Multiprotocol Label Switching | EPFL Graph Search

Multiprotocol Label Switching (MPLS) is a routing technique in telecommunications networks that directs data from one node to the next based on labels rather than network addresses. Whereas network addresses identify endpoints the labels identify established paths between endpoints. MPLS can encapsulate packets of various network protocols, hence the multiprotocol component of the name. MPLS supports a range of access technologies, including T1/E1, ATM, Frame Relay, and DSL. Role and functioning In an MPLS network, labels are assigned to data packets. Packet-forwarding decisions are made solely on the contents of this label, without the need to examine the packet itself. This allows one to create end-to-end circuits across any type of transport medium, using any protocol. The primary benefit is to eliminate dependence on a particular OSI model data link layer (layer 2) technology, and eliminate the need for multiple layer-2 networks to satisfy different types of traffic. Mult

Collaborative routing in mobile partitioned networks

Natasa Sarafijanovic-Djukic

Embedded wireless networks find a broad spectrum of applications in transportation, environmental monitoring, logistics, supply chain management, and "pocketswitched" communication. The node mobility patterns in these applications tend to give rise to spatially heterogeneous node distributions, which may cause network partitions. In this thesis, we consider the problem of routing in mobile networks under such challenging conditions. More specifically, we endeavor to identify features of mobility common to different applications, in order to devise routing methods that are tailored to exploit these features. We explore two features in particular, (i) predictability and (ii) stable and heterogeneous spatial node distribution. A mobility process is predictable if the future location of a node can be well estimated, given knowledge of its current and past locations and possibly other statistics. We show how the performance of routing can be improved by explicitly incorporating mobility prediction. Specifically, we consider the performance of Last Encounter Routing (LER) under a simple synthetic random waypoint (RWP) mobility model. We extend the LER algorithm so that it takes into account predicted node trajectories when making routing decisions, and we show that this significantly improves its performance. A mobility process has a stable spatial node distribution if, informally, the node density remains the same over time, even though individual nodes are not constrained in space. This is a common feature of many mobility patterns because the spatial distribution is determined by the natural or constructed environment, regardless of the behavior of individual nodes. This typically leads to heterogeneous connectivity and to network partition, where highly connected clusters are interspersed with low-connectivity regions. We model such a situation with a set of stable concentration points (CPs) characterized by high node density, and with a mobility process that describes how nodes move between these islands of connectivity. We study two instances of this model: the G-model, where the CPs and the flow of nodes are abstracted as a graph, and the H-model, where nodes perform heterogeneous random walks on the plane. We exploit the presence of this stable CP topology in order to develop an efficient routing algorithm under these two mobility models. Our routing algorithm, Island Hopping (IH), exploits knowledge of the CP topology to make routing decisions. IH achieves a very good delay-throughput trade-off compared with several other existing routing algorithms, and it scales well with the network size. In many situations, it would be unrealistic to assume that CPs and the flows of mobile nodes among them are known a-priori. We develop methods, collectively called Collaborative Graph Discovery (COGRAD), that allow the nodes to discover the CP graph without any explicit signals from the environment (such as GPS coordinates or fixed beacons). We show that COGRAD can replace an oracle with knowledge of the CP topology after a sufficient warm-up period, allowing IH to operate even in scenarios without any cues from the environment.

EPFL2010

Cybersecurity Solutions for Active Power Distribution Networks

Teklemariam Tsegay Tesfay

An active distribution network (ADN) is an electrical-power distribution network that implements a real-time monitoring and control of the electrical resources and the grid. Effective monitoring and control is realised by deploying a large number of sensing and actuating devices and a communication network to facilitates the two-way transfer of data. The reliance of ADN operations on a large number of electronic devices and on communication networks poses a challenge in protecting the system against cyber-attacks. Identifying these challenges and commissioning appropriate solutions is of utmost importance to realize the full potential of a smart grid that seamlessly integrates distributed generation, such as renewable energy sources. As a first step, we perform a thorough threat analysis of a typical ADN. We identify potential threats against field devices, the communication infrastructure and servers at control centers. We also propose a check-list of security solutions and best practices that guarantee a distribution network's resilient operation in the presence of malicious attackers, natural disasters, and other unintended failures that could potentially lead to islanded communication zone. For the next step, we investigate the security of MPLS-TP, a technology that is mainly used for long-distance inter-domain communication in smart grid. We find that an MPLS-TP implementation in Cisco IOS has serious security vulnerabilities in two of its protocols, BFD and PSC. These two protocols control protection-switching features in MPLS-TP. In our test-bed, we demonstrate that an attacker who has physical access to the network can exploit the vulnerabilities in order to inject forged BFD or PSC messages that affect the network's availability. Third, we consider multicast source authentication for synchrophasor data communication in grid monitoring systems (GMS). Ensuring source authentication without violating the stringent real-time requirement of GMS is challenging. Through an extensive review of existing schemes, we identified a set of schemes that satisfy some desirable requirements for GMS. The identified schemes are ECDSA, TV-HORS and Incomplete- key-set. We experimentally compared these schemes using computation, communication and key management overheads as performance metrics. A tweak in ECDSA's implementation to make it use pre-generated tokens to generate signatures significantly improves the computation overhead of ECDSA, making it the preferred scheme for GMS. This finding is contrary to the generally accepted view that asymmetric cryptography is inapplicable for real-time systems. Finally, we studied a planning problem that arises when a utility wants to roll out a software patch that requires rebooting to all PMUs while maintaining system observability. The problem we address is how to find a partitioning of the set of the deployed PMUs into as few subsets as possible such that all the PMUs in one subset can be patched in one round while all the PMUs in the other subsets provide full observability. We show that the problem is NP-complete in the general case and and formulated it as binary integer linear programming (BILP) problem. We have also provided an heuristic algorithm to find an approximate solution. Furthermore, we have identified a special case of the problem where the grid is a tree and provided a polynomial-time algorithm that finds an optimal patching plan that requires only two rounds to patch the PMUs.

EPFL2017

Cybersecurity Solutions for Active Power Distribution Networks

Teklemariam Tsegay Tesfay

EPFL2017

Collaborative routing in mobile partitioned networks

Natasa Sarafijanovic-Djukic

EPFL2010