4,909 research outputs found
Energy management in communication networks: a journey through modelling and optimization glasses
The widespread proliferation of Internet and wireless applications has
produced a significant increase of ICT energy footprint. As a response, in the
last five years, significant efforts have been undertaken to include
energy-awareness into network management. Several green networking frameworks
have been proposed by carefully managing the network routing and the power
state of network devices.
Even though approaches proposed differ based on network technologies and
sleep modes of nodes and interfaces, they all aim at tailoring the active
network resources to the varying traffic needs in order to minimize energy
consumption. From a modeling point of view, this has several commonalities with
classical network design and routing problems, even if with different
objectives and in a dynamic context.
With most researchers focused on addressing the complex and crucial
technological aspects of green networking schemes, there has been so far little
attention on understanding the modeling similarities and differences of
proposed solutions. This paper fills the gap surveying the literature with
optimization modeling glasses, following a tutorial approach that guides
through the different components of the models with a unified symbolism. A
detailed classification of the previous work based on the modeling issues
included is also proposed
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
A Survey on the Contributions of Software-Defined Networking to Traffic Engineering
Since the appearance of OpenFlow back in 2008, software-defined networking (SDN) has gained momentum. Although there are some discrepancies between the standards developing organizations working with SDN about what SDN is and how it is defined, they all outline traffic engineering (TE) as a key application. One of the most common objectives of TE is the congestion minimization, where techniques such as traffic splitting among multiple paths or advanced reservation systems are used. In such a scenario, this manuscript surveys the role of a comprehensive list of SDN protocols in TE solutions, in order to assess how these protocols can benefit TE. The SDN protocols have been categorized using the SDN architecture proposed by the open networking foundation, which differentiates among data-controller plane interfaces, application-controller plane interfaces, and management interfaces, in order to state how the interface type in which they operate influences TE. In addition, the impact of the SDN protocols on TE has been evaluated by comparing them with the path computation element (PCE)-based architecture. The PCE-based architecture has been selected to measure the impact of SDN on TE because it is the most novel TE architecture until the date, and because it already defines a set of metrics to measure the performance of TE solutions. We conclude that using the three types of interfaces simultaneously will result in more powerful and enhanced TE solutions, since they benefit TE in complementary ways.European Commission through the Horizon 2020 Research and Innovation Programme (GN4) under Grant 691567
Spanish Ministry of Economy and Competitiveness under the Secure Deployment of Services Over SDN and NFV-based Networks Project S&NSEC under Grant TEC2013-47960-C4-3-
QoS multicast tree construction in IP/DWDM optical internet by bio-inspired algorithms
Copyright @ Elsevier Ltd. All rights reserved.In this paper, two bio-inspired Quality of Service (QoS) multicast algorithms are proposed in IP over dense wavelength division multiplexing (DWDM) optical Internet. Given a QoS multicast request and the delay interval required by the application, both algorithms are able to find a flexible QoS-based cost suboptimal routing tree. They first construct the multicast trees based on ant colony optimization and artificial immune algorithm, respectively. Then a dedicated wavelength assignment algorithm is proposed to assign wavelengths to the trees aiming to minimize the delay of the wavelength conversion. In both algorithms, multicast routing and wavelength assignment are integrated into a single process. Therefore, they can find the multicast trees on which the least wavelength conversion delay is achieved. Load balance is also considered in both algorithms. Simulation results show that these two bio-inspired algorithms can construct high performance QoS routing trees for multicast applications in IP/DWDM optical Internet.This work was supported in part ny the Program for New Century Excellent Talents in University, the Engineering and Physical Sciences Research Council (EPSRC) of UK under Grant EP/E060722/1, the National Natural Science Foundation of China under Grant no. 60673159 and 70671020, the National High-Tech Reasearch and Development Plan of China under Grant no. 2007AA041201, and the Specialized Research Fund for the Doctoral Program of Higher Education under Grant no. 20070145017
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
- …