An Efficient Fault-Tolerant Approach for Mobile IP in Wireless Systems

1. CS 6204 Paper Presentation An Efficient Fault-Tolerant Approach for Mobile IP in Wireless Systems Jenn-Wei Lin and Joseph Arul Paper Presented by: Vidhya Dass 10/31/2006 1

2. Agenda • Introduction • The Proposed Approach • Fault tolerance of FA • Fault tolerance of HA • Evaluation • Analytical comparison & Simulation • Conclusion 2

3. Introduction • Mobile IP : Support wireless users with continuous network connections while changing locations • Functionality of Mobile IP in wireless system provided by: • Mobility agents in architecture of wireless systems(HA and FA) • Drawbacks : No fault tolerance for MA failure • Approach : Resource sharing to redirect workloads of faulty FA(HA) to other failure free FA(HA) 3

4. Basic mobile IP in wireless system HA IP Network CH Home network FA Wireless Data serving area RAN RAN RAN MN 4

5. Related work : • 1.MA statically equipped with one or more redundant MA’s to work in standby or load sharing mode • MA fails, one backup member selected as primary mobility agent • ARP : Used to map IP address of faulty MA onto network link layer address of selected backup member • Disadvantages : Long registration delay since MN registers with all MA • 2.Checkpointing and logging technique : Store mobility bindings in stable storage 5

6. GOAL : Provide Fault tolerance capability in wireless system with mobile IP functionality • Fault tolerance in telecom system is “five nines”(99.999) reliability requirement for network design but Hardware failures follow bathtub curve. Provide fault tolerance for MA failures. 6

7. Wireless data network model System model 7

8. OA & M functions : • Configuration management: Configures equipment with suitable resource parameters • Fault management: Detecting and reporting failures in equipment • Performance management: Measures resource utilization, loading status, concerned values in equipment • Security management: Monitors access rights to equipment • Assumptions : • Failures only occur in MA: Detect failure by not receiving agent advertisement messages within a time period • Fail - Stop approach: Faulty MA not send agent advertisement messages 8

9. The ProposedApproach • Dynamically select multiple failure free MA as backup set for faulty MA when a failure is detected • Workloads of faulty MA redirected to failure free MA in backup set • Faulty FA : One or more failure free FA dynamically selected (backup set), system initiated handoff issued to virtually move all MN to service area of backup FA (Continuous data executable property) • Faulty HA : One or more failure free HA dynamically selected (backup), intercept packets moving toward faulty HA and send them to corresponding MN 9

10. Fault tolerance of Foreign Agent • (FA_failure-affected MN’s) :MN in serving area and arriving MN, cannot execute wireless data sessions • System initiated handoff to dynamically select multiple failure free FA’s, which are backup set of faulty FA • FA_failure-affected MN’s virtually moved to serving areas of failure free FA • Failure free FA’s adds visitor entries for FA_failure-affected MN, that have moved into it • Informs MN’s corresponding HAs of new serving FAs and CoA for mobility bindings • Workloads of faulty FA redirected to other failure free FA 10

11. Achieve virtual movement of FA_failure-affected MN’s : Modify RAN-FA interconnection network which is determined by RAN’s internal FA-serving record • Initially: • FA-serving record of RAN : Identifier of fixed FA • FA Failure detected : FA-serving record of failure-affected RAN(initially served by faulty FA) reset with identifiers of backup members • FA_failure-affected MNs served by backup members but their location is same(still located in respective radio coverage area) 11

12. RAN-FA Remapping for fault tolerance 12

13. Implementation of Foreign Agent • FA Failure detected : Failure event sent to OA&M fault management • fault management initiates proposed fault tolerant approach for FA • 1.Interacts with performance management to acquire loading status of failure free FAs, finds number of FA_failure-affected MNs • 2.Select multiple failure free FA as backup members of faulty FA • 3.Configuration management informed to configure backup members of faulty FA by resetting appropriate parameters to some equipment in core network & update mobility bindings of MNs 13

14. Fault tolerance of Home Agent • HA functions : Mobility binding maintenance, packet interception & packet tunneling • HA_failure-affected MN : MN’s managed by faulty HA not able to receive packets from CHs • Select one or more failure free HA dynamically as backup members • Mobility bindings of faulty HA restored by searching all FA’s visitor lists • Distribute bindings to backup members: Up-to-date location of all MN’s known from FA’s visitor list entry(MN’s data link layer address, IP address and home agent address) 14

15. Packet interception of faulty HA restored on backup using tunneling. Routers collocated with HA on same network segment, don’t forward packet to faulty HA but tunnel packets to backup HA which again tunnels it to located FAs(packet from CH to HA_failure-affected MN sent by twice tunneling) • Packet tunneling function already present in failure free HA 15

16. Packet route to HA_failure-affected MN 16

17. Implementation of Home Agent • Select multiple failure free HAs with low traffic(from OA&M) as backup set and one among them, as HA’s backup manager • Mobility binding restoration: mobility- reconstruction message sent to each FA and responses divided by HA backup manager based on MN’s IP address. Assigns groups to HA backup members • Collocated routers remove routing entries of faulty HA and add routing entries of backup members, with its interface set to virtual interface pointing to software program to perform packet tunneling 17

18. Changing the packet interceptor Mobility binding reconstruction 18 Redirecting the packet interception

19. Failure Recovery • FA recovery procedure: • Recovered FA determines failure affected RANs (configuration management of OA&M) • Failure affected RANs reset FA-serving records to identifier of recovered FA • Recovered FA creates visitor entries for FA-Failure-affected MNs & HAs of these MNs updated with mobility bindings 19

20. HA recovery procedure: • Modify routing tables of collocated routers of recovered HA - packet interceptors of HA_failure-affected MN changed • Mobility bindings of recovered HA reconstructed - search all FAs visitor lists 20

21. Evaluation • Workload redirection causes • Performance degradation of failure free MA • Control message overhead • Traffic behavior of FA, HA modeled as M/G/c/c queuing model • Assumption: Data request sent to FA & response packet intercepted by HA follow Poisson process • Service time of data request and processing time of packet tunneling not follow any specific distribution 21

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23. Performance degradation of MA • Performance degradation of failure free FA due to resources being contended by MN’s virtually moved and original MN’s served • Represented as increasing blocking probability PFA_blocking - new data request possibly blocked at failure free FA in comparison to prefailure • Erlang’s loss formula from the M/G/c/c queuing model: Blocking probability of data request to a failure free FA {Pre-failure} 23

24. Blocking probability due to original and redirected workload • New blocking probability of a data request to a failure free FA when FFA FAs fail • Increasing blocking probability {Post-failure} Pre-failure Post-failure 24

25. Performance degradation of a failure free HA(HAk) - Increasing blocking probability that causes an intercepted packet to be blocked at failure free HA in comparison with prefailure Pre-failure Post-failure 25

26. Control message overhead • Control messages issued from OA&M for assisting fault tolerance of MA: • FA_Loading • RAN_Mapping • Binding_Update • HA_Loading • Interceptor_Change • Binding_Restoration 26

27. Cost of FA_Loading = TFA_Loading + TFA_Response • Cost of RAN_Mapping = TRAN_Mapping Transmission time from performance management to fault management Transmission time from fault management to performance management Transmission time from configuration management to RAN(single memory access) 27

28. Simultaneous transmission of mobility binding update command from fault management Total time required for failure free FAs to send mobility binding updates about all FA_failure-affected MNs • Cost of Binding_Update = Fraction of time due to serial, simultaneous transmissions from FAs to HAs Total number of FA_failure-affected MN Average transmission time of registration from FA to HA 28

29. Cost of HA_Loading = THA_Loading + THA_Response • Cost of Interceptor_Change = TInterceptor_Change Transmission time from fault management to performance management Transmission time from performance management to fault management Transmission time from configuration management to collocated router of faulty HA(only memory access of routing table) 29

30. Cost of Binding_Restoration = Transmission time of mobility binding restoration to each HA from fault management Total time required for restoring lost mobility binding table of faulty HA Fraction since all FA’s perform serial simultaneous transmission to HA manager Average time of sending qualified visitor entry from FA to HA manager Total number of HA_failure-affected MN 30

31. are negligible due to high speed physical interface of OA&M network. Size of messages is negligible and so is cost. where Probability of ‘n’ in processing data requests/response packets in faulty MA Assumption : Each MN is not allowed to simultaneously issue more than one data session . So PFA_n (P HA_n) represented as probability of n FA_failure-affected MNs(HA_failure-affected MNs) in faulty FA(HA) 31

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33. Analytical comparison & Simulation • Previous Approaches: • Primary MA has redundant MA in network segment • Co-working mode of primary and redundant MA: Standby and Load sharing (Different performance degradation) • Standby mode:{Pre-failure}Blocking probability of selected redundancy 0 (No workload) Post-failure performance degradation of selected redundancy Pre-failure 0 33

34. Load Sharing mode: • {Pre-failure}Load distributed among primary and all redundancies of that primary • {Post-failure}If selected as primary then redundant MA has to handle twice the original load Post-failure Pre-failure Where (1+RAgent) is primary MA+ Redundant MA’s in network segment Arrival rate of data to MA based on load sharing mode 34

35. 35 Tolerate N-1 failures in N MA system Improvement least

36. Traffic intensity of MA: Expected number of arrivals per mean service time at a MA • Performance degradation of MA : Increasing blocking probability of failure free MA 36

37. Proposed Approach : Workload of faulty MA evenly redirected to all failure free MA • Ratio of redirecting workloads to failure free MA • Previous Approach : Load sharing mode: Number of redundancies in network segment affects increasing blocking probability 37

38. 38 Previous Approach One redundant MA take over one faulty MA. Independent of Fagent Increasing blocking probability  as Agent/Agent  CAgent=50 Current Approach Increasing blocking prob  as FAgent  Increasing blocking probability not always  as Agent/Agent 

39. CAgent=50 Total number of resource units in FA and HA is 50 Average number of in processing data requests inan FA(HA) cannot be greater than 50. Maximum number of NFA_MN(N HA_MN) is 50 Conclusion : Overhead of mobility binding update is restricted by the total resources in FA(HA) Equal Failure recovery overhead depends on this graph NFA_MN & NHA_MN under one faulty FA (HA) 39

40. Below 10% • Simulated using NS-2 • Same workloads to an FA and HA then PFA_Blocking and PHA_Blocking should be equal but simulation doesn’t agree??? Stopped with 8 faulty MA’s??? Why didn’t they consider all the cases for Number of faulty MA??? Difference rate is varying randomly??? Only considering MN in data session for FA_failure-affected MN not justified 40

41. Conclusion • Utilizes available resources in other failure free MA to dynamically generate backup set for each faulty MA • Advantages : • No Hardware support required • No failure free overhead • Distribute fault tolerant overhead to avoid significant performance degradation on single failure free MA • Good when is 200 and FAgent is small 41

42. Thank you Questions