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Tree LANS with collision avoidance : protocol, switch architecture, and performance
Packet collisions and their resolution create a performance bottleneck in random access LANs. A hardware solution to this problem is to use collision avoidance switches. These switches allow the implementation of random access protocols without the penalty of collisions among packets. We review and compare the designs of some tree LANs that use collision avoidance switches. They have the potential of combining the benefits of random access (low delay when traffic is light, simple and distributed, and therefore robust, protocols) with excellent network utilization and concurrency of transmission. The collision avoidance LANs we review are broadcast star, Hubnet-like tree, Tinker-Tree, and a treenet that allows concurrent broadcasts within non-intersecting subtrees. After this review, we present a slotted-time, infinite user analysis of the broadcast star network
Delay distributions of slotted ALOHA and CSMA
We derive the closed-form delay distributions of slotted ALOHA and nonpersistent carrier sense multiple access (CSMA) protocols under steady state. Three retransmission policies are analyzed. We find that under a binary exponential backoff retransmission policy, finite average delay and finite delay variance can be guaranteed for G<2S and G<4S/3, respectively, where G is the channel traffic and S is the channel throughput. As an example, in slotted ALOHA, S<(ln2)/2 and S<3(ln4-ln3)/4 are the operating ranges for finite first and second delay moments. In addition, the blocking probability and delay performance as a function of r/sub max/ (maximum number of retransmissions allowed) is also derived
An investigation of networking techniques for the ASRM facility
This report is based on the early design concepts for a communications network for the Advanced Solid Rocket Motor (ASRM) facility being built at Yellow Creek near Iuka, MS. The investigators have participated in the early design concepts and in the evaluation of the initial concepts. The continuing system design effort and any modification of the plan will require a careful evaluation of the required bandwidth of the network, the capabilities of the protocol, and the requirements of the controllers and computers on the network. The overall network, which is heterogeneous in protocol and bandwidth, is being modeled, analyzed, simulated, and tested to obtain some degree of confidence in its performance capabilities and in its performance under nominal and heavy loads. The results of the proposed work should have an impact on the design and operation of the ASRM facility
Full-duplex MAC Protocol Design and Analysis
The idea of in-band full-duplex (FD) communications revives in recent years
owing to the significant progress in the self-interference cancellation and
hardware design techniques, offering the potential to double spectral
efficiency. The adaptations in upper layers are highly demanded in the design
of FD communication systems. In this letter, we propose a novel medium access
control (MAC) using FD techniques that allows transmitters to monitor the
channel usage while transmitting, and backoff as soon as collision happens.
Analytical saturation throughput of the FD-MAC protocol is derived with the
consideration of imperfect sensing brought by residual self- interference (RSI)
in the PHY layer. Both analytical and simulation results indicate that the
normalized saturation throughput of the proposed FD-MAC can significantly
outperforms conventional CSMA/CA under various network conditions
Increasing throughput in IEEE 802.11 by optimal selection of backoff parameters
Engineering and Physical Sciences Research Council. Grant Number: EP/G012628/
A particle system in interaction with a rapidly varying environment: Mean field limits and applications
We study an interacting particle system whose dynamics depends on an
interacting random environment. As the number of particles grows large, the
transition rate of the particles slows down (perhaps because they share a
common resource of fixed capacity). The transition rate of a particle is
determined by its state, by the empirical distribution of all the particles and
by a rapidly varying environment. The transitions of the environment are
determined by the empirical distribution of the particles. We prove the
propagation of chaos on the path space of the particles and establish that the
limiting trajectory of the empirical measure of the states of the particles
satisfies a deterministic differential equation. This deterministic
differential equation involves the time averages of the environment process.
We apply our results to analyze the performance of communication networks
where users access some resources using random distributed multi-access
algorithms. For these networks, we show that the environment process
corresponds to a process describing the number of clients in a certain loss
network, which allows us provide simple and explicit expressions of the network
performance.Comment: 31 pages, 2 figure
Extremely high data-rate, reliable network systems research
Significant progress was made over the year in the four focus areas of this research group: gigabit protocols, extensions of metropolitan protocols, parallel protocols, and distributed simulations. Two activities, a network management tool and the Carrier Sensed Multiple Access Collision Detection (CSMA/CD) protocol, have developed to the point that a patent is being applied for in the next year; a tool set for distributed simulation using the language SIMSCRIPT also has commercial potential and is to be further refined. The year's results for each of these areas are summarized and next year's activities are described
Performance Comparison of the RPL and LOADng Routing Protocols in a Home Automation Scenario
RPL, the routing protocol proposed by IETF for IPv6/6LoWPAN Low Power and
Lossy Networks has significant complexity. Another protocol called LOADng, a
lightweight variant of AODV, emerges as an alternative solution. In this paper,
we compare the performance of the two protocols in a Home Automation scenario
with heterogenous traffic patterns including a mix of multipoint-to-point and
point-to-multipoint routes in realistic dense non-uniform network topologies.
We use Contiki OS and Cooja simulator to evaluate the behavior of the
ContikiRPL implementation and a basic non-optimized implementation of LOADng.
Unlike previous studies, our results show that RPL provides shorter delays,
less control overhead, and requires less memory than LOADng. Nevertheless,
enhancing LOADng with more efficient flooding and a better route storage
algorithm may improve its performance
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