Bernhard Heep

OverSim: A Flexible Overlay Network Simulation Framework

A fundamental problem in studying peer-to- peer networks is the evaluation of new protocols. This paper presents OverSim, a flexible overlay network simulation framework based on OMNeT++. It was designed to fulfill a number of requirements that have been partially neglected by existing simulation frameworks. OverSim includes several structured and unstructured peer-to-peer protocols like Chord, Kademlia and Gia. These protocol implementations can be used for both simulation as well as real world networks. To facilitate the implementation of additional protocols and to make them more comparable OverSim provides several common functions like a generic lookup mechanism for structured peer-to-peer networks and an RPC interface. Several exchangeable underlay network models allow to simulate complex heterogeneous underlay networks as well as simplified networks for large- scale simulations. We show that with OverSim simulations of overlay networks with up to 100,000 nodes are feasible.

OverSim: A scalable and flexible overlay framework for simulation and real network applications

OverSim facilitates rapid prototyping of new overlay protocols by providing functions common to most overlay protocols. The framework allows to use the same implementations for scalable simulations and in real networks. OverSim benefits from features like an efficient event scheduler and strong GUI support. The large number of implemented overlay protocols and the availability to collect various statistical data make OverSim a powerful tool and reference platform for the peer-to-peer research community. OverSim is welldocumented, actively developed as an open source project on http://www.oversim.org/, has an active mailing list with a strong user base and is open to contributions.

R/Kademlia: Recursive and topology-aware overlay routing

Structured peer-to-peer overlays offer a basis for a broad range of applications, such as distributed storage, application layer multicast, and mobility support. This paper introduces R/Kademlia, a low bandwidth and low latency variant of the popular overlay protocol Kademlia. R/Kademlia utilizes recursive overlay routing instead of iterative lookups of keys, thus a higher routing performance can be achieved in network scenarios with churn rates that are characteristic for public KAD networks. Both Proximity Routing and Proximity Neighbor Selection are effectively applicable, which leads to a further decrease of routing latencies. Similar to the original protocol, nodes in a R/Kademlia network meet other nodes during user-triggered routing procedures, hence no expensive periodic tasks are needed. For the simulative evaluation of R/Kademlia, the Performance vs. Cost framework (PVC) and the overlay framework OverSim were employed, where both routing modes-iterative and recursive-were simulated and compared in different network scenarios with varying churn rates.

Fast but economical: A simulative comparison of structured peer-to-peer systems

In the past many proposals for structured peer-to-peer protocols have been published. They differ in properties like overlay topology and routing table maintenance. Furthermore, each protocol exhibits various parameters e.g. to adjust the size of the routing table or stabilization intervals, making it difficult to choose an optimal protocol and parameter set for a given scenario (e.g. churn rate, number of nodes). For this purpose, we developed the overlay simulation framework OverSim and implemented six well known structured overlay protocols. In this paper we first compare these protocols among each other. Furthermore, we study several recursive and iterative routing variants and show the effect of routing table redundancy and lookup parallelism on routing latency and bandwidth costs. For each overlay protocol we identify an optimal parameter set for a typical peer-to-peer scenario. Finally, we show how overlay protocols adapt to variations in churn rate and network size. Our results show considerable advantages of the protocols Kademlia and Bamboo, while De Bruijn based protocols reveal a lack of stability under churn.

A P2PSIP Demonstrator Powered by OverSim

A fundamental problem in studying peer-to-peer networks is the evaluation of new protocols. This commonly involves both the simulation of the protocol in a large-scale network as well as the testing of the protocol in connection with real applications in networks like PlanetLab. To facilitate these tasks we developed the overlay simulation framework OverSim. It was designed to fulfill a number of requirements that have been partially neglected by existing simulation frameworks. In our demonstrator we show how OverSim can not only be used to simulate overlay protocols in large-scale networks, but also demonstrate its real-world capabilities by means of a P2PSIP testbed.

OverArch: A common architecture for structured and unstructured overlay networks

There exists a variety of different peer-to-peer (P2P) protocols to support a wide range of distributed services, such as content distribution or data storage. In order to promote interoperability and facilitate the development of new P2P applications, common application programming interfaces (APIs) have been proposed. Unfortunately, most of these interfaces have stagnated, and fail to meet present research or business requirements. In this regard, this paper presents a novel common architecture and API which combines structured and unstructured overlay networks and strives to overcome the limitations of previous architectures. Our work defines a set of generalized components that are common in todays P2P systems, and provides a clean interface that facilitates the rapid development of new P2P applications and services. We validate the proposed architecture by presenting a concrete implementation including a broad range of protocols within the P2P simulator OverSim.

Coordinate-based routing: Refining nodeIds in structured peer-to-peer systems

Structured peer-to-peer systems—also known as key-based routing protocols—offer a base for a broad range of applications. In the past, different topology adaptation mechanisms for minimizing key-based routing latencies were proposed and deployed with several todays state-of-the-art protocols. In this paper we introduce coordinate-based routing (CBR), a topology adaptation method, that utilizes landmark-based network coordinate systems and a global a-priori knowledge of node distribution to preserve the uniform distribution of node identifiers. With CBR, a notable decrease of routing latencies in prefix-based KBR-protocols can be achieved, even in combination with other topology adaptation mechanisms enabled. Additionally, CBR allows for a location-based replication strategy in distributed storage applications, which supports the lookup of closer replicas with respect to proximity. Simulation results show a significant decrease of KBR routing latencies and twice as fast get()-operations in DHTs.

Maintenance and privacy in unstructured GeoCast overlays for smart traffic applications

In times of increasing mobility and climate change, there is a need for new services to cope with the special challenges of electric vehicles, like recuperation and charging management. Established systems of so called smart traffic applications are usually server-based and bear the risk of uncontrollable gathering of private data by service providers. In this paper we propose a decentralized overlay protocol for smart traffic applications that meets the requirements of several scenarios of future traffic. Our system offers a scalable GeoCast [1] service, where participants (e.g. vehicles) are able to gain information from specific geographic regions. In the following, we briefly describe three scenarios that would benefit from such a GeoCast service. After that, the main part of this paper discusses maintenance and privacy issues regarding the GeoCast overlay.

dCBR: A global view on network coordinates for more efficient peer-to-peer systems

Minimizing routing latencies in structured peer-to-peer systems that provide the key-based routing service (KBR) is an important field of research as many novel applications are based on these systems. These applications and their users would benefit from faster overlay routing procedures. In this paper we present decentralized Coordinate-based Routing (dCBR), a method to achieve low routing latencies in structured peer-to-peer systems by exploiting decentralized network coordinates like Vivaldi and KBR monitoring systems. A global view on network coordinates is distributed among all participating overlay nodes and utilized to generate either topology-based and uniform distributed node identifiers for overlay nodes. This way, a better routing performance is achieved and load-balancing is maintained. dCBR is the successor of the previously proposed Coordinate-based Routing (CBR) system, which—combined with Proximity Neighbor Selection (PNS)—significantly decreases routing latencies, due to the fact that it allows for target-oriented routing. dCBR enables the usage of decentralized network coordinate systems in a CBR-based network, making the overlay independent of a landmark node infrastructure.

Effizientes Routing in strukturierten P2P Overlays

Als Fundament fur neuartige Netzwerkanwendungen sind strukturierte P2P Overlays attraktiv. In diesen Strukturen folgen Datenpakete logischen Verbindungen zwischen den Netzwerkteilnehmern, die jedoch meist komplexen Wegen durch das zugrunde liegende Netzwerk entsprechen. Die in dieser Arbeit vorgestellten Konzepte verringern die daraus resultierenden hohen Routing-Latenzen im Overlay. Schwerpunkt dabei ist ein Verfahren zur Vergabe von auf Netzwerk-Koordinaten basierenden Teilnehmerkennungen.