5 research outputs found
Low-Latency Millimeter-Wave Communications: Traffic Dispersion or Network Densification?
This paper investigates two strategies to reduce the communication delay in
future wireless networks: traffic dispersion and network densification. A
hybrid scheme that combines these two strategies is also considered. The
probabilistic delay and effective capacity are used to evaluate performance.
For probabilistic delay, the violation probability of delay, i.e., the
probability that the delay exceeds a given tolerance level, is characterized in
terms of upper bounds, which are derived by applying stochastic network
calculus theory. In addition, to characterize the maximum affordable arrival
traffic for mmWave systems, the effective capacity, i.e., the service
capability with a given quality-of-service (QoS) requirement, is studied. The
derived bounds on the probabilistic delay and effective capacity are validated
through simulations. These numerical results show that, for a given average
system gain, traffic dispersion, network densification, and the hybrid scheme
exhibit different potentials to reduce the end-to-end communication delay. For
instance, traffic dispersion outperforms network densification, given high
average system gain and arrival rate, while it could be the worst option,
otherwise. Furthermore, it is revealed that, increasing the number of
independent paths and/or relay density is always beneficial, while the
performance gain is related to the arrival rate and average system gain,
jointly. Therefore, a proper transmission scheme should be selected to optimize
the delay performance, according to the given conditions on arrival traffic and
system service capability
A Network Calculus Approach for the Analysis of Multi-Hop Fading Channels
A fundamental problem in the delay and backlog analysis across multi-hop
paths in wireless networks is how to account for the random properties of the
wireless channel. Since the usual statistical models for radio signals in a
propagation environment do not lend themselves easily to a description of the
available service rate on a wireless link, the performance analysis of wireless
networks has resorted to higher-layer abstractions, e.g., using Markov chain
models. In this work, we propose a network calculus that can incorporate common
statistical models of fading channels and obtain statistical bounds on delay
and backlog across multiple nodes. We conduct the analysis in a transfer
domain, which we refer to as the `SNR domain', where the service process at a
link is characterized by the instantaneous signal-to-noise ratio at the
receiver. We discover that, in the transfer domain, the network model is
governed by a dioid algebra, which we refer to as (min,x)-algebra. Using this
algebra we derive the desired delay and backlog bounds. An application of the
analysis is demonstrated for a simple multi-hop network with Rayleigh fading
channels and for a network with cross traffic.Comment: 26 page
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Performance modelling and evaluation of heterogeneous wired / wireless networks under Bursty Traffic. Analytical models for performance analysis of communication networks in multi-computer systems, multi-cluster systems, and integrated wireless systems.
Computer networks can be classified into two broad categories: wired networks and
wireless networks, according to the hardware and software technologies used to
interconnect the individual devices. Wired interconnection networks are hardware
fabrics supporting communications between individual processors in highperformance
computing systems (e.g., multi-computer systems and cluster systems).
On the other hand, due to the rapid development of wireless technologies, wireless
networks have emerged and become an indispensable part for people¿s lives. The
integration of different wireless technologies is an effective approach to
accommodate the increasing demand of the users to communicate with each other
and access the Internet.
This thesis aims to investigate the performance of wired interconnection
networks and integrated wireless networks under the realistic working conditions.
Traffic patterns have a significant impact on network performance. A number of
recent measurement studies have convincingly demonstrated that the traffic
generated by many real-world applications in communication networks exhibits
bursty arrival nature and the message destinations are non-uniformly distributed.
Analytical models for the performance evaluation of wired interconnection networks
and integrated wireless networks have been widely reported. However, most of these
models are developed under the simplified assumption of non-bursty Poisson process
with uniformly distributed message destinations.
To fill this gap, this thesis first presents an analytical model to investigate the
performance of wired interconnection networks in multi-computer systems. Secondly,
the analytical models for wired interconnection networks in multi-cluster systems are
developed. Finally, this thesis proposes analytical models to evaluate the end-to-end
delay and throughput of integrated wireless local area networks and wireless mesh
networks. These models are derived when the networks are subject to bursty traffic
with non-uniformly distributed message destinations which can capture the
burstiness of real-world network traffic in the both temporal domain and spatial
domain. Extensive simulation experiments are conducted to validate the accuracy of
the analytical models. The models are then used as practical and cost-effective tools
to investigate the performance of heterogeneous wired or wireless networks under
the traffic patterns exhibited by real-world applications
Multistage Packet-Switching Fabrics for Data Center Networks
Recent applications have imposed stringent requirements within the Data Center Network (DCN) switches in terms of scalability, throughput and latency. In this thesis, the architectural design of the packet-switches is tackled in different ways to enable the expansion in both the number of connected endpoints and traffic volume.
A cost-effective Clos-network switch with partially buffered units is proposed and two packet scheduling algorithms are described. The first algorithm adopts many simple and distributed arbiters, while the second approach relies on a central arbiter to guarantee an ordered packet delivery.
For an improved scalability, the Clos switch is build using a Network-on-Chip (NoC) fabric instead of the common crossbar units. The Clos-UDN architecture made with Input-Queued (IQ) Uni-Directional NoC modules (UDNs) simplifies the input line cards and obviates the need for the costly Virtual Output Queues (VOQs). It also avoids the need for complex, and synchronized scheduling processes, and offers speedup, load balancing, and good path diversity.
Under skewed traffic, a reliable micro load-balancing contributes to boosting the overall network performance. Taking advantage of the NoC paradigm, a wrapped-around multistage switch with fully interconnected Central Modules (CMs) is proposed. The architecture operates with a congestion-aware routing algorithm that proactively distributes the traffic load across the switching modules, and enhances the switch performance under critical packet arrivals.
The implementation of small on-chip buffers has been made perfectly feasible using the current technology. This motivated the implementation of a large switching architecture with an Output-Queued (OQ)
NoC fabric. The design merges assets of the output queuing, and
NoCs to provide high throughput, and smooth latency variations.
An approximate analytical model of the switch performance is also proposed.
To further exploit the potential of the NoC fabrics and their modularity features, a high capacity Clos switch with Multi-Directional NoC
(MDN) modules is presented. The Clos-MDN switching architecture exhibits a more compact layout than the Clos-UDN switch. It scales better and faster in port count and traffic load. Results achieved in this thesis demonstrate the high performance, expandability and programmability features of the proposed packet-switches which makes them promising candidates for the next-generation data center networking infrastructure