Timing Verification as a Service Darryl Veitch darryl.veitch@uts.edu.au School of Electrical and Data Engineering UNIVERSITY OF TECHNOLOGY SYDNEY
Timing Data is Di ff erent Ubiquitous n timestamps a part of almost all measurement ๏ Universal n only a small number of key `types’ ๏ each with the same generic concerns : ๏ are my timestamps reliable? ๏ how accurate are they? ๏ Suggests potential for broad solutions n i) fix the timing system [ watch this space ] ii) evaluate/verify/certify achievable by a service? the timing system ๏ the timestamps ๏ 2
What Could Possibly Go Wrong? 3
Timing Purposes ➙ Timing `Data Types’ Event ordering n monotonicity wrt true time (TAI) ๏ uniqueness ๏ Time interval duration n same clock: running at stable, correct rate ๏ different clocks: absolute time up to a constant ๏ Absolute time n globally comparable metric and label ๏ synchronization to universal standard (TAI, UTC) ๏ 4
Di ff erent Clocks for Each Time Type Causal Clock ( Event ordering ) n hardware counter, or message passing logic ๏ Expect: perfection ๏ Difference Clock ( Time interval duration ) n local hardware counter ๏ timestamp exchange to remote reference ๏ smart calibration ๏ Expect: very robust, very accurate ๏ Absolute Clock ( Absolute time ) n stable local hardware counter ๏ frequent exchange with remote reference ๏ very smart calibration ๏ Expect: vulnerability, much less accurate ๏ 5
Timing Hierarchy (in an ideal current world) 6
Verification Dimensions System components n Internet timing system ๏ remote server side ๏ client side {hardware, clock, timestamping, final timestamps} ๏ Timeliness n general certification ๏ on-demand auditing ๏ ongoing monitoring ๏ detailed audit during experiment ๏ Auditing body n independent 3rd party (free or not) ๏ available software ๏ built into timing system ๏ Verification approach n remote ๏ with server and/or client cooperation ๏ Clock Type n Causal / Difference / Absolute ๏ 7
Eg 1: Server Health Monitoring (SHM) System components n Internet timing system ๏ remote server side ๏ client side {hardware, clock, timestamping, final timestamps} ๏ Timeliness n general certification ๏ on-demand auditing ๏ ongoing monitoring ๏ detailed audit during experiment ๏ Auditing body n independent 3rd party (free or not) ๏ available software ๏ built into timing system ๏ Verification approach n remote ๏ with server and/or client cooperation ๏ Clock Type n Causal / Difference / Absolute ๏ 8
Don’t Use that Server ! 320 318 No RTT `events’: 316 ➙ no routing changes RTT [ms] ➙ no major congestion 314 ➙ R(i) should bound A(i) 312 310 308 − 80 38.8 39 39.2 39.4 39.6 Tb [day] Large Asym events: − 90 ➙ can’t be routing − 100 ➙ can’t be congestion A [ms] ➙ must be server − 110 − 120 − 130 Longitudinal study (2011,2015) Out of 102 servers, 37 38.8 39 39.2 39.4 39.6 Tb [day] bad over entire period ! 9
Eg 2: Client clock vetting for RTT/IAT System components n Internet timing system ๏ remote server side ๏ client side {hardware, clock, timestamping, final timestamps} ๏ Timeliness n general certification ๏ on-demand auditing ๏ ongoing monitoring ๏ detailed audit during experiment ๏ Auditing body n independent 3rd party (free or not) ๏ available software ๏ built into timing system ๏ Verification approach n remote ๏ with server and/or client cooperation ๏ Clock Type n Causal / Difference / Absolute ๏ 10
Eg 3: Clock Outsourcing System components n Internet timing system ๏ remote server side ๏ client side {hardware, clock, timestamping, final timestamps} ๏ Timeliness n general certification ๏ on-demand auditing ๏ ongoing monitoring ๏ detailed audit during experiment ๏ Auditing body n independent 3rd party (free or not) ๏ available software ๏ built into timing system ๏ Verification approach n remote ๏ with server and/or client cooperation ๏ Clock Type n Causal / Difference / Absolute ๏ 11
Eg 4: Network Timing Core System components n Internet timing system ๏ remote server side ๏ client side {hardware, clock, timestamping, final timestamps} ๏ Timeliness n general certification ๏ on-demand auditing ๏ ongoing monitoring ๏ detailed audit during experiment ๏ Auditing body n independent 3rd party (free or not) ๏ available software ๏ built into timing system ๏ Verification approach n remote ๏ with server and/or client cooperation ๏ Clock Type n Causal / Difference / Absolute ๏ 12
NTP Forest, with Tree-rot How would we know our tree is rotten? No tools! 13
Meshed Stratum-1 + Privileged Stratum-2 NMI and AARNet have agreed to support public trails. 14
Summary Timing isn’t going away n Timing underpins other measurement n Timing has problems, but they are finite n Many can be fixed via expertise wrapped in a service n Let’s just do it n 15
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