9999% to 99.99999%, in order
   to reduce the downtime of the production line.  It requires the
   industrial network to equip extra measures to support it.

   Third, machine-to-machine communications should be enabled
   straightforwardly, notwithstanding the plethora of (proprietary)
   dialects that coexist at the shop floor level, which enables the
   interoperability of different shop floor devices.  This requires
   connectors to translate such dialects towards a common one and
   metadata to express the semantics.  Intermediate nodes may use
   semantics to process packet payloads according to the information



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   they carry.  For example, an intermediate node may average a given
   number of consecutive temperature values (data aggregation) rather
   than drop values of little application interest (data filtering).

   Lastly, machines should keep communicating on the move without
   affecting overall performance.  For example, an automated guided
   vehicle may move from a shop floor subnet to another.  By doing so,
   the vehicle changes the WiFi access point (i.e., SGW) used to access
   the network.  As a result, the flows sent out by such a vehicle need
   to be rescheduled accordingly.  This requires not only to reconfigure
   network devices dynamically, but also to do so in compliance with
   other flows already in place.

   In this context, edge computing plays a crucial role in enabling the
   design and implementation of novel distributed control functions with
   parts that are hosted on the edge nodes located in the production
   plant premises and close to the controlled sensors/actuators,
   primarily to increase reliability and decrease latency.  In the
   following, we discuss a framework for QoS-Enabled Semantic Routing in
   Industrial Networks capable of synchronizing several entities in a
   simplified manner via a unique logical configuration interface
   ("Northbound interface").

4.  Principles and Design Guidelines

   Future industrial networks will be characterized by an unprecedented
   degree of heterogeneity and complexity.  Traditional solutions,
   mainly based on the direct interconnection of machines one to each
   other and machines towards the control room, cannot provide the
   required degree of flexibility.  This leads to exploring novel
   solutions to manage the deluge of data generated by IIoT devices and
   provide QoS-driven network (re)configuration.

   By considering the momentum of MOM as an enabler of the Industry 4.0
   vision, we believe it will become a pillar of future industrial
   ecosystems.  Although it enables critical features to facilitate
   message dispatching independent from actual machine location, it does
   not control how packets flow through middle network devices along the
   routing path.  In fact, once a message is sent from a broker to a
   consumer (or vice versa, from a producer to a broker), the path the
   message traverses is beyond the MOM's control.  However, the ability
   to dictate the behavior of middle network devices is essential to
   satisfy stringent QoS requirements.  This is where the SDN paradigm
   comes in.







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   The SDN controller eases configuration and management of network
   devices, which act as the (distributed) communication substrate
   between the machines and the MOM.  In addition, the SDN controller
   provides network-wide abstractions to define and enforce fine-grained
   network policies.

   At the top level, the MOM identifies the destination nodes a message
   should be dispatched, along with the delivery semantics (e.g., at
   most once, at least once, or exactly once) to be applied.  At the
   bottom level, AGWs deployed close to machines act as intermediaries
   between the machines (and the plethora of protocols they speak) and
   the MOM.  In the middle level, the SDN controller exploits its
   network-wide view to (re)configure the network devices according to
   the QoS requirements.

   Based on the MOM-SDN interplay, network devices can be properly
   configured:

   *  To select the best route towards the destination and forward
      messages accordingly;

   *  To manage competing traffic flows in a coordinated manner, e.g.,
      to ensure prompt dispatching of mission-critical messages even if
      at the expense of less critical messages;

   *  To enforce INP for traffic optimization, e.g., by merging
      consecutive packets in a single one.

   For example, by considering two traffic flows between the MOM broker
   and a machine, proper routing table management allows to forward
   traffic flows tagged as "mission-critical" via a large-bandwidth low-
   latency path (if available).  Besides, traffic flows tagged as "not-
   urgent" may be delayed, where the magnitude of the imposed delay may
   also depend on the current level of network saturation.  Finally, an
   INP-enabled network device may exploit the semantics about the
   carried data to provide content-based message management.  For
   instance, it is possible to forward packets only if they satisfy a
   given rule, e.g., if they carry temperature values greater than a
   given threshold, or to apply functions to send pre-processed values,
   e.g., sending only one packet with the average temperature resulting
   from a series of received temperature values.  Note that content-
   based message management enables decisions on what is carried within
   packet payloads rather than only on packet headers (mere forwarding).
   However, since payload inspection and manipulation may introduce
   additional delays, content-based message management should be
   enforced as much as possible but without burdening mission-critical
   traffic flows.




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   From a functional point of view, the INP level sits atop the data
   forwarding level.  As in the case of SDN deployment, we do not argue
   that all the network devices should be INP-enabled.  Instead, we
   promote a pragmatic approach where legacy and novel solutions
   cooperate effectively.  Since the SDN controller holds a network-wide
   view, it knows which network devices offer INP and which do not.
   Therefore, traffic can be optimally handled by maximizing INP (e.g.,
   routing of packets carrying values that can be averaged towards
   network devices providing that aggregation function) while ensuring
   QoS requirements.

5.  Architecture

   The proposed architecture, mostly working at the application layer,
   adopts the typical SDN approach by identifying two main areas:
   Control Plane and Data Plane.  In the Control Plane, the following
   components are deployed: the MOM controller, interacting with the MOM
   broker; the In-Network Processing (INP) controller, managing the INP
   units; the SDN controller, controlling network elements; and the
   Gateway controller, managing the many application gateways deployed
   in the environment.  The Data Plane consists of the implementation of
   the MOM, the INP units, the SDN-enabled network elements, and the
   Gateway components.

                               PROTO E
      +-------------+-------------+---------------------+     NORTHBOUND
      |             |             |                     |          IFACE
      v             v             v                     v
+-----+-----+ +-----+-----+ +-----+-----+         +-----+-----+
|  GATEWAY  | |    SDN    | |    INP    |         |    MOM    |  CONTROL
|CONTROLLER | |CONTROLLER | |CONTROLLER |         |CONTROLLER |    PLANE
+-----+-----+ +-----+-----+ +-----+-----+         +-----+-----+
      ^             ^             ^                     ^
      |PROTO A      |PROTO B      |PROTO C       PROTO D|     SOUTHBOUND
      |             |             |                     |         IFACES
      v             |             v                     v
+-----+-----+       |       +-----+-----+         +-----+-----+
|  GATEWAY  |       |       | INP UNIT  |         |    MOM    |
+-----------+       v       +-----------+         +-----------+     DATA
+-------------------+-----------------------------------------+    PLANE
|                                SDN                          |
+-------------------------------------------------------------+

     Figure 2: Functional/layered view of the SDN-MOM distributed
                            architecture.

   Each component has different duties and responsibilities:




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   *  The MOM Controller is demanded to control and re-route the traffic
      flowing into the MOM topics.  It uses information coming from the
      northbound interface and returns back control messages for the SDN
      controller.  It also performs decisions based on the message
      headers and on the information received from the SDN Controller
      and the Gateway Controller.  The messages can be forwarded to a
      specific topic, duplicated among different topics, or consumed and
      pulled out from the flow.  At the same time, the MOM Controller
      issues information that will be used from the SDN controller to
      correctly configure the SDN devices for achieving the desired
      level of QoS on the specific output flow.

   *  The Message-Oriented Middleware (MOM) is one of the core pieces of
      our infrastructure.  It is the logical single point of
      communication between several firm sectors.  It contains topics
      written by the Gateways and can be read by multiple other
      Gateways, based on the plant communication requirements.  The MOM
      is responsible for guaranteeing differentiated QoS policies with
      different semantics.  Typically, the at-most-once semantic can be
      used for best-effort machinery traffic.  Otherwise, at-least-once
      semantic can be used for monitoring mission-critical assets and
      for controlling traffic.  Moreover, some messages can be sent with
      high priority, guarantying differentiated traffic management and
      avoiding congestion.

   *  The SDN Controller centralizes network intelligence in a separate
      component, disassociating the packet forwarding process from the
      routing processes.  The SDN Control Plane consists of one or more
      controllers that are considered as the brain of the network, where
      all intelligence is embedded.  The SDN Controller configures the
      network resources.  In our infrastructure, the SDN Controller has
      full knowledge of the network and the paths, guarantying a fine-
      grained ruling of the traffic coming from the Gateways.
      Differentiated policies can be applied based on the content of the
      messages, following the received northbound rules.  The traffic
      can be duplicated, aggregated, blocked, forwarded, and re-routed
      on different data paths.














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   *  The Gateway Controller emits control messages directed to the
      Gateways of the infrastructure.  It works in strict coordination
      with the MOM Controller and SDN Controller, to avoid congestions
      and to maintain topic abstractions coherent with the real machine
      distribution.  Its management duties comprehend: checking of the
      state of all the gateways, which must be configured coherently
      with the machine on which are acting; synchronization with SDN and
      MOM controllers, that can send re-configuration messages to avoid
      congestion.  Practically, it can manage the header that is applied
      from the Gateways to each packet, modify the priority of the
      messages, and define levels of QoS applied directly to the data-
      extraction phase.

   *  The Gateways duties comprehend the data gathering, the data
      transformation to an internal MOM-specific representation, the
      header addition, and the interconnection between the industrial
      machinery world and the MOM topic-centric world.  In industrial
      scenarios, it is common to have machines that use different
      languages and protocols for data exporting and representation
      (e.g.  Modbus, Profibus, OPC UA, OMG DDS, EtherCAT).  For this
      purpose, the Gateways can be specialized with ad-hoc libraries and
      push or pull strategies based on the specific machinery from which
      to gather information.  Moreover, the QoS can be managed directly
      at this level, avoiding high useless throughput when the plant is
      working in a normal condition.

   *  The INP Controller is demanded to control the INP elements of the
      platform.  Its duties comprehend synchronization between INP
      units, deployment of the correct function for the specific INP
      unit input flow, management of the QoS on the INP components.

   *  The INP Units are hardware/software components demanded to reduce
      or pre-process the data in ingress.  The flows are manipulated
      accordingly to INP Controller rules and the typical map/reduce
      functions can be applied in the flow.

   Figure 2 depicts a schematic of the entire infrastructure.  Dashed
   paths between controller entities in the control plane (Protocol E),
   and between control and data planes represent the management/
   configuration data exchanges that are logically separate from data
   flows (Protocols A, B, C, D).  Data flows start from the Gateways
   (connected to the machinery via the machine-specific protocols) and
   are sent through the SDN Component, which traverses the entire
   platform.

   The proposed platform can be seen as an integration of several
   software architectures in a unique system capable of interacting with
   them in a uniform and controlled way.  In this draft, we omit our



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   specific implementation of each protocol, and we ask the RFC
   community for possible implementations capable of satisfying each
   step necessities and requirements.  Although certain interfaces can
   be easily implemented using standard de facto protocols, for
   instance, Protocol B can be found in to Open Networking Foundation,
   "OpenFlow Switch Specification", Version 1.5.1, October 2015,
   https://opennetworking.org/wp-content/uploads/2014/10/openflow-
   switch-v1.5.1.pdf (https://opennetworking.org/wp-
   content/uploads/2014/10/openflow-switch-v1.5.1.pdf), and Protocol C
   can be The P4 Language Consortium, "P416 Language Specification",
   Version 1.2.1, June 2020, https://p4.org/p4-spec/docs/
   P4-16-v1.2.1.html (https://p4.org/p4-spec/docs/P4-16-v1.2.1.html),
   the others interfaces remain open issues and must be implemented as
   ad-hoc solutions.

6.  Conventions and Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "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.

7.  Security Considerations

   While this Internet Draft is not primarily focused on addressing
   security issues, it is of paramount importance to provide some
   security considerations.  In particular note that since the proposed
   solution should be adopted in industrial environments, possible
   security threats could cause not only issues related to the IT
   domain, such as service unavailability and data leak, but also to the
   OT domain, thus also including potential impact to the safety of
   human operators.  To this purpose, we consider of paramount
   importance (and push for) the adoption of best practices in terms of
   security and safety of industrial environments and thus we advise the
   application of the IEC 62443 family standard as a prerequisite for
   the deployment of the proposed solution.  In addition, by focusing on
   the proposed solution we recognize that while it is suitable to
   maximize the QoS of higher priority industrial applications, it
   should not be achieved to the total detriment of lower priority
   industrial applications, whose packets should be anyway delivered.

8.  IANA Considerations

   This document has no IANA actions.

9.  References




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9.1.  Normative References

   [I-D.draft-farrel-irtf-introduction-to-semantic-routing-03]
              Farrel, A. and D. King, "An Introduction to Semantic
              Routing", Work in Progress, Internet-Draft, draft-farrel-
              irtf-introduction-to-semantic-routing-03, 22 January 2022,
              <https://datatracker.ietf.org/doc/html/draft-farrel-irtf-
              introduction-to-semantic-routing-03>.

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

   [RFC7426]  Haleplidis, E., Ed., Pentikousis, K., Ed., Denazis, S.,
              Hadi Salim, J., Meyer, D., and O. Koufopavlou, "Software-
              Defined Networking (SDN): Layers and Architecture
              Terminology", RFC 7426, DOI 10.17487/RFC7426, January
              2015, <https://doi.org/10.17487/RFC7426>.

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

9.2.  Informative References

   [BELLAVISTA2018]
              Bellavista, P., Dolci, A., and C. Giannelli, "MANET-
              oriented SDN: Motivations, Challenges, and a Solution
              Prototype", DOI 10.1109/wowmom.2018.8449805, 2018 IEEE
              19th International Symposium on "A World of Wireless,
              Mobile and Multimedia Networks" (WoWMoM), June 2018,
              <https://doi.org/10.1109/wowmom.2018.8449805>.

   [BELLO2020]
              Bello, L., Lombardo, A., Milardo, S., Patti, G., and M.
              Reno, "Experimental Assessments and Analysis of an SDN
              Framework to Integrate Mobility Management in Industrial
              Wireless Sensor Networks", DOI 10.1109/tii.2020.2963846,
              IEEE Transactions on Industrial Informatics Vol. 16, pp.
              5586-5595, August 2020,
              <https://doi.org/10.1109/tii.2020.2963846>.

   [IEC62443] International Electrotechnical Commission, "IEC 62443:
              Industrial network and system security".






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   [KAUR2018] Kaur, K., Garg, S., Aujla, G., Kumar, N., Rodrigues, J.,
              and M. Guizani, "Edge Computing in the Industrial Internet
              of Things Environment: Software-Defined-Networks-Based
              Edge-Cloud Interplay", DOI 10.1109/mcom.2018.1700622, IEEE
              Communications Magazine Vol. 56, pp. 44-51, February 2018,
              <https://doi.org/10.1109/mcom.2018.1700622>.

   [LI2018]   Li, X., Li, D., Wan, J., Liu, C., and M. Imran, "Adaptive
              Transmission Optimization in SDN-Based Industrial Internet
              of Things With Edge Computing",
              DOI 10.1109/jiot.2018.2797187, IEEE Internet of Things
              Journal Vol. 5, pp. 1351-1360, June 2018,
              <https://doi.org/10.1109/jiot.2018.2797187>.

   [NATESHA2021]
              V, N. and R. Guddeti, "Fog-Based Intelligent Machine
              Malfunction Monitoring System for Industry 4.0",
              DOI 10.1109/tii.2021.3056076, IEEE Transactions on
              Industrial Informatics Vol. 17, pp. 7923-7932, December
              2021, <https://doi.org/10.1109/tii.2021.3056076>.

   [PORTS2019]
              Ports, D. and J. Nelson, "When Should The Network Be The
              Computer?", DOI 10.1145/3317550.3321439, Proceedings of
              the Workshop on Hot Topics in Operating Systems, May 2019,
              <https://doi.org/10.1145/3317550.3321439>.

   [RFC5870]  Mayrhofer, A. and C. Spanring, "A Uniform Resource
              Identifier for Geographic Locations ('geo' URI)",
              DOI 10.17487/rfc5870, RFC Editor report, June 2010,
              <https://doi.org/10.17487/rfc5870>.

   [ZILBERMAN2019]
              Zilberman, N., "In-Network Computing", 2019,
              <https://www.sigarch.org/in-network-computing-draft/>.

Acknowledgments

   TODO acknowledge.

Authors' Addresses

   Paolo Bellavista
   University of Bologna
   Email: paolo.bellavista@unibo.it






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   Luca Foschini
   University of Bologna
   Email: luca.foschini@unibo.it


   Lorenzo Patera
   University of Bologna
   Email: lorenzo.patera@unibo.it


   Mattia Fogli
   University of Ferrara
   Email: mattia.fogli@unife.it


   Carlo Giannelli
   University of Ferrara
   Email: carlo.giannelli@unife.it


   Cesare Stefanelli
   University of Ferrara
   Email: cesare.stefanelli@unife.it


   David Zhe Lou
   Huawei
   Email: zhe.lou@huawei.com























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