30,917 research outputs found
Wardrop Equilibrium in Discrete-Time Selfish Routing with Time-Varying Bounded Delays
This paper presents a multi-commodity, discrete-
time, distributed and non-cooperative routing algorithm, which is
proved to converge to an equilibrium in the presence of
heterogeneous, unknown, time-varying but bounded delays.
Under mild assumptions on the latency functions which describe
the cost associated to the network paths, two algorithms are
proposed: the former assumes that each commodity relies only on
measurements of the latencies associated to its own paths; the
latter assumes that each commodity has (at least indirectly) access
to the measures of the latencies of all the network paths. Both
algorithms are proven to drive the system state to an invariant set
which approximates and contains the Wardrop equilibrium,
defined as a network state in which no traffic flow over the
network paths can improve its routing unilaterally, with the latter
achieving a better reconstruction of the Wardrop equilibrium.
Numerical simulations show the effectiveness of the proposed
approach
A Survey of Network Optimization Techniques for Traffic Engineering
TCP/IP represents the reference standard for the implementation of interoperable communication networks. Nevertheless, the layering principle at the basis of interoperability severely limits the performance of data communication networks, thus requiring proper configuration and management in order to provide effective management of traffic flows. This paper presents a brief survey related to network optimization using Traffic Engineering algorithms, aiming at providing additional insight to the different alternatives available in the scientific literature
Polycyclic aromatic hydrocarbons biodegradation using isolated strains under indigenous condition
The treatment and disposal of domestic sIudge is an expensive and environmentally sensitive
problem. It is also a growing problem since sludge production will continue to increase as
new wastewzter treatment plants are built due to population increase. The large volume of
domestic sIudge produced had made it difficult for many countries including Malaysia to
assure complete treatment of the sludge before discharging to the receiving environment.
Domestic sludge contains diverse range of pollutants such as pathogen, inorganic and organic
compounds. These pollutants are toxic, mutagenic or carcinogenic and may threaten human
health. Iiilproper disposal and handling of sludge may pose serious impact to the environment
especially on soil and water cycles. Previous studies on Malaysian domestic sludge only
reported on bulk parameters and heavy metals. Thus, no study reported on organic micro
pollutants, namely, polycylic aromatic hydrocarbons (PAHs). Their recalcitrance and
persistence make them problematic environmental contaminants. Microbial degradation is
considered to be the primary mechanism of PAHs removal from the environment. Much has
been reported on biodegradation of PAHs in several countries but there is a lack of
information quantitative on this subject in Malaysia. This study is carried out to understand
the nature of domestic sludge and to provide a better understanding on the biodegradation
processes of PAHs. The methodology of this study comprised field activities, laboratory work
and mathematical modelling. Field activities involved sampling of domestic sludge from
Kolej Mawar, Universiti Teknologi MARA, Shah Alam, Selangor. Laboratory activities
include seven phases of experimental works. First phase is characterization study of domestic
sludge based on bulk parameters, heavy metals and PAHs. Second phase is enrichment and
purification of bacteria isolated from domestic sludge using single PAHs and mixed PAHs as
growth substrate. This was followed by identification of bacteria using BIOLOG system. The
fourth phase focussed on turbidity test to monitor growth rate of the isolated bacteria.
Preliminary degradation study involves optimization of the process at different substrate
concentration, bacteria concentration, pH and temperature. The optimum conditions
established from optimization study were used in degradation study. In biodegradation study,
two experimental conditions were performed. These conditions include using bacteria isolated
from single PAHs as substrate and bacteria isolated from mixed PAHs. Protein and pH tests
were done during degradation study. Final activity is mathematical modelling of the
biodegradation process. In general results on bulk parameters are comparable to previous
studies. Zinc was the main compound with a mean concentration of 11 96.4 mglkg. PAHs
were also detected in all of the samples, with total concentration between 0.72 to 5.36 mglkg
dry weight for six PAHs. In the examined samples, phenanthrene was the main compound
with a mean concentration of 1.0567 mglkg. The results fiom purification studies of bacteria
strains sucessfull isolated 13 bacteria strains fiom single PAH substrate while three bacteria
were isolated from the mixed PAHs substrate. Based on bacteria growth rates, only six strains
grown on single PAHs and three strains grown on mixed PAHs were used for further studies.
Results from the optimization study of biodegradation indicated that maximum rate of PAHs
removal occurred at 100 mg~-' of PAHs, 10% bacteria concentration, pH 7.0 and 30°C. The
results showed that bacteria grown on lower ring of PAHs are not able to grow on higher ring
of PAHs. As for example Micrococcus diversus grown on napthalene as sole carbon source
was unable to degrade other PAHs like acenapthylene, acenapthene, fluorene, phenanthrene
and antlracene. In the case of bacteria isolated from mixed PAHs, the results showed that
most of the napthalene was degraded by isolated strains with the highest average degradation
rate followed by acenapthylene, acenapthene, fluorene, phenanthrene and anthracene. 377.1�781.8�781�+
D4ff + c\,cpda~ition trends were observed in the study could be attributed to the different
subsr , i,lo\~ir 'Led during isolation process. Interaction through cometabolism and synergistic
ocolq bacteria strains isolated from single substrate. Thus, only synergistic interaction
was oL, :a 77ed for bacteria isolated from mixed substrate. Corynebacterium urolyticum
re\e;;ed I,, be the best strain in degrading PAHs. The experimental results have led to a model
conccl~t desclibing I'AHs degradation
Multipath optimized link state routing for mobile ad hoc networks
International audienceMultipath routing protocols for Mobile Ad hoc NETwork (MANET) address the problem of scalability, security (confidentiality and integrity), lifetime of networks, instability of wireless transmissions, and their adaptation to applications. Our protocol, called MP-OLSR (MultiPath OLSR), is a multipath routing protocol based on OLSR. The Multipath Dijkstra Algorithm is proposed to obtain multiple paths. The algorithm gains great flexibility and extensibility by employing different link metrics and cost functions. In addition, route recovery and loop detection are implemented in MP-OLSR in order to improve quality of service regarding OLSR. The backward compatibility with OLSR based on IP source routing is also studied. Simulation based on Qualnet simulator is performed in different scenarios. A testbed is also set up to validate the protocol in real world. The results reveal that MP-OLSR is suitable for mobile, large and dense networks with large traffic, and could satisfy critical multimedia applications with high on time constraints
Duplicating RTP streams
Packet loss is undesirable for real-time multimedia sessions but can
occur due to a variety of reasons including unplanned network
outages. In unicast transmissions, recovering from such an outage
can be difficult depending on the outage duration, due to the
potentially large number of missing packets. In multicast
transmissions, recovery is even more challenging as many receivers
could be impacted by the outage. For this challenge, one solution
that does not incur unbounded delay is to duplicate the packets and
send them in separate redundant streams, provided that the underlying
network satisfies certain requirements. This document explains how
Real-time Transport Protocol (RTP) streams can be duplicated without
breaking RTP or RTP Control Protocol (RTCP) rule
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