Jouni Karvo

Working day movement model

Abstract movement models, such as Random Waypoint, do not capture reliably the properties of movement in the real life scenarios. We present and analyse a movement model for delay-tolerant network simulations that is able to produce inter-contact time and contact time distributions that follow closely the ones found in the traces from the real-world measurement experiments. We validate the movement model using the ONE simulator.

Opportunistic email distribution and access in challenged heterogeneous environments

The communication paradigms for delay-tolerant networking have been modeled after email. Supporting email over DTNs in a backwards compatible manner in a heterogeneous environment has yet to be fully defined. In this paper, we present a set of conventions for and extensions to the DTNRG architecture. We have implemented a system that is able to deliver emails within a DTN network, from a DTN network to the Internet, and from the Internet to the DTN network. Our system architecture includes multiple solutions for integrating traditional and DTN-based mail delivery: DTN-based messaging clients for mobile phones and PDAs, a dedicated, stand-alone DTN gateway between the Internet and the DTN network, and a personal DTN mail application proxy. The latter bridges to unmodified mail user agents running on a laptop.

Time scales and delay-tolerant routing protocols

Numerous routing protocols have been proposed for Delay Tolerant Networking. One class of routing protocols aims at optimizing the delivery performance by using knowledge of previous encounters for forecasting the future contacts to determine suitable next hops for a given packet. Protocols pursuing such an approach face a fundamental challenge of choosing the right protocol parameters and the right time scale for estimation. These, in turn, depend on the mobility characteristics of the mobile nodes which are likely to vary within one scenario and across different ones. We characterise this issue, which has been overlooked in this field so far, using PROPHET and MaxPROP as two representative routing protocols and derive mechanisms to dynamically and independently determine routing parameters in mobile nodes.

Blocking of dynamic multicast connections in a single link

In this paper, a method for calculating blocking experienced by dynamic multicast connections in a single link is presented. A service center at the root of a tree-type network provides a number of channels distributed to the users by multicast trees which evolve dynamically as users join and leave the channels. We reduce this problem to a generalized Engset system with nonidentical users and generally distributed holding times, and derive the call and channel blocking probabilities as well as the link occupancy distribution.

Blocking of Dynamic Multicast Connections

Multicast connections have a bandwidth saving nature. This means that a multicast connection – in taking the form of a tree with streams merging at the nodes – requires much less capacity from the network links than a bunch of separate point-to-point connections providing the same connectivity. In this paper, we consider dynamic multicast connections that can be used to model, for example, TV or radio delivery on a telecommunications network, such as an ATM network with virtual circuits. We show how to calculate the blocking probabilities of requests to join such a tree. First, we consider the blocking probabilities occurring in a single link. The resulting model is able to capture heterogeneous capacity requirements for different multicast channels. Then we extend the results to a whole network using the reduced load approximation. The accuracy of the approximation method is studied by simulations.

Multicasting vs. unicasting in mobile communication systems

We evaluate the multicasting gain over unicast in the cellular networks, where cells are engineered for a specific target call blocking probability. Our approach is Monte-Carlo simulation of dynamic multicast connections, and the traditional Engset model for the unicast traffic. We predict the gain given by multicasting by using earlier studied traffic patterns, and conclude that intervention of the network operator is needed to secure a significant multicasting gain.

Efficient importance sampling for Monte Carlo simulation of multicast networks

We consider the problem of estimating blocking probabilities in a multicast loss system via simulation, applying the static Monte Carlo method with importance sampling. An approach is introduced where the original estimation problem is first decomposed into independent simpler sub-problems, each roughly corresponding to estimating the blocking probability contribution from a single link. Then we apply importance sampling to solve each sub-problem. The importance sampling distribution is the original distribution conditioned on that the state is in the blocking state region of a single link. Samples can be generated from this distribution using the so called inverse convolution method. Finally, a dynamic control algorithm is used for optimally allocating the samples between different sub-problems. The numerical results demonstrate that the variance reduction obtained with the method is remarkable, between 400 and 36000 in the considered examples.

Blocking probabilities of multi-layer multicast streams

We present two new algorithms for calculating call blocking probabilities for multi-layer multicast streams with the assumption that blocked calls are lost. Users may join and leave the multicast connections freely, thus creating dynamic multicast trees. We define the state space, and give two recursive algorithms; for the general case and for the special case where all multicast channels are statistically indistinguishable. Our recursive algorithms are linear with respect to the number of links. The special case is also polynomial with respect to the number of channels.

A Deployment Tool for Public Safety Ad-hoc Networks

Public protection and disaster relief is a promising application area for ad-hoc networks. We propose architecture and show a prototype implementation of an application for helping network deployment on the scene. The application has a graphical interface showing network status and proposing actions for additional measures to ensure the uninterrupted and reliable operation of the network. The tool is designed for a user with no experience of network planning

Efficient Simulation of Blocking Probabilities for Multi-layer Multicast Streams

This paper presents an efficient algorithm for Monte-Carlo simulation of time blocking probabilities for multi-layer multicast streams with the assumption that blocked calls are lost. Users may join and leave the multicast connections freely, thus creating dynamic multicast trees. The earlier published algorithms are applicable to small networks or networks with few users. The present simulation algorithm is based on the inverse convolution method, and is the only effective way to handle large systems, known to the author.