1. 1 The Threat of Uncertainty in Service-Oriented Architecture Yuhui Chen, Anatoliy Gorbenko, Vyacheslav Kharchenko, Alexander Romanovsky, Olga Tarasyuk Newcastle University (UK) National Aerospace University "KhAI“ (Ukraine)

2. OBJECTIVE The objective of the study is to investigate the uncertainty of response time and performance of Web Services and instability of a communication medium (the Internet) as well as their influence on SOA dependability

3. OVERVIEW Setting the Experiments TCP Workflow Overview Delay Analysis Invocation Delay Analysis PINGing Delay Analysis Tracing Route Analysis WS Performance Assessment Summary

4. Setting the Experiments Start time: Jun 04 20:01:24 End time: Jun 09 08:02:51 Total number of invokes: > 650 Total number of pings: > 200000

5. TCP Workflow Overview RPT  RT – 2*RTT RPT - Request Processing Time RT - Response Time RTT - Round Trip Time

6. Response Delay Analysis (1) Invoking FASTA WS from NU

7. Response Delay Analysis (2) Invoking FASTA WS from NU

8. Response Delay Analysis (3) Invoking BLAST WS from NU

9. Response Delay Analysis (4) Invoking BLAST WS from NU

10. Response Delay Analysis (5) Summary Deviation takes from 15 to 50% (!!!) of average RT

11. PINGing Delay Analysis (1) Time Slots

12. PINGing Delay Analysis (2) Time Slot_1 (network delay is high stable) Total duration was about 105 hours Number of intermediate hosts was 17

13. PINGing Delay Analysis (3) Time Slot_2 (network delay is stable enough) The duration was about 3 hours Number of intermediate hosts was 20

14. PINGing Delay Analysis (4) Time Slot_3 (network delay is unstable) The duration was about 20 min Number of intermediate hosts was 17 (= TimeSlot_1)

15. PINGing Delay Analysis (5) PINGing DDBJ host from KhAI The duration was about 2 days Number of intermediate hosts was 26

16. PINGing Delay Analysis (6) Summary

17. Tracing Route Analysis Route length

18. TRACERT Delay Analysis (1) Tracing Route from KhAI

19. TRACERT Delay Analysis (2) Tracing Route

20. TRACERT Delay Analysis (3) Tracing Route

21. WS Performance Assessment Approximate estimation of Web Service’s Request Processing Time (RPT) taking of networks delay RPT  RT – 2*RTT RPT - Request Processing Time RT - Response Time (Invocation) RTT - Round Trip Time (Ping)

22. Summary Deviation of Response Time (RT) takes from 15 to 50% (!!!) of average one for Fasta and Blast WSs It is noteworthy that even in spite of sufficiently stable network delay during Time_slot_1 and Time_slot_2 a response time of the Fasta and, especially, Blast WSs has significant instability that can be explained only by internal reasons or unstable WS loading. 6.3% (Blast) and 4% (Fasta) of the requests had the response time 1.5 times greater than the average one, and for several responses it took even 5 times greater. These cases would potentially cause timing errors Network brings additional uncertainty into response time

23. Discussion Network instability significantly depends on the QoS of a local Internet Service Provider (ISP) and network route. Occasional transient and long-term Internet congestions, packet losses and network route changes that are difficult-to-predict also reduce stability of SOS operation.

24. Solutions Uncertainty existing in SOA should be treated as a threat to dependability (similar and in addition to the faults, errors and failures). This issue will require developing new resilience-explicit techniques and end-to-end QoS mechanisms. Good measurement of uncertainty is important but this is only the beginning.

25. Solutions The future solutions will need to deal with a number of issues such as uncertainty of fault assumptions, uncertainty of components behaviour and dependability, uncertainty of error detection, etc. One of the possible solutions for resisting the uncertainty is to use service and path redundancy and diversity inherent to SOA. The traditional adaptive techniques based on the control feedback will not be directly applicable in the current form as they are intended for predictable behaviour.