There has been much interest in both unstructured and structured overlays recently. Unstructured ... more There has been much interest in both unstructured and structured overlays recently. Unstructured overlays, like Gnutella, build a random graph and use flooding or random walks on the graph to discover data stored by overlay nodes. Structured overlays assign keys to data items and build a graph that maps each key to a specific node. The structure of the graph enables efficient discovery of data items given their keys but it does not support complex queries.
Worm containment must be automatic because worms can spread too fast for humans to respond. Recen... more Worm containment must be automatic because worms can spread too fast for humans to respond. Recent work has proposed network-level techniques to automate worm containment; these techniques have limitations because there is no information about the vulnerabilities exploited by worms at the network level. We propose Vigilante, a new end-toend approach to contain worms automatically that addresses these limitations. Vigilante relies on collaborative worm detection at end hosts, but does not require hosts to trust each other. Hosts run instrumented software to detect worms and broadcast self-certifying alerts (SCAs) upon worm detection. SCAs are proofs of vulnerability that can be inexpensively verified by any vulnerable host. When hosts receive an SCA, they generate filters that block infection by analysing the SCA-guided execution of the vulnerable software. We show that Vigilante can automatically contain fast-spreading worms that exploit unknown vulnerabilities without blocking innocuous traffic.
This paper presents Scribe, a large-scale event notification infrastructure for topic-based publi... more This paper presents Scribe, a large-scale event notification infrastructure for topic-based publish-subscribe applications. Scribe supports large numbers of topics, with a potentially large number of subscribers per topic. Scribe is built on top of Pastry, a generic peer-to-peer object location and routing substrate overlayed on the Internet, and leverages Pastry's reliability, self-organization and locality properties. Pastry is used to create a topic (group) and to build an efficient multicast tree for the dissemination of events to the topic's subscribers (members). Scribe provides weak reliability guarantees, but we outline how an application can extend Scribe to provide stronger ones.
Structured peer-to-peer overlay networks provide a substrate for the construction of large-scale,... more Structured peer-to-peer overlay networks provide a substrate for the construction of large-scale, decentralized applications, including distributed storage, group communication, and content distribution. These overlays are highly resilient; they can route messages correctly even when a large fraction of the nodes crash or the network partitions. But current overlays are not secure; even a small fraction of malicious nodes can prevent correct message delivery throughout the overlay. This problem is particularly serious in open peer-to-peer systems, where many diverse, autonomous parties without preexisting trust relationships wish to pool their resources. This paper studies attacks aimed at preventing correct message delivery in structured peer-to-peer overlays and presents defenses to these attacks. We describe and evaluate techniques that allow nodes to join the overlay, to maintain routing state, and to forward messages securely in the presence of malicious nodes.
IEEE Journal on Selected Areas in Communications, 2002
This paper presents Scribe, a scalable applicationlevel multicast infrastructure. Scribe supports... more This paper presents Scribe, a scalable applicationlevel multicast infrastructure. Scribe supports large numbers of groups, with a potentially large number of members per group. Scribe is built on top of Pastry, a generic peer-to-peer object location and routing substrate overlayed on the Internet, and leverages Pastry's reliability, self-organization, and locality properties. Pastry is used to create and manage groups and to build efficient multicast trees for the dissemination of messages to each group. Scribe provides best-effort reliability guarantees, and we outline how an application can extend Scribe to provide stronger reliability. Simulation results, based on a realistic network topology model, show that Scribe scales across a wide range of groups and group sizes. Also, it balances the load on the nodes while achieving acceptable delay and link stress when compared with Internet protocol multicast.
We present an application-level implementation of anycast for highly dynamic groups. The implemen... more We present an application-level implementation of anycast for highly dynamic groups. The implementation can handle group sizes varying from one to the whole Internet, and membership maintenance is efficient enough to allow members to join for the purpose of receiving a single message. Key to this efficiency is the use of a proximity-aware peer-to-peer overlay network for decentralized, lightweight group maintenance; nodes join the overlay once and can join and leave many groups many times to amortize the cost of maintaining the overlay. An anycast implementation with these properties provides a key building block for distributed applications. In particular, it enables management and location of dynamic resources in large scale peer-to-peer systems. We present several resource management applications that are enabled by our implementation.
Structured peer-to-peer overlay networks such as CAN, Chord, Pastry, and Tapestry can be used to ... more Structured peer-to-peer overlay networks such as CAN, Chord, Pastry, and Tapestry can be used to implement Internet-scale application-level multicast. There are two general approaches to accomplishing this: tree building and flooding. This paper evaluates these two approaches using two different types of structured overlay: 1) overlays which use a form of generalized hypercube routing, e.g., Chord, Pastry and Tapestry, and 2) overlays which use a numerical distance metric to route through a Cartesian hyper-space, e.g., CAN. Pastry and CAN are chosen as the representatives of each type of overlay.
Self-organizing peer-to-peer (p2p) overlay networks like CAN, Chord, Pastry and Tapestry (also ca... more Self-organizing peer-to-peer (p2p) overlay networks like CAN, Chord, Pastry and Tapestry (also called distributed hash tables or DHTs) offer a novel platform for a variety of scalable and decentralized distributed applications. These systems provide efficient and fault-tolerant routing, object location, and load balancing within a self-organizing overlay network. One important aspect of these systems is how they exploit network proximity in the underlying Internet.
This paper presents Virtual Ring Routing (VRR), a new network routing protocol that occupies a un... more This paper presents Virtual Ring Routing (VRR), a new network routing protocol that occupies a unique point in the design space. VRR is inspired by overlay routing algorithms in Distributed Hash Tables (DHTs) but it does not rely on an underlying network routing protocol. It is implemented directly on top of the link layer. VRR provides both traditional point-to-point network routing and DHT routing to the node responsible for a hash table key.
In tree-based multicast systems, a relatively small number of interior nodes carry the load of fo... more In tree-based multicast systems, a relatively small number of interior nodes carry the load of forwarding multicast messages. This works well when the interior nodes are dedicated infrastructure routers. But it poses a problem in cooperative application-level multicast, where participants expect to contribute resources proportional to the benefit they derive from using the system. Moreover, many participants may not have the network capacity and availability required of an interior node in high-bandwidth multicast applications. SplitStream is a high-bandwidth content distribution system based on application-level multicast. It distributes the forwarding load among all the participants, and is able to accommodate participating nodes with different bandwidth capacities. We sketch the design of SplitStream and present some preliminary performance results.
Page 1. 1 1 Security for Structured Peer-to-peer Overlay Networks By Miguel Castro et al. OSDI&am... more Page 1. 1 1 Security for Structured Peer-to-peer Overlay Networks By Miguel Castro et al. OSDI'02 Presented by Shiping Chen in IT818 2 Acknowledgement ∎ Some of the following slides are borrowed from talks by Yun Mao (University of Pennsylvania) 3 Outline ...
Overlay networks are widely used to deploy functionality at edge nodes without changing network r... more Overlay networks are widely used to deploy functionality at edge nodes without changing network routers. Each node in an overlay network maintains pointers to a set of neighbor nodes. These pointers are used both to maintain the overlay and to implement application functionality, for example, to locate content stored by overlay nodes. If an attacker controls a large fraction of the neighbors of correct nodes, it can "eclipse" correct nodes and prevent correct overlay operation. This Eclipse attack is more general than the Sybil attack. Attackers can use a Sybil attack to launch an Eclipse attack by inventing a large number of seemingly distinct overlay nodes. However, defenses against Sybil attacks do not prevent Eclipse attacks because attackers may manipulate the overlay maintenance algorithm to mount an Eclipse attack. This paper discusses the impact of the Eclipse attack on several types of overlay and it proposes a novel defense that prevents the attack by bounding the degree of overlay nodes. Our defense can be applied to any overlay and it enables secure implementations of overlay optimizations that choose neighbors according to metrics like proximity. We present preliminary results that demonstrate the importance of defending against the Eclipse attack and show that our defense is effective. * Work started during a summer internship at
Structured peer-to-peer overlay networks provide a useful substrate for building distributed appl... more 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.
In tree-based multicast systems, a relatively small number of interior nodes carry the load of fo... more In tree-based multicast systems, a relatively small number of interior nodes carry the load of forwarding multicast messages. This works well when the interior nodes are highlyavailable, dedicated infrastructure routers but it poses a problem for application-level multicast in peer-to-peer systems. SplitStream addresses this problem by striping the content across a forest of interior-node-disjoint multicast trees that distributes the forwarding load among all participating peers. For example, it is possible to construct efficient SplitStream forests in which each peer contributes only as much forwarding bandwidth as it receives. Furthermore, with appropriate content encodings, SplitStream is highly robust to failures because a node failure causes the loss of a single stripe on average. We present the design and implementation of SplitStream and show experimental results obtained on an Internet testbed and via large-scale network simulation. The results show that SplitStream distributes the forwarding load among all peers and can accommodate peers with different bandwidth capacities while imposing low overhead for forest construction and maintenance.
Hand-held and palm-held computing devices are becoming increasingly strong. For example, today’s ... more Hand-held and palm-held computing devices are becoming increasingly strong. For example, today’s high-end devices have the same (theoretical) computing power and memory capacity as high-end desktops of merely five years ago. Judging from the development of laptops, this trend is likely to continue at an even faster paste in the next few years. These powerful computing devices come equipped with commodity operating systems, such as Linux and Windows CE, which will progressively resemble their desktop OS counterparts as the devices become even more powerful. At the same time, hand-held and palm-held computing devices are being equipped with wireless and cellular communication capabilities, whose bandwidth is gradually approaching standard LAN speeds. Of particular interest to us is wireless communication, due to its hardware broadcast nature, as well as its relative high bandwidth, low cost, and low power consumption when compared to cellular communication.
Structured peer-to-peer (p2p) overlay networks provide a useful substrate for building distribute... more Structured peer-to-peer (p2p) overlay networks provide a useful substrate for building distributed applications. They map object keys to overlay nodes and offer a primitive to send a message to the node responsible for a key. They can implement, for example, distributed hash tables and multicast trees. However, there are concerns about the performance and dependability of these overlays in realistic environments. Several studies have shown that current p2p environments have high churn rates: nodes join and leave the overlay continuously. This paper presents techniques that continuously detect faults and repair the overlay to achieve high dependability and good performance in realistic environments. The techniques are evaluated using large-scale network simulation experiments with fault injection guided by real traces of node arrivals and departures. The results show that previous concerns are unfounded; our techniques can achieve dependable routing in realistic environments with an average delay stretch below two and a maintenance overhead of less than half a message per second per node.
This paper introduces PIC, a practical coordinate-based mechanism to estimate Internet network di... more This paper introduces PIC, a practical coordinate-based mechanism to estimate Internet network distance (i.e., round-trip delay or network hops). Network distance estimation is important in many applications, for example, network-aware overlay construction and server selection. There are several proposals for distance estimation in the Internet but they all suffer from problems that limit their benefit. Most rely on a small set of infrastructure nodes that are a single point of failure and limit scalability. Others use sets of peers to compute coordinates but these coordinates can be arbitrarily wrong if one of these peers is malicious. While it may be reasonable to secure a small set of infrastructure nodes, it is unreasonable to secure all peers. PIC addresses these problems: it does not rely on infrastructure nodes and it can compute accurate coordinates even when some peers are malicious. We present PIC's design, experimental evaluation, and an application to network-aware overlay construction and maintenance.
We present a comparison of structured and unstructured overlays that decouples overlay topology m... more We present a comparison of structured and unstructured overlays that decouples overlay topology maintenance from query mechanism. Structured overlays provide efficient support for simple exact-match queries but they constrain overlay topology to achieve this. Unstructured overlays do not constrain overlay topology or query complexity because they use flooding or random walks to discover data. It is commonly believed that structured overlays are more expensive to maintain, that their topology constraints make it harder to exploit heterogeneity, and that they cannot support complex queries efficiently. We performed a detailed comparison study using simulations driven by real-world traces that debunks these widespread myths. We describe techniques that exploit structural constraints to achieve low maintenance overhead and we present a modified neighbour selection algorithm that can exploit heterogeneity effectively. We also describe techniques to perform floods and random walks on structured topologies. These techniques exploit structural constraints to support complex queries with better performance than unstructured overlays.
presente. Lancei ao mar um madeiro, espetei-lhe um pau e um lençol. Com palpite marinheiro medi a... more presente. Lancei ao mar um madeiro, espetei-lhe um pau e um lençol. Com palpite marinheiro medi a altura do sol. Deu-me o vento de feição, levou-me ao cabo do mundo... ANTÓNIO GEDEÃO PRÓLOGO Este livro resulta de uma dissertação de doutoramento concluída em 2000 e apresentada em 2001 na Universidade de Lisboa. A publicação não a resume ou aligeira no aparato erudito, apenas, pois nalguns casos houve até de acrescentar notas e reescrever texto, dado que nos anos transcorridos as publicações da especialidade foram em número e relevância apreciável, isto sem esquecer as dissertações académicas. Por outro lado houve também o ensejo de rectificar questões de pormenor, mas globalmente este volume é mais pequeno que a dissertação em causa; para isso concorre a não reprodução da nova leitura do Livro de Fernando Oliveira, restringindo-se os apêndices aos regimentos gerais e especiais. O livro, como a tese antes dele, beneficiou muito de conselhos e ajudas várias de amigos e colegas exemplares no entendimento e na prática do que pode e deve ser o intercâmbio científico; o número de trabalhos citados a partir de originais dactilografados que pude utilizar ilustra-o bem. Para todos fica aqui expresso o reconhecimento devido, dirigido em primeiro lugar aos membros do júri que apreciou as provas públicas e sugeriu aspectos mais carentes de revisão, a par das palavras de incentivo que tanto significam naquela hora: os Professores Doutores Manuel Villaverde Cabral, Aurélio de Oliveira, Maria do Rosário Themudo Barata, João Marinho dos Santos e António Marques de Almeida. Uma palavra em particular é devida ao Professor Doutor António Dias Farinha, orientador da dissertação além de arguente.
There has been much interest in both unstructured and structured overlays recently. Unstructured ... more There has been much interest in both unstructured and structured overlays recently. Unstructured overlays, like Gnutella, build a random graph and use flooding or random walks on the graph to discover data stored by overlay nodes. Structured overlays assign keys to data items and build a graph that maps each key to a specific node. The structure of the graph enables efficient discovery of data items given their keys but it does not support complex queries.
Worm containment must be automatic because worms can spread too fast for humans to respond. Recen... more Worm containment must be automatic because worms can spread too fast for humans to respond. Recent work has proposed network-level techniques to automate worm containment; these techniques have limitations because there is no information about the vulnerabilities exploited by worms at the network level. We propose Vigilante, a new end-toend approach to contain worms automatically that addresses these limitations. Vigilante relies on collaborative worm detection at end hosts, but does not require hosts to trust each other. Hosts run instrumented software to detect worms and broadcast self-certifying alerts (SCAs) upon worm detection. SCAs are proofs of vulnerability that can be inexpensively verified by any vulnerable host. When hosts receive an SCA, they generate filters that block infection by analysing the SCA-guided execution of the vulnerable software. We show that Vigilante can automatically contain fast-spreading worms that exploit unknown vulnerabilities without blocking innocuous traffic.
This paper presents Scribe, a large-scale event notification infrastructure for topic-based publi... more This paper presents Scribe, a large-scale event notification infrastructure for topic-based publish-subscribe applications. Scribe supports large numbers of topics, with a potentially large number of subscribers per topic. Scribe is built on top of Pastry, a generic peer-to-peer object location and routing substrate overlayed on the Internet, and leverages Pastry's reliability, self-organization and locality properties. Pastry is used to create a topic (group) and to build an efficient multicast tree for the dissemination of events to the topic's subscribers (members). Scribe provides weak reliability guarantees, but we outline how an application can extend Scribe to provide stronger ones.
Structured peer-to-peer overlay networks provide a substrate for the construction of large-scale,... more Structured peer-to-peer overlay networks provide a substrate for the construction of large-scale, decentralized applications, including distributed storage, group communication, and content distribution. These overlays are highly resilient; they can route messages correctly even when a large fraction of the nodes crash or the network partitions. But current overlays are not secure; even a small fraction of malicious nodes can prevent correct message delivery throughout the overlay. This problem is particularly serious in open peer-to-peer systems, where many diverse, autonomous parties without preexisting trust relationships wish to pool their resources. This paper studies attacks aimed at preventing correct message delivery in structured peer-to-peer overlays and presents defenses to these attacks. We describe and evaluate techniques that allow nodes to join the overlay, to maintain routing state, and to forward messages securely in the presence of malicious nodes.
IEEE Journal on Selected Areas in Communications, 2002
This paper presents Scribe, a scalable applicationlevel multicast infrastructure. Scribe supports... more This paper presents Scribe, a scalable applicationlevel multicast infrastructure. Scribe supports large numbers of groups, with a potentially large number of members per group. Scribe is built on top of Pastry, a generic peer-to-peer object location and routing substrate overlayed on the Internet, and leverages Pastry's reliability, self-organization, and locality properties. Pastry is used to create and manage groups and to build efficient multicast trees for the dissemination of messages to each group. Scribe provides best-effort reliability guarantees, and we outline how an application can extend Scribe to provide stronger reliability. Simulation results, based on a realistic network topology model, show that Scribe scales across a wide range of groups and group sizes. Also, it balances the load on the nodes while achieving acceptable delay and link stress when compared with Internet protocol multicast.
We present an application-level implementation of anycast for highly dynamic groups. The implemen... more We present an application-level implementation of anycast for highly dynamic groups. The implementation can handle group sizes varying from one to the whole Internet, and membership maintenance is efficient enough to allow members to join for the purpose of receiving a single message. Key to this efficiency is the use of a proximity-aware peer-to-peer overlay network for decentralized, lightweight group maintenance; nodes join the overlay once and can join and leave many groups many times to amortize the cost of maintaining the overlay. An anycast implementation with these properties provides a key building block for distributed applications. In particular, it enables management and location of dynamic resources in large scale peer-to-peer systems. We present several resource management applications that are enabled by our implementation.
Structured peer-to-peer overlay networks such as CAN, Chord, Pastry, and Tapestry can be used to ... more Structured peer-to-peer overlay networks such as CAN, Chord, Pastry, and Tapestry can be used to implement Internet-scale application-level multicast. There are two general approaches to accomplishing this: tree building and flooding. This paper evaluates these two approaches using two different types of structured overlay: 1) overlays which use a form of generalized hypercube routing, e.g., Chord, Pastry and Tapestry, and 2) overlays which use a numerical distance metric to route through a Cartesian hyper-space, e.g., CAN. Pastry and CAN are chosen as the representatives of each type of overlay.
Self-organizing peer-to-peer (p2p) overlay networks like CAN, Chord, Pastry and Tapestry (also ca... more Self-organizing peer-to-peer (p2p) overlay networks like CAN, Chord, Pastry and Tapestry (also called distributed hash tables or DHTs) offer a novel platform for a variety of scalable and decentralized distributed applications. These systems provide efficient and fault-tolerant routing, object location, and load balancing within a self-organizing overlay network. One important aspect of these systems is how they exploit network proximity in the underlying Internet.
This paper presents Virtual Ring Routing (VRR), a new network routing protocol that occupies a un... more This paper presents Virtual Ring Routing (VRR), a new network routing protocol that occupies a unique point in the design space. VRR is inspired by overlay routing algorithms in Distributed Hash Tables (DHTs) but it does not rely on an underlying network routing protocol. It is implemented directly on top of the link layer. VRR provides both traditional point-to-point network routing and DHT routing to the node responsible for a hash table key.
In tree-based multicast systems, a relatively small number of interior nodes carry the load of fo... more In tree-based multicast systems, a relatively small number of interior nodes carry the load of forwarding multicast messages. This works well when the interior nodes are dedicated infrastructure routers. But it poses a problem in cooperative application-level multicast, where participants expect to contribute resources proportional to the benefit they derive from using the system. Moreover, many participants may not have the network capacity and availability required of an interior node in high-bandwidth multicast applications. SplitStream is a high-bandwidth content distribution system based on application-level multicast. It distributes the forwarding load among all the participants, and is able to accommodate participating nodes with different bandwidth capacities. We sketch the design of SplitStream and present some preliminary performance results.
Page 1. 1 1 Security for Structured Peer-to-peer Overlay Networks By Miguel Castro et al. OSDI&am... more Page 1. 1 1 Security for Structured Peer-to-peer Overlay Networks By Miguel Castro et al. OSDI'02 Presented by Shiping Chen in IT818 2 Acknowledgement ∎ Some of the following slides are borrowed from talks by Yun Mao (University of Pennsylvania) 3 Outline ...
Overlay networks are widely used to deploy functionality at edge nodes without changing network r... more Overlay networks are widely used to deploy functionality at edge nodes without changing network routers. Each node in an overlay network maintains pointers to a set of neighbor nodes. These pointers are used both to maintain the overlay and to implement application functionality, for example, to locate content stored by overlay nodes. If an attacker controls a large fraction of the neighbors of correct nodes, it can "eclipse" correct nodes and prevent correct overlay operation. This Eclipse attack is more general than the Sybil attack. Attackers can use a Sybil attack to launch an Eclipse attack by inventing a large number of seemingly distinct overlay nodes. However, defenses against Sybil attacks do not prevent Eclipse attacks because attackers may manipulate the overlay maintenance algorithm to mount an Eclipse attack. This paper discusses the impact of the Eclipse attack on several types of overlay and it proposes a novel defense that prevents the attack by bounding the degree of overlay nodes. Our defense can be applied to any overlay and it enables secure implementations of overlay optimizations that choose neighbors according to metrics like proximity. We present preliminary results that demonstrate the importance of defending against the Eclipse attack and show that our defense is effective. * Work started during a summer internship at
Structured peer-to-peer overlay networks provide a useful substrate for building distributed appl... more 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.
In tree-based multicast systems, a relatively small number of interior nodes carry the load of fo... more In tree-based multicast systems, a relatively small number of interior nodes carry the load of forwarding multicast messages. This works well when the interior nodes are highlyavailable, dedicated infrastructure routers but it poses a problem for application-level multicast in peer-to-peer systems. SplitStream addresses this problem by striping the content across a forest of interior-node-disjoint multicast trees that distributes the forwarding load among all participating peers. For example, it is possible to construct efficient SplitStream forests in which each peer contributes only as much forwarding bandwidth as it receives. Furthermore, with appropriate content encodings, SplitStream is highly robust to failures because a node failure causes the loss of a single stripe on average. We present the design and implementation of SplitStream and show experimental results obtained on an Internet testbed and via large-scale network simulation. The results show that SplitStream distributes the forwarding load among all peers and can accommodate peers with different bandwidth capacities while imposing low overhead for forest construction and maintenance.
Hand-held and palm-held computing devices are becoming increasingly strong. For example, today’s ... more Hand-held and palm-held computing devices are becoming increasingly strong. For example, today’s high-end devices have the same (theoretical) computing power and memory capacity as high-end desktops of merely five years ago. Judging from the development of laptops, this trend is likely to continue at an even faster paste in the next few years. These powerful computing devices come equipped with commodity operating systems, such as Linux and Windows CE, which will progressively resemble their desktop OS counterparts as the devices become even more powerful. At the same time, hand-held and palm-held computing devices are being equipped with wireless and cellular communication capabilities, whose bandwidth is gradually approaching standard LAN speeds. Of particular interest to us is wireless communication, due to its hardware broadcast nature, as well as its relative high bandwidth, low cost, and low power consumption when compared to cellular communication.
Structured peer-to-peer (p2p) overlay networks provide a useful substrate for building distribute... more Structured peer-to-peer (p2p) overlay networks provide a useful substrate for building distributed applications. They map object keys to overlay nodes and offer a primitive to send a message to the node responsible for a key. They can implement, for example, distributed hash tables and multicast trees. However, there are concerns about the performance and dependability of these overlays in realistic environments. Several studies have shown that current p2p environments have high churn rates: nodes join and leave the overlay continuously. This paper presents techniques that continuously detect faults and repair the overlay to achieve high dependability and good performance in realistic environments. The techniques are evaluated using large-scale network simulation experiments with fault injection guided by real traces of node arrivals and departures. The results show that previous concerns are unfounded; our techniques can achieve dependable routing in realistic environments with an average delay stretch below two and a maintenance overhead of less than half a message per second per node.
This paper introduces PIC, a practical coordinate-based mechanism to estimate Internet network di... more This paper introduces PIC, a practical coordinate-based mechanism to estimate Internet network distance (i.e., round-trip delay or network hops). Network distance estimation is important in many applications, for example, network-aware overlay construction and server selection. There are several proposals for distance estimation in the Internet but they all suffer from problems that limit their benefit. Most rely on a small set of infrastructure nodes that are a single point of failure and limit scalability. Others use sets of peers to compute coordinates but these coordinates can be arbitrarily wrong if one of these peers is malicious. While it may be reasonable to secure a small set of infrastructure nodes, it is unreasonable to secure all peers. PIC addresses these problems: it does not rely on infrastructure nodes and it can compute accurate coordinates even when some peers are malicious. We present PIC's design, experimental evaluation, and an application to network-aware overlay construction and maintenance.
We present a comparison of structured and unstructured overlays that decouples overlay topology m... more We present a comparison of structured and unstructured overlays that decouples overlay topology maintenance from query mechanism. Structured overlays provide efficient support for simple exact-match queries but they constrain overlay topology to achieve this. Unstructured overlays do not constrain overlay topology or query complexity because they use flooding or random walks to discover data. It is commonly believed that structured overlays are more expensive to maintain, that their topology constraints make it harder to exploit heterogeneity, and that they cannot support complex queries efficiently. We performed a detailed comparison study using simulations driven by real-world traces that debunks these widespread myths. We describe techniques that exploit structural constraints to achieve low maintenance overhead and we present a modified neighbour selection algorithm that can exploit heterogeneity effectively. We also describe techniques to perform floods and random walks on structured topologies. These techniques exploit structural constraints to support complex queries with better performance than unstructured overlays.
presente. Lancei ao mar um madeiro, espetei-lhe um pau e um lençol. Com palpite marinheiro medi a... more presente. Lancei ao mar um madeiro, espetei-lhe um pau e um lençol. Com palpite marinheiro medi a altura do sol. Deu-me o vento de feição, levou-me ao cabo do mundo... ANTÓNIO GEDEÃO PRÓLOGO Este livro resulta de uma dissertação de doutoramento concluída em 2000 e apresentada em 2001 na Universidade de Lisboa. A publicação não a resume ou aligeira no aparato erudito, apenas, pois nalguns casos houve até de acrescentar notas e reescrever texto, dado que nos anos transcorridos as publicações da especialidade foram em número e relevância apreciável, isto sem esquecer as dissertações académicas. Por outro lado houve também o ensejo de rectificar questões de pormenor, mas globalmente este volume é mais pequeno que a dissertação em causa; para isso concorre a não reprodução da nova leitura do Livro de Fernando Oliveira, restringindo-se os apêndices aos regimentos gerais e especiais. O livro, como a tese antes dele, beneficiou muito de conselhos e ajudas várias de amigos e colegas exemplares no entendimento e na prática do que pode e deve ser o intercâmbio científico; o número de trabalhos citados a partir de originais dactilografados que pude utilizar ilustra-o bem. Para todos fica aqui expresso o reconhecimento devido, dirigido em primeiro lugar aos membros do júri que apreciou as provas públicas e sugeriu aspectos mais carentes de revisão, a par das palavras de incentivo que tanto significam naquela hora: os Professores Doutores Manuel Villaverde Cabral, Aurélio de Oliveira, Maria do Rosário Themudo Barata, João Marinho dos Santos e António Marques de Almeida. Uma palavra em particular é devida ao Professor Doutor António Dias Farinha, orientador da dissertação além de arguente.
Uploads
Papers by Miguel Castro