Irish NTP Subnet. Performance Issues. Hugh Melvin & Paraic Quinn. Dept. of Information Technology NUI,G

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1 Irish Subnet Performance Issues Hugh Melvin & Paraic Quinn Dept. of Information Technology NUI,G The support of the Informatics Research Initiative of Enterprise Ireland is gratefully acknowledged.

2 Outline Importance of Synchronised Time Role of Synch. Time within ECRG Research Operation & Robustness Issues Irish Subnet Performance Challenges

3 Importance of Synchronised Time Network-level Issues Network monitoring, measurement, fault isolation and control Application level Issues Transaction Timestamping Increasingly important in different domains Logistics/Billing/Finance/Security Internet Multimedia QoS Issues

4 Synch. Time within ECRG Research IP2000 A requirement for effective agent co-ordination 3 domains Software Development / Financial Services / Manufacturing VLAB (Virtual Logistics Multi Agent Broker:IP2001) Improved transport efficiencies GPS/GIS/GPRS/ supporting technologies

5 IP 2000 Design Supply Chain Software Financial Services Enable Chain Supply Design Services Broker Manufacturing CORBA JAVA XML GPRS

6 Interfaces Communications Subsystems # Carrier Load Suppliers Broker / Virtual Marketplace 1 Bidder (3 rd Party Product conforming to the V-LAB spec) Bidder (Manual by hand) Bidder (V-LAB) 2 Fleet Management (Manual by hand) Fleet Management (3 rd Party Product conforming to the V-LAB spec) Fleet Management (V-LAB) 3 Truck Truck Truck Truck Truck Truck Truck Truck Truck Truck Truck Truck Truck 4 Location/Positioning systems (GPS)

7 Cause/Extent of the Problem Crystal Oscillator Manufacturing Tolerances Frequency Errors (skew) Drift Temperature Ageing 1999 Survey 20,000 clocks Median skew of 78 ppm (> 6 sec/day)

8 Network Time Protocol Synchronises Internet clocks to UTC Over 500,000 peers deployed in the Internet Achievable accuracy level low tens of milliseconds on WAN milliseconds on LAN submicrosecond on standalone PCs precision time source reqd cesium oscillator / GPS receiver / radio signal Unix daemon ported to diff platforms Unix, Windows, VMS and embedded systems

9 How works Peer 1 Filter 1 Peer 2 Peer 3 Filter 2 Filter 3 Intersection and Clustering Algorithms Combining Algorithm Loop Filter P/F-Lock Loop Messages Timestamps VFO Multiple peers provide redundancy and diversity Algorithms to improve accuracy and robustness Filtering Intersection and Clustering Combining

10 Timing Signal System GPS/Radio Clock Timing Signals Timing Signal GPS Satellite Primary Server Stratum 1 Sec. Server Strat. 2 Sec. Server Strat. 2 Secondary Server Stratum 3 Secondary Server (Stratum 3) Secondary Server Stratum 3

11 Robustness Issues Local/Accurate Reference Source Local Independent Peers Low RTD Redundancy Path Diversity Minimise SPOF Risk of Delay Asymmetry

12 Asymmetric Delay Offset is ½[(B-A) - (D-C)] seconds Round Trip Delay is [(D-A) - (C-B)] 0.03 seconds Incorrect due to asymm delay (10/20)!! Offset is actually 10

13 Testbed GPS Satellite GPS Satellite Remote servers GPS Receiver Internet NUIG stratum-2 server (Linux) NUIG stratum-1 server (LInux) Remote servers NUIG LAN Internet NUIG stratum-2 server (Win 2000) TCD stratum-2 servers HEAnet NUIG stratum-2 client (Linux) NUIG stratum-2 client (Win 2000)

14 Testbed Design Issues Irish Subnet Robustness Importance of local Reference source Windows versus Linux platforms Diurnal Variation Comparison with equivalent server on mainland Europe Performance Delay/SPOF

15 Irish Subnet Inherently weak Stratum 1 peer servers overseas High RTD / SPOF and Risk of Asymm Redundancy without diversity Stratum 2 servers Similar Issues

16 NUI,G Linux St.2 Client (st.1 peers)

17 Linux St.2 DCU Client (st. 1 peers)

18 Linux St. 2 NUI,G client (st. 2 peers)

19 Win St. 2 client (st.2 peers)

20 Diurnal Variation (Linux)

21 Diurnal Variation (Win 2000)

22 Network Asymmetry?

23 French St. 1 Performance Comparison

24 NUI,G Stratum 1 Server

25 Conclusions Irish subnet weak Testbed results impressive nonetheless Performance msec level synch on LAN low msec across HEAnet OS Dependency Linux vs Windows : expected performance gains Evidence of asymmetry Diurnal variations evident on both OS or Network?..most likely Network

26 Conclusions Testbed Results continued inria vs NUI,G stratum 1 performance NUI,G marginally better (GPS clock?) inria Greater redundancy Greater path diversity & independence Lower RTD More robust

27 Challenges Strengthen Irish subnet More st1 and 2 servers More reference sources Greater path diversity initiatives already underway Management & Control critical rubbish in, rubbish out! Any Q??

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