651 research outputs found
On detection algorithms for spurious retransmissions in TCP
In TCP, a spurious packet retransmission can be caused by either spurious timeout (STO) or spurious fast retransmit (SFR). The "lost" packets are unnecessarily retransmitted and the evoked congestion control process causes network underutilization. In this paper, we focus on spurious retransmission detection. We first present a survey on some important and interesting spurious retransmission detection algorithms. Based on the insights obtained, we propose a novel yet simple detection algorithm called split-and-retransmit (SnR). SnR only requires a minor modification to the TCP sender while leaving the receiver intact. The key idea is to split the retransmitted packet into two smaller ones before retransmitting them. As the packet size is different, the ACK triggered will carry different ACK numbers. This allows the sender to easily distinguish between the original transmission and the retransmission of a packet without relying on, e.g., TCP options. We then compare our SnR with STODER, F-RTO and Newreno under both loss-free and lossy network environments. We show that our SnR is resilient to packet loss and yields good performance under various simulation settings. ©2010 IEEE.published_or_final_versionThe 2010 IEEE Wireless Communications and Networking Conference (WCNC), Sydney, Australia, 18-21 April 2010. In Proceedings of WCNC, 2010, p. 1-
Design and implementation of simulation tools, protocols and architectures to support service platforms on vehicular networks
Tesis por compendioProducts related with Intelligent Transportation Systems (ITS) are becoming
a reality on our roads.
All car manufacturers are starting to include Internet
access in their vehicles and to integrate smartphones directly from the
dashboard, but more and more services will be introduced in the near future.
Connectivity through "vehicular networks" will become a cornerstone of every
new proposal, and offering an adequate quality of service is obviously desirable.
However, a lot of work is needed for vehicular networks to offer performances
similar to those of the wired networks.
Vehicular networks can be characterized by two main features: high variability
due to mobility levels that can reach up to 250 kilometers per hour,
and heterogeneity, being that various competing versions from different vendors
have and will be released. Therefore, to make the deployment of efficient
services possible, an extensive study must be carried out and adequate tools
must be proposed and developed. This PhD thesis addresses the service deployment
problem in these networks at three different levels: (i) the physical
and link layer, showing an exhaustive analysis of the physical channel and
models; (ii) the network layer, proposing a forwarding protocol for IP packets;
and (iii) the transport layer, where protocols are proposed to improve data
delivery.
First of all, the two main wireless technologies used in vehicular networks
where studied and modeled, namely the 802.11 family of standards, particularly
802.11p, and the cellular networks focusing on LTE. Since 802.11p is a
quite mature standard, we defined (i) a propagation and attenuation model
capable of replicating the transmission range and the fading behavior of real
802.11p devices, both in line-of-sight conditions and when obstructed by small
obstacles, and (ii) a visibility model able to deal with large obstacles, such
as buildings and houses, in a realistic manner.
Additionally, we proposed a
model based on high-level performance indicators (bandwidth and delay) for
LTE, which makes application validation and evaluation easier.
At the network layer, a hybrid protocol called AVE is proposed for packet
forwarding by switching among a set of standard routing strategies. Depending
on the specific scenario, AVE selects one out of four different routing solutions:
a) two-hop direct delivery, b) Dynamic MANET On-demand (DYMO), c)
greedy georouting, and d) store-carry-and-forward technique, to dynamically
adapt its behavior to the specific situation.
At the transport layer, we proposed a content delivery protocol for reliable
and bidirectional unicast communication in lossy links that improves content
delivery in situations where the wireless network is the bottleneck.
It has
been designed, validated, optimized, and its performance has been analyzed
in terms of throughput and resource efficiency.
Finally, at system level, we propose an edge-assisted computing model that
allows reducing the response latency of several queries by placing a computing
unit at the network edge. This way, traffic traversal through the Internet is
avoided when not needed.
This scheme could be used in both 802.11p and
cellular networks, and in this thesis we decided to focus on its evaluation using
LTE networks.
The platform presented in this thesis combines all the individual efforts to
create a single efficient platform. This new environment could be used by any
provider to improve the quality of the user experience obtainable through the
proposed vehicular network-based services.Los productos relacionados con los Sistemas Inteligentes de Transporte (ITS)
se están transformando en una realidad en nuestras carreteras. Todos los
fabricantes de coches comienzan a incluir acceso a internet en sus vehículos y a
facilitar su integración con los teléfonos móviles, pero más y más servicios se
introducirán en el futuro.
La conectividad usando las "redes vehiculares" se
convertirá en la piedra angular de cada nueva propuesta, y ofrecer una calidad
de servicio adecuada será, obviamente, deseable. Sin embargo, se necesita
una gran cantidad de trabajo para que las redes vehiculares ofrezcan un
rendimiento similar al de las redes cableadas.
Las redes vehiculares quedan definidas por sus dos características básicas:
alto dinamismo, pues los nodos pueden alcanzar una velocidad relativa de más
de 250 km/h; y heterogeneidad, por la gran cantidad de propuestas diferentes
que los fabricantes están lanzando al mercado. Por ello, para hacer posible el
despliegue de servicios sobre ellas, se impone la necesidad de hacer un estudio
en profundidad de este entorno, y deben de proponerse y desarrollarse las
herramientas adecuadas.
Esta tesis ataca la problemática del despliegue de servicios en estas redes
a tres niveles diferentes: (i) el nivel físico y de enlace, mostrando varios análisis
en profundidad del medio físico y modelos derivados para su simulación;
(ii) el nivel de red, proponiendo un protocolo de difusión de la información
para los paquetes IP; y (iii) el nivel de transporte, donde otros protocolos son
propuestos para mejorar el rendimiento del transporte de datos.
En primer lugar, se han estudiado y modelado las dos principales tecnologías
inalámbricas que se utilizan para la comunicación en redes vehiculares,
la rama de estándares 802.11, en concreto 802.11p; y la comunicación celular,
en particular LTE. Dado que el estándar 802.11p es un estándar bastante
maduro, nos centramos en crear (i) un modelo de propagación y atenuación
capaz de replicar el rango de transmisión de dispositivos 802.11p reales, en
condiciones de visión directa y obstrucción por pequeños obstáculos, y (ii) un
modelo de visibilidad capaz de simular el efecto de grandes obstáculos, como
son los edifcios, de una manera realista.
Además, proponemos un modelo
basado en indicadores de rendimiento de alto nivel (ancho de banda y retardo)
para LTE, que facilita la validación y evaluación de aplicaciones.
En el plano de red, se propone un protocolo híbrido, llamado AVE, para
el encaminamiento y reenvío de paquetes usando un conjunto de estrategias
estándar de enrutamiento. Dependiendo del escenario, AVE elige entre cuatro
estrategias diferentes: a) entrega directa a dos saltos, b) Dynamic MANET
On-demand (DYMO) c) georouting voraz, y d) una técnica store-carry-and-
forward, para adaptar su comportamiento dinámicamente a cada situación.
En el plano de transporte, se propone un protocolo bidireccional de distribución
de contenidos en canales con pérdidas que mejora la entrega de contenidos
en situaciones en las que la red es un cuello de botella, como las redes
inalámbricas.
Ha sido diseñado, validado, optimizado, y su rendimiento ha
sido analizado en términos de productividad y eficiencia en la utilización de
recursos.
Finalmente, a nivel de sistema, proponemos un modelo de computación
asistida que permite reducir la latencia en la respuesta a muchas consultas
colocando una unidad de computación en el borde de la red, i.e., la red de
acceso. Este esquema podría ser usado en redes basadas en 802.11p y en redes
celulares, si bien en esta tesis decidimos centrarnos en su evaluación usando
redes LTE.
La plataforma presentada en esta tesis combina todos los esfuerzos individuales
para crear una plataforma única y eficiente. Este nuevo entorno puede
ser usado por cualquier proveedor para mejorar la calidad de la experiencia de
usuario en los servicios desplegados sobre redes vehiculares.Els productes relacionats amb els sistemes intel · ligents de transport (ITS)
s'estan transformant en una realitat en les nostres carreteres. Tots els fabri-
cants de cotxes comencen a incloure accés a internet en els vehicles i a facilitar-
ne la integració amb els telèfons mòbils, però en el futur més i més serveis s'hi
introduiran. La connectivitat usant les xarxes vehicular esdevindrà la pedra
angular de cada nova proposta, i oferir una qualitat de servei adequada serà,
òbviament, desitjable.
No obstant això, es necessita una gran quantitat de
treball perquè les xarxes vehiculars oferisquen un rendiment similar al de les
xarxes cablejades.
Les xarxes vehiculars queden definides per dues característiques bàsiques:
alt dinamisme, ja que els nodes poden arribar a una velocitat relativa de més
de 250 km/h; i heterogeneïtat, per la gran quantitat de propostes diferents
que els fabricants estan llançant al mercat.
Per això, per a fer possible el
desplegament de serveis sobre aquestes xarxes, s'imposa la necessitat de fer un
estudi en profunditat d'aquest entorn, i cal proposar i desenvolupar les eines
adequades.
Aquesta tesi ataca la problemàtica del desplegament de serveis en aquestes
xarxes a tres nivells diferents: (i) el nivell físic i d'enllaç , mostrant diverses
anàlisis en profunditat del medi físic i models derivats per simular-lo; (ii) el
nivell de xarxa, proposant un protocol de difusió de la informació per als
paquets IP; i (iii) el nivell de transport, on es proposen altres protocols per a
millorar el rendiment del transport de dades.
En primer lloc, s'han estudiat i modelat les dues principals tecnologies
sense fils que s'utilitzen per a la comunicació en xarxes vehiculars, la branca
d'estàndards 802.11, en concret 802.11p; i la comunicació cel · lular, en partic-
ular LTE. Atès que l'estàndard 802.11p és un estàndard bastant madur, ens
centrem a crear (i) un model de propagació i atenuació capaç de replicar el
rang de transmissió de dispositius 802.11p reals, en condicions de visió directa
i obstrucció per petits obstacles, i (ii) un model de visibilitat capaç de simular
l'efecte de grans obstacles, com són els edificis, d'una manera realista. A més,
proposem un model basat en indicadors de rendiment d'alt nivell (ample de
banda i retard) per a LTE, que facilita la validació i l'avaluació d'aplicacions.
En el pla de xarxa, es proposa un protocol híbrid, anomenat AVE, per
a l'encaminament i el reenviament de paquets usant un conjunt d'estratègies
estàndard d'encaminament.
Depenent de l'escenari , AVE tria entre quatre
estratègies diferents: a) lliurament directe a dos salts, b) Dynamic MANET
On-demand (DYMO) c) georouting voraç, i d) una tècnica store-carry-and-
forward, per a adaptar-ne el comportament dinàmicament a cada situació.
En el pla de transport, es proposa un protocol bidireccional de distribució
de continguts en canals amb pèrdues que millora el lliurament de continguts
en situacions en què la xarxa és un coll de botella, com les xarxes sense fils.
Ha sigut dissenyat, validat, optimitzat, i el seu rendiment ha sigut analitzat
en termes de productivitat i eficiència en la utilització de recursos.
Finalment, a nivell de sistema, proposem un model de computació assistida
que permet reduir la latència en la resposta a moltes consultes col · locant una
unitat de computació a la vora de la xarxa, és a dir, la xarxa d'accés. Aquest
esquema podria ser usat en xarxes basades en 802.11p i en xarxes cel · lulars, si
bé en aquesta tesi decidim centrar-nos en la seua avaluació usant xarxes LTE.
La plataforma presentada en aquesta tesi combina tots els esforços indi-
viduals per a crear una plataforma única i eficient. Aquest nou entorn pot ser
usat per qualsevol proveïdor per a millorar la qualitat de l'experiència d'usuari
en els serveis desplegats sobre xarxes vehiculars.Báguena Albaladejo, M. (2017). Design and implementation of simulation tools, protocols and architectures to support service platforms on vehicular networks [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/85333TESISCompendi
Exploiting the power of multiplicity: a holistic survey of network-layer multipath
The Internet is inherently a multipath network: For an underlying network with only a single path, connecting various nodes would have been debilitatingly fragile. Unfortunately, traditional Internet technologies have been designed around the restrictive assumption of a single working path between a source and a destination. The lack of native multipath support constrains network performance even as the underlying network is richly connected and has redundant multiple paths. Computer networks can exploit the power of multiplicity, through which a diverse collection of paths is resource pooled as a single resource, to unlock the inherent redundancy of the Internet. This opens up a new vista of opportunities, promising increased throughput (through concurrent usage of multiple paths) and increased reliability and fault tolerance (through the use of multiple paths in backup/redundant arrangements). There are many emerging trends in networking that signify that the Internet's future will be multipath, including the use of multipath technology in data center computing; the ready availability of multiple heterogeneous radio interfaces in wireless (such as Wi-Fi and cellular) in wireless devices; ubiquity of mobile devices that are multihomed with heterogeneous access networks; and the development and standardization of multipath transport protocols such as multipath TCP. The aim of this paper is to provide a comprehensive survey of the literature on network-layer multipath solutions. We will present a detailed investigation of two important design issues, namely, the control plane problem of how to compute and select the routes and the data plane problem of how to split the flow on the computed paths. The main contribution of this paper is a systematic articulation of the main design issues in network-layer multipath routing along with a broad-ranging survey of the vast literature on network-layer multipathing. We also highlight open issues and identify directions for future work
Techniques for improving the scalability of data center networks
Data centers require highly scalable data and control planes for ensuring good performance of distributed applications. Along the data plane, network throughput and latency directly impact application performance metrics. This has led researchers to propose high bisection bandwidth network topologies based on multi-rooted trees for data center networks. However, such topologies require efficient traffic splitting algorithms to fully utilize all available bandwidth. Along the control plane, the centralized controller for software-defined networks presents new scalability challenges. The logically centralized controller needs to scale according to network demands. Also, since all services are implemented in the centralized controller, it should allow easy integration of different types of network services.^ In this dissertation, we propose techniques to address scalability challenges along the data and control planes of data center networks.^ Along the data plane, we propose a fine-grained trac splitting technique for data center networks organized as multi-rooted trees. Splitting individual flows can provide better load balance but is not preferred because of potential packet reordering that conventional wisdom suggests may negatively interact with TCP congestion control. We demonstrate that, due to symmetry of the network topology, TCP is able to tolerate the induced packet reordering and maintain a single estimate of RTT.^ Along the control plane, we design a scalable distributed SDN control plane architecture. We propose algorithms to evenly distribute the load among the controller nodes of the control plane. The algorithms evenly distribute the load by dynamically configuring the switch to controller node mapping and adding/removing controller nodes in response to changing traffic patterns. ^ Each SDN controller platform may have different performance characteristics. In such cases, it may be desirable to run different services on different controllers to match the controller performance characteristics with service requirements. To address this problem, we propose an architecture, FlowBricks, that allows network operators to compose an SDN control plane with services running on top of heterogeneous controller platforms
Mitigating TCP Degradation over Intermittent Link Failures Using Intermediate Buffers
This thesis addresses the improvement of data transmission performance in a challenged network. It is well known that the popular Transmission Control Protocol degrades in environments where one or more of the links along the route is intermittently available. To avoid this degradation, this thesis proposes placing at least one node along the path of transmission to buffer and retransmit as needed to overcome the intermittent link. In the four-node, three-link testbed under particular conditions, file transmission time was reduced 20 fold in the case of an intermittent second link when the second node strategically buffers for retransmission opportunity
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