A collaborative P2P Scheme for NAT Traversal Server discovery based on topological information

In the current Internet picture more than 70% of the hosts are located behind Network Address Translators (NATs). This is not a problem for the client/server paradigm. However, the Internet has evolved, and nowadays the largest portion of the traffic is due to peer-to-peer (p2p) applications. This scenario presents an important challenge: two hosts behind NATs (NATed hosts) cannot establish direct communications. The easiest way to solve this problem is by using a third entity, called Relay, that forwards the traffic between the NATed hosts. Although many efforts have been devoted to avoid the use of Relays, they are still needed in many situations. Hence, the selection of a suitable Relay becomes critical to many p2p applications. In this paper, we propose the Gradual Proximity Algorithm (GPA): a simple algorithm that guarantees the selection of a topologically close-by Relay. We present a measurement-based analysis, showing that the GPA minimizes both the delay of the relayed communication and the transit traffic generated by the Relay, being a QoS-aware and ISP-friendly solution. Furthermore, the paper presents the Peer-to-Peer NAT Traversal Architecture (P2P-NTA), which is a global, distributed and collaborative solution, based on the GPA. This architecture addresses the Relay discovery/selection problem. We have performed large-scale simulations based on real measurements, which validate our proposal. The results demonstrate that the P2P-NTA performs similarly to direct communications with reasonably large deployments of p2p applications. In fact, only 5% of the communications experience an extra delay that may degrade the QoS due to the use of Relays. Furthermore, the amount of extra transit traffic generated is only 6%. We also show that the P2P-NTA largely outperforms other proposals, where the QoS degradation affects up to more than 50% of the communications, and the extra traffic generated goes beyond 80%.This work has been partially funded by the Grants MEDIANET (S2009/TIC-1466) from the Regional Government of Madrid and CON-PARTE (TEC2007-67966-C03- 03) by the Ministry of Science and Innovation of Spain.Publicad

Prospects of peer-to-peer SIP for mobile operators

Tämän diplomityön tarkoituksena on esitellä kehitteillä oleva Peer-to-Peer Session Initiation Protocol (P2PSIP), jonka avulla käyttäjät voivat itsenäisesti ja helposti luoda keskenään puhe- ja muita multimediayhteyksiä vertaisverkko-tekniikan avulla. Lisäksi tarkoituksena on arvioida P2PSIP protokollan vaikutuksia ja mahdollisuuksia mobiilioperaattoreille, joille sitä voidaan pitää uhkana. Tästä huolimatta, P2PSIP:n ei ole kuitenkaan tarkoitus korvata nykyisiä puhelinverkkoja. Työn alussa esittelemme SIP:n ja vertaisverkkojen (Peer-to-Peer) periaatteet, joihin P2PSIP-protokollan on suunniteltu perustuvan. SIP mahdollistaa multimedia-istuntojen luomisen, sulkemisen ja muokkaamisen verkossa, mutta sen monipuolinen käyttö vaatii keskitettyjen palvelimien käyttöä. Vertaisverkon avulla käyttäjät voivat suorittaa keskitettyjen palvelimien tehtävät keskenään hajautetusti. Tällöin voidaan ylläpitää laajojakin verkkoja tehokkaasti ilman palvelimista aiheutuvia ylläpito-kustannuksia. Mobiilioperaattorit ovat haasteellisen tilanteen edessä, koska teleliikennemaailma on muuttumassa yhä avoimemmaksi. Tällöin operaattoreiden asiakkaille aukeaa mahdollisuuksia käyttää kilpailevia Internet-palveluja (kuten Skype) helpommin ja tulevaisuudessa myös itse muodostamaan kommunikointiverkkoja P2PSIP:n avulla. Tutkimukset osoittavat, että näistä uhista huolimatta myös operaattorit pystyvät näkemään P2PSIP:n mahdollisuutena mukautumisessa nopeasti muuttuvan teleliikennemaailman haasteisiin. Nämä mahdollisuudet sisältävät operaattorin oman verkon optimoinnin lisäksi vaihtoehtoisten ja monipuolisempien palveluiden tarjoamisen asiakkailleen edullisesti. Täytyy kuitenkin muistaa, että näiden mahdollisuuksien toteuttamisten vaikutusten ei tulisi olla ristiriidassa operaattorin muiden palveluiden kanssa. Lisäksi tulisi muistaa, että tällä hetkellä keskeneräisen P2PSIP-standardin lopullinen luonne ja ominaisuudet voivat muuttaa sen vaikutuksia.The purpose of this thesis is to present the Peer-to-Peer Session Initiation Protocol (P2PSIP) being developed. In addition, the purpose of this thesis is to evaluate the impacts and prospects of P2PSIP to mobile operators, to whom it can be regarded as a threat. In P2PSIP, users can independently and easily establish voice and other multimedia connections using peer-to-peer (P2P) networking. However, P2PSIP is not meant to replace the existing telephony networks of the operators. We start by introducing the principles of SIP and P2P networking that the P2PSIP is intended to use. SIP enables to establish, terminate and modify multimedia sessions, but its versatile exploitation requires using centralized servers. By using P2P networking, users can decentralize the functions of centralized servers by performing them among themselves. This enables to maintain large and robust networks without maintenance costs resulted of running such centralized servers. Telecommunications market is transforming to a more open environment, where mobile operators and other service providers are challenged to adapt to the upcoming changes. Subscribers have easier access to rivalling Internet-services (such as Skype) and in future they can form their own communication communities by using P2PSIP. The results show that despite of these threats, telecom operators can find potential from P2PSIP in concurrence in adaptation to the challenges of the rapidly changing telecom environment. These potential roles include optimization of the network of the operator, but as well roles to provide alternative and more versatile services to their subscribers at low cost. However, the usage of P2PSIP should not conflict with the other services of the operator. Also, as P2PSIP is still under development, its final nature and features may change its impacts and prospects

PEER-TO-PEER APPROACH OF LOCATING SERVANTS

ABSTRACT This paper explores the possible overlay architectures that can be adopted to provide such services, showing how an unstructured solution based on a scale-free overlay topology is an effective option to deploy in this context. Consequently, we propose EQUATOR (Equivalent servant locator), an unstructured overlay implementing the above mentioned operating principles, based on an overlay construction algorithm that well approximates an ideal scale-free construction model

Descubrimiento dinámico de servidores basado en información de localización usando una tabla de Hash distribuida balanceada

The current Internet includes a large number of distributed services. In order to guarantee the QoS of the communications in these services, a client has to select a close-by server with enough available resources. To achieve this objective, in this Thesis, we propose a simple and practical solution for Dynamic and Location Aware Server Discovery based on a Distributed Hash Table (DHT). Specifically, we decide to use a Chord DHT system (although any other DHT scheme can be used). In more detail, the solution works as follows. The servers offering a given service S form a Chord-like DHT. In addition, they register their location (topological and/or geographical) information in the DHT. Each client using the service S is connected to at least one server from the DHT. Eventually, a given client C realizes that it is connected to a server providing a bad QoS, then, it queries the DHT in order to find an appropriate server (i.e. a close-by server with enough available resources). We define 11 design criteria, and compare our solution to the Related Work based on them. We show that our solution is the most complete one. Furthermore, we validate the performance of our solution in two different scenarios: (i) NAT Traversal Server Discovery and (ii) Home Agent Discovery in Mobile IP scenarios. The former serves to validate our solution in a highly dynamic environment whereas the latter demonstrates the appropriateness of our solution in more classical environments where the servers are typically always-on hosts. The extra overhead suffered from the servers involved in our system comes from their participation in the Chord DHT. Therefore, it is critical to fairly balance the load among all the servers. In our system as well as in other P2P systems (e.g. P2PSIP) the stored objects are small, then routing dominates the cost of publishing and retrieving objects. Therefore, in the second part of this Thesis, we address the issue of fairly balancing the routing load in Chord DHTs. We present an analytical model to evaluate the routing fairness of Chord based on the well accepted Jain’s Fairness Index (FI). Our model shows that Chord performs poorly. Following this observation, we propose a simple enhancement to the Chord finger selection algorithm with the goal of mitigating this effect. The key advantage of our proposal as compared to previous approaches is that it adds a neglible overhead to the basic Chord algorithm. We validate the goodness of the proposed solution analytically and by large scale simulations.-------------------------------------------------------------------------------------------------------------------------------------------------------------En los últimos años un gran número de servicios distribuídos han aparecido en Internet. Para garantizar la Calidad de Servicio de las comunicaciones en estos servicios sus clientes deben conectarse a un servidor cercano con suficientes recursos disponibles. Para alcanzar este objetivo, en esta Tesis, se propone una solución simple y práctica para el Descubrimiento Dinámico de Servidores basado en Información de Localizació usando una Tabla de Hash Distribuída (DHT). En concreto, hemos decidido usar una DHT de tipo Chord (aunque cualquier otro tipo de DHT puede usarse). A continuación describimos brevemente nuestra solución. Los servidores que ofrecen un servicio específico S forman una DHT tipo Chord donde registran su información de localización (topológica y/o geográfica). Cada cliente que usa el servicio S está conectado al menos a un servidor de la DHT. En caso de que un cliente C perciba que el servidor al que está conectado está ofreciendo una mala Calidad de Servicio, C consulta la DHT para encontrar un servidor más apropiado (p.ej. un servidor cercano con suficientes recursos disponibles). En la Tesis se definen 11 criterios de diseño y se compara nuestra solución con las soluciones existentes en base a ellos, demostrando que la nuestra es la solución más completa. Además, validamos el rendimiento de nuestra solución en dos escenarios diferentes: (i) Descubrimiento de Servidores para atravesar Traductores de Direcciones de Red (NATs) y (ii) Descubrimiento de Agentes Hogar (HAs) en escenarios de Movilidad IP. El primero sirve para validar el rendimiento de nuestra solución en escenarios altamente dinámicos mientras que el segundo demuestra la validez de la solución en un escenario más clásico donde los servidores son máquinas que están ininterrumpidamente funcionando. Los servidores involucrados en nuestro sistema sufren una sobrecarga debido a su participación en la DHT tipo Chord. Desafortunadamente, esta sobrecarga es inherente al sistema anteriormente descrito y no se puede eliminar. En cambio lo que sí podemos hacer es balancear la carga de la manera más justa posible entre todos los servidores. En nuestro sistema, al igual que en otros sistemas P2P (p.ej. P2PSIP) los objetos almacenados tienen un tamaño pequeño, produciendo que sea la tarea de enrutamiento la que domina el coste de publicar y obtener objetos. Por lo tanto, en la segunda parte de esta Tesis abordamos el reparto equilibrado de la carga de enrutamiento en DHTs tipo Chord. En primer lugar, definimos un modelo analítico para evaluar el reparto de la carga de enrutamiento entre los nodos que forman una DHT tipo Chord. Para ello nos basamos en una métrica aceptada por la comunidad investigadora como es el Jain’s Fairness Index (FI). El modelo resultante demuestra que Chord tiene un rendimiento pobre en el reparto justo de la carga de enrutamiento. Basándonos en esta observación proponemos una modificación simple al algoritmo de selección de punteros de Chord para mejorar el reparto de la carga de enrutamiento. La ventaja fundamental de nuestra solución en comparación con otras propuestas anteriores es que nuestra solución añade un coste despreciable al algoritmo básico de Chord. Finalmente, validamos el rendimiento de nuestra solución analíticamente y por medio de simulaciones a gran escala

SPAD: a distributed middleware architecture for QoS enhanced alternate path discovery

In the next generation Internet, the network will evolve from a plain communication medium into one that provides endless services to the users. These services will be composed of multiple cooperative distributed application elements. We name these services overlay applications. The cooperative application elements within an overlay application will build a dynamic communication mesh, namely an overlay association. The Quality of Service (QoS) perceived by the users of an overlay application greatly depends on the QoS experienced on the communication paths of the corresponding overlay association. In this paper, we present SPAD (Super-Peer Alternate path Discovery), a distributed middleware architecture that aims at providing enhanced QoS between end-points within an overlay association. To achieve this goal, SPAD provides a complete scheme to discover and utilize composite alternate end-to end paths with better QoS than the path given by the default IP routing mechanisms

Hybrid Multicasting Using Automatic Multicast Tunnels (AMT)

Native Multicast plays an important role in distributing and managing delivery of some of the most popular Internet applications, such as IPTV and media delivery. However, due to patchy support and the existence of multiple approaches for Native Multicast, the support for Native Multicast is fragmented into isolated areas termed Multicast Islands. This renders Native Multicast unfit to be used as an Internet wide application. Instead, Application Layer Multicast, which does not have such network requirements but is more expensive in terms of bandwidth and overhead, can be used to connect the native multicast islands. This thesis proposes Opportunistic Native Multicast (ONM) which employs Application LayerMulticast (ALM), on top of a DHT-based P2P overlay network, and AutomaticMulticast Tunnelling (AMT) to connect these islands. ALM will be used for discovery and initiating the AMT tunnels. The tunnels will encapsulate the traffic going between islands' Primary Nodes (PNs). AMT was used for its added benefits such as security and being better at traffic shaping and Quality Of Service (QoS). While different approaches for connecting multicast islands exists, the system proposed in the thesis was designed with the following characteristics in mind: scalability, availability, interoperability, self-adaptation and efficiency. Importantly, by utilising AMT tunnels, this approach has unique properties that improve network security and management

Structured Peer-to-Peer Overlays for NATed Churn Intensive Networks

The wide-spread coverage and ubiquitous presence of mobile networks has propelled the usage and adoption of mobile phones to an unprecedented level around the globe. The computing capabilities of these mobile phones have improved considerably, supporting a vast range of third party applications. Simultaneously, Peer-to-Peer (P2P) overlay networks have experienced a tremendous growth in terms of usage as well as popularity in recent years particularly in fixed wired networks. In particular, Distributed Hash Table (DHT) based Structured P2P overlay networks offer major advantages to users of mobile devices and networks such as scalable, fault tolerant and self-managing infrastructure which does not exhibit single points of failure. Integrating P2P overlays on the mobile network seems a logical progression; considering the popularities of both technologies. However, it imposes several challenges that need to be handled, such as the limited hardware capabilities of mobile phones and churn (i.e. the frequent join and leave of nodes within a network) intensive mobile networks offering limited yet expensive bandwidth availability. This thesis investigates the feasibility of extending P2P to mobile networks so that users can take advantage of both these technologies: P2P and mobile networks. This thesis utilises OverSim, a P2P simulator, to experiment with the performance of various P2P overlays, considering high churn and bandwidth consumption which are the two most crucial constraints of mobile networks. The experiment results show that Kademlia and EpiChord are the two most appropriate P2P overlays that could be implemented in mobile networks. Furthermore, Network Address Translation (NAT) is a major barrier to the adoption of P2P overlays in mobile networks. Integrating NAT traversal approaches with P2P overlays is a crucial step for P2P overlays to operate successfully on mobile networks. This thesis presents a general approach of NAT traversal for ring based overlays without the use of a single dedicated server which is then implemented in OverSim. Several experiments have been performed under NATs to determine the suitability of the chosen P2P overlays under NATed environments. The results show that the performance of these overlays is comparable in terms of successful lookups in both NATed and non-NATed environments; with Kademlia and EpiChord exhibiting the best performance. The presence of NATs and also the level of churn in a network influence the routing techniques used in P2P overlays. Recursive routing is more resilient to IP connectivity restrictions posed by NATs but not very robust in high churn environments, whereas iterative routing is more suitable to high churn networks, but difficult to use in NATed environments. Kademlia supports both these routing schemes whereas EpiChord only supports the iterating routing. This undermines the usefulness of EpiChord in NATed environments. In order to harness the advantages of both routing schemes, this thesis presents an adaptive routing scheme, called Churn Aware Routing Protocol (ChARP), combining recursive and iterative lookups where nodes can switch between recursive and iterative routing depending on their lifetimes. The proposed approach has been implemented in OverSim and several experiments have been carried out. The experiment results indicate an improved performance which in turn validates the applicability and suitability of ChARP in NATed environments