Steffen Gebert

Heuristic Approaches to the Controller Placement Problem in Large Scale SDN Networks

Software Defined Networking (SDN) marks a paradigm shift towards an externalized and logically centralized network control plane. A particularly important task in SDN architectures is that of controller placement, i.e., the positioning of a limited number of resources within a network to meet various requirements. These requirements range from latency constraints to failure tolerance and load balancing. In most scenarios, at least some of these objectives are competing, thus no single best placement is available and decision makers need to find a balanced trade-off. This work presents POCO, a framework for Pareto-based Optimal COntroller placement that provides operators with Pareto optimal placements with respect to different performance metrics. In its default configuration, POCO performs an exhaustive evaluation of all possible placements. While this is practically feasible for small and medium sized networks, realistic time and resource constraints call for an alternative in the context of large scale networks or dynamic networks whose properties change over time. For these scenarios, the POCO toolset is extended by a heuristic approach that is less accurate, but yields faster computation times. An evaluation of this heuristic is performed on a collection of real world network topologies from the Internet Topology Zoo. Utilizing a measure for quantifying the error introduced by the heuristic approach allows an analysis of the resulting trade-off between time and accuracy. Additionally, the proposed methods can be extended to solve similar virtual functions placement problems which appear in the context of Network Functions Virtualization (NFV).

Pareto-optimal resilient controller placement in SDN-based core networks

Recently, Software Defined Networking (SDN) has gained a lot of attention, even for the use in core communication networks. When deploying SDN in large core networks, the number and location of controllers must be carefully planned. A first study on this topic by Heller et al. [3] was followed by more detailed publications that included resilience or dynamic controller provisioning. In our previous work [2], we provide an overview over related work and include different resilience issues in the controller placement process. We argued that it is not sufficient to look only at node-to-controller latencies but a controller placement should also fulfill certain resilience constraints especially for the control plane.

Internet access traffic measurement and analysis

The fast changing application types and their behavior require consecutive measurements of access networks. In this paper, we present the results of a 14-day measurement in an access network connecting 600 users with the Internet. Our application classification reveals a trend back to HTTP traffic, underlines the immense usage of flash videos, and unveils a participant of a Botnet. In addition, flow and user statistics are presented, which resulting traffic models can be used for simulation and emulation of access networks.

Specialized Heuristics for the Controller Placement Problem in Large Scale SDN Networks

The Software Defined Networking (SDN) concept introduces a paradigm shift in the networking world towards an externalized control plane which is logically centralized. When designing an SDN-based WAN architecture, it is of vital importance to find a feasible solution to the controller placement problem, i.e., to decide where to position a limited amount of resources within the network. In addition to time-independent constraints regarding aspects like scalability, resilience, and control plane communication delays, dynamically changing network conditions like traffic patterns or bandwidth demands need to be considered as well. Consequently, such dynamic environments call for a regular and fast recalculation of placements in order to adapt to the current situation in a timely manner. While an exhaustive evaluation of all possible solutions can be performed within a practically feasible time frame for small and medium-sized networks, such an approach is out of scope for large problem instances which have significantly higher time and memory requirements. Therefore, this work investigates a specialized heuristic, which takes into account a particular set of optimization objectives and returns solutions representing the possible trade-offs between them. Due to its low computation time and acceptable margin of error, this heuristic can be employed by automatic decision systems operating in dynamic environments.

Demonstrating the optimal placement of virtualized cellular network functions in case of large crowd events

This demonstration shows how Network Function Virtualisation (NFV) [1] can be used by a network provider to dynamically provide required mobile core network functions in case of a large ”Mega” event like a soccer game or a music festival. Economical reasons may not justify the installation or continuous maintenance of expensive dedicated hardware which is necessary to cope with the high load generated by visitors of such an event only in some parts of the network and only for a short time. The Evolved Packet Core (EPC) in nowadays’ mobile LTE networks consists of several, specialized components: first pure control-plane elements like Mobility Management Entities (MME) which can be installed on virtualized IT hardware in the cloud already today and second gateways which are a mixture of controland user-plane. This demonstration focuses on the Serving Gateway (SGW) which switches GTP (GPRS Tunneling Protocol) tunnels in a LTE network. In such an LTE network with ≈ 10 mio. subscribers about 10 SGW devices are in use. On the way to a successful deployment of NFV-based EPC components, several challenges have to be met. This includes the deployment, interconnection and configuration of LTE components in the cloud. As such, entities that instantiate and orchestrate the virtualized functions are required. The presented demonstration shows a scenario of NFVbased dynamic capacity addition to a LTE mobile network, indicated in Figure 1. By incorporating the new demands added by the increased access capacity, virtualized SGW instances are launched at the optimal locations in the network, by re-programming SDN enabled network elements (NE+). Figure 1(a) shows the normal configuration of the LTE network including the statically located SGW devices as well as

Performance benchmarking of a software-based LTE SGW

Network Functions Virtualization (NFV) is a concept that aims at providing network operators with benefits in terms of cost, flexibility, and vendor independence by utilizing virtualization techniques to run network functions as software on commercial off-the-shelf (COTS) hardware. In contrast, prior solutions rely on specialized hardware for each function. Performance evaluation of such systems usually requires a dedicated testbed for each individual component. Rather than analyzing these proprietary black-box components, Virtualized Network Functions (VNFs) are pieces of software that run on COTS hardware and whose properties can be investigated in a generic testbed. However, depending on the underlying hardware, operating system, and implementation, VNFs might behave differently. Therefore, mechanisms for the performance evaluation of VNFs should be similar to benchmarking of software, where different implementations are compared by applying them to predefined test cases and scenarios. This work presents a first step towards a benchmarking framework for VNFs. Given two different implementations of a VNF that acts as LTE Serving Gateway (SGW), influence factors and key performance indicators are identified and a comparison between the two mechanisms is drawn.

POCO-PLC: Enabling dynamic pareto-optimal resilient controller placement in SDN networks

Recently, Software Defined Networking (SDN) has gained a lot of attention. The paradigm shift towards centralized architectures with a separation of control plane and data plane is expected for several use cases, including amongst others core communication networks, data center networks, or Network Function Virtualization (NFV). An important issue during SDN deployment is the placement of controllers in the network. The first to address this topic were Heller et al. [3] followed by other researchers who added different resilience issues into their observations. An overview on relevant publications can be found in our previous work [1], where we also introduced our POCO toolset. Here, a powerful and user friendly POCO-PLC toolset is provided and presented that facilitates the analysis and optimization of the controller placement in SDN networks under dynamic conditions. A general overview on the functionality and architecture of POCO-PLC is given. Then, possible use cases enabled by POCO-PLC is indicated.

OFCProbe: A platform-independent tool for OpenFlow controller analysis

Controller performance and behavior are key to the operation of an SDN network. Therefore, choosing the right controller implementation and corresponding set of applications is essential. In order to facilitate this decision we previously introduced a tool for controller performance analysis called “OFCBenchmark”. In this paper, we present “OFCProbe” a platform-independent and extended re-design of our original approach. We describe the new architecture and explain the implemented features. Finally, we provide some sample results to illustrate the kind of investigations that can be performed using the tool.

An SDN/NFV-Enabled Enterprise Network Architecture Offering Fine-Grained Security Policy Enforcement

In recent years, the number of attacks and threat vectors against enterprise networks have been constantly increasing in numbers and variety. Despite these attacks, the main security systems, for example network firewalls, have remained rather unchanged. In addition, new challenges arise not only to the level of provided security, but also to the scalability and manageability of the deployed countermeasures such as firewalls and intrusion detection systems. Due to the tight integration into the physical networks infrastructure, a dynamic resource allocation to adapt the security measures to the current network conditions is a difficult undertaking. This article covers different architectural design patterns for the integration of SDN/NFV-based security solutions into enterprise networks.

Investigating the impact of network topology on the processing times of SDN controllers

Software Defined Networking (SDN) introduces the concept of logically-centralized controllers in charge of managing the forwarding behavior of network elements. The new possibilities enabled through the centralization of control logic come with a certain risk: The controller might become a performance bottleneck. Therefore, ensuring sufficient controller performance is one of the crucial tasks prior to a successful SDN deployment. Furthermore, fine-grained traffic engineering, e.g., to achieve higher link utilization, results in a higher frequency of requests that are sent to the controller, which leads to an increased controller load. It is therefore important to analyze the capabilities of SDN controllers prior to deployment. This paper investigates two software implementations, the OpenDaylight and Ryu controllers. The control message throughput of different controllers has been studied several times already; however, it is not yet known what influence the number and topology of connected switches have. This paper investigates this influence in detail for a fat-tree data center topology and a WAN topology as well as 261 topologies with varying characteristics from the Internet Topology Zoo.