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Versions: 00                                                            
Detnet                                                X. Vilajosana, Ed.
Internet-Draft                                              Worldsensing
Intended status: Informational                               T. Mahmoodi
Expires: January 8, 2017                           King's College London
                                                               S. Spirou
                                                        Intracom Telecom
                                                            P. Vizarreta
                                     Technical University of Munich, TUM
                                                            July 7, 2016


                   Wind Park requirements for Detnet
              draft-vilajosana-detnet-windfarm-usecase-00

Abstract

   This document analyses the use case requirements for deterministic
   flows in a wind park network.  It inlcudes the intra-domain and
   inter-domain requirements.

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
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   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
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   (http://trustee.ietf.org/license-info) in effect on the date of
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   to this document.  Code Components extracted from this document must



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   2
   3.  Use Case description  . . . . . . . . . . . . . . . . . . . .   3
   4.  Traffic Demand  . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Intra-Domain network considerations . . . . . . . . . . . . .   6
   6.  Inter-Domain network considerations . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  Wind Park Networks Future . . . . . . . . . . . . . . . . . .   8
   9.  Wind Park Network Wish List . . . . . . . . . . . . . . . . .   9
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     11.2.  External Informative References  . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The wind power industry has been selected as a representative example
   of industrial networks with strict performance, security, and
   reliability requirements.  A Wind Park network is part of a
   Supervisory Control and Data Acquisition (SCADA) system that
   regulates power production from each wind turbine and from the entire
   park.  The SCADA system extends beyond the Wind Park, over the
   Internet, to a remote control centre.  Moreover, this network
   interconnects sensors and actuators and a hierarchy of purpose-built
   controllers and repositories via domain-specific protocols (e.g., IEC
   1041, MODBUS2) in a static and secure topology.  In this document the
   Intra domain requirements, referring to the network consiserations in
   terms of latency, jitter, delay tolerance, within the same
   administrative domain will be presented.  Analogously, and as Wind
   Parks are connected to remote Control Centers the requirements and
   considerations for the Inter domain reliability, jitter, latency and
   delay tolerance will be outlined.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].






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3.  Use Case description

   In a Wind Park, the wind turbines represent a complex system of
   sensors, actuators and an internal controller, located offshore or in
   remote locations that communicate with a central control or master
   SCADA station over reliable communication network.  Wind turbines are
   grouped in radials to maximize the energy production.  The size of
   the wind park varies significantly; having the biggest offshore wind
   parks up to 200 wind turbines.  Depending on the size of the park,
   there might be an additional substation located close to turbines to
   facilitate power transportation to the utility grid with minimum
   losses [Sie13], [Kri03].  On another side, local control center
   combines several functionalities necessary for control and management
   of the wind park.  SCADA comprise power plant control function to
   synchronize and coordinate operation of the wind turbines in the
   park, network management system (NMS) for network configuration,
   performance and fault monitoring and different servers to collect and
   store the metering data and status information from sensors, as well
   as gateway to the other control centers and Internet [Spe09],
   [Pet11].  The communication system between field devices and SCADA
   has to be reliable to facilitate control and management of the wind
   park.  Wind power plant control and monitoring system have stringent
   latency requirements, and reconfiguration of the network in the case
   of a failure has to be done quickly.  The most common way to improve
   reliability is to connect wind turbines in a ring in order to provide
   resistance to single link or node failure.  Additionally, backup
   microwave links can be built to improve the overall system
   availability.























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   Figure 1: Wind turbine control network


        |
        |
        |  +-----------------+
        |  |   +----+        |
        |  |   |WTRM| WGEN   |
   WROT x==|===|    |        |
        |  |   +----+    WCNV|
        |  |WNAC             |
        |  +---+---WYAW---+--+
        |      |          |
        |      |          |        +----+
               |WTRF      |        |WMET|
               |          |        |    |
        Wind Turbine      |        +--+-+
        Controller        |           |
          WTUR |          |           |
          WREP |          |           |
          WSLG |          |           |
          WALG |     WTOW |           |


4.  Traffic Demand

   Figure 1 presents the subsystems that operate a wind turbine.  This
   subsystems include the rotor (WROT) control, the nacelle control
   (WNAC), the transmission control (WTRM), the generator (WGEN), the
   yaw controller of the tower head (WYAW), the in-turbine power
   converter (WCNV), the in-tower power transformer (WTRF) and an
   external meteorological station providing real time information to
   the controllers of the tower (WMET).  Traffic characteristics
   relevant for the network planning and dimensioning process in a wind
   turbine scenario are listed below.  The values in this section are
   based mainly on the relevant references [Ahm14] [Spe09].  Each
   logical node (Figure 1) is a part of the metering network and
   produces analogue measurements and status information that must
   comply with different specifications in terms of data rate.












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   Table 2: Wind turbine data rate constraints

+----------+----------+----------+------------+----------+-------------+
|Subsystem |# Sensors | # Analog | Data  rate | # Status | Data  rate  |
|          |          |  Samples |(bytes/sec) | Samples  | (bytes/sec) |
+----------+----------+----------+------------+----------+-------------+
|   WROT   |    14    |     9    |     642    |     5    |     10      |
|   WTRM   |    18    |    10    |    2828    |     8    |     16      |
|   WGEN   |    14    |    12    |   73764    |     2    |      4      |
|   WCNV   |    14    |    12    |   74060    |     2    |      4      |
|   WTRF   |    12    |     5    |   73740    |     2    |      4      |
|   WNAC   |    12    |     9    |     112    |     3    |      6      |
|   WYAW   |     7    |     8    |     220    |     4    |      8      |
|   WTOW   |     4    |     1    |       8    |     3    |      6      |
|   WMET   |     7    |     7    |     228    |     -    |      -      |
+----------+----------+----------+------------+----------+-------------+
|   Total  |   102    |    73    |  225544    |    29    |     58      |
+----------+----------+----------+------------+----------+-------------+


   Quality of Service (QoS) requirements of different services are
   presented in the Table 2.  The requirements are defined by IEEE 1646
   standard [IEEE1646] and IEC 61400 standard [IEC61400].




























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   Table 3: Wind turbine Reliability and Latency constraints


   +-----------+----------+-------------+-----------------+
   |  Service  |  Latency | Reliability |Packet Loss Rate |
   +-----------+----------+-------------+-----------------+
   | Analogue  |          |             |                 |
   | measure   |   16 ms  |    99.99%   |   < 10-6     |
   +-----------+----------+-------------+-----------------+
   |  Status   |          |             |                 |
   |information|   16 ms  |    99.99%   |   < 10-6     |
   +-----------+----------+-------------+-----------------+
   |Protection |          |             |                 |
   |  traffic  |    4 ms  |   100.00%   |   < 10-9     |
   +-----------+----------+-------------+-----------------+
   | Reporting |          |             |                 |
   |and logging|    1 s   |    99.99%   |   < 10-6     |
   +-----------+----------+-------------+-----------------+
   |  Video    |          |             |   no specific   |
   | surveill. |    1 s   |    99.00%   |   requirement   |
   +-----------+----------+-------------+-----------------+
   | Internet  |          |             |   no specific   |
   |connection |   60 min |    99.00%   |   requirement   |
   +-----------+----------+-------------+-----------------+
   | Control   |          |             |                 |
   | traffic   |   16 ms  |   100.00%   |   < 10-9     |
   +-----------+----------+-------------+-----------------+
   | Data      |          |             |                 |
   | polling   |   16 ms  |    99.99%   |   < 10-6     |
   +-----------+----------+-------------+-----------------+

5.  Intra-Domain network considerations

   A Wind turbine is composed of a large set of subsystems (sensors,
   actuators) that require time critical operation.  The time-
   criticallity of different actions is shwon in Table 3.  These
   subsystems are connected to an intra-domain network used to monitor
   and control the operation of the turbine and connect it to the SCADA
   subsystems.  The different components are inter-connected using fiber
   optics, industrial buses, industrial ethernet, EtherCat or a
   combination of them.  Industrial signaling and control protocols such
   as Modbus, Profibus, Profinet and EtherCat are used directly on top
   of the L2 or encapsulated over TCP/IP.

   The Data collected from sensors or condition monitoring systems is
   multiplexed into fiber cables for transmission to the base of the
   tower and to remote control centers.  The turbine controller
   continuously monitors the condition of the wind turbine and collects



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   statistics on its operation.  As the name implies, the controller
   also manages a large number of switches, hydraulic pumps, valves, and
   motors within the wind turbine.

   There is usually a controller both at the bottom of the tower and in
   the nacelle.  The communication between these two controllers usually
   takes place using fiber optics instead of copper links.  Sometimes, a
   third controller is installed in the hub of the rotor and manages the
   pitch of the blades.  That unit usually communicates with the nacelle
   unit using serial communications.

6.  Inter-Domain network considerations

   As mentioned in the introduction, a remote control center that
   belongs to a grid operator, regulates the power output, enables
   remote actuation and monitors the health of one or more Wind Parks in
   tandem.  It connects to the local control center in a Wind Park over
   the Internet (Figure 2), via firewalls at both ends.  The AS path
   between the local control center and the Wind Park typically involves
   several ISPs at different tiers.  For example, a remote control
   center in Denmark can regulate a Wind Park in Greece over the normal,
   public AS path between the two locations.

   The remote control center is part of the SCADA system, setting the
   desired power output to the Wind Park and reading off the result once
   the new power output level has been set.  Traffic between the remote
   control center and the Wind Park typically consists of protocols like
   IEC 104 [IEC104], OPC XML-DA [OPCXML], Modbus [MODBUS], and SNMP
   [RFC3411].  Usually, QoS requirements are not strict, so no SLAs or
   service provisioning mechanisms (e.g., VPN) are employed.  Traffic
   flow across the domains is best effort.  In case of events like
   equipment failure, tolerance for alarm delay is in the order of
   minutes, due to redundant systems already in place.


















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+--------------+
|              |
|              |
| Wind Park #1 +----+
|              |    |      XXXXXX
|              |    |      X    XXXXXXXX               +----------------+
+--------------+    |   XXXX    X      XXXXX           |                |
                    +---+                  XXX         | Remote Control |
                        XXX    Internet      +---------+     Center     |
                    +----+X                XXX         |                |
+--------------+    |    XXXXXXX            XX         |                |
|              |    |          XX     XXXXXXX          +----------------+
|              |    |            XXXXX
| Wind Park #2 +----+
|              |
|              |
+--------------+

7.  Security Considerations

   On top of the classical requirements for protection of control
   signaling, it must be noted that Wind Farm networks operate on
   critical infrastructures with heterogeneous devices and networks.
   This includes heterogeneous L2 technologies that must be secured in a
   per link model.  Control and signaling occur at the transport layer
   and therefore end to end security mechanism must be installed.

8.  Wind Park Networks Future

   In the future we expect cloud-based SCADA systems controlling,
   storing and monitoring the critical and non-critical subsystems of
   the windfarm.  We foresee an increase in the number of sensing
   devices and technologies, combining wireless and wired capillars.  We
   foresee heterogeneous L2 technologies, homogenized by common IPv6
   frameworks such as those developed by 6TiSCH, 6lo, LPWAN and 6MAN.
   We expect windfarm networks to be operated by standardized and common
   management planes, enabling the orchestration of the different
   building blocks and underlaying technologies and being able to
   Internet-connect enabling service gurantees and remote operation with
   quality of service.  Therefore protocols for network management, flow
   control, increased reliability and security are mandatory in order to
   improve the operation of critical infrastructures, including in this
   case Wind Farms.








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9.  Wind Park Network Wish List

   The community would like to see a set of protocols that enable the
   inter-domain and the intra-domain operation of a wind park
   infrastructure satisfying the timing, security, availability and QoS
   constraints described above, such that the resulting converged
   network can replace the heterogeneous, sometimes propieatary field
   networks.  Ideally this connectivity should extend to the open
   Internet.  This would imply an architecture that can guarantee

      Low communication delays from <4 ms to 1000ms in the inter-domain
      network

      Low communication delays from <150 ms to 5000 ms in the intra-
      domain network

      Low jitter (< 1 ms)

      Tight feedback intervals (4ms - 10ms) in the intra-domain

      High network availability (up to 99.9999% )

10.  Acknowledgements

   This requirements have been extracted from the study of Wind Farms
   conducted within the 5GPPP Virtuwind Project.  The project is funded
   by tge European Union's Horizon 2020 research and innovation
   programme under grant agreement No 671648 (VirtuWind).

11.  References

11.1.  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,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3411]  Harrington, D., Presuhn, R., and B. Wijnen, "An
              Architecture for Describing Simple Network Management
              Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
              DOI 10.17487/RFC3411, December 2002,
              <http://www.rfc-editor.org/info/rfc3411>.








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11.2.  External Informative References

   [IEC61400]
              "International standard 61400-25: Communications for
              monitoring and control of wind power plants", June 2013.

   [IEEE1646]
              "Communication Delivery Time Performance Requirements for
              Electric Power Substation Automation", IEEE Standard
              1646-2004 , Apr 2004.

   [Sie13]    "Creating the most from wind, retrieved from siemens.com/
              wind-equipment", ACM International Conference on Mobile
              Computing and Networking (MobiCom) , June 2013.

   [Kri03]    Kristoffersen, J. and P. Christiansen, "Horns Rev Offshore
              Wind Farm: Its Main Controller and Remote Control
              System.", Wind Engineering, p. 351-360. , June 2003.

   [Spe09]    Sperotto, A., Sadre, R., Vliet, F., and A. Pras, "A First
              Look into SCADA Network Traffic", IP Operations and
              Management, p. 518-521. , June 2009.

   [Ahm14]    Ahmed, M. and R. Kim, "Communication network architectures
              for smart-wind power farms", Energies, p. 3900-3921. ,
              June 2014.

   [Pet11]    Pettener, A., "SCADA and communication networks for large
              scale offshore wind power systems", EIET Conference on
              Renewable Power Generation. , June 2011.

   [IEC104]   International Electrotechnical Commission, "International
              Standard IEC 60870-5-104: Network access for IEC
              60870-5-101 using standard transport profiles", June 2006.

   [OPCXML]   OPC Foundation, "OPC XML-Data Access Specification", Dec
              2004.

   [MODBUS]   Modbus Organization, Inc., "MODBUS Application Protocol
              Specification", Apr 2012.

Authors' Addresses









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   Xavier Vilajosana (editor)
   Worldsensing
   483 Arago
   Barcelona, Catalonia  08013
   Spain

   Phone: +34 (646) 633 681
   Email: xvilajosana@worldsensing.com


   Toktam Mahmoodi
   King's College London
   Strand, London WC2R 2LS
   London, London  WC2R 2LS
   UK

   Email: toktam.mahmoodi@kcl.ac.uk


   Spiros Spirou
   Intracom Telecom
   19.7 km Markopoulou Ave.
   Peania, Attiki  19002
   Greece

   Email: spis@intracom-telecom.com


   Petra Vizarreta
   Technical University of Munich, TUM
   Maxvorstadt, Arcisstrasse 21
   Munich, Germany  80333
   GE

   Email: petra.vizarreta@lkn.ei.tum.de
















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