Ran Li , Xiaoliang Wang , Xiaohong Jiang Adviser: Frank , Yeong - Sung Lin

Network Survivability Against Region FailureSignal Processing, Communications and Computing (ICSPCC), 2011 IEEE International Conference on Ran Li , Xiaoliang Wang , Xiaohong Jiang Adviser: Frank , Yeong - Sung Lin PresentbyJason Chang

Agenda • INTRODUCTION • Background • Region failure model and SPM routing • REGION-DISJOINT MULTI-PATHROUTING • Optimization of Traffic Throughput • Complexity Analysis • SPM AGAINST SINGLE REGION FAILURE • Problem Formulation • NETWORK UPGRADE PROBLEM • NUMERICAL RESULT • CONCLUSION

Background • Communication has been a tremendous success with significant impact on our daily life. • people are increasingly relying on large-scale communications • large-scale computer networks are now facing more and more potential threats • It is essential for the large-scale computer networks to have the capability of guaranteeing mission-critical information change.

Background • Previously work around network survivability mainly focuses on single link or node failure in a logical topology. • link cut and router software/hardware error are the main failure modes • Network scale is increasing and network robustness is becoming more stringent , the multiple simultaneous failure scenarios have been address in some recent research works. • technique of providing protection if a second link fails before recovering from the first link failure • resilient routing schemes • SRLG(shared risk link group) • Based on graph-theoretical optimization technique , the strategies for protection and restoration of optical paths against SLRG failures

Background • In real networks some disruptive events which may simultaneously affect multiple network components confined to a specific area are so called region failure. • Region failures may lead to catastrophic data loss and may take a long time to be recovered. • Due to the fact that the network failures due to a region failure are geographically correlated , the geographical layout of network components needs to be carefully take into account in the region failure-related network survivability analysis.

Background • Intuitively , the region failure can be considered as a highly localized event where the failed nodes and links are clustered in a geographical area.

Background • In recent years , various methodologies have been proposed to evaluate the impact of region failure. • identify the most vulnerable region to a region failure in real network physical topologies , where the region failures are modeled as line-segment cuts or circular cuts arbitrarily placed on network plane • analyze network failures after randomly localized linear cut • physical connectivity • logical connectivity under physical link failure

Background • The classical Menger’s theorem(i.e. the max-flow min-cut theorem) does not hold any more for region-based connectivity analysis.

Region failure model and SPM routing • The region failure is modeled as a circular disk of radius r , which centers at a network node. • Any network component intersecting with this region will be destroyed and removed from the network. • Approach to dealing with network components failure is to provide both backup path and primary path for each traffic demand.

Region failure model and SPM routing • To improve the efficiency of protection : • shared backup path protection • self – protection multipath routing • For simplicity , we assume that the cost effective self-protecting multipath routing is adopted and all routing paths are known in advance.

Region failure model and SPM routing • Self-protecting multi-path routing (SPM) is based on the idea of traffic load-balance. • In IP/MPLS networks , it is possible to setup two or more working path , and the spare capacity of these working path can be applied to provide backup for each other when network failure occurs.

Region failure model and SPM routing • SPM consists of disjoint paths and the traffic is distributed over all of them according to a traffic distribution function. • Due to the fact that two of the routing path may be covered by a single region, only one of them can be applied.

Optimization of Traffic Throughput

Optimization of Traffic Throughput • The optimization function aims at maximizing the traffic throughput：

Optimization of Traffic Throughput • Additionally , paths between a source-destination pair should be region-disjoint：

Complexity Analysis • As the number of connections is less than and the number of paths for one connection is less than the outdegree of the source node, ,the number of variable is thus bounded by . • The total number of equations in the constraint (1) is, while the number of equations in the constraint (2) is .

Problem Formulation • The SPM consist of multiple paths over which the traffic is distributed according to a load balancing function. • The backup capacities may be shared by different flows in various failure scenario. • Our target is maximize network throughput under any single region failure.

Problem Formulation

Problem Formulation • We use as the traffic spilt ration of path P for demand from s to d in case of a region failure • The throughput of this demand can be expressed as:

Problem Formulation • The function of LP model can then be expressed as:

Network Upgrade Problem • For a network can not accommodate all the traffic with regard to any single region failure , we may need to upgrade the network by providing additional link capacity. • To realize a minimum capacity for a upgrade for a given network such that it can serve all traffic matrix in case of any single region failure.

Network Upgrade Problem • We denote the additional capacity require by link as,then we have:

Numerical Result • Two real network topologies are adopted in our simulation , the USA network and the NFSNET network. • Set capacity as 1 for all the links. • The demands are generated randomly with equal probability between any pair of nodes. • Bandwidth requirements are over provided in the interval of 0 – 50 with uniform distribution.

Numerical Result • USA network : • 26 nodes • 41 links • Max distance : 187 • Average distance : 111 • Minimum distance : 66

Numerical Result • NFSNET network : • 79 nodes • 109 links • Max distance : 154 • Average distance : 175 • Minimum distance : 36

Numerical Result • The throughput decreases as the region size increase :

Numerical Result • The worst region failure in the network that results in the maximum throughput degradation : (in USA network)

Numerical Result • The worst region failure in the network that results in the maximum throughput degradation : (in NFSNET network)

Conclusion • Evaluate the impact of region failures on networksurvivability. • Apply the region – disjoint self – protecting multi – path routing. • The existing networks are actually very vulnerable to the region failure. • It is critical to design a fault – tolerant network against region failure.

Thanksforyourlistening

Ran Li , Xiaoliang Wang , Xiaohong Jiang Adviser: Frank , Yeong - Sung Lin