12 research outputs found
Stochastic Analysis of a Churn-Tolerant Structured Peer-to-Peer Scheme
We present and analyze a simple and general scheme to build a churn
(fault)-tolerant structured Peer-to-Peer (P2P) network. Our scheme shows how to
"convert" a static network into a dynamic distributed hash table(DHT)-based P2P
network such that all the good properties of the static network are guaranteed
with high probability (w.h.p). Applying our scheme to a cube-connected cycles
network, for example, yields a degree connected network, in which
every search succeeds in hops w.h.p., using messages,
where is the expected stable network size. Our scheme has an constant
storage overhead (the number of nodes responsible for servicing a data item)
and an overhead (messages and time) per insertion and essentially
no overhead for deletions. All these bounds are essentially optimal. While DHT
schemes with similar guarantees are already known in the literature, this work
is new in the following aspects:
(1) It presents a rigorous mathematical analysis of the scheme under a
general stochastic model of churn and shows the above guarantees;
(2) The theoretical analysis is complemented by a simulation-based analysis
that validates the asymptotic bounds even in moderately sized networks and also
studies performance under changing stable network size;
(3) The presented scheme seems especially suitable for maintaining dynamic
structures under churn efficiently. In particular, we show that a spanning tree
of low diameter can be efficiently maintained in constant time and logarithmic
number of messages per insertion or deletion w.h.p.
Keywords: P2P Network, DHT Scheme, Churn, Dynamic Spanning Tree, Stochastic
Analysis
Storage and Search in Dynamic Peer-to-Peer Networks
We study robust and efficient distributed algorithms for searching, storing,
and maintaining data in dynamic Peer-to-Peer (P2P) networks. P2P networks are
highly dynamic networks that experience heavy node churn (i.e., nodes join and
leave the network continuously over time). Our goal is to guarantee, despite
high node churn rate, that a large number of nodes in the network can store,
retrieve, and maintain a large number of data items. Our main contributions are
fast randomized distributed algorithms that guarantee the above with high
probability (whp) even under high adversarial churn:
1. A randomized distributed search algorithm that (whp) guarantees that
searches from as many as nodes ( is the stable network size)
succeed in -rounds despite churn, for
any small constant , per round. We assume that the churn is
controlled by an oblivious adversary (that has complete knowledge and control
of what nodes join and leave and at what time, but is oblivious to the random
choices made by the algorithm).
2. A storage and maintenance algorithm that guarantees (whp) data items can
be efficiently stored (with only copies of each data item)
and maintained in a dynamic P2P network with churn rate up to
per round. Our search algorithm together with our
storage and maintenance algorithm guarantees that as many as nodes
can efficiently store, maintain, and search even under churn per round. Our algorithms require only polylogarithmic in bits to
be processed and sent (per round) by each node.
To the best of our knowledge, our algorithms are the first-known,
fully-distributed storage and search algorithms that provably work under highly
dynamic settings (i.e., high churn rates per step).Comment: to appear at SPAA 201
Controlling the cost of reliability in peer-to-peer overlays
Abstract-Structured peer-to-peer overlay networks provide a useful substrate for building distributed applications but there are general concerns over the cost of maintaining these overlays. The current approach is to configure the overlays statically and conservatively to achieve the desired reliability even under uncommon adverse conditions. This results in high cost in the common case, or poor reliability in worse than expected conditions. We analyze the cost of overlay maintenance in realistic dynamic environments and design novel techniques to reduce this cost by adapting to the operating conditions. With our techniques, the concerns over the overlay maintenance cost are no longer warranted. Simulations using real traces show that they enable high reliability and performance even in very adverse conditions with low maintenance cost
Tiny Groups Tackle Byzantine Adversaries
A popular technique for tolerating malicious faults in open distributed
systems is to establish small groups of participants, each of which has a
non-faulty majority. These groups are used as building blocks to design
attack-resistant algorithms.
Despite over a decade of active research, current constructions require group
sizes of , where is the number of participants in the system.
This group size is important since communication and state costs scale
polynomially with this parameter. Given the stubbornness of this logarithmic
barrier, a natural question is whether better bounds are possible.
Here, we consider an attacker that controls a constant fraction of the total
computational resources in the system. By leveraging proof-of-work (PoW), we
demonstrate how to reduce the group size exponentially to while
maintaining strong security guarantees. This reduction in group size yields a
significant improvement in communication and state costs.Comment: This work is supported by the National Science Foundation grant CCF
1613772 and a C Spire Research Gif
Peer-to-Peer Networks and Computation: Current Trends and Future Perspectives
This research papers examines the state-of-the-art in the area of P2P networks/computation. It attempts to identify the challenges that confront the community of P2P researchers and developers, which need to be addressed before the potential of P2P-based systems, can be effectively realized beyond content distribution and file-sharing applications to build real-world, intelligent and commercial software systems. Future perspectives and some thoughts on the evolution of P2P-based systems are also provided
Attack, Defense and Contagion in Networks
Connections between individuals facilitate the exchange of goods, resources and information and create benefits. These connections may be exploited by adversaries to spread their attacks as well. What is the optimal way to design and defend networks in the face of attacks We develop a model with a Designer and an Adversary. The Designer moves first and chooses a network and an allocation of defense resources across nodes. The Adversary then allocates attack resources on nodes and determines how successful attacks should navigate the network. Our main result is that, in a wide variety of circumstances, a star network with all defense resources allocated to the central hub node is optimal for the Designer. The Adversary targets undefended peripheral nodes; upon capture of these nodes the resources mount a concerted attack on the center
Networks, complexity and internet regulation: scale-free law
No description supplie
Dynamically Fault-Tolerant Content Addressable Networks
We describe a content addressable network which is robust in the face of massive adversarial attacks and in a highly dynamic environment. Our network is robust in the sense that at any time, an arbitrarily large fraction of the peers can reach an arbitrarily large fraction of the data items. The network can be created and maintained in a completely distributed fashion