Enhanced Multipath Routing And Proactive Route Maintenance For Congestion Minimization And Transient Link Failures

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1 Enhanced Multipath Routing And Proactive Route Maintenance For Congestion Minimization And Transient Link Failures Selvamani K 1, Kanimozhi S 2, Elakkiya R 3 and Kannan A 4 1,3 Department of Computer Science and Engineering, Anna University, Chennai, Tamilnadu, India 2,4 Department of Information Science and Technology, Anna University, Chennai, Tamilnadu, India Abstract - The usage of internet is highly increasing for mission-critical applications and hence internet is always expected to be available for the users. But unfortunately service disruptions happened even in well designed and managed networks due to link failures and most of the failures are transient. Existing works on multipath routing scheme has focused only on the heuristic methods. But in this proposed work, we focus on optimal congestion reduction schemes to minimize the congestion in a network. This deployed link state routing protocols react to link failures through the global link state and the routing table re-computation by causing significant discontinuity in forwarding after the failure. This paper aims in providing fast global re-routing called Failure Insensitive Routing (FIR) for handling these transient link failures and efficient multipath routing for congestion minimization. This proposed approach detects the link failures and forwards the packets using interface-specific forwarding technique and suppresses the link state advertisement and triggers the local re-routing using backward table. This approach also aims to formulate multipath routing to restrict the quality (length) of the selected paths and the number of routing paths per destination. Keywords: Fast Rerouting; Transient Failures; Multipath Routing; Congestion Avoidance; 1 Introduction Currently deployed protocols called Link-state protocols perform global routing table to route around the failures which usually takes few seconds. It also raises the congesting situation due to network link failures. Whenever a link fails in a network, the traffic is rerouted around the failure leading to congestion on a link, which will increase the traffic than ever before. In such cases, a mechanism called congestion control is used to maximize the throughput and to minimize the impact of the packet loss. In real-time applications, such as VoIP which has emerged in recent years requires a fast rerouting mechanism before all routers on the network update their routing tables. In addition to this fast rerouting is more appropriate than global routing the link when failures are transient. Moreover, to support time-sensitive applications, the network needs to survive failures with minimal disruption to the service. Hence it is necessary to develop a fast local routing protocol for link state protocols to handle transient link failures and efficient multipath routing algorithm for congestion minimization. 2 Related Works Multi-Protocol Label Switching (MPLS) based approaches to failure recovery [5] leverage explicit routing for fast rerouting. An explicitly routed protection LSP (Label Switched Path) is set up to provide a backup path for each vulnerable physical link and acts as a parallel virtual link. When the physical link fails, the upstream node switches traffic from the physical link to the virtual link. The label stacking capability of MPLS is used to re-route all the LSPs that used to go over the failed link by nesting them into the protection LSP. Since rerouting is done locally at the point of failure without the need to perform any signaling at the time of failure, MPLS can handle transient failures effectively with minimal disruption to forwarding of data. However, deployment of MPLS necessitates changes in the forwarding plane of traditional routers. Our objective is to provide fast local rerouting to deal with transient link failures with minimal changes to the current networking infrastructure. Previous studies and proposals on Multi-Path routing in the previous context have focused on heuristic methods. In [2], a Multi-Path routing scheme, termed Equal Cost Multi- Path (ECMP), has been proposed for balancing the load along multiple shortest paths using a simple round-robin distribution. By limiting itself to shortest paths, ECMP considerably reduces the load balancing capabilities of multipath routing; moreover, the equal partition of flows along the (shortest) paths (resulting from the round robin distribution) further limits the ability to decrease congestion through load balancing. OSPF-OMP [2] allows splitting traffic among paths unevenly; however, that often results in an inefficient flow distribution. Both [1] and [2] considered multipath routing as an optimization problem with an objective function that minimizes the congestion of the most utilized link in the network. In this paper, we focus on

2 multipath routing algorithms that both select the routing paths and split traffic among them. The pathology of link overload [9] in the network is studied and has proposed a deflection routing algorithm to alleviate overload by exploiting the highly meshed nature of the backbone and a judicious use of link weights. This proposal is based on the Sprint network which is built using a pure IP philosophy, though it can be applied to other networks, say those enabled with MPLS. In blacklist-based interface-specific [7] forwarding (BISF) is proposed that infers a blacklist, a list of links that might have failed, based on a packet s incoming interface and its destination, and determines the next-hop by excluding the blacklisted links. To enhance failure resiliency without jeopardizing routing stability, a local rerouting based approach [8] called failure insensitive routing is demonstrated. In Tabu-search heuristic [10] is proposed for choosing link weights which allow a network to function almost optimally during short link failures. The heuristic takes into account possible link failure scenarios when choosing weights, thereby mitigating the effect of such failures. 3 Proposed Methodology This paper aims in combining the enhanced FIR protocol for handling link failures and multipath algorithm for congestion minimization which provides better quality of source over link failures and network congestion. The proposed techniques for handling link failures and congestion minimization are explained as follows. 3.1 Handling Transient Link Failures In this proposed system, local rerouting called Enhanced Failure Insensitive Routing (EFIR) for handling the link failures and enhanced Multipath algorithms for congestion minimization are considered together to obtain better quality of service in case of network failure. Moreover, the idea is to calculate backup paths in advance before the network link fails. Whenever a failure is detected, the interrupted packets are immediately forwarded through the identified backup paths in order to minimize the service disruption. The two main key ideas that underpin this Proactive enhanced FIR approach based on local rerouting are interface-specific forwarding and Failure Inferencing. Under FIR, routers infer link failures based on packets and pre-compute interfacespecific forwarding tables (backup paths) in a distributed manner and trigger local rerouting without relying on network-wide link-state advertisements. Hence, this proposed EFIR enhances failure resiliency and routing stability by suppressing the advertisement of transient failures and locally rerouting packets along loop-free paths during the suppression period. 3.2 Congestion Minimization This second technique that performs enhanced Multipath routing called Restricted K-Path Routing (RKPR) for congestion minimization which combines the two algorithms called Restricted Multipath (RMP) and K-Path Routing (KPR). The main idea is to select paths based on quality of service and number of paths detected in the network. To minimize the route congestion and to minimize the service disruption, the packets are forwarded through multiple paths. In this work, two fundamental constraints are considered. First, each path that has been selected for routing should have adequate quality for sending the packets. Hence it is necessary to prohibit the substantially inferior paths which are considered as longer path. Second, practical restriction is on the number of routing paths per destination. Therefore, in practice, it is desirable to use few paths as possible to minimize the network congestion. Through comprehensive simulations, this system proves that Multipath solutions obtained by optimal congestion reduction schemes are fundamentally more efficient than solutions obtained by heuristics. This approach reduces the overheads and congestion resulted in earlier works. 4 Concept of Enhanced FIR In EFIR technique, when a link fails, the adjacent node to it locally reroute the packets to the affected destinations and all other nodes simply forward packets according to their pre-computed interface-specific forwarding tables without being explicitly aware of the failure. Once the failed link comes up again, forwarding resumes over the recovered link. Figure 1.1 shows the topology used for simulation of our technique EFIR which is considered in [7]. Figure 1.1 Topology used for simulation of EFIR The algorithm for the proposed EFIR technique is documented in figure 1.2.

3 EFIR Implementation Input : Transient Link Failure. Output: Local rerouting of packets during failure. Algorithm: i.start ii.identify the key links (set of links whose individual or combined failure causes the node to reroute the packet to its parent). iii.compute the shortest path by eliminating the key links with the help of fuzzy rules. iv.perform routing through the path found in step-iii. v.repeat the step-ii, iii and iv during each transient failure. vi.stop Figure 1.2 Algorithm for EFIR Using the conventional forwarding tables, local rerouting is not viable as it causes forwarding loops. Under enhanced technique of EFIR, forwarding loops are avoided by inferring a link s failure from packet s incoming interface. When the path 2 5 is down in the figure 1.1, node 2 locally reroutes packets from nodes 1 to 6 back to node 1 instead of dropping them. When a packet destined to 6 arrives at node 1 from node 2, then node 1 can infer that some link along its shortest path to 6 must have failed, as otherwise, 2 should never forward packets destined to 6 to node 1. The key links associated with the interface and destination 6 is 2 5, 5 6. It should be noted that these inferences about potential link failures are made not on the fly but in advance. 5 Multipath Algorithms The Paths for rerouting the packets from source to destination are selected based on these two main algorithms namely Restricted Multi-Path algorithm (RMP) and K-Path Routing algorithm. These two algorithms are illustrated as follows. 5.1 RMP (Restricted MultiPath) Consider a network G(V,E), two nodes s,t V, a length le>0, and a capacity for each link ce>0, a demand, and a length restriction L for each routing path. Find a feasible path flow that minimizes the network congestion factor such that, if P P(s, t) is the set of paths in P(s, t) that are assigned a positive flow, then, for each p P, it holds that L(p) L. Remark 1: For convenience, and without loss of generality, we assume that the length le of each link e E is not larger than the length restriction L. Clearly, links that are longer than L are erased. 5.2 KPR (K-Path Routing) In a given network G(V,E), the two nodes s, t V, a capacity ce>0 for each link e E, a demand > 0, and a restriction on the number of routing paths K. Find a feasible path flow that minimizes the network congestion factor, such that, if P P(s, t) is the set of paths in P(s, t) that are assigned a positive flow, then P K Input : Network traffic from network layer, length, flow rate. Output: Multipath routing with minimum number of path and reduced flow rate. Algorithm of the RKPR: i. Start ii. Create a traffic type of RMP and KPR. iii. Create the integrated traffic type that selects maximum of three paths to any destination in the network using c++. iv. Also, reduce the flow rate using the agent created using c++ for the path selected in step-iii. v. Multicast the packets using the traffic agent created to the destination. vi. Stop Figure 1.3 Algorithm for RKPR Remark 2: In both problems, the source to destination pair (s, t) is assumed to be connected, i.e., P(s, t) 1. Remark 3: In both problem formulations, it is possible to limit the link congestion factor fe/ce of each e E to any desired congestion level e by replacing the given capacity value ce with a new capacity value e ce. Clearly, the capacity constraint fe e ce (that both problems must satisfy) assures that the link congestion factor would be at most e. 6 Results and Performance Evaluation Our performance evaluations are based on the simulations of seven nodes as shown in figure 1.4 for handling link failure and 25 nodes for congestion minimization scenario that form a network with symmetric links over a rectangular (1500m * 500m) flat space in 100 sec of simulation time. The minimum speed for each node as 2ms except for the static case, and vary the maximum speed to 15ms to evaluate the impact of Transient Failure on our routing performance. Figure 1.5 shows the routing of enhanced FIR during failure of link 1-4. Figure 1.6 shows the ratio between the network congestion produced by an optimal Multipath routing assignment and the network congestion produced by ECMP using wax man topology.

4 Table 1.1 shows the implementation analysis of FIR that compares the throughput of OSPF with and without FIR. TABLE 1.1 ANALYSIS OF LINK FAILURE WITH AND WITHOUT FIR Time in sec OSPF without link failure No. of packets received in bytes During link link failure without FIR During link failure with FIR Figure 1.6 Congestion Rate for OMP and RKPR The following graphs shows the simulated results obtained from the implementation using NS-2 for the proposed method. This hybrid approach proves in considerable amount of performance over the existing individual methods. Fig 1.7 Simulation of RKPR in NS-2 Figure 1.4 Rerouting by EFIR in NS-2 Figure 1.5 Xgraph with and without EFIR 7 Conclusion and Future Work One fundamental challenge for IP Backbone network is to provide uninterrupted service availability during transient link failures and congestion. This proposed work explores a novel Pro-active approach for handling such transient link failures and an optimal congestion reduction scheme for congestion minimization. This algorithm can drastically reduce the network congestion at the price of routing along minimum number of paths that are slightly longer than the shortest path. In this work, we have presented a network layer routing solution that performs local rerouting and a Multipath routing in a unified framework. RMP-KPR algorithm restricts the number of path and flow rate to reduce the congestion along the path. We have also developed a formal model to analyze the routing stability and network availability under both Multipath and RMP-KPR approaches through simulations and graph comparison. Our results indicate that the improvement due to hybrid RMP-KPR algorithm is markedly better when the path and flow rate are restricted.

5 Our routing mechanism assumes a forwarding table per each interface and is applicable to links with symmetric weights. One possible extension is to deploy FIR in networks with asymmetric weights, broadcast LANs, and multiple areas. The distributed implementation of Algorithm RMP remains an open issue for future investigation. Also there is a possibility of providing security and energy efficient to make ease of the multipath routing that can minimize the network target. [10] S. Iyer, S. Bhattacharyya, N. Taft, and C. Diot, An Approach to Alleviate Link Overload as Observed on an IP Backbone, in Proceedings of IEEE INFOCOM, pp , References [1] Ron Banner, Ariel Orda, Multipath Routing Algorithms for Congestion Minimization, IEEE/ACM Transaction on Networking, Vol. 15, Issue 2, pp , Apr [2] H.Han, S.Shakkottai, C.V.Hollot, R.Srikanth, and D.Towsley, Multipath TCP: A Joint Congestion Control and Routing Scheme to Exploit Path Diversity in the Internet, IEEE/ACM Transaction on Networking, Vol. 14, Issue 6, pp , Dec [3] Merindol Pascal, Pansiot Jean-Jacques and Cateloin Stephane, Path Computation for Incoming Interface Multipath Routing in ECUMN 07: Proceedings of the Fourth European Conference on Universal MultiService Networks, [4] Kyeongia Lee, Armand Toguveni and Ahmed Rahmani, Hybrid Multipath Routing Algorithms for Load Balancing in MPLS Based IP Networks in AINA 06: Proceedings of the 20th International Conference on Advanced Information Networking and Application, [5] Wei Lin, Bin Liu and Yi Tang, Traffic Distribution over Equal-Costs-Multi- Paths using LRU-based Caching with Counting Scheme, in AINA 06: Proceedings of the 20th International Conference on Advanced Information Networking and Application, 2006 [6] Larry L.Peterson & Bruce S.Davie, Computer Networks A systems Approach, Morgan Kaufmann publishers, second edition, [7] S.Nelakuditi, Sanghwan Lee, Yinzhe Yu, Zhi-Li Zhang and Chen-Nee Chuah, Fast Local Rerouting for Handling Transient Link Failures, IEEE/ACM Transactions on Networking, Vol. 15, Issue 2, pp: , April [8] "Handling Failures in IP Networks through Interface Specific forwarding [9] A. Nucci, B. Schroeder, S.Bhattacharyya, N. Taft, and C. Diot, IGP Link Weight Assignment for Transient Link Failures, Presented at the ITC18, Berlin, Germany, 2003.