6,839 research outputs found
Internet's Critical Path Horizon
Internet is known to display a highly heterogeneous structure and complex
fluctuations in its traffic dynamics. Congestion seems to be an inevitable
result of user's behavior coupled to the network dynamics and it effects should
be minimized by choosing appropriate routing strategies. But what are the
requirements of routing depth in order to optimize the traffic flow? In this
paper we analyse the behavior of Internet traffic with a topologically
realistic spatial structure as described in a previous study (S-H. Yook et al.
,Proc. Natl Acad. Sci. USA, {\bf 99} (2002) 13382). The model involves
self-regulation of packet generation and different levels of routing depth. It
is shown that it reproduces the relevant key, statistical features of
Internet's traffic. Moreover, we also report the existence of a critical path
horizon defining a transition from low-efficient traffic to highly efficient
flow. This transition is actually a direct consequence of the web's small world
architecture exploited by the routing algorithm. Once routing tables reach the
network diameter, the traffic experiences a sudden transition from a
low-efficient to a highly-efficient behavior. It is conjectured that routing
policies might have spontaneously reached such a compromise in a distributed
manner. Internet would thus be operating close to such critical path horizon.Comment: 8 pages, 8 figures. To appear in European Journal of Physics B (2004
Compact routing on the Internet AS-graph
Compact routing algorithms have been presented as candidates for scalable routing in the future Internet, achieving near-shortest path routing with considerably less forwarding state than the Border Gateway Protocol. Prior analyses have shown strong performance on power-law random graphs, but to better understand the applicability of compact routing algorithms in the context of the Internet, they must be evaluated against real- world data. To this end, we present the first systematic analysis of the behaviour of the Thorup-Zwick (TZ) and Brady-Cowen (BC) compact routing algorithms on snapshots of the Internet Autonomous System graph spanning a 14 year period. Both algorithms are shown to offer consistently strong performance on the AS graph, producing small forwarding tables with low stretch for all snapshots tested. We find that the average stretch for the TZ algorithm increases slightly as the AS graph has grown, while previous results on synthetic data suggested the opposite would be true. We also present new results to show which features of the algorithms contribute to their strong performance on these graphs
Memory and information processing in neuromorphic systems
A striking difference between brain-inspired neuromorphic processors and
current von Neumann processors architectures is the way in which memory and
processing is organized. As Information and Communication Technologies continue
to address the need for increased computational power through the increase of
cores within a digital processor, neuromorphic engineers and scientists can
complement this need by building processor architectures where memory is
distributed with the processing. In this paper we present a survey of
brain-inspired processor architectures that support models of cortical networks
and deep neural networks. These architectures range from serial clocked
implementations of multi-neuron systems to massively parallel asynchronous ones
and from purely digital systems to mixed analog/digital systems which implement
more biological-like models of neurons and synapses together with a suite of
adaptation and learning mechanisms analogous to the ones found in biological
nervous systems. We describe the advantages of the different approaches being
pursued and present the challenges that need to be addressed for building
artificial neural processing systems that can display the richness of behaviors
seen in biological systems.Comment: Submitted to Proceedings of IEEE, review of recently proposed
neuromorphic computing platforms and system
Survey of Inter-satellite Communication for Small Satellite Systems: Physical Layer to Network Layer View
Small satellite systems enable whole new class of missions for navigation,
communications, remote sensing and scientific research for both civilian and
military purposes. As individual spacecraft are limited by the size, mass and
power constraints, mass-produced small satellites in large constellations or
clusters could be useful in many science missions such as gravity mapping,
tracking of forest fires, finding water resources, etc. Constellation of
satellites provide improved spatial and temporal resolution of the target.
Small satellite constellations contribute innovative applications by replacing
a single asset with several very capable spacecraft which opens the door to new
applications. With increasing levels of autonomy, there will be a need for
remote communication networks to enable communication between spacecraft. These
space based networks will need to configure and maintain dynamic routes, manage
intermediate nodes, and reconfigure themselves to achieve mission objectives.
Hence, inter-satellite communication is a key aspect when satellites fly in
formation. In this paper, we present the various researches being conducted in
the small satellite community for implementing inter-satellite communications
based on the Open System Interconnection (OSI) model. This paper also reviews
the various design parameters applicable to the first three layers of the OSI
model, i.e., physical, data link and network layer. Based on the survey, we
also present a comprehensive list of design parameters useful for achieving
inter-satellite communications for multiple small satellite missions. Specific
topics include proposed solutions for some of the challenges faced by small
satellite systems, enabling operations using a network of small satellites, and
some examples of small satellite missions involving formation flying aspects.Comment: 51 pages, 21 Figures, 11 Tables, accepted in IEEE Communications
Surveys and Tutorial
Compact routing for the future internet
The Internet relies on its inter-domain routing system to allow data
transfer between any two endpoints regardless of where they are
located. This routing system currently uses a shortest path routing algorithm
(modified by local policy constraints) called the Border Gateway
Protocol. The massive growth of the Internet has led to large routing
tables that will continue to grow. This will present a serious
engineering challenge for router designers in the long-term,
rendering state (routing table) growth at this pace unsustainable.
There are various short-term engineering solutions that may slow the
growth of the inter-domain routing tables, at the expense of increasing
the complexity of the network. In addition, some of these require manual configuration, or
introduce additional points of failure within the network. These solutions may
give an incremental, constant factor, improvement. However,
we know from previous work that all shortest path routing algorithms
require forwarding state that grows linearly with the size of the
network in the worst case.
Rather than attempt to sustain inter-domain routing through a
shortest path routing algorithm, compact routing algorithms exist that
guarantee worst-case sub-linear state requirements at all nodes by
allowing an upper-bound on path length relative to the theoretical
shortest path, known as path stretch. Previous work has shown
the promise of these algorithms when applied to synthetic graphs
with similar properties to the known Internet
graph, but they haven't been studied in-depth on Internet topologies
derived from real data.
In this dissertation, I demonstrate the consistently strong
performance of these compact routing algorithms for inter-domain routing by performing
a longitudinal study of two compact routing algorithms on the Internet
Autonomous System (AS) graph over time.
I then show, using the k-cores graph decomposition algorithm, that
the structurally important nodes in the AS graph are highly stable
over time. This property makes these nodes suitable for use as the
"landmark" nodes used by the most stable of the compact routing
algorithms evaluated, and the use of these nodes shows similar strong
routing performance.
Finally, I present a decentralised compact routing algorithm for
dynamic graphs, and present state requirements and message overheads
on AS graphs using realistic simulation inputs.
To allow the continued long-term growth of Internet routing state, an
alternative routing architecture may be required. The use of the
compact routing algorithms presented in this dissertation offer
promise for a scalable future Internet routing system
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