385 research outputs found
Analysis of exhaustive limited service for token ring networks
Token ring operation is well-understood in the cases of exhaustive, gated, gated limited, and ordinary cyclic service. There is no current data, however, on queueing models for the exhaustive limited service type. This service type differs from the others in that there is a preset maximum (omega) on the number of packets which may be transmitted per token reception, and packets which arrive after token reception may still be transmitted if the preset packet limit has not been reached. Exhaustive limited service is important since it closely approximates a timed token service discipline (the approximation becomes exact if packet lengths are constant). A method for deriving the z-transforms of the distributions of the number of packets present at both token departure and token arrival for a system using exhaustive limited service is presented. This allows for the derivation of a formula for mean queueing delay and queue lengths. The method is theoretically applicable to any omega. Fortunately, as the value of omega becomes large (typically values on the order of omega = 8 are considered large), the exhaustive limited service discipline closely approximates an exhaustive service discipline
Hybrid token-CDMA MAC protocol for wireless networks.
Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2009.Ad hoc networks are commonly known to implement IEEE 802.11 standard as their medium
access control (MAC) protocol. It is well known that token passing MAC schemes
outperform carrier-sense-multiple-access (CSMA) schemes, therefore, token passing MAC
protocols have gained popularity in recent years. In recent years, the research extends the
concept of token passing ' scheme to wireless settings since they have the potential of
achieving higher channel utilization than CSMA type schemes.
In this thesis, a hybrid Token-CDMA MAC protocol that is based on a token passing scheme
with the incorporation of code division multiple access (CDMA) is introduced. Using a
dynamic code distribution algorithm and a modified leaky-bucket policing system, the
hybrid protocol is able to provide both Quality of Service (QoS) and high network resource
utilization, while ensuring the stability of a network. This thesis begins with the introduction
of a new MAC protocol based on a token-passing strategy. The input traffic model used in
the simulation is a two-state Markov Modulated Poisson Process (MMPP). The data rate
QoS is enforced by implementing a modified leaky bucket mechanism in the proposed MAC
scheme. The simulation also takes into account channel link errors caused by the wireless
link by implementing a multi-layered Gilbert-Elliot model. The performance of the proposed
MAC scheme is examined by simulation, and compared to the performance of other MAC
protocols published in the literature. Simulation results demonstrate that the proposed hybrid
MAC scheme is effective in decreasing packet delay and significantly shortens the length of
the queue.
The thesis continues with the discussion of the analytical model for the hybrid Token CDMA
protocol. The proposed MAC scheme is analytically modelled as a multiserver
multiqueue (MSMQ) system with a gated service discipline. The analytical model is
categorized into three sections viz. the vacation model, the input model and the buffer model.
The throughput and delay performance are then computed and shown to closely match the
simulation results. Lastly, cross-layer optimization between the physical (PHY) and MAC
layers for the hybrid token-CDMA scheme is discussed. The proposed joint PHY -MAC
approach is based on the interaction between the two layers in order to enable the stations to
dynamically adjust the transmission parameters resulting in reduced mutual interference and
optimum system performance
Scalable Extraction of Training Data from (Production) Language Models
This paper studies extractable memorization: training data that an adversary
can efficiently extract by querying a machine learning model without prior
knowledge of the training dataset. We show an adversary can extract gigabytes
of training data from open-source language models like Pythia or GPT-Neo,
semi-open models like LLaMA or Falcon, and closed models like ChatGPT. Existing
techniques from the literature suffice to attack unaligned models; in order to
attack the aligned ChatGPT, we develop a new divergence attack that causes the
model to diverge from its chatbot-style generations and emit training data at a
rate 150x higher than when behaving properly. Our methods show practical
attacks can recover far more data than previously thought, and reveal that
current alignment techniques do not eliminate memorization
Excellence at Work: Policy Option Papers for the National Governors\u27 Association
State-level initiatives are proposed that address key issues affecting the competitiveness of the U.S. economy.https://research.upjohn.org/up_press/1201/thumbnail.jp
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