Ivan Gojmerac

Adaptive multipath routing for dynamic traffic engineering

This paper proposes adaptive multi-path routing (AMP) as a simple algorithm for dynamic traffic engineering within autonomous systems. In contrast to related multipath routing proposals, AMP does not employ a global perspective of the network in each node. It restricts available information to a local scope, which opens the potential of reducing signaling overhead and memory consumption in routers. Having implemented AMP in ns-2, the algorithm is compared to standard routing strategies for a realistic simulation scenario. The results demonstrate the stability of AMP as well as the significant performance gains achieved.

Radio resource allocation in urban femto-WiFi convergence scenarios

The recent tremendous growth of mobile broadband traffic demand forces mobile operators to find ways for offloading their macro-infrastructure. This can be achieved by a combination of two concepts, i.e., introducing/deploying a finer grid of base-stations (femto-cells) together with increasing the share of traffic volume that is handled by communication-links operating in unlicensed bands (e.g., IEEE802.11-based wireless-LAN). Both concepts are supported by the recent proliferation of wireline broadband (DSL/cable) which enables the cost effective backhauling of small sites using standard internet access. However, new challenges in terms of network-planning arise as these small cells are deployed randomly, their resulting spatial density in urban environments may get very high, and thus the aspect of interference-mitigation is of vital importance. The contribution of this paper is twofold: first we provide a comparison of licensed-band femto-cell versus unlicensed WiFi technologies. We try to outline characteristic differences and respective limitations in terms of efficiency of radio-resource sharing mechanisms, with a specific focus on macro-cell offloading scenarios. Second, we present the results of a measurement campaign that allows to quantify the current density of WiFi access points in the 2.4GHz WiFi band in urban environments. We subsequently use these data sets to extrapolate the coverage ratios that are achievable by aggregating low-power WiFi/femto cells. This can be used to provide novel insights into specific radio-resource management problems which a mobile operator needs to solve when moving towards smaller cells and less-controllable deployment procedures.

Adaptive Multipath Routing Based on Local Distribution of Link Load Information

Adaptive Multi-Path routing (AMP) is a new simple algorithm for dynamic traffic engineering within autonomous systems. In this paper, we describe an AMP variant which is related to the well-known Optimized Multi-Path (OMP) routing protocol. Whereas OMP requires global knowledge about the whole network in each node, the AMP algorithm is based on a backpressure concept which restricts the distribution of load information to a local scope, thus simplifying both signaling and load balancing mechanisms. The proposed algorithm is investigated using ns-2 simulations for a real medium-size network topologyand load scenarios by performing comparisons to several standard routing strategies.

Measurement-Based Small-Cell Coverage Analysis for Urban Macro-Offload Scenarios

In order to cope with the expected future growth of mobile broadband traffic, network operators will be forced to dramatically increase their Radio Access Network (RAN) capacities. As neither the purchase of additional spectrum nor the deployment of new radio technologies will be able to solve this problem in the long run, we focus on a strategy for offloading the macro-infrastructure by introducing small cell sites of high spatial density (e.g., femto-cells) or by shifting significant volumes of traffic towards connections operating in the unlicensed bands (e.g., IEEE 802.11 Wi-Fi). In this paper, we address related coverage and interference issues, based on a recent measurement campaign conducted in a representative district of the city of Vienna, Austria. We provide fine-grained coverage results for both Wi-Fi and 3G which may serve as a reliable starting point for analyzing the feasibility and efficiency of future nomadic and mobile offloading strategies. Moreover, our results demonstrate that the signal strengths of user provided indoor Wi-Fi access points most often match or even exceed those of the macro-cell infrastructure in urban outdoor environments.

Internet security meets the IP multimedia subsystem: an overview

In this paper, we discuss the security threats of next-generation telecommunication core networks induced by the adoption of Internet technology. The 3GPP IP multimedia subsystem (IMS) is based on the Internet protocol (IP) and hence inherits many security problems from the Internet world. We provide a review of the most prominent vulnerabilities, covering both fundamental functions like routing and name resolution as well as message tampering and implementation attacks, and we show their impact on the IMS. Further, we address the topics of denial of service (DoS) attacks and unsolicited communication (UC). Despite the large number of security threats, the IMS standardization foresees no security monitoring and fully relies on standard countermeasures as known from the Internet. This paper provides a survey of these threats and relates them to the available solutions. We motivate the need for a powerful and modular monitoring platform for the IMS and provide an overview of the existing work in this research field. Copyright

IDRD: Enabling inter-domain route diversity

In the present Internet, inter-domain routing is based on BGP-4 which does not allow for the use of multiple paths, but rather selects a single path per destination prefix. However, as the global Internet connectivity graph displays vast inherent path diversity, we believe that there is a lack of mechanisms which put this latent potential into use. To this end, we propose Inter-Domain Route Diversity (IDRD) as a mechanism which allows for diverse inter-domain paths to be propagated among carriers and used for packet forwarding. Our proposal is aimed to be efficient, backwards compatible, and incrementally deployable. In order to make use of the existing path diversity, we also propose a relaxation of the multipath route selection policy that is provably stable, while being more flexible. Our extensive evaluation of path disjointness in the Internet connectivity graph illustrates the potential benefits of IDRD. While the evaluation shows that the traditional “prefer customer” rule heavily impedes the use and propagation of the underlying diversity, it also demonstrates that our proposed relaxation of the multipath route selection policy enables near-optimal utilization of the underlying path diversity in the real Internet inter-domain topology.

Intrusion Detection in IMS: Experiences with a Hellinger Distance-Based Flooding Detector

With the imminent roll-out of the 3GPP IP Multimedia Subsystem (IMS), IMS-specific security threats and corresponding counter-mechanisms are gaining increasing attention. One of the most promising recent intrusion detection approaches dealing with unforeseen anomalies caused by flooding attacks is based on a specific metric for the distance between two empirical probability distributions, the so-called Hellinger distance. In this paper, we discuss the application of this concept for IMS networks as well as the resulting implementation of a flooding detector, and describe some practical experiences based utilizing different traffic generation tools. The results show that shorter analysis cycles and precise parameterization in general trigger higher detection rates.

Wi-Fi Offload: Tragedy of the commons or land of milk and honey?

Fueled by its recent success in provisioning on-site wireless Internet access, Wi-Fi is currently perceived as the best positioned technology for pervasive mobile macro network offloading. However, the broad transitions of multiple collocated operators towards this new paradigm may result in fierce competition for the common unlicensed spectrum at hand. In this light, our paper game-theoretically dissects market convergence scenarios by assessing the competition between providers in terms of network performance, capacity constraints, cost reductions, and revenue prospects. We will closely compare the prospects and strategic positioning of fixed line operators offering Wi-Fi services with respect to competing mobile network operators utilizing unlicensed spectrum. Our results highlight important dependencies upon inter-operator collaboration models, and more importantly, upon the ratio between backhaul and Wi-Fi access bit-rates. Furthermore, our investigation of medium-to long-term convergence scenarios indicates that a rethinking of control measures targeting the large-scale monetization of unlicensed spectrum may be required, as otherwise the used free bands may become subject to tragedy-of-commons type of problems.

Internet-wide multipath: A scalability analysis of path identification schemes

In the present Internet, inter-domain routing is based on BGP-4 which prevents the use of multiple paths, but rather selects a single path per destination prefix. However, as the global Internet connectivity graph displays vast inherent path diversity, multipath routing has been identified as an important feature for the Future Internet, for both robustness and traffic engineering purposes. Some works propose to enable the propagation of multiple inter-domain routes per prefix [1], [2], [3]. While these works propose the use of a new packet field (which we call Path-ID) to specify the path which is to be followed by packets, they do not discuss about the scalability of such an approach. Indeed, as such a field is globally significant, it can lead to some scalability issues which could make such proposals impossible to implement. We propose the study of the scalability of such a field in order to answer the recurring but un-answered question: “Will Internet-wide multipath make the FIB explode?”. To this end, we propose some Path-ID global identification schemes, identify their weaknesses and propose simple and realistic assumptions which resolve their scalability issues. At the end, we show that these simple assumptions are sufficient to enable vast multipath in the Internet while remaining manageable.

An algorithmic framework for discrete-time flow-level simulation of data networks

In this paper, we present a comprehensive algorithmic framework for discrete-time flow-level simulation of data networks. We first provide a simple algorithm based upon iterative equations useful for the simulation of networks with static traffic demands, and we show how to determine packet loss and throughput rates using a simple example network. We then extend these basic equations to a simulation method capable of handling queue and link delays in dynamic traffic scenarios and compare results from flow-level simulation to those obtained by packet-level simulation. Finally, we illustrate the tradeoff between computational complexity and simulation accuracy which is controlled by the duration of a single iteration interval Δ.