Marcel Caria

Divide and conquer: Partitioning OSPF networks with SDN

Software Defined Networking (SDN) is an emerging network control paradigm focused on logical centralization and programmability. At the same time, distributed routing protocols, most notably OSPF and IS-IS, are still prevalent in IP networks, as they provide shortest path routing, fast topological convergence after network failures, and, perhaps most importantly, the confidence based on decades of reliable operation. Therefore, a hybrid SDN/OSPF operation remains a desirable proposition. In this paper, we propose a new method of hybrid SDN/OSPF operation. Our method is different from other hybrid approaches, as it uses SDN nodes to partition an OSPF domain into sub-domains thereby achieving the traffic engineering capabilities comparable to full SDN operation. We place SDN-enabled routers as subdomain border nodes, while the operation of the OSPF protocol continues unaffected. In this way, the SDN controller can tune routing protocol updates for traffic engineering purposes before they are flooded into sub-domains. While local routing inside sub-domains remains stable at all times, inter-sub-domain routes can be optimized by determining the routes in each traversed sub-domain. As the majority of traffic in non-trivial topologies has to traverse multiple subdomains, our simulation results confirm that a few SDN nodes allow traffic engineering up to a degree that renders full SDN deployment unnecessary.

A performance study of network migration to SDN-enabled Traffic Engineering

In this paper, we analyze the question of network migration to Software Defined Networking (SDN) from the perspective of Traffic Engineering (TE). For a given network topology and migration planning horizon, we ask the question of which routers in the IP network should migrate to SDN-enabled operation to reduce the need for network capacity upgrades over a given time horizon. We propose an algorithm to determine the optimum schedule for node substitution within a network, which shows that already a few SDN routers, when strategically located, provide a stably large number of path alternatives to be used in TE, thus substantially reducing the need for large network capacity upgrades.

A comparative performance study of load adaptive energy saving schemes for IP-over-WDM networks

Load adaptive energy saving schemes for backbone IP networks use dynamic transport circuit services to adapt the active network resources to the current traffic demand in order to reduce the networks energy consumption. Recently, several approaches, categorized as Switch-off schemes, have been proposed which attempt to reduce the energy consumption of already existing networks by switching off IP ports and links during periods of low traffic. Although it has been shown that these schemes can notably decrease the networks energy consumption, they are prone to instabilities in the IP routing service and decreased resilience due to reduced connectivity, and they may induce monitoring reconfigurations. To address these challenges, we propose the Switch-On scheme in an IP-over-WDM network, where the network is designed so that the essential IP connectivity is maintained during low traffic periods while dynamic circuits are switched on in the optical layer to boost network capacity during periods of high traffic demand. Switching on the optical links during peak network loads can address some of the challenges associated with switching off IP ports and links during the low traffic periods. In this paper, we provide a comparative analysis of load adaptive energy saving schemes and present a discussion of the trade-off between energy efficiency and routing stability. The performance results and analytical study show that the multilayer approaches in IP-over-WDM networks carry significant potential for improvement in energy efficiency.

SDN Partitioning: A Centralized Control Plane for Distributed Routing Protocols

Hybrid IP networks that use both control paradigms - distributed and centralized - promise the best of two worlds: 1) programmability of software-defined networking (SDN) and 2) reliability and fault tolerance of distributed routing protocols, like open shortest path first (OSPF). Typically, a hybrid network deploys SDN to control prioritized traffic and OSPF to assure care-free operation of best effort traffic. We propose a new hybrid network architecture, called SDN partitioning (SDNp), which establishes centralized control over the distributed routing protocol by partitioning the topology into sub-domains with SDN-enabled border nodes. In our approach, OSPFs routing updates have to traverse SDN border nodes to reach neighboring sub-domains. This allows the central controller to modify how sub-domains view one another, which in turn allows to steer inter-sub-domain traffic. The degree of dynamic control against simplicity of OSPF can be traded off by adjusting the size of the sub-domains. This paper studies the technical requirements, presents a novel scheme for balanced topology partitioning, and provides the corresponding network management models for SDNp. Our performance evaluation shows that - already in its minimum configuration with two sub-domains - SDNp provides significant improvements in all respects compared to legacy routing protocols, whereas smaller sub-domains provide network control capabilities comparable to full SDN deployment.

To switch on or off: A simple case study on energy efficiency in IP-over-WDM networks

In this paper, we present a simple case study on energy efficiency in IP-over-WDM networks with dynamic circuit capability and compare two different load adaptive schemes, referred to as switch-on and switch-off. While the switch-off technique was already proposed for energy conservation, the switch-on approach is a new paradigm which is based purely on one-time implementations of dynamic circuit capability. Our results show that both approaches can significantly reduce the power consumption and decrease the necessary totally installed capacity, but unlike the switch-off scheme, the switch-on scheme does not affect the path redundancy in the network. Furthermore, switch-on can reduce the number of routing reconfigurations required in the network. While this seems ideal, our results also show that the switch-on scheme uses a large number of small capacity interfaces which may not be suitable from a network planning perspective as it might require frequent capacity upgrades, which alone is an interesting avenue for future research.

Effective Usage of Dynamic Circuits for IP Routing

The Internet is susceptible to congestion due to progressively increasing traffic as well as short-lived traffic surges. Traditional mechanisms to counter these effects over-provision the IP network to a significant degree. At the same time, the advent of dynamic circuits in L2/L1 networks has fueled the research in the area of network engineering which deals with the ability to add capacity in the higher layer (IP) by establishing dynamic circuits in the lower layers. However, effective usage of dynamic circuits is a challenge, as they can lead to IP routing instabilities. We present an approach wherein IP bypass links are established using dynamic circuits to alleviate congestion while keeping the routing stable in the IP layer. Proposed is an ILP based approach which computes the optimal set of circuits with and without the knowledge of the traffic matrix in the IP layer. The results show that even without the knowledge of the traffic matrix, the proposed method computes only a marginally higher number of bypasses, albeit at a higher capacity.

Achieving IP routing stability with optical bypass

The evolution of next generation services has led to significant increase in Internet backbone traffic, and multi-layer (hybrid) IP over circuit/optical layer solutions are being explored to cope up with the growing demands for capacity. Optical circuit bypass is typically used to increase capacity in the IP layer without need for over-provisioning, which in turn reduces OPEX of the IP network. Current proposals for IP topology reconfigurations in multi-layer networks do not take into consideration the effect of modifying the network topology on routing stability. We present a new bypass-based IP topology upgrade mechanism which can be used with high frequency without significantly affecting routing in the network. We present an ILP based approach to compute the optimal bypasses in the IP layer in case of congestion and numerical results show that our proposed solution is scalable and efficient.

A comparative performance analysis of IP traffic offloading schemes over Dynamic Circuits

We present an novel analytical framework for modeling current IP offloading schemes and show their comparative performance. We analyze relevant parameters, including IP routing re-convergence time, the number of affected IP routes, and the cost of circuit capacity used for offloading. Our results show that emerging offloading solutions based on invisible bypasses can better maintain network stability and reduce the routing reconfiguration effort compared to the traditional traffic engineering approaches that modify the IP routing.

Insights on SDN migration trajectory

As the Software Defined Networking (SDN) paradigm gains momentum, network operators wonder about how to go about replacing their legacy IP routers with SDN-compliant ones. While forklift network upgrades are impractical in operational networks, the promise of SDN is too compelling. Thus, a viable solution is to gradually migrate over time, leading to hybrid OSPF/SDN networks. Although recent studies proposed device architectures, protocols and algorithms required in such hybrid networks, a single routing domains SDN migration trajectory - as a whole - has hardly been studied. Significance of the sequence in which IP routers are replaced with SDN routers and optimal sequence of router replacements need to be investigated. In this paper, we address these questions based on SDNs traffic engineering (TE) gains and an operators SDN investment constraints. We propose optimization techniques and heuristics to plan an effective migration schedule in a single routing domain and demonstrate the significance of such a schedule using relevant network management metrics. Our results suggest: (a) the sequence of IP routers migrating to SDN largely determine the resulting TE gains, and, (b) to determine the best migration sequence, novel greedy algorithms perform almost as good as optimization techniques.

How to slice the day: Optimal time quantization for energy saving in the internet backbone networks

Load adaptive energy saving (LAES) schemes have been widely considered as a solution to reduce the energy consumption in networks. In LEAS, the time is sliced into time periods according to the daily pattern of traffic loads, such as peak and off-peak traffic, and energy saving operations are typically activated during the off-peak traffic. The effectiveness of LAES depends on the number of time slices precisely. A larger number of small time slices is desirable due to a better adaptiveness to traffic fluctuations. At the same time, energy saving operations should not be too frequent, as they have impact on routing stability and operational procedures. In this paper, we study the effect of nonuniform time quantization on the efficiency of energy saving. We propose a novel time quantization algorithm and show that optimizing time quantization can considerably reduce the number of energy saving operations, while comparably saving the same energy as previously reported.