Massively multi-player online games (MMOGs) have stringent latency requirements and must support large numbers of concurrent players. To handle these conflicting requirements, it is common to divide the virtual environment into virtual regions. As MMOGs are world-spanning games, it is plausible to disperse these regions on geographically distributed servers. Core selection can then be applied to locate an optimal server for placing a region, based on player latencies. Functionality for migrating objects supports this objective, with a distributed name server ensuring that references to the moved objects are maintained. As a result we anticipate a decrease in the aggregate latency for the affected players. The core selection relies on a set of servers and measurements of the interacting players latencies. Measuring these latencies by actively probing the network is not scalable for a large number of players. We therefore explore the use of latency estimation techniques to gather this information.

Latency reduction in distributed interactive applications has been studied intensively. Such applications may have stringent latency requirements and dynamic user groups. We focus on using application-layer multicast with a centralized approach to the group management. The groups are organized in overlay networks that are created using graph algorithms. We investigate many spanning tree problems with particular focus on reducing the diameter of a tree, i.e., the maximum pairwise latency between users. In addition, we focus on reducing the time it takes to execute membership changes. In that context, we use core-selection heuristics to find well-placed group nodes, and edge-pruning algorithms to reduce the number of edges in an otherwise fully meshed overlay. Our edge-pruning algorithms strongly connect well-placed group nodes to the remaining group members, to create new and pruned group graphs, such that, when a tree algorithm is applied to a pruned group graph, it is manipulated into creating trees with a smaller diameter. We implemented and analyzed experimentally spanning-tree heuristics, core-selection heuristics and edge-pruning algorithms. We found that faster heuristics that do not explicitly optimize the diameter are able to compete with slower heuristics that do optimize it.

Distributed interactive applications may have stringent latency requirements and dynamic user groups. These applications may benefit from a group communication system, and to improve the system support for such applications, we investigate graph algorithms that construct low-latency overlay networks for application-layer multicast. In particular, we focus on reducing the diameter and the pair-wise latencies in the overlay. The overlay construction time is also considered, as it is often time-dependent in our dynamic target applications. Here, we have implemented and experimentally analyzed spanning-tree heuristics and mesh construction heuristics, and compared their performance and applicability to distributed interactive applications. We found that trees are faster to construct and save considerable amounts of resources in the network. Meshes, on the other hand, yield lower pair-wise latencies and increases the fault tolerance, but at the expense of increased resource consumption.

Distributed interactive applications have become increasingly popular, making it important to address their communication needs, where one of the needs is group communication. In this paper, we consider the applications in which it is at any given time possible to divide its users into groups. The group membership changes over time, and the group division is unrelated to the physical proximity. As a way of enabling the group communication in distributed interactive applications, we choose application layer multicast. We use simulation to evaluate several dynamic algorithms for managing overlay multicast trees. They are compared with respect to four metrics that can be relevant for a distributed interactive application. These are total tree cost, diameter, reconfiguration time and stability. We demonstrate algorithms that perform well for these metrics although they do not consider all users during reconfiguration.

Abstract — Communication in highly interactive distributed applications, such as massive multiplayer online games, can often be performed efficiently using multicast, i.e., application level multicast. However, in applications with a very dynamic group management, the multicast tree will have frequent changes, and in applications that have stringent latency requirement, this operation needs to be fast. Current multicast approaches either have no notion of reconfiguration, they do not care about tree reconstruction latency or wrongly assume that this is a fast, atomic operation. In this paper, we have focused on dynamic reconfiguration and have tested different ways for a node to join a tree. Our results show that this is an important issue for the class of highly interactive distributed applications. I.

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Desirable features of routing protocols for mobile ad hoc networks (MANETs) include ability to adapt to changing network conditions due to mobility and provide quality control mechanisms during the life time of a route. Current routing protocols that provide quality of service (QoS) for MANETs have proposed routing based on a single QoS metric. This paper proposes a QoS aware source initiated ad-hoc routing protocol (QuaSAR) that adds quality control to all the phases of an on-demand routing protocol. QuaSAR gathers information about battery power, signal strength, bandwidth and latency during route discovery and uses in route choosing. Additionally, our approach has proactive route maintenance features in addition to the reactive maintenance. We conducted simulation experiments using ns-2 network simulator and compared our results with dynamic source routing (DSR). Our performance results demonstrate that our technique has increased throughput and packet delivery ratio.