Measuring Availability in Telecommunications Networks Mattias Thulin, November 2004

1. Measuring Availability in Telecommunications Networks Mattias Thulin, November 2004

2. Disposition • Introduction • Method • Network Availability • SDH Network description • ITU-T standard G.826 • Analysis • Implementation • Result • Conclusions 2

3. Song Networks • Nordic network provider • Optical fiber network covering Northern Europe • Products: • IP-VPN • Internet connections • Telephone services • Hosting • Carrier services

4. Introduction • Market demand for network quality • Important to measure network availability • Maintain service-level agreements • Attract new customers • Indicator of network quality for internal maintenance • Methods of measuring and defining Network Availability vary between operators

5. Purpose • How is Network Availability defined? • How can it be measured? • Why should it be measured? • What standards exist? • Are there any recommended values for availability parameters? • How can availability measurements be applied to Song Networks SDH transmission network?

6. Delimitations • General study on Network Availability • Develop a method for availability measurement • Nortel SDH equipment • Four rings • 44 links • Oriented towards network-operation

7. Method • Literature study • Network study • Monitoring system Preside • Interviews • Standards • Design model for availability measurement and presentation

8. Network Availability - definition The ability of a functional unit to be in a state to perform a required function under given conditions at a given instant of time or over a given time interval, assuming that the required external resources are provided. ISO 2382-14, 1997

9. Network Availability – The “five-nines” • Percentage value of uptime for a given time period • “Five-nines” 99,999% • Viewed as desired uptime in network core-level

10. Theoretic Availability Summing availability

11. Reactive Availability • Data from trouble-tickets • Good for measuring customer-experienced availability • Easy to identify what equipment failed and what solved the error • Can lack information of short interruptions and outside of office hours

12. Customer- vs. Network-management oriented • Important to know for whom or for what purpose are we measuring • Customer oriented • Includes all layers • Calculate downtime when the customer connection is not working. • Network-management oriented • What links have lower availability? • Considered as downtime although the traffic is rerouted

13. SDH Network Description • SDH – Synchronous Digital Hierarchy • Based on American standard SONET • Normally build in ring structure • Error correction and retransmission is done by overlaying protocols

14. Song Networks’ SDH network Nordic ring Europe ring Sweden ring Baltic ring

15. Song Networks’ SDH network Sweden ring: 9 Network Elements Nordic ring: 7 Network Elements European ring: 7 Network Elements Baltic ring: 3 Network Elements

16. Surveillance and statistics NE NE NE NE OPC NE NE Preside

17. Preside • Global performance • Alarm lists • Query performance statistics

18. Preside log files • Comma-delimited text files (CSV) • One file per Network Element • 96 15-min counts (past 24 hours) • 8 24-hour counts (past week) 1200,Ottawa,OC48,Term,DS3,G7,2,Line,Rx,Ne,SES,03/07/99,03/07/99,16:00, 0,0,0,2,3,8,12,6, 0,0,1,0,0,0,0,1,0,0,0,2,0,0,0,1,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0

19. ITU-T Standard G.826 Parameters: Bit-error Errored Block (EB) 1 bit-error/block Errored Second (ES) 1 sec with  1 EB Severly Errored Second (SES) 1 sec with 30% EB

20. Unavailable Second (UAS) A period of unavailable time begins at the onset of ten consecutive SES events. These ten seconds are considered to be part of unavailable time. A new period of available time begins at the onset of ten consecutive non-SES events. These ten seconds are considered to be part of available time. (ITU-T G.826, 2002)

21. Analysis • Define availability • Develop model for calculating average availability • Define database structure for saving availability statistics • Specify format for availability reports

22. Analysis • Follow ITU-T Standard G.826 • Apply to all active links in the network • Calculate average availability per link, per ring and total network • Present first five significant figures • First calculate average UAS, convert to percentage in last step to avoid rounding error

23. Availability for a ring is the average UAS for all the links in the ring Analysis + + 3

24. Database Parser Analyze Report Log Files Implementation

25. Implementation - parser program • Programmed in Java for platform independence • Parse all log-files in directory for: • NE • Link • Day • UAS count • Insert into MySQL database table

26. Implementation – report generating • Web interface for easy access • Input parameters: start and end date • PHP-script query database for UAS values and calculate average availability • Per link • Per ring • Total network • Report can be saved to PDF format (PHP-script)

27. Implementation – Graphic reports • Crystal Reports • Start-date and end-date are entered and the program queries database and produces graphic reports • Can be exported to PDF file

28. Result Between 2004-07-12 and 2004-09-19

29. Between 2004-07-12 and 2004-09-19 Result

30. Between 2004-07-12 and 2004-09-19 Result

31. Conclusions • Background study can be used for planning future measurements • Positive feedback from network operations management for the weekly reports • Need more statistic in the database to observe general trends • By studying trends Song Networks can cut maintenance spending and better forecast future cost by directing resources to maintain a high network quality • Future work: • Measure backbone availability from a customer point of view using relational databases • How do errors in the backbone affect distribution layer?

32. Questions?