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Wireless Mesh Network Management - Fault and Performance Diagnosis: A Survey

Vijay P Gabale (CSE, IIT Bombay) MTech Seminar under the guidance of Prof. Bhaskaran Raman. Wireless Mesh Network Management - Fault and Performance Diagnosis: A Survey. Agenda. Overview Motivation Enterprise vs. Long-Distance Networks Techniques Fault Diagnosis - Examples

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Wireless Mesh Network Management - Fault and Performance Diagnosis: A Survey

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  1. Vijay P Gabale (CSE, IIT Bombay) MTech Seminar under the guidance of Prof. Bhaskaran Raman Wireless Mesh Network Management - Fault andPerformance Diagnosis:A Survey

  2. Agenda Overview Motivation Enterprise vs. Long-Distance Networks Techniques Fault Diagnosis - Examples Future scope Conclusion

  3. Wireless Network Woes! My machine says: wireless connection unavailable. Why is the network performance so low? Is someone interfering with my transmissions? Do we have complete coverage in all the buildings? I wonder if some one has sneakily installed an unauthorized access point.

  4. Wireless Network Anomalies RF holes Interference Hidden terminal Rogue Access Points Which anomaly was the cause of undesired network performance?

  5. Challenges Quantification of possible causes Attribution of a performance problem to a specific root cause i.e. recognizing a fault Network management to proactively deal with likely faults Avoiding personal visits to nodes in long distance links

  6. Effects System downtime Loss of productivity (loss of faith) Recovery cost Number of wireless related complaints logged by the IT department of a major US corporation Source:[4]

  7. Agenda Overview Motivation Enterprise vs. Long-Distance Networks Techniques Fault Diagnosis - Examples Future scope Conclusion

  8. Enterprise Network Comprises of dense deployment of access points & clients in a university or corporate building Challenges RF holes Interference Hidden terminals Rogue Access Points Solution space : Characterizing & then analyzing entire wireless behaviour, Online and Offline diagnosis

  9. Long-Distance Network Comprises of point to point links of several meters to build a multi-hop mesh network Challenges Physical visits are costly Remote locations could sometimes become inaccessible Lack of trained personnel Poor power quality Solution space : In-node recovery or inference techniques, Independent control mechanisms

  10. Diagnostic Questions! What is the per packet signal strength at every node – RF holes How many concurrent receptions are there – Hidden Terminal How is the noise level varying over time – Interference Is there any foreign node wandering in the network – Rogue AP Is the remote node working? What is the software or hardware status of the node? – Primary link failure or Software-Hardware failures

  11. Agenda Introduction Motivation Enterprise vs. Long-Distance Networks Techniques Fault Diagnosis - Examples Future scope Conclusion

  12. Existing Techniques Offline data collection & analysis : [1], [6] Online anomaly detection : [2] Simulation : [3] Daemon running as a part of the node : [4] Software & Hardware redundancies : [5], [7]

  13. Offline data collection & analysis Steps : Dense deployment of monitors Synchronization & unification at a central server Inference techniques Example : Jigsaw[1], MacWild[6] Fault Diagnosis : Pr (Interference | Concurrent Transmissions) Over-protective 802.11g clients and access points

  14. Offline data collection & analysis - Framework Central Server source : MacWild[6]

  15. Offline data collection & analysis Steps : Dense deployment of monitors Synchronization & unification at a central client Inference techniques Example : Jigsaw[1], MacWild[6] Fault Diagnosis : Pr (Loss due to Interference | Concurrent Transmissions) Over-protective 802.11g clients and access points

  16. Online anomaly detection Steps : Deploy multiple monitors Sample physical layer parameters Dynamic interference engine Example : Mojo[2] Fault Diagnosis : Threshold for Hidden Terminal, Capture Effect, Non 802.11 interference

  17. Simulation Steps : Traces to drive simulation Deviation of observed behavior from expected behavior Decision trees to make distinction between possible faults Example : Troubleshooting Wireless Mesh Networks[3] Fault Diagnosis : External noise, Packet dropping, Misbehaving clients

  18. Simulation (contd…) Decision Tree If simSent – realSent > ThreshSentDiff If simNoise – realNoise > ThreshNoiseDiff CW misuse If simLoss – realLoss > ThreshLossDiff External Noise Packet dropping Normal

  19. Daemon running as a part of the node An application resides at client side Takes reactive or proactive actions in response to an event Example : Client Conduit technique[4] Fault Detection : Rogue APs, RF holes

  20. Software & Hardware redundancies Experiences of software & hardware failures Techniques : Software & hardware watchdogs Independent control mechanisms Tracking & predicting health of a node Example : Beyond Pilots[5], Fault Diagnosis[7] Fault Diagnosis : Erratic power conditions, Primary link failure, Non 802.11 interference, Antenna misalignment

  21. Agenda Introduction Motivation Enterprise vs. Long-Distance Networks Techniques Fault Diagnosis - Examples Future scope Conclusion

  22. Problem : Intermittent Connectivity Symptoms : Irregular changes in connectivity or total failure • Causes : Weak RF signal, Lack of signal, unpredictable ambiance, obstructions Parameter : Received signal strength How to tackle total failure? How to track a mobile node?

  23. Remedy : Client Conduit It is a mechanism to allow disconnected users to convey messages to system and network administrators.

  24. Problem : Rogue Access Point What is Rogue Access Point? Security holes, unwanted RF interference and network load. Access Point Database Location, MAC, Channel

  25. Remedy : Client Conduit Is MAC Registered? Is AP at Expected Location? Yes No Yes No No Rogue AP Detected No Is AP Advertising Expected SSID? Is AP on Expected Channel? Yes

  26. Problem & Remedy : Hidden Terminal • Symptoms : Degraded performance, lower throughput • Causes : One transmitter not able to hear other transmissions to the same receiver, heterogeneous transmit powers • Remedy : Quantify number of concurrent transmissions • Around 40% • Capture Effect : Around 5%

  27. Problem & Remedy : Non 802.11 Interference Symptoms : Retransmissions at the MAC layer, No concurrent transmissions detected Quantify noise level Moving window average Threshold

  28. Problem : Connectivity problems over Long-Distance Links Symptoms : Remote node NOT Reachable • Causes: IP address misconfiguration, routing misconfiguration, power shutdown at remote node, a board failure, malfunctioning wireless card Solution : Link Local IP addressing SMS backchannel

  29. Solution : Troubleshooting a Link Does Link Local IP Addressing Work? Yes Log In & Fix Configuration Problem Power Unavailable Wait for Power Visit not required No Power available, Router Down Send SMS query and Get the result Reboot or Visit & Replace Get Status Report: Signal Strength, Noise Visit may be Required Router is Up

  30. Problem & Remedy : Software and Hardware Failures Symptoms : Node suddenly goes down, node does not respond on trying to connect over the primary link • Causes : Damaged power supplies or router boards, damaged CF cards, low voltages leave router in wedged state, battery problems • Techniques : Software and hardware watchdogs, power controllers, Low Voltage Disconnect, read only boot loader

  31. Agenda Overview Motivation Enterprise vs. Long-Distance Networks Techniques Fault Diagnosis - Examples Future scope Conclusion

  32. Future Scope Comprehensive Network Monitoring & Inference Tool Quantify Performance Improvement User Friendly GUIs Automatic Recovery

  33. Conclusion Classification of Techniques to resolve fault diagnosis Enterprise as well as Long-Distance Mesh Networks Faults: Connectivity, Hidden Terminal, Interference, Hardware Failures Need for ‘Complete Monitoring & Inference’ Suit to Detect Root Level Causes

  34. Appendix – Comparison Table

  35. Appendix – Comparison Table (contd…)

  36. References of the Survey [1] Yu-Chung Cheng, John ellardo, and Peter Benko. Jigsaw:Solving the Puzzle of Enterprise 802.11 Analysis. SIGCOMM’06. [2] Anmol Sheth, Christian Doerr, Dirk Grun wald, Richard Han, and Dougla Sicker. Mojo :a Distributed Physical Layer Anomaly Detection System for 802.11WLANS. MOBISYS’06. [3] Lili Qiu, Paramvir Bahl, Ananth Rao, and Lidong Zhou. Troubleshooting-Wireless Mesh Networks. SIGCOMM’06. [4] Atul Adya, Paramvir Bahl, Ranveer Chandra, and Lilli Qiu. Architecture and techniques for diagnosing faults in ieee 802.11 infrastructure networks. MOBICOM’04. [5] Sonesh Surana, Rabin Patra, Sergiu Nedevschi and Manuel Ramos. Beyond Pilots: Keeping Rural Wireless Networks Alive.To appear in USENIX NSDI’08.

  37. [6] Ratul Mahajan, Maya Rodrig, David Wetherall, and John Zahorjan. Analyzing the MAC Level Behavior of Wireless Networks in the Wild. SIGCOMM, 2006. [7] Sonesh Surana, Rabin Patra, and Eric Brewer. Simplifying Fault Diagnosis in Locally Managed Rural wifi networks.SIGCOMM NSDR, 2007. [8] Yu-Chung Cheng, Mikhali Afanasyev, Patrick Verkaik, and Peter Benko. Automating Cross-Layer Diagnosis of Enterprise Wireless Networks. SIGCOMM, 2007. [9] Kameswari Chebrolu, Bhaskaran Raman, and Sayandeep Sen. Long-distance 802.11b Links: Performance Measurements and Experience.MOBICOM, 2006. References of the Survey

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