A study of teletraffic problems in multicast networks

This dissertation studies teletraffic engineering of dynamic multicast connections. The traditional models in teletraffic engineering do not handle multicast connections properly, since in a dynamic multicast tree, users may join and leave the connection freely, and thus the multicast tree evolves in time. A model called multicast loss system is used to calculate blocking probabilities in a single link and in tree-type networks. In a single link case, the problem is a generalised Engset problem, and a method for calculating call blocking probabilities for users is presented. Application of the reduced load approximation for multicast connections is studied. Blocking probabilities in a cellular system are studied by means of simulation. The analysis is mainly concentrated on tree type networks, where convolution-truncation algorithms and simulation methods for solving the blocking probabilities exactly are derived. Both single layer and hierarchically coded streams are treated. The presented algorithms reduce significantly the computational complexity of the problem, compared to direct calculation from the system state space. An approximative method is given for background traffic. The simulation method presented is an application of the Inverse Convolution Monte-Carlo method, and it gives a considerable variance reduction, and thus allows simulation with smaller sample sizes than with traditional simulation methods. Signalling load for dynamic multicast connections in a node depends on the shape of the tree as well as the location of the node in the tree. This dissertation presents a method for calculating the portion of signalling load that is caused by call establishments and tear-downs.reviewe

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

On Improving Connectivity of Static Ad-Hoc Networks by Adding Nodes

Abstract — The connectivity of a given static, disconnected adhoc network can be improved by placing additional nodes in the network, forming connections between separate clusters of connected nodes. Finding optimal locations to place the additional nodes is a difficult problem. We give definitions of two problems: connecting the network with a minimal number of additional nodes, and maximizing utility from a given number of additional nodes in case complete connectivity cannot be established. The former problem reduces in a limit case to that of the Euclidean Steiner minimal tree. We present heuristic algorithms that can be used to efficiently attack these problems: a minimum spanning tree algorithm and two greedy algorithms, all applicable to both problems. The algorithms are feasible in their computation effort. We study the performance of these algorithms by simulations. We also consider the generalization of the problem to k-connectivity and recognize its relation to another NP-hard problem, namely, that of graph augmentation. I

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