IMDEA Networks Institute Digital Repository
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1915 research outputs found
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Disjoint Multipath Routing and Failure Recovery
Get PDFApplications such as Voice over IP and video delivery require continuous network service, requiring fast failure recovery mechanisms. Proactive Fast failure recovery mechanisms
have been recently proposed to improve network performance
during the failure transients. The proposed mechanisms need
extra infrastructural support in the form of routing table
entries, extra addresses etc. In this paper, we study if the extra
infrastructure support can be exploited to build disjoint paths in
those frameworks, while keeping the recovery path lengths close
to the primary paths. Our evaluations show that it is possible
to extend the proactive recovery mechanisms to provide support
for nearly-disjoint paths.TRUEpu
A Survey of Services Placement Mechanisms for Future Mobile Communication Networks
Get PDFMobile communication networks experience a tremendous
growth. According to the vision of Wireless World Research
Forum (WWRF), there will be 7 trillion wireless devices serving 7
billion people by the year 2017. Ubiquitous access to information
anywhere, anytime and anyhow at low cost is one of the essential
features of future mobile communication networks, which will
interconnect a heterogeneity of various systems and be much more
dynamic and flexible in terms of changes in access technology,
topology, services, etc. Moreover, there will be a need to match
resources supply with application demands as these demands are
expected to fluctuate over time. This makes an adequate service
placement in such networks of a major importance. In this paper
we survey the existing service placement mechanisms and present
a qualitative comparison of existing mechanisms. Moreover we
also highlight the short comings of existing approaches so that the
new approaches can remove the short comings of existing
approaches.TRUEpu
Performance of Quantized Congestion Notification in TCP Incast scenarios in data centers
Get PDFThis paper analyzes the performance of Ethernet
layer congestion control mechanism Quantized Congestion Noti-
fication (QCN) during data access from clustered servers in data
centers. We analyze the reasons why QCN does not perform
adequately in these situations and propose several modifications
to the protocol to improve its performance in these scenarios.
We trace the causes of QCN performance degradation to flow
rate variability, and show that adaptive sampling at the switch
and adaptive self-increase of flow rates at the rate limiter
improve performance in a TCP Incast setup significantly. We
compare the performance of QCN against TCP modifications
in a heterogeneous environment, and show that modifications to
QCN yield better performance.TRUEpu
On the Design of Scalable Peer-to-Peer Video Caching
Get PDFAdditional ID number: Technical Report CIS-TR-10-10Peer-to-Peer(P2P)video caching is a promising approach to accommodate asynchronous requests from cached content at individual peers. However, coherently managing a distributed, heterogeneous, dynamic and potentially large scale cache space is a challenging task. In particular, a key challenge is to effectively control the number of cached copies for popular streams in order to accommodate their concurrent requests with minimum thrashing in the cached content. A few prior studies on P2P video caching rely on the global cache state in order to achieve this goal and, therefore, exhibit limited scalability.
This paper examines key issues in the design of a scalable P2P video caching mechanism that can effectively control the number of cached copies for popular streams by only leveraging the local information at each peer.We argue that the local notion of popularity can serve a sane effective measure to perform cache replacement at individual peers. We sketch two straw-man P2P video caching techniques that rely on the trends in the popularity of individual streams to control the required number of copies in a reactive or proactive fashion. Using simulation, we examine the performance of the proposed mechanisms along with the distributed(and uncoordinated) version of LRU and LFU mechanisms that only use local work load at each peer.Our results show that distributed and uncoordinated P2P video caching generally exhibit good performance across a wide range of scenarios.pu
Supporting mobility in an IMS-based P2P IPTV service: a Proactive Context Transfer mechanism
Get PDFIn recent years, IPTV has received an increasing amount of interest from the industry, commercial providers and the research community, alike. In this context, standardization bodies, such as ETSI and ITU-T, are specifying the architecture of IPTV systems based on IP multicast. An interesting alternative to support the IPTV service delivery relies on the peer-to-peer (P2P) paradigm to distribute and push the streaming effort towards the network
edge. However, while P2P IPTV was studied in fixed access technologies, there has been little attention paid to the implications arising in mobile environments. One of these involves the service handover when the user moves to a different network. By analyzing previous work from the perspective of an IPTV service, we concluded that a proactive approach is necessary for the handling of inter-network handovers. In this paper, we propose a new general
handover mechanism for the IP Multimedia Subsystem (IMS), while studying its applicability to a P2P IPTV service. Our solution, called Proactive Context Transfer Service, incorporates the existing IEEE 802.21 technology in order to minimize the handover delay. The proposal is validated by comparing it against solutions derived from previous work.TRUEpu
On the energy efficiency of IEEE 802.11 WLANs
No full textUnderstanding the energy consumption of wireless interfaces is critical to provide guidelines for the design and implementation of new protocols or interfaces. In this work we analyze the energy performance of an IEEE 802.11 WLAN. Our contributions are as follows: i) we present an accurate analytical model that is able to predict the energy consumption, ii) we present an approximate model that sacrifices accuracy for the sake of analytical tractability, iii) based on this simplified analysis, we derive the optimal configuration to maximize energy efficiency of a WLAN, and iv) finally, we also analyze the tradeoff between throughput and energy efficiency that IEEE 802.11 imposes. While most of these results consider a homogeneous WLAN scenario where all stations share the same energy features, we also discuss the case of heterogeneous environments, where different devices show different power consumption characteristics.TRUEpu
Self-organizing Dynamic Fractional Frequency Reuse on the uplink of OFDMA systems
Get PDFReverse link (or uplink) performance of cellular
systems is becoming increasingly impor t ant with the emergence
of new upl ink-bandwidth intensive applications such as Video
Share [14], where end users upload video clips captured through
their mobile devices. In particular, it is important to design the
system to provide good us e r throughput in most of the coverage
area, including at the cell edge. Soft fractional frequency reuse
(FFR) is one of the techniques for mitigating inter-cell interference in cellular systems, leading to overall spectral efficiency
enhancements and/or cell edge throughput improvements. We
propose a novel algorithm tha t dynamically creates efficient soft
FFR patterns on the upl ink of orthogonal frequency division
multiple access (OFDMA) based cellular systems; this allows the
system to "automatically" adapt to user traffic distribution and
system layout.
Our algorithm is based on systematically ascending towards
a local maximum of the system-wide sum of user utilities, which
depend on user throughputs. We show that this can be done in a
semi-autonomous fashion: each sector does its resource allocation
independently, with only an in frequent periodic exchange of
interference costs between neighboring sectors. The proposed
algorithm, called Multi-sector Gr adi ent for Upl ink (MGR-UL),
allocates in-sector resources (power, frequency, time-slots to each
user) in a way tha t simultaneously takes into a c count both
the benefit to its "own" users ' utility and the cost of creating
interference to neighboring sectors; along with tha t each sector
estimates the cost of interference to itself. Extensive simulation
results show tha t significant pe r formanc e benefits (up to 69%
in total throughput in some typical scenarios) can be achieved
with respect to a baseline approach. Simulations also show the
automa tic formation of soft FFR patterns.TRUEpu
OmTCP: Increasing Performance in Server Farms
Get PDFISSN: 1550-3607Normal TCP/IP operation is for the routing system
to select a best path that remains stable for some time, and for
TCP to adjust to the properties of this path to optimize
throughput. By executing TCP’s congestion control algorithms
on multiple paths at the same time, a multipath TCP can shift its
traffic to a less congested path, thus maximizing both the
throughput for the multipath TCP user and leaving more
capacity available for other traffic on more congested paths.
And when a path fails, this can be detected and worked around
by multipath TCP much more quickly than by waiting for the
routing system to repair the failure.
This paper proposes a one-ended multipath TCP that is
implemented on the sending host only, without requiring
modifications on the receiving host, for the purposes of
maximizing performance in transmissions from multiply
connected large servers towards singly connected end-users and
recovering from failures more quickly.TRUEpu
Exploiting Microscopic Spectrum Opportunities in Cognitive Radio Networks via Coordinated Channel Access
Get PDFUnder the current opportunistic spectrum access (OSA) paradigm, a common belief is that a cognitive radio (CR) can use a channel only when this channel is not being used by any neighboring primary radio (PR). Therefore, the existence of a spectrum opportunity hinges on the absence of active cochannel PRs in a macroscopic region. In this paper, we propose the concept of microscopic spectrum opportunity and show that CRs can still utilize this type of opportunities without interfering with active cochannel
PRs, even when these PRs are close to them. As a result, a channel may at the same time present different levels of availability to different CRs. Channel access needs to be carefully coordinated between these CRs to avoid collisions, and more importantly, ensure efficient utilization of the spectrum opportunity from a network’s standpoint. In this paper, we formulate the coordinated channel access as a joint power/rate control and channel assignment optimization problem, with the objective of maximizing the sum-rate achieved by the cognitive radio network (CRN). We develop both centralized and distributed algorithms to solve this problem. Our simulation results
show that even when accounting for the implementation overhead, significant throughput gain is achieved under our designs.TRUEpu
On the Trade-Off between Throughput Maximization and Energy Consumption Minimization in IEEE 802.11 WLANs
Get PDFISSN 1976-5541 (Online)Understanding and optimizing the energy consumption of wireless devices is critical to maximize the network lifetime and to provide guidelines for the design of new protocols and interfaces. In this work, we first provide an accurate analysis of the energy performance of an IEEE 802.11 WLAN, and then we derive the configuration to optimize it. We further analyze the impact of the energy configuration of the stations on the throughput performance, and we discuss under which circumstances throughput and energy efficiency can be both jointly maximized and where
they constitute different challenges. Our findings are that, although an energy-optimized configuration typically yields gains in terms of throughput as compared against the default configuration, it comes with a reduction in performance as compared against the maximum-bandwidth configuration, a reduction that depends on the energy parameters of the wireless interface.TRUEpu