Articles written in Sadhana

    • Provisioning in transport networks using power-aware resource allocation algorithms


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      Transport technologies such as Optical Transport Network and Synchronous Digital Hierarchy are widely used in access and core networks to carry different types of traffic. These technologies define a hierarchy for multiplexing lower rate traffic containers onto higher rate traffic containers. Provisioning refers to the process of allocation of resources to meet a given traffic demand. Due to the continued expansion of transport networks, the power consumption increases, becoming a bottleneck for further expansion. Power-aware allocation ofresources to traffic demands will enable power-efficient operation and help in minimizing the capital and operational costs of the network. In this paper, the power consumed by a switch matrix having the capability to switch different traffic containers at different amounts is considered. The objective is to minimize the number of network elements deployed in the network by allocating resources to traffic demands in power-efficient ways. A formulation based on Integer Linear Programming is first presented; later, four different heuristic approaches,based on how higher order trails are used and the use of grooming, are proposed. It is found that the grooming based heuristics perform better in terms of the total power consumption relative to the weighted number of requests accepted. In the grooming heuristics, threshold on link utilization is set to determine when grooming is to be done, and for the same performance evaluation, it is found that the threshold of 80% gives better results.

    • Testbed evaluation of a seamless handover mechanism for an SDN-based enterprise WLAN


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      Many modern-day applications require seamless connectivity to provide a good quality experience to mobile users. Thus, mobility management mechanism becomes a crucial aspect of all the wireless technologies used to connect to the Internet. In this letter, we present the testbed implementation details of aNetwork Address Translation (NAT)-based, client-unaware, seamless handover mechanism for a Software- Defined Enterprise WLAN framework. The results from the testbed implementation corroborate that the handover mechanism can provide uninterrupted connectivity during a handover process.

    • Design and evaluation of low-cost network architecture for persistent WiFi connectivity in trains


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      With the exponential growth in the number of mobile devices, providing Internet access via WiFi in trains is rapidly becoming a necessity. Cellular network is predominantly used for the backhaul connection to the train. However, the railway companies of developing countries may not go for cellular-network-based solutionsmainly for two reasons: (1) high deployment cost of a cellular network and (2) lack of sufficient coverage of existing cellular networks of telecom companies along the railway tracks. In this paper, we propose a Software Defined Networking (SDN)-based architecture to provide Internet connectivity inside trains. The backhaulconnection to the train, in the proposed architecture, is provided via WiFi. Deployment of such an architecture is more cost-efficient than that of a dedicated cellular network of the same capacity, or that of the existing cellularnetworks of telecom companies, since there are no running tariffs and the spectrum is free. Moreover, this architecture can be used to provide connectivity in the coverage holes of the existing networks of the telecom companies. Through simulation, we show that the architecture can provide high throughput and packet delivery ratio while maintaining per packet delay within reasonable limits inside a train.

    • An online distributed approach to Network Function Placement in NFV-enabled networks


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      Network Function Placement (NFP) involves placing virtual network functions (VNFs) on the nodes of a network such that the data that flow through the network are processed by a chain of service functions along their path from source to destination. There are three aspects to this problem: (i) routing the flows efficiently through the network, (ii) placement of the VNFs on the nodes and (iii) steering each flow through a chain of VNFs, known as the service function chain (SFC). Routing must attempt to find ‘‘optimal’’ paths through the network (for e.g., shortest paths), possibly subject to constraints such as path latency and link bandwidth. The VNFs consume resources on the nodes where they are placed and are constrained by the capacity of the nodes. Steering must ensure that each flow has along its path a sequence of VNFs, likely in a certain order. One way to specify this problem is to define a multi-commodity flow problem with additional constraints based on the steering and placement requirements. Simultaneously solving all three aspects of this problem, trying to optimize various parameters and within the various constraints, is a hard problem, with even asimplified version shown to be NP-complete in this paper. Attempting to optimally solve this problem in real time while flows are getting provisioned and de-provisioned in parallel is an intractable problem, especially in large networks. Hence various types of heuristics have been used to solve this problem. In this paper we introduce a distributed, online solution that employs a message-passing protocol for nodes to negotiate the placement of the VNFs, with the minimization of the number of VNF instances being the primary objective. Wecompare the performance of the solution to that of the theoretically optimal solution and other proposed heuristics on both the Fat-tree topology and the BCube topology. The results show that this solution performs better than other heuristics. The average ratio of the result of the proposed solution to that of the optimal solution, taken as the approximation ratio, is found to be 1.5 for the tested scenarios

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