268 research outputs found
Shared Risk Link Group (SRLG)-Diverse Path Provisioning Under Hybrid Service Level Agreements in Wavelength-Routed Optical Mesh Networks
The static provisioning problem in wavelength-routed optical networks has been studied for many years. However, service providers are still facing the challenges arising from the special requirements for provisioning services at the optical layer. In this paper, we incorporate some realistic constraints into the static provisioning problem, and formulate it under different network resource availability conditions.We consider three classes of shared risk link group (SRLG)-diverse path protection schemes: dedicated, shared, and unprotected. We associate with each connection request a lightpath length constraint and a revenue value. When the network resources are not sufficient to accommodate all the connection requests, the static provisioning problem is formulated as a revenue maximization problem, whose objective is maximizing the total revenue value. When the network has sufficient resources, the problem becomes a capacity minimization problem with the objective of minimizing the number of used wavelength-links. We provide integer linear programming (ILP) formulations for these problems. Because solving these ILP problems is extremely time consuming, we propose a tabu search heuristic to solve these problems within a reasonable amount of time. We also develop a rerouting optimization heuristic, which is based on previous work. Experimental results are presented to compare the solutions obtained by the tabu search heuristic and the rerouting optimization heuristic. For both problems, the tabu search heuristic outperforms the rerouting optimization heuristic
Shared Risk Link Group (SRLG)-Diverse Path Provisioning Under Hybrid Service Level Agreements in Wavelength-Routed Optical Mesh Networks
The static provisioning problem in wavelength-routed optical networks has been studied for many years. However, service providers are still facing the challenges arising from the special requirements for provisioning services at the optical layer. In this paper, we incorporate some realistic constraints into the static provisioning problem, and formulate it under different network resource availability conditions.We consider three classes of shared risk link group (SRLG)-diverse path protection schemes: dedicated, shared, and unprotected. We associate with each connection request a lightpath length constraint and a revenue value. When the network resources are not sufficient to accommodate all the connection requests, the static provisioning problem is formulated as a revenue maximization problem, whose objective is maximizing the total revenue value. When the network has sufficient resources, the problem becomes a capacity minimization problem with the objective of minimizing the number of used wavelength-links. We provide integer linear programming (ILP) formulations for these problems. Because solving these ILP problems is extremely time consuming, we propose a tabu search heuristic to solve these problems within a reasonable amount of time. We also develop a rerouting optimization heuristic, which is based on previous work. Experimental results are presented to compare the solutions obtained by the tabu search heuristic and the rerouting optimization heuristic. For both problems, the tabu search heuristic outperforms the rerouting optimization heuristic
Novel Approaches and Architecture for Survivable Optical Internet
Any unexpected disruption to WDM (Wavelength Division Multiplexing) based optical networks which carry data traffic at tera-bit per second may result in a huge loss to its end-users and the carrier itself. Thus survivability has been well-recognized as one of the most important objectives in the design of optical Internet.
This thesis proposes a novel survivable routing architecture for the optical Internet. We focus on a number of key issues that are essential to achieve the desired service scenarios, including the tasks of (a) minimizing the total number of wavelengths used for establishing working and protection paths in WDM networks; (b) minimizing the number of affected working paths in case of a link failure; (c) handling large scale WDM mesh networks; and (d) supporting both Quality of Service (QoS) and best-effort based working lightpaths. To implement the above objectives, a novel path based shared protection framework namely Group Shared protection (GSP) is proposed where the traffic matrix can be divided into multiple protection groups (PGs) based on specific grouping policy, and optimization is performed on these PGs. To the best of our knowledge this is the first work done in the area of group based WDM survivable routing approaches where not only the resource sharing is conducted among the PGs to achieve the best possible capacity efficiency, but also an integrated survivable routing framework is provided by incorporating the above objectives. Simulation results show the effectiveness of the proposed schemes
Survivable paths in multilayer networks
We consider the problem of protection in multilayer networks. In single-layer networks, a pair of disjoint paths can be used to provide protection for a source-destination pair. However, this approach cannot be directly applied to layered networks where disjoint paths may not always exist. In this paper, we take a new approach which is based on finding a set of paths that may not be disjoint but together will survive any single physical link failure. We consider the problem of finding the minimum number of survivable paths. In particular, we focus on two versions of this problem: one where the length of a path is restricted, and the other where the number of paths sharing a fiber is restricted. We prove that in general, finding the minimum survivable path set is NP-hard, whereas both of the restricted versions of the problem can be solved in polynomial time. We formulate the problems as Integer Linear Programs (ILPs), and use these formulations to develop heuristics and approximation algorithms.National Science Foundation (U.S.) (NSF grant CNS-0830961)National Science Foundation (U.S.) (NSF grant CNS-1017800)United States. Defense Threat Reduction Agency (grant HDTRA-09-1-005)United States. Defense Threat Reduction Agency (grant HDTRA1-07-1-0004
Novel Approaches and Architecture for Survivable Optical Internet
Any unexpected disruption to WDM (Wavelength Division Multiplexing) based optical networks which carry data traffic at tera-bit per second may result in a huge loss to its end-users and the carrier itself. Thus survivability has been well-recognized as one of the most important objectives in the design of optical Internet.
This thesis proposes a novel survivable routing architecture for the optical Internet. We focus on a number of key issues that are essential to achieve the desired service scenarios, including the tasks of (a) minimizing the total number of wavelengths used for establishing working and protection paths in WDM networks; (b) minimizing the number of affected working paths in case of a link failure; (c) handling large scale WDM mesh networks; and (d) supporting both Quality of Service (QoS) and best-effort based working lightpaths. To implement the above objectives, a novel path based shared protection framework namely Group Shared protection (GSP) is proposed where the traffic matrix can be divided into multiple protection groups (PGs) based on specific grouping policy, and optimization is performed on these PGs. To the best of our knowledge this is the first work done in the area of group based WDM survivable routing approaches where not only the resource sharing is conducted among the PGs to achieve the best possible capacity efficiency, but also an integrated survivable routing framework is provided by incorporating the above objectives. Simulation results show the effectiveness of the proposed schemes
Designing Survivable Wavelength Division Multiplexing (WDM) Mesh Networks
This thesis focuses on the survivable routing problem in WDM mesh networks where the objective is to minimize the total number of wavelengths used for establishing working and protection paths in the WDM networks. The past studies for survivable routing suffers from the scalability problem when the number of nodes/links or connection requests grow in the network. In this thesis, a novel path based shared protection framework namely Inter-Group Shared protection (I-GSP) is proposed where the traffic matrix can be divided into multiple protection groups (PGs) based on specific grouping policy. Optimization is performed on these PGs such that sharing of protection wavelengths is considered not only inside a PG, but between the PGs. Simulation results show that I-GSP based integer linear programming model, namely, ILP-II solves the networks in a reasonable amount of time for which a regular integer linear programming formulation, namely, ILP-I becomes computationally intractable. For most of the cases the gap between the optimal solution and the ILP-II ranges between (2-16)%. The proposed ILP-II model yields a scalable solution for the capacity planning in the survivable optical networks based on the proposed I-GSP protection architecture
Disaster Resilient Optical Core Networks
During the past few years, the number of catastrophic disasters has increased and its impact sometimes incapacitates the infrastructures within a region. The communication network infrastructure is one of the affected systems during these events. Thus, building a resilient network backbone is essential due to the big role of networks during disaster recovery operations. In this thesis, the research efforts in building a disaster-resilient network are reviewed and open issues related to building disaster-resilient networks are discussed. Large size disasters not necessarily impact the communication networks, but instead it can stimulate events that cause network performance degradation. In this regard, two open challenges that arise after disasters are considered one is the short-term capacity exhaustion and the second is the power outage.
First, the post-disaster traffic floods phenomena is considered. The impact of the traffic floods on the optical core network performance is studied. Five mitigation approaches are proposed to serve these floods and minimise the incurred blocking. The proposed approaches explore different technologies such as excess or overprovisioned capacity exploitation, traffic filtering, protection paths rerouting, rerouting all traffic and finally using the degrees of freedom offered by differentiated services. The mitigation approaches succeeded in reducing the disaster induced traffic blocking.
Second, advance reservation provisioning in an energy-efficient approach is developed. Four scenarios are considered to minimise power consumption. The scenarios exploit the flexibility provided by the sliding-window advance reservation requests. This flexibility is studied through scheduling and rescheduling scenarios. The proposed scenarios succeeded in minimising the consumed power.
Third, the sliding-window flexibility is exploited for the objective of minimising network blocking during post-disaster traffic floods. The scheduling and rescheduling scenarios are extended to overcome the capacity exhaustion and improve the network blocking. The proposed schemes minimised the incurred blocking during traffic floods by exploiting sliding window.
Fourth, building blackout resilient networks is proposed. The network performance during power outages is evaluated. A remedy approach is suggested for maximising network lifetime during blackouts. The approach attempts to reduce the required backup power supply while minimising network outages due to limited energy production. The results show that the mitigation approach succeeds in keeping the network alive during a blackout while minimising the required backup power
Survivable paths in multilayer networks
Thesis (S.M.)--Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 75-77).We consider the problem of protection in multilayer networks. In single-layer net- works, a pair of disjoint paths can be used to provide protection for a source-destination pair. However, this approach cannot be directly applied to layered networks where disjoint paths may not always exist. In this thesis, we take a new approach which is based on finding a set of paths that may not be disjoint but together will survive any single physical link failure. First, we consider the problem of finding the minimum number of survivable paths. In particular, we focus on two versions of this problem: one where the length of a path is restricted, and the other where the number of paths sharing a fiber is restricted. We prove that in general, finding the minimum survivable path set is NP-hard, whereas both of the restricted versions of the problem can be solved in polynomial time. We formulate the problem as Integer Linear Programs (ILPs), and use these formulations to develop heuristics and approximation algorithms. Next, we consider the problem of finding a set of survivable paths that uses the minimum number of fibers. We show that this problem is NP-hard in general, and develop heuristics and approximation algorithms with provable approximation bounds. We also model the dependency of communication networks on the power grid as a layered network, and investigate the survivability of communication networks in this layered setting. Finally, we present simulation results comparing the different algorithms.by Marzieh Parandehgheibi.S.M
Virtualisation and resource allocation in MECEnabled metro optical networks
The appearance of new network services and the ever-increasing network traffic and number
of connected devices will push the evolution of current communication networks towards the
Future Internet.
In the area of optical networks, wavelength routed optical networks (WRONs) are evolving
to elastic optical networks (EONs) in which, thanks to the use of OFDM or Nyquist WDM,
it is possible to create super-channels with custom-size bandwidth. The basic element in
these networks is the lightpath, i.e., all-optical circuits between two network nodes. The
establishment of lightpaths requires the selection of the route that they will follow and the
portion of the spectrum to be used in order to carry the requested traffic from the source to
the destination node. That problem is known as the routing and spectrum assignment (RSA)
problem, and new algorithms must be proposed to address this design problem.
Some early studies on elastic optical networks studied gridless scenarios, in which a slice
of spectrum of variable size is assigned to a request. However, the most common approach to
the spectrum allocation is to divide the spectrum into slots of fixed width and allocate multiple,
consecutive spectrum slots to each lightpath, depending on the requested bandwidth. Moreover,
EONs also allow the proposal of more flexible routing and spectrum assignment techniques,
like the split-spectrum approach in which the request is divided into multiple "sub-lightpaths".
In this thesis, four RSA algorithms are proposed combining two different levels of
flexibility with the well-known k-shortest paths and first fit heuristics. After comparing the
performance of those methods, a novel spectrum assignment technique, Best Gap, is proposed
to overcome the inefficiencies emerged when combining the first fit heuristic with highly
flexible networks. A simulation study is presented to demonstrate that, thanks to the use of
Best Gap, EONs can exploit the network flexibility and reduce the blocking ratio.
On the other hand, operators must face profound architectural changes to increase the
adaptability and flexibility of networks and ease their management. Thanks to the use of
network function virtualisation (NFV), the necessary network functions that must be applied
to offer a service can be deployed as virtual appliances hosted by commodity servers, which
can be located in data centres, network nodes or even end-user premises. The appearance of
new computation and networking paradigms, like multi-access edge computing (MEC), may
facilitate the adaptation of communication networks to the new demands. Furthermore, the
use of MEC technology will enable the possibility of installing those virtual network functions
(VNFs) not only at data centres (DCs) and central offices (COs), traditional hosts of VFNs, but
also at the edge nodes of the network. Since data processing is performed closer to the enduser,
the latency associated to each service connection request can be reduced. MEC nodes
will be usually connected between them and with the DCs and COs by optical networks.
In such a scenario, deploying a network service requires completing two phases: the
VNF-placement, i.e., deciding the number and location of VNFs, and the VNF-chaining,
i.e., connecting the VNFs that the traffic associated to a service must transverse in order to
establish the connection. In the chaining process, not only the existence of VNFs with available
processing capacity, but the availability of network resources must be taken into account to
avoid the rejection of the connection request. Taking into consideration that the backhaul of
this scenario will be usually based on WRONs or EONs, it is necessary to design the virtual
topology (i.e., the set of lightpaths established in the networks) in order to transport the tra c
from one node to another. The process of designing the virtual topology includes deciding the
number of connections or lightpaths, allocating them a route and spectral resources, and finally
grooming the traffic into the created lightpaths.
Lastly, a failure in the equipment of a node in an NFV environment can cause the
disruption of the SCs traversing the node. This can cause the loss of huge amounts of data
and affect thousands of end-users. In consequence, it is key to provide the network with faultmanagement
techniques able to guarantee the resilience of the established connections when a
node fails.
For the mentioned reasons, it is necessary to design orchestration algorithms which solve
the VNF-placement, chaining and network resource allocation problems in 5G networks
with optical backhaul. Moreover, some versions of those algorithms must also implements
protection techniques to guarantee the resilience system in case of failure.
This thesis makes contribution in that line. Firstly, a genetic algorithm is proposed to solve
the VNF-placement and VNF-chaining problems in a 5G network with optical backhaul based
on star topology: GASM (genetic algorithm for effective service mapping). Then, we propose
a modification of that algorithm in order to be applied to dynamic scenarios in which the
reconfiguration of the planning is allowed. Furthermore, we enhanced the modified algorithm
to include a learning step, with the objective of improving the performance of the algorithm.
In this thesis, we also propose an algorithm to solve not only the VNF-placement and
VNF-chaining problems but also the design of the virtual topology, considering that a WRON
is deployed as the backhaul network connecting MEC nodes and CO. Moreover, a version
including individual VNF protection against node failure has been also proposed and the
effect of using shared/dedicated and end-to-end SC/individual VNF protection schemes are
also analysed.
Finally, a new algorithm that solves the VNF-placement and chaining problems and
the virtual topology design implementing a new chaining technique is also proposed.
Its corresponding versions implementing individual VNF protection are also presented.
Furthermore, since the method works with any type of WDM mesh topologies, a technoeconomic
study is presented to compare the effect of using different network topologies in
both the network performance and cost.Departamento de Teoría de la Señal y Comunicaciones e Ingeniería TelemáticaDoctorado en Tecnologías de la Información y las Telecomunicacione
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