65,719 research outputs found
ILP formulations for p-cycle design without candidate cycle enumeration
The concept of p-cycle (preconfigured protection cycle) allows fast and efficient span protection in wavelength division multiplexing (WDM) mesh networks. To design p-cycles for a given network, conventional algorithms need to enumerate cycles in the network to form a candidate set, and then use an integer linear program (ILP) to find a set of p-cycles from the candidate set. Because the size of the candidate set increases exponentially with the network size, candidate cycle enumeration introduces a huge number of ILP variables and slows down the optimization process. In this paper, we focus on p-cycle design without candidate cycle enumeration. Three ILPs for solving the problem of spare capacity placement (SCP) are first formulated. They are based on recursion, flow conservation, and cycle exclusion, respectively. We show that the number of ILP variables/constraints in our cycle exclusion approach only increases linearly with the network size. Then, based on cycle exclusion, we formulate an ILP for solving the joint capacity placement (JCP) problem. Numerical results show that our ILPs are very efficient in generating p-cycle solutions. © 2009 IEEE.published_or_final_versio
p-Cycle Based Protection in WDM Mesh Networks
Abstract
p-Cycle Based Protection in WDM Mesh Networks
Honghui Li, Ph.D.
Concordia University, 2012
WDM techniques enable single fiber to carry huge amount of data. However, optical WDM
networks are prone to failures, and therefore survivability is a very important requirement
in the design of optical networks. In the context of network survivability, p-cycle based
schemes attracted extensive research interests as they well balance the recovery speed and
the capacity efficiency. Towards the design of p-cycle based survivableWDM mesh networks,
some issues still need to be addressed. The conventional p-cycle design models and solution
methods suffers from scalability issues. Besides, most studies on the design of p-cycle
based schemes only cope with single link failures without any concern about single node
failures. Moreover, loop backs may exist in the recovery paths along p-cycles, which lead
to unnecessary stretching of the recovery path lengths.
This thesis investigates the scalable and efficient design of segment p-cycles against single
link failures. The optimization models and their solutions rely on large-scale optimization
techniques, namely, Column Generation (CG) modeling and solution, where segment pcycle
candidates are dynamically generated during the optimization process. To ensure full
node protection in the context of link p-cycles, we propose an efficient protection scheme,
called node p-cycles, and develop a scalable optimization design model. It is shown that,
depending on the network topology, node p-cycles sometimes outperform path p-cycles in
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terms of capacity efficiency. Also, an enhanced segment p-cycle scheme is proposed, entitled
segment Np-cycles, for full link and node protection. Again, the CG-based optimization
models are developed for the design of segment Np-cycles. Two objectives are considered,
minimizing the spare capacity usage and minimizing the CAPEX cost. It is shown that
segment Np-cycles can ensure full node protection with marginal extra cost in comparison
with segment p-cycles for link protection. Segment Np-cycles provide faster recovery speed
than path p-cycles although they are slightly more costly than path p-cycles. Furthermore,
we propose the shortcut p-cycle scheme, i.e., p-cycles free of loop backs for full node and
link protection, in addition to shortcuts in the protection paths. A CG-based optimization
model for the design of shortcut p-cycles is formulated as well. It is shown that, for full node
protection, shortcut p-cycles have advantages over path p-cycles with respect to capacity
efficiency and recovery speed. We have studied a whole sequence of protection schemes
from link p-cycles to path p-cycles, and concluded that the best compromise is the segment
Np-cycle scheme for full node protection with respect to capacity efficiency and recovery
time. Therefore, this thesis offers to network operators several interesting alternatives to
path p-cycles in the design of survivable WDM mesh networks against any single link/node
failures
Heuristic Solution to Protect Communications in WDM Networks using P-cycles
Optical WDM mesh networks are able to transport huge amount of information.
The use of such technology however poses the problem of protection against
failures such as fibre cuts. One of the principal methods for link protection
used in optical WDM networks is pre-configured protection cycle (p-cycle). The
major problem of this method of protection resides in finding the optimal set
of p-cycles which protect the network for a given distribution of working
capacity. Existing heuristics generate a large set of p-cycle candidates which
are entirely independent of the network state, and from then the good sub-set
of p-cycles which will protect the network is selected. In this paper, we
propose a new algorithm of generation of p-cycles based on the incremental
aggregation of the shortest cycles. Our generation of p-cycles depends on the
state of the network. This enables us to choose an efficient set of p-cycles
which will protect the network. The set of p-cycles that we generate is the
final set which will protect the network, in other words our heuristic does not
go through the additional step of p-cycle selectio
Practical issues for the implementation of survivability and recovery techniques in optical networks
Optimization Methods for Optical Long-Haul and Access Networks
Optical communications based on fiber optics and the associated technologies have seen remarkable progress over the past two decades. Widespread deployment of optical
fiber has been witnessed in backbone and metro networks as well as access segments connecting to customer premises and homes. Designing and developing a reliable, robust and efficient end-to-end optical communication system have thus
emerged as topics of utmost importance both to researchers and network operators. To fulfill these requirements, various problems have surfaced and received attention,
such as network planning, capacity placement, traffic grooming, traffic scheduling, and bandwidth allocation. The optimal network design aims at addressing (one or more of) these problems based on some optimization objectives. In this thesis, we consider two of the most important problems in optical networks; namely the survivability in optical long-haul networks and the problem of bandwidth allocation and scheduling in optical access networks. For the former, we present efficient and accurate models for availability-aware design and service provisioning in p-cycle based survivable networks. We also derive optimization models for survivable network design based on p-trail, a more general protection structure, and compare its performance with p-cycles. Indeed, major cost savings can be obtained when the optical access and long-haul subnetworks become closer to each other by means of consolidation of access and metro networks. As this distance between long-haul and access networks reduces, and the need and expectations from passive optical access networks (PONs) soar, it becomes crucial to efficiently manage bandwidth in the access while providing the desired level of service availability in the long-haul backbone. We therefore address in this thesis the problem of bandwidth management and scheduling in passive optical networks; we design efficient joint and non-joint scheduling and bandwidth allocation methods for multichannel PON as well as next generation 10Gbps Ethernet PON (10G-EPON) while addressing the problem of coexistence between 10G-EPONs
and multichannel PONs
Dynamic Information Flow Tracking on Multicores
Dynamic Information Flow Tracking (DIFT) is a promising technique for detecting software attacks. Due to the computationally intensive nature of the technique, prior efficient implementations [21, 6] rely on specialized hardware support whose only purpose is to enable DIFT. Alternatively, prior software implementations are either too slow [17, 15] resulting in execution time increases as much as four fold for SPEC integer programs or they are not transparent [31] requiring source code modifications. In this paper, we propose the use of chip multiprocessors (CMP) to perform DIFT transparently and efficiently. We spawn a helper thread that is scheduled on a separate core and is only responsible for performing information flow tracking operations. This entails the communication of registers and flags between the main and helper threads. We explore software (shared memory) and hardware (dedicated interconnect) approaches to enable this communication. Finally, we propose a novel application of the DIFT infrastructure where, in addition to the detection of the software attack, DIFT assists in the process of identifying the cause of the bug in the code that enabled the exploit in the first place. We conducted detailed simulations to evaluate the overhead for performing DIFT and found that to be 48 % for SPEC integer programs
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