Table of Contents

Welcome Message from the General Co-Chairs .................................................. 2

Welcome Message from the Program Co-Chairs ................................................ 3

ISPCS 2019 Symposium Committee ........................................................................ 4

ISPCS 2019 Organizers & Sponsors ......................................................................... 5

ISPCS 2019 Promotional Partners ............................................................................ 5

Plugfest ................................................................................................................................ 8

Sync School ......................................................................................................................... 8

Symposium ......................................................................................................................... 9 Keynote Speakers ......................................................................................................... 14 ISPCS 2020 Announcement ...................................................................................... 17

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Welcome Message from the General Co-Chairs Welcome to the 2019 International IEEE Symposium on Precision Clock Synchronization for Measurement, Control, and Communication (ISPCS). This year marks the 13th anniversary of the conference. It comes at a particularly exciting time as the next edition of the IEEE 1588 standard is in the final stages of completion of its IEEE-SA balloting process, and it is expected to be completed early next year once the process is completed and approved by IEEE-SA to be released for publication. It will be referred to as PTP v2.1 and will bring several new features to the protocol while preserving backwards compatibility with existing devices.

The Symposium is the principal forum in which researchers and practitioners from academia, industry, and government can exchange ideas and findings regarding precise clock synchronization over networks using protocols such as PTP. This year, we have an excellent program with three keynote speakers that will discuss the state of the art in precision clock synchronization from their respective industries. In addition to the cutting-edge research that will be presented here, we will also be covering the highlights of the next edition of the standard, from the industry professionals that are creating it.

The Plugfest is a key part of ISPCS, where implementers bring their IEEE 1588-compatible devices, software, and systems to demonstrate interoperability among them. The PTP ecosystem benefits from cooperation among vendors to resolve compatibility issues across a wide range of devices and systems and improve their customers’ experience with their end products. This year, we will test several of the new features that are being defined in the next edition of the standard. Participants will also have an opportunity to show their equipment in an exhibition to attendees.

This year, we are proud to present the ISPCS Sync School for the first time. The Sync School is a full-day session that is focused on relating practical information on PTP. Sync School participants will learn how to deploy and operate PTP on their networks. They will also get the chance to interact with demonstration PTP networks in a "hands-on" fashion. It is our hope that this session will aid users to achieve the best possible clock synchronization on their networks and applications.

This year, we are gathering for ISPCS in Portland, Oregon, which is home to an abundance of technology companies. It is well-known for its gardens, innovative restaurants, and Powell’s Books, one of the largest bookstores in the world. We encourage you to explore the city and take advantage of all Portland has to offer.

We would like to thank you, the attendees of ISPCS, for finding the conference valuable enough to take time out of your busy schedules to network with your peers here in Portland. We would also like to thank our sponsors whose support is instrumental to making the conference possible. And special thanks to the members of the ISPCS Organizing Committee for their dedication in the planning process, and to our event managers at Conference Catalysts, for all their hard work in making this conference a success.

With all that, we hope that you have a rewarding and insightful experience at ISPCS and that you enjoy the wonderful city of Portland and the Pacific Northwest.

Denis Reilly and Kang B. Lee ISPCS 2019 General Co-Chairs

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Welcome Message from the Program Co-Chairs

On behalf of the Program Committee, we are pleased to welcome you to ISPCS 2019, the thirteenth IEEE Symposium on Precision Clock Synchronization for Measurement Control and Communication. We welcome our speakers and attendees to Portland after holding the symposium in Europe last year.

We are delighted to have three keynote presentations this year. The first keynote, Highly Accurate Time Dissemination and Network Synchronization, will be given by Helmut Imlau, with Deutsche Telekom Technik GmbH. The second keynote, Clock Synchronization for the Low-latency Financial Sectors, will be given by Pedro V. Estrela, PhD, holding various positions in the financial industry. The third keynote, We’re Synchronized—Now Compute!, will be given by Kevin B. Stanton, PhD, a senior principal engineer at Intel.

The symposium Call for Papers resulted in high quality submissions coming from around the world. Just like the submissions, the members of the program committee formed a geographically diverse group representing both academia and industry. After careful deliberation, the program committee selected 17 papers to be presented at the conference, including full papers published in the ISPCS 2019 Proceedings.

Welcome to ISPCS 2019 and thank you for your attendance and contributions!

Radim Bartos and Lee Cosart ISPCS 2019 Program Committee Co-Chairs

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ISPCS 2019 Symposium Committee

ISPCS 2019 General Co-Chairs: Denis Reilly, Orolia USA Kang B. Lee, National Institute of Standards and Technology

ISPCS 2019 Program Co-Chairs: Lee Cosart, Microsemi Radim Bartos, University of New Hampshire

ISPCS 2019 Promotional Partners Chair: Hans Weibel, Zurich University of Applied Sciences

ISPCS 2019 Plugfest Committee: Douglas Arnold (Co-Chair), Meinberg USA Ken Harris (Co-Chair), Rockwell Automation Heiko Gerstung, Meinberg Nikolaus Kerö, Oregano Maciej Lipinski, CERN Sven Meier, NetTimeLogic Bob Noseworthy, University of New Hampshire Brandon Smith, UNH-IOL Judy Zhu, Kyland

ISPCS 2019 Program Committee: Douglas Arnold, Meinberg USA Rodney Cummings, National Instruments Grzegorz Daniluk, CERN Samer Darras, Microsemi Greg Dowd, Microsemi Pedro Estrela, IMC Financial Markets Paolo Ferrari, University of Brescia Geoffrey Garner, Consultant Rahul Nandkumar Gore, ABB Corporate Research Center Sulaiman Hussaini, University of Michigan Hubert Kirrmann, Solutil Maciej Lipinski, CERN John MacKay, Progeny Systems Cristian Marinescu, OMICRON Electronics GmbH

Sven Meier, NetTimeLogic GmbH Peter Meyer, Microsemi Tal Mizrahi, Huawei Network.IO Innovation Lab Claudio Narduzzi, Universita' di Padova Stefano Rinaldi, University of Brescia Peter Roberts, Nokia Silvana Rodrigues, Integrated Device Technology (IDT) Opher Ronen, Oscilloquartz an ADVA Optical Networking Company Stefano Ruffini, Ericsson Sebastian Schriegel, Fraunhofer IOSB-INA Karim Traore, Microsemi Hans Weibel, Zurich University of Applied Sciences

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ISPCS 2019Organizers & Sponsors

ISPCS 2019Promotional Partners

Platinum Partner:

Meinberg is a global leader in time synchronization solutions. The company’s flagship IEEE 1588 grandmaster clocks and NTP timeserver appliances have set the industry standard for innovation, flexibility and reliability – making them one of the market’s top network time synchronization solutions.

The Bad Pyrmont, Germany-based company designs and produces a range of devices, including:

- High-end PTP and NTP timeserver products - GPS, GLONASS, Galileo and BeiDou receivers, DCF77 / WWVB / MSF receivers - IRIG / AFNOR time code generators / readers - An array of accessories (antennas, diplexers, converters, signal distribution systems, etc.)

As a global company, Meinberg products are used around the world, delivering synchronization for mission critical applications in power grid/substation automation, digital broadcasting, telecommunication networks, aerospace, financial applications and cutting-edge research. All of its products are backed by a service network of distributors and partners located in over 40 countries.

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Silver Partners:

Advanced Test Equipment Rentals (ATEC) is a leading provider of component testing, signal analysis and communications test instruments worldwide. ATEC specializes in short-term and long-term rentals and also offers equipment for sale. Since its inception in 1981, ATEC has dedicated itself to guiding customers to the right equipment, empowering them with technical knowledge and delivering reliable, affordable rental solutions. Personnel in the defense, aerospace, automotive, communications, biomedical, consumer electric, health and safety fields along with others rely on ATEC’s vast inventory, next-day shipping and ISO 17025 accredited calibration lab for their testing needs.

ALBEDO Telecom is an International manufacturer of telecom synchronization nodes, testers and networking devices. We help R&D laboratories, Mobile and Telecom operators to install optical and electrical infrastructures that support any kind of applications based on voice, video and data. ALBEDO's core expertise range from PTP, SyncE, GbE, 10GbE, E1/T1, Jitter/Wander, OTDR, Cabling measurements, QoS and SLA technologies implemented in WAN emulators, Taps, Testers, Clocks and Systems. ALBEDO also offers consultancy and training services. ALBEDO has direct operations and representatives in more than 82 countries all over the world.

Calnex is the world-leader in test and measurement solutions to prove the performance of Ethernet synchronisation. Network Equipment Manufacturers use Calnex equipment to prove performance to rigorous standards for R&D and System Test. While Network Operators use Calnex equipment to test performance during trials and to troubleshoot problems in their networks. To date, Calnex has shipped products to over 330 customers in over 60 countries around the world. Calnex was named the 2015 winner of the Queen’s Award for Enterprise for International Trade, the UK’s highest accolade for business success.

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IEEE Standards Association (IEEE SA) is a leading consensus building organization that nurtures, develops and advances global technologies, through IEEE. We bring together a broad range of individuals and organizations from a wide range of technical and geographic points of origin to facilitate standards development and standards related collaboration. With collaborative thought leaders in more than 160 countries, we promote innovation, enable the creation and expansion of international markets and help protect health and public safety. Collectively, our work drives the functionality, capabilities and interoperability of a wide range of products and services that transform the way people live, work, and communicate.

Microchip Technology Inc. is a leading semiconductor supplier of smart, connected and secure embedded control solutions. Its easy-to-use development tools and comprehensive product portfolio enable customers to create optimal designs which reduce risk while lowering total system cost and time to market. The company’s solutions serve more than 125,000 customers across the industrial, automotive, consumer, aerospace and defense, communications and computing markets. Headquartered in Chandler, Arizona, Microchip offers outstanding technical support along with dependable delivery and quality.

For 40 years, NI has worked with engineers and scientists to provide answers to the most challenging questions. Through these pursuits, NI customers have brought hundreds of thousands of products to market, overcome innumerable technological roadblocks, and engineered a better life for us all. If you can turn it on, connect it, drive it, or launch it, chances are NI technology helped make it happen.

Oscilloquartz is a pioneer in time and frequency synchronization. We design, manufacture and deploy end-to-end synchronization systems that ensure the delivery and assurance of highly precise timing information over next-generation packet and legacy networks. As an ADVA Optical Networking company, we’re creating new opportunities for tomorrow's networks.

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Plugfest Sunday, September 22 - Tuesday, September 24Plugfest Co-Chairs: Douglas Arnold, Ken Harris Room: Belmont Ballroom

Sunday, September 22, 2019

09:00 Organizers Set-Up 12:00 Lunch 13:00 Attendee Set-Up and Default Profile Test 17:00 End of Sunday Session

Monday, September 23, 2019

08:30 Doors Open 09:00 Power and Telecom Profile Testing 11:45 Lunch 13:00 Power and Telecom Profile Testing 17:00 Free Testing 19:00 End of Monday Session

Tuesday, September 24, 2019

08:30 Doors Open 09:00 New Profiles/Technology Testing 11:45 Lunch 13:00 New Profiles/Technology Testing 15:00 Open Viewing for Non-Plugfest ISPCS Attendees 16:30 Tear Down, Pack Up 17:30 End of Tuesday Session

Sync School Tuesday, September 24 Room: Windsor Ballroom

08:30 Morning Lectures 10:00 Break 11:45 Lunch 12:45 Afternoon Sessions 14:30 Break 17:00 End of Sync School Session

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Symposium Wednesday, September 25, 2019 08:00 Registration & Morning Coffee

Belmont Foyer

09:00 Opening Session Belmont AB Conference General Co-Chair Remarks: Kang Lee and Denis Reilly Program Committee Co-Chair Remarks: Radim Bartos and Lee Cosart

09:30 Keynote Presentation I Belmont AB Session Chair: Lee Cosart (Microsemi, USA)

“Highly Accurate Time Dissemination and Network Synchronization” Helmut Imlau, Deutsche Telekom Technik GmbH

10:30 Morning Break Belmont Foyer

10:50 Session I: PTP and NTP Security Belmont AB Session Chair: Kang B Lee (NIST, USA)

10:50 Next Steps in Security for Time Synchronization: Experiences from implementing IEEE 1588 v2.1 Ezzeldin Shereen (KTH Royal Institute of Technology, Sweden) Florian Bitard (KTH Royal Institute of Technology & French Civil Aviation University, France) György Dán (KTH Royal Institute of Technology, Sweden) Tolga Sel (Siemens AG, Germany) Steffen Fries (Siemens AG, Germany)

11:15 Secure Precision Time Protocol in Packet Switched Networks Prasanth Kemparaj (Juniper Networks, India) Satheesh Kumar S (Juniper Networks, India)

11:40 Guards and Watchdogs in One-Way Synchronization with Delay-Related Authentication Mechanisms Martin Langer (Ostfalia Hochschule Wolfenbüttel, Germany) Kristof Teichel (Physikalisch-Technische Bundesanstalt, Germany) Kai Heine (Ostfalia Hochschule Wolfenbüttel, Germany) Dieter Sibold (Physikalisch-Technische Bundesanstalt, Germany) Rainer Bermbach (Ostfalia Hochschule Wolfenbüttel, Germany)

12:05 Lunch Belmont C

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13:15 Session I: PTP and NTP Security (continued) Belmont AB Session Chair: Kang B Lee (NIST, USA)

13:15 Redundant Schemes or How to Counter the Delay Attack on Time Synchronization Protocols Cristian Marinescu (OMICRON Electronics GmbH, Austria) Johannes Neyer (OMICRON, Austria) Lukas Gassner (OMICRON, Austria)

13:40 Securing Unprotected NTP Implementations Using an NTS Daemon Martin Langer (Ostfalia Hochschule Wolfenbüttel, Germany) Thomas Behn (Meinberg Funkuhren GmbH & Co. KG, Germany) Rainer Bermbach (Ostfalia Hochschule Wolfenbüttel, Germany)

14:05 Promotional Partner Presentations Belmont AB Session Chair: Hans Weibel (Zurich University of Applied Sciences, Switzerland)

15:35 Work in Progress Introductions Belmont AB Session Chair: Radim Bartos (University of New Hampshire, USA)

15:35 White Rabbit Time Synchronization for Radiation Detector Readout Electronics Wolfgang Hennig (XIA LLC, USA) Shawn Hoover (XIa LLC, USA)

15:40 Performance Evaluation of IEEE 802.1AS-based Time Distribution over 802.11 Dave A Cavalcanti (Intel Corporation, USA) Ganesh Venkatesan (Intel Corp., USA) Susruth Sudhakaran (Intel Corporation, USA) Mohammad Mamunur Rashid (Intel Corporation, USA) Christopher Hall (Intel Corporation, USA)

15:45 Afternoon Break Belmont Foyer

16:10 Special Industry Session Belmont AB Session Chair: Lee Cosart (Microsemi, USA)

16:10 Enterprise Computing and the Precision Time Protocol Stephen R Guendert (IBM Corporation & IEEE, USA)

16:35 Relative Timing Agreement Among Clocks Connected to a Common Boundary Clock Douglas Arnold (Meinberg, USA) Andreja Jarc (Meinberg, Germany) Daniel von der Heide (Meinberg, Germany)

17:00 End of Wednesday Session

19:30 Plugtoberfest! Welcome Reception (*Sponsored by Meinberg – wear “Lederhosen” or “Dirndl” for an extra drink ticket) Gustav’s Pub & Grill – Buses will depart at 18:45. 10350 SW Greenburg Rd, Tigard, OR 97223

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Thursday, September 26, 2019 08:00 Morning Coffee

Belmont Foyer

09:00 Keynote Presentation II Belmont AB Session Chair: Lee Cosart (Microsemi, USA)

“Clock Synchronization for the Low-latency Financial Sectors” Pedro V. Estrela, Consultant

10:00 Morning Break Belmont Foyer

10:30 Session II: Measurements, Monitoring, and Calibration Belmont AB Session Chair: Douglas Arnold (Meinberg, USA)

10:30 Insitu determination of the fiber delay coefficient in time-dissemination networks Peter Jansweijer (Nikhef, The Netherlands) Henk Peek (Nikhef, The Netherlands)

10:55 Exploiting Smartphone Peripherals for Precise Time Synchronization Sandeep Sandha (UCLA, USA) Joseph Noor (University of California, Los Angeles, USA) Fatima M Anwar (University of California Los Angeles, USA) Mani B. Srivastava (University of California, Los Angeles, USA)

11:20 ARTT: A Scalable Approach for Monitoring the Quality of Time in Distributed Systems Brandon Smith (University of New Hampshire & University of New Hampshire Interoperability Laboratory, USA) Robert Noseworthy (University of New Hampshire, USA) Radim Bartos (University of New Hampshire, USA)

11:45 Lunch Belmont C

13:15 Session II: Measurements, Monitoring, and Calibration (continued) Belmont AB Session Chair: Douglas Arnold (Meinberg, USA)

13:15 Calibrating NTP Faten Mkacher (Grenoble Informatics Laboratory & Gorgy Timing Company, France) Andrzej Duda (Grenoble Institute of Technology, France)

13:40 Test Results of IEEE 1588v2 Network Synchronization Holdover Performance using Various Types of Reference Oscillators Robert M Kaminsky (Silicon Labs, USA)

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14:05 Session III: Power, Industrial, and IoT Applications Belmont AB Session Chair: Radim Bartos (University of New Hampshire, USA)

14:05 Are Cloud Services Aware of Time? An Experimental Analysis oriented to Industry 4.0 Stefano Rinaldi (University of Brescia, Italy) Paolo Bellagente (University of Brescia, Italy) Paolo Ferrari (University of Brescia, Italy) Alessandra Flammini (University of Brescia, Italy) Emiliano Sisinni (University of Brescia, Italy)

14:30 A timing impairment module for electrical synchrometrology Dhananjay Anand (NIST, USA) Colin Freiheit (University of Vermont, USA) Marc Weiss (Marc Weiss Consulting & NIST, USA) Kishan Shenoi (Qulsar, USA) Hamid Ossareh (University of Vermont, USA)

14:55 Software-based Time Synchronization for Integrating Power Hardware in the Loop Emulation in IEEE1588 Power Profile Testbed Stefano Rinaldi (University of Brescia, Italy) Federico Bonafini (University of Brescia, Italy) Paolo Ferrari (University of Brescia, Italy) Alessandra Flammini (University of Brescia, Italy) Marco Pasetti (University of Brescia, Italy) Emiliano Sisinni (University of Brescia, Italy)

15:20 PM Break Belmont Foyer

16:00 Plugfest Report Belmont AB

16:20 Sync School Report Belmont AB

16:40 Best Paper Award Belmont AB

16:50 IPSCS 2020 Invitation Belmont AB

17:00 End of Thursday Session

19:00 Conference Dinner Renata Restaurant 626 SE Main St, Portland, OR 97214

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Friday, September 27, 2019 08:00 Morning Coffee

Belmont Foyer

09:00 Keynote Presentation III Belmont AB Session Chair: Lee Cosart (Microsemi, USA)

“We're Synchronized-Now Compute!” Kevin Stanton, Intel

10:00 Session IV: Upcoming Revision of the IEEE 1588 Standard Belmont AB Session Chair: Denis Reilly (Orolia USA, USA)

Overview of IEEE 1588 Draft Revision Douglas Arnold, Meinberg USA

Security in the IEEE 1588 Draft Revision Karen O’Donoghue, Internet Society

10:50 AM Break Belmont Foyer

11:10 Session IV: Upcoming Revision of the IEEE 1588 Standard (continued) Belmont AB Session Chair: Denis Reilly (Orolia USA, USA)

The New High Accuracy Default PTP Profile in the IEEE 1588 Draft Revision Maciej Lipinski, CERN

11:35 Closing Session Belmont AB

11:45 End of Symposium

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Keynote Speakers Pedro V. Estrela

“Clock Synchronization for the Low-latency Financial Sectors” BIO PEDRO V. ESTRELA, PhD, is a Performance Engineer working for the financial Industry since 2008, specialized in all aspects of TimeKeeping required to optimize Low-latency, fully automated, high-frequency trading systems. In this period Pedro built state-of-the-art PTPv2 time distribution

systems on several worldwide networks. Pedro's work on PTPv2 included a complete rework of the open source PTPd client, the addition of the NTP robustness watchdog to this client, and close integration with Vendor PTP solutions. This work also directly triggered the development of the “PTP Enterprise profile” by the IETF. All these aspects were described in two ISPCS papers, the latter of which was given the best paper award of the 2014 conference. Other work as a Performance engineer included optimizing all latency components of short-distance co-location links, namely by measuring and reverse-engineering all steps of the trading loop and automatically comparing the performance to its competitors. The same was the case for optimizing medium-distance Microwave and Fiber networks, plus building and productizing prototypes of ShortWave technologies that lower the Latency between very large distances (continents). Pedro holds both a PhD (2007) and a MSc (2003) in Computer Science, specialization on mobile networks, from IST-TU Lisbon, Portugal. ABSTRACT The modern regulated Financial sector requires clock synchronization to meet several Risk, Performance and Regulatory criteria. Private market-makers have obligations to provide continuous Prices to the markets; they require the fastest technologies to avoid the risk of having stale prices to the markets. Public exchanges continuously match the received Orders, centrally, first by best price and then by best time; they require the same technologies to ensure a transparent, fair and deterministic service. All parties are fully regulated; among the rules, all steps of the Financial Trades must be reported with accurate timestamps. This keynote will cover the latest clock synchronization Best Practices taken from these cutting-edge environments, for both viewpoints (Exchanges / Market-Makers). It will be detailed how electronic markets work, why specific technologies are faster, and how GPS+PTP+WR are used to monitor and optimize all of the above. The latest robustness improvements that avoid the well-known PTP single-point-of-failure and leap second issues will be covered - and why these additional features are essential to comply with the latest accuracy regulations, which have no provisions for outliers (MIFID-II RTS 25). By focusing on this highly competitive industry, the speaker will make a case why other large distributed industries will essentially find the same problems of PTPv2, when inevitably they pursue a higher-accuracy path.

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Keynote Speakers (Continued) Helmut Imlau

“Highly Accurate Time Dissemination and Network Synchronization” BIO Helmut Imlau received his Diplom-Ingenieur in electrical engineering, and after that has served in different positions inside the T-Group, and is now with Deutsche Telekom Technik GmbH. He has long experience in the field of transport networks and deep expertise in the areas of synchronization and measurement. He is responsible for synchronization architecture and system engineering, with a current focus is on Deutsche Telekom's synchronization strategy, including phase synchronization for 5G. He is a member of the ITU-T Study Group 15 Question 13 on synchronization, and has written well over 100 contributions with focus on Ethernet Physical Layer Synchronization (SyncE), phase synchronization, accurate time transfer, clocks and measurement methods. His current work at the ITU-T includes cnPRTC architecture with the goals of increasing synchronization network robustness and reducing dependency on GNSS; high-accuracy time transfer methods such as optical time transfer (OTT) and the IEEE 1588 High Accuracy Profile; increasingly accurate telecom boundary clocks (T-BC) such as the Class C and Class D T-BC in G.8273.2; and the incorporation of multi-band GNSS in a PRTC in G.8272. He is head of the T-Group standardization project Timing and Synchronization, a member of ITSF Steering Group, and has made numerous presentations at the ITSF and WSTS conferences. ABSTRACT This talk analyzes methods of time dissemination in hierarchical synchronization networks and provides a mapping between the dissemination method and the network level. The need for time dissemination for the coherent network primary reference time clock (cnPRTC) architecture according to ITU-T G.8275 is explained. The following three methods will be discussed: Optical Time Transfer (e. g. according to ELSTAB), the IEEE 1588 High Accuracy Profile (“White Rabbit”), and the ITU-T specified PTP solution with full timing support from the network (PTP-FTS).

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Keynote Speakers (Continued) Kevin Stanton

“We’re Synchronized- Now Compute!”

BIO Kevin B. Stanton, Ph.D. is a senior principal engineer at Intel, where he is responsible for time-related standards, technologies, and applications for cyber-physical and general-computing systems. He made substantial contributions to the IEEE 1588/PTP and 802.1 TSN standards, and drove expansion of 1588-based time synchronization over 802.11/Wi-Fi wireless links. He believes that accurate time (with bounded uncertainty) will one day be made available to every important computing device in the galaxy.

ABSTRACT For decades, computer timekeeping and time synchronization protocols have progressed along their own timelines with major enhancements in one driving advancement in the other. These lines of progression have reached a point where we can begin to see a future where Distributed, Time-Coordinated Software can itself rely on Time-Synchronization that is as secure, as robust, and more accurate than the best-case latency of today’s data networking technologies. In this talk we discuss the history of computer timekeeping that led us to this point, important leaps forward in capabilities (and jumps backward), and characteristics of a future state that will democratize new programming paradigms that will both leverage today’s time synchronization technologies, and push them further to deliver more.

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ISPCS 2020 Announcement

www.ispcs.org

October 4 – 9, 2020 Vienna, Austria

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Notes

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Notes

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Notes

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