An Efficient Fault-Tolerant Approach for Mobile IP in

Wireless Systems

Jenn-Wei Lin and Joseph Arul

Paper Presented by: Vidhya Dass

CS 6204 Paper Presentation

10/31/2006

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Agenda

IntroductionThe Proposed ApproachFault tolerance of FAFault tolerance of HAEvaluationAnalytical comparison & SimulationConclusion

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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 failureApproach : Resource sharing to redirect

workloads of faulty FA(HA) to other failure free FA(HA)

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CH

IP Network

FA

RAN RAN RAN

MN

Wireless Data serving area

HA

Home network

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Basic mobile IP in wireless system

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

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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.

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System model

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Wireless data network model

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

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The Proposed Approach

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

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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

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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)

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RAN-FA Remapping for fault tolerance

Implementation of Foreign AgentFA 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

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Fault tolerance of Home Agent HA functions : Mobility binding maintenance, packet

interception & packet tunnelingHA_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)

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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

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16Packet route to HA_failure-affected MN

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

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Mobility binding reconstructionChanging the packet interceptor

Redirecting the packet interception

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

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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

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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

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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:

{Pre-failure}Blocking probability of data request to a failure free FA

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New blocking probability of a data request to a failure free FA when FFA FAs fail

Increasing blocking probability

{Post-failure}

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Blocking probability due to original and redirected workload

Post-failure Pre-failure

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

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Post-failure Pre-failure

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

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Cost of FA_Loading = TFA_Loading + TFA_Response

Cost of RAN_Mapping = TRAN_Mapping

Transmission time from fault management to performance management

Transmission time from performance management to fault management

Transmission time from configuration management to RAN(single memory access)

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Cost of Binding_Update =

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

Total number of FA_failure-affected MN

Average transmission time of registration from FA to HA

Fraction of time due to serial, simultaneous transmissions from FAs to HAs

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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)

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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

Total number of HA_failure-affected MN

Average time of sending qualified visitor entry from FA to HA manager

Fraction since all FA’s perform serial simultaneous transmission to HA manager 30

are negligible due to high speed physical interface of OA&M network. Size of messages is negligible and so is cost.

Probability of ‘n’ in processing data requests/response packets in faulty MA

where

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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Analytical comparison & Simulation

Previous Approaches:Primary MA has redundant MA in network

segmentCo-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)

performance degradation of selected redundancy

0

Post-failure

Pre-failure

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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

Where (1+RAgent) is primary MA+ Redundant MA’s in network segment

Arrival rate of data to MA based on load sharing mode

Post-failure Pre-failure

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Tolerate N-1 failures in N MA system

least

Improvement

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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

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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

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Previous ApproachOne redundant MA take over one faulty MA. Independent of Fagent

Increasing blocking probability as Agent/Agent

Current ApproachIncreasing blocking prob as FAgent

Increasing blocking probability not always as Agent/Agent

CAgent=50

NFA_MN & NHA_MN under one faulty FA (HA)

Equal

Total number of resource units in FA and HA is 50

Average number of in processing data

requests in an 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)

CAgent=50

Failure recovery overhead depends on this graph

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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???

Below 10%

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

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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

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Thank you

Questions