Marcus Brunner

Detecting SPIT Calls by Checking Human Communication Patterns

SPam over Internet Telephony (SPIT) is expected to become a very serious issue in the next years. The threat is going to spin out from the well known email spam problem by bot nets being re-programmed to initiate not just spam emails but also Voice over IP (VoIP) calls. Preventing SPIT is a new problem, because many well-established methods for blocking email spam cannot be applied. Currently, several SPIT prevention methods are being proposed but SPIT prevention research is still at a very early stage. In this paper, we propose an innovative way to detect SPIT calls by comparing applying hidden Turing tests that compare them with typical human communication patterns. For passing these tests, significant resource consumptions at the SPIT generating bot nets would be required which contradicts the spammers objective of placing as many SPIT calls as possible, The proposed method has several advantages compared to other methods that also interact with the caller. We validated its feasibility with a prototype implementation that we integrated into our modular VoIP security system called VoIP SEAL.

Protocol enhancements for intermittently connected hosts

Internet users are increasingly mobile. Their hosts are often only intermittently connected to the Internet, due to using multiple access networks, gaps in wireless coverage or explicit user choice. When such hosts communicate using the current Internet protocols, intermittent connectivity can significantly decrease performance and even cause connections to fail altogether. This paper experimentally measures the behavior of Internet communication across a dynamically changing, intermittently connected path. An analysis of the experimental results finds that address changes together with transport-layer timeout and retransmission behaviors are the main limiting factors. Based on these experimental results, this paper proposes a solution that combines the Host Identity Protocol (HIP) with two new protocol enhancements, the TCP User Timeout Option and the TCP Retransmission Trigger. Detailed experiments with HIP and a prototype implementation of these protocol enhancements show that they tolerate address changes and arbitrary-length disconnections while significantly increasing performance under intermittent connectivity to within 86-96% of a scenario with constant connectivity.

Self-Managing Distributed Systems

Current self-healing systems are built from “convergent” actions that only make repairs when necessary. Using an algebraic model of system administration, we challenge the traditional notion of “convergence” and propose a stronger definition with improved algebraic properties. Under the new definition, the structure of traditional configuration management systems is a natural emergent property of the algebraic model. We discuss the impact of the new definition, as well as the changes required in current convergent tools in order to conform to the new definition.

Distributed autonomic resource management for network virtualization

Network virtualization is an emerging trend claimed to reduce the costs of future networks. The key strategy in network virtualization is of slicing physical resources (links, routers, servers, etc.) to create virtual networks composed of subsets of these slices. One important challenge on network virtualization is the resource management of the physical or substrate networks. Sophisticated management techniques should be used to accomplish such management. The sophisticated techniques offered by autonomic communications rise as an appropriated alternative to address the challenges of managing the efficient use of substrate resources on network virtualization. Thus, this paper proposes a distributed self-organizing model to manage the substrate network resources. An evaluation scenario is depicted and simulations show that approximately 36.8% of the network traffic load can be spared when the self-organizing model is enabled in the evaluated scenario.

Self-organized energy efficient cellular networks

Base stations (BSs) are the main energy expenditure elements of cellular networks, considering the high coverage requirements and the fact that the total provisioned capacity is intended to match peak hour traffic demand. In this paper, we introduce energy saving algorithms based on coordination between network elements. We introduce the notion of energy partitions - associations of powered-on and powered-off BSs - to deliver energy saving with the objective of matching offered capacity with the traffic demand in a flexible manner. Our energy saving algorithms are based on shared knowledge of load and coverage information and enable an appropriate cell reconfiguration for achieving a network-level energy saving. Through a simulation-based evaluation, we analyze the performance of centralized and distributed algorithms under different network topologies and traffic conditions, highlight the benefits and drawbacks, and provide recommendations for deployment scenarios.

An Experimental Evaluation of Voice Quality Over the Datagram Congestion Control Protocol

Most Internet telephony applications currently use either TCP or UDP to carry their voice-over-IP (VoIP) traffic. This choice can be problematic, because TCP is not well suited for interactive traffic and UDP is unresponsive to congestion. The IETF has recently standardized the new Datagram Congestion Control Protocol (DCCP). DCCP has been designed to carry media traffic and is congestion-controlled. This paper experimentally evaluates the voice quality that Internet telephony calls achieve over prototype implementations of basic DCCP and several DCCP variants, under different network conditions and with different codecs. It finds that the currently-specified DCCP variants perform less well than expected when compared to UDP and TCP. Based on an analysis of these results, the paper suggests several improvements to DCCP and experimentally validates that a prototype implementation of these modifications can significantly increase voice quality.

Probabilistic decentralized network management

This work proposes a probabilistic management paradigm for solving some major challenges of decentralized network management. Specifically, we show how to cope with 1) the overhead of redundant information gathering and processing, 2) the decentralized management in dynamic and unpredictable environments, and 3) the considerable effort required for decentralized coordination of management functions. To this end, we describe a framework for probabilistic decentralized management in the context of In-Network Management (INM). We demonstrate how this framework can be applied to a network of information, a novel clean-slate approach towards an information-centric future Internet. We show by means of a simulation study in the area of performance and fault management that we can significantly reduce the effort and resources dedicated to management, while we are able to achieve a sound level of accuracy of the overall network view.

ISE03-2: SPam over Internet Telephony (SPIT) Prevention Framework

SPam over Internet telephony (SPIT) is expected to become a threat inhibiting the delivery of voice services over the Internet in the near future both because of its technical and economical characteristics. Experiences with email SPAM and its analogies with SPIT suggest that SPIT will be difficult to detect with a single detection method. Moreover, personalized management of detection strategies will be needed to increase effectiveness and to adapt the methods to special environments. This paper presents a modular framework for SPIT prevention designed to be easily manageable and extensible. Additionally, the framework makes use of a two-stage architecture in order to exploit the knowledge coming both from the signaling and from the media flows while still allowing real-time delivery of the media content to the user. Following the experience gained with our prototype implementation we also present the most important design issues we encountered and suggest solutions to these issues.

Self Organized Network Management Functions for Energy Efficient Cellular Urban Infrastructures

Energy efficiency is a significant requirement for the design and management of mobile networks and has recently gained substantial attention from both network operators and the research community. The general concept of energy saving management aims to match the capacity offered by operators to the actual demand at given times and geographic areas. This paper introduces the notion of energy partition, an association of powered-on and powered-off BSs to deliver network-level energy saving. It then elaborates how such concept is applied to perform energy re-configuration to flexibly re-act to load variations encouraging none or minimal extra energy consumption. A simulation-based study evaluates the performance of the proposed algorithms under different network topologies and traffic conditions, highlights the benefits and drawbacks, and provides recommendations for deployment scenarios.

Scalability of a mobile cloud management system

Ubiquitous network access allows people to access an ever increasing range of services from a variety of mobile terminals, including laptops, tablets and smartphones. A flexible and economically efficient way of provisioning such services is through Cloud Computing. Assuming that several cloud-enabled datacenters are made available at the edges of the Internet, service providers may take advantage of them by optimally locating service instances as close as possible to their users. By localizing traffic at the edges of access networks, such an approach may result beneficial for both service and network providers. In this paper we present Follow-Me Cloud (FMC), a technology developed at NEC Laboratories Europe that allows transparent migration of services in TCP/IP networks, thanks to the dynamic configuration of a set of coordinated OpenFlow switches located at the edge of the network. In particular, in this paper we analyze the scalability properties of an FMC-based system and propose a role separation strategy based on distribution of control plane functions which enables scale-out of the system. By means of simulation, we prove that the application of the proposed separation strategy results in less state retained by individual OpenFlow controllers and in more effective localization of network traffic.