Papers by Akbar Ghaffarpour Rahbar
Due to its finer granularity, optical packet switching can efficiently use the bandwidth provided... more Due to its finer granularity, optical packet switching can efficiently use the bandwidth provided by all-optical networking. This research develops a new framework to manage the bandwidth in buffer-less slotted all-optical packet-switched networks suitable for the next generation IP networks where the quality of service must be addressed. We first present an ingress switch architecture along with a new control and signaling structure for the slotted-OPS network. Then we design different components of our ingress switch architecture including packet scheduling, retransmission management, and bandwidth access units. A class-based packet scheduling is designed to reduce the inter-transmission time from different source routers, and to provide packet differentiation so that fairness issues for DiffServ support are addressed and resolved. The contention problem at the core switch is studied. Inexpensive contention avoidance and resolution schemes in the optical domain are considered. For...
Computer Networks, 2021
Abstract Due to the huge amount of traffic passing in an Elastic Optical Network (EON), an unpred... more Abstract Due to the huge amount of traffic passing in an Elastic Optical Network (EON), an unpredictable failure may lead to loss of huge amount of data. It is important to have an efficient strategy to recover the affected connections within the smallest possible time and restoring the whole requested bandwidth. In this paper, a proactive restoration mechanism with low re-provisioning (PR-LR) time is proposed that can fast the recovery process of the disrupted connections by precomputing some parts of the recovery phase. In addition, the PR-LR mechanism requires fewer redundant resources than dedicated-based algorithms and provides low computing load. The PR-LR algorithm decreases the computing load by computing the backup paths of delay-sensitive connections before failure on the best-effort resources, but it does not reserve these backup paths until a failure occurs. The simulation results demonstrate that the PR-LR mechanism can reduce the computing load almost 86% at high traffic loads and 96% at low traffic loads in comparison to the FR-TP algorithm proposed in [1] .
Wireless Personal Communications, 2019
Clustering could be one of the important approaches in saving energy and load balancing in IoT ne... more Clustering could be one of the important approaches in saving energy and load balancing in IoT networks with high density. This paper uses these two factors to improve the network performance and network routing scheme. This paper proposes a Double Leveled Unequal Clustering routing protocol in which traffic load is shared among cluster members to reduce the energy consumption and dropping probability in crucial nodes by sending packets independent of cluster head. A new clustering approach is also proposed that optimally creates unequal-sized clusters with the lowest common spaces between clusters to reduce the number of cluster heads. This approach aims to fulfill the following purposes: decrease the number of clusters to reduce the number of cluster heads and thus reduce the load on crucial nodes, reduce the energy consumption with optimizing the created clusters, optimize the channel bandwidth usage, reduce the interference between control packets by avoiding congestion using framing times, control the redundant control packets by descending the number of reclusterings, and decrease the drop timeout (i.e., whether a packet can wait for a time duration to be sent. If it cannot wait, it will be dropped automatically) by simultaneous transmissions as well as drop of interference by utilizing multichannel approach. In addition, nodes can turn off their radios in the semi-sleep mode for saving their energy within their idle times. In this way, overall lifetime of the network can be increased by enhancing lifetime of the nodes. According to simulation results, under the proposed approach, throughput of the network increases while the energy consumption decreases due to less reclustering.
Optical Switching and Networking, 2016
With exponential growth of users traffic demands, the efficient and cost-effective usage of bandw... more With exponential growth of users traffic demands, the efficient and cost-effective usage of bandwidth and spectrum plays an important role to improve service provisioning. This study first reviews different bandwidth granularities in optical networks. Each type of optical networks has its basic traffic unit and granularity. From this viewpoint, the optical networks are divided into fixed-grid and flex-grid networks. Fixed-grid networks (like OPS, OBS, ź) have rigid nature and inflexibly assign resources to demands. However, flex-grid networks have fine nature and flexibly assign the resources to demands to avoid wasting of resources. This difference is based on modulation format. Optical frequency division multiplex (OFDM) provides superior advantages of high spectrum efficiency, robustness against inter-carrier and inter-symbol interference, adaptability to server channel conditions, and so on. An elastic optical network (EON) is a flex-grid network. One efficient type of EON is OFDM-based EON that is able to allocate the available resources in a network according to users' demands. Therefore, it makes the network more efficient and flexible. Besides, EON generates elastic optical paths (the paths with variable bit rates), and divides available spectrum flexibly according to traffic demands of clients. In this paper, the bandwidth granularity of each optical network is studied. In addition, we propose a cost model to compare the costs of SLICE networks and conventional networks. Finally, an Integer Linear Programming (ILP) is presented to tolerate the desired blocking probability, while minimizing the network cost.
Optical Switching and Networking, 2015
Optical packets contention in optical packet switched (OPS) networks can lead to Optical packet l... more Optical packets contention in optical packet switched (OPS) networks can lead to Optical packet loss which will reduce network performance. In this paper, a new contention avoidance technique is proposed which utilizes the combination of traffic shaping at ingress switches and a time slot reservation technique using the coordination of egress switches. This novel protocol is called egress coordination OPS (EGCOPS) suitable for buffer-less slotted-OPS networks. Simulation results show that the EGCOPS outperforms the original slotted-OPS protocol in terms of optical packet loss rate (PLR), with or without using wavelength conversion. However, the packet shaping feature of EGCOPS can increase the delay of users' packets at the queues of ingress switches. There is a trade-off between the PLR improvement and the additional delay applied to the users' packets. Still, EGCOPS parameters can be selected in such a way that additional delay can be tolerable by users' applications.
2008 International Symposium on Telecommunications, 2008
We explain the authentication and key agreement protocols for third-generation (3G) wireless comm... more We explain the authentication and key agreement protocols for third-generation (3G) wireless communications. This protocol is known as 3GPP-AKA. We show this protocol is vulnerable to false base station attacks, and therefore, it needs synchronization between MS (mobile station) and HN (home network) that increases the complexity of system. Then, we analyze two techniques which are called adaptive protocol for AKA and extension of AKA. Any of these techniques eliminate some of the weaknesses of 3GPP-AKA. We combine these two techniques and propose a new technique, called improved adaptive protocol for AKA (IAP-AKA). We show this technique can be a good successor for 3GPP-AKA by eliminating synchronization, bandwidth wastage, and vulnerability to false base station attacks.
2008 International Symposium on High Capacity Optical Networks and Enabling Technologies, 2008
Heuristic Surveillance of Targets in Sensor Networks Saeed Kamel and Akbar Ghaffar Pour Rahbar Co... more Heuristic Surveillance of Targets in Sensor Networks Saeed Kamel and Akbar Ghaffar Pour Rahbar Computer Networks Research Lab, Electrical Engineering Department, Sahand University of Technology, Tabriz, Iran. Emails: {saeed [email protected], ghaffarpourgsut.ac.ir} ...
2008 International Symposium on High Capacity Optical Networks and Enabling Technologies, 2008
Abstract The need for survivability in optical networks is becoming more and more important becau... more Abstract The need for survivability in optical networks is becoming more and more important because of the huge amount of aggregated traffic that is carried in an optical network. A number of protection schemes have been proposed for mesh networks, where their main objective is to provide a network that can restore a failure quickly and efficiently via a simple automated system. In this paper, we review and compare the protection schemes suitable for multicast traffic in optical networks with mesh topology. The schemes are compared with ...
IEEE Transactions on Circuits and Systems for Video Technology, 2013
A critical challenge for video-on-demand (VoD) services is to provide an entertainment service wi... more A critical challenge for video-on-demand (VoD) services is to provide an entertainment service with minimum playback delay. A passive optical network (PON) that employs a high-speed optical fiber from an optical line terminal (OLT) to a number of optical network units (ONUs) can offer high bandwidth for multimedia applications (such as VoD services) in an access network. In this paper, we propose two novel video streaming techniques, called OLT broadcasting with ONU fast patching (BFP) and prediction-based OLT broadcasting and ONU fast patching (PBFP). The BFP scheme utilizes the ONU fast patching scheme at each ONU, and proposes a heuristic algorithm to find near optimum solutions of related optimization problem so that the worst-case playback delay (WPD) is minimized. The PBFP adds a prediction level for video popularity to the BFP scheme and uses a seamless channel transition technique to seamlessly change the number of channels allocated to videos. We study the efficiency of the proposed schemes when they are used in a shared wavelength division multiplexed passive optical network (Shared-WDM-PON) that adapts the broadcast nature of a GPON's downstream wavelength to WDM-PONs. Our simulation results indicate that the proposed schemes can improve both WPD and average playback delay performance parameters. Index Terms-Broadcasting, multicasting, passive optical network (PON), patching, video-on-demand (VoD). Nomenclature D i Duration of watching video i from 1 to L i in minutes e The number of unassigned patching channels G l The group of segments from S 1 to S l i The counter of video titles id ij The interest degree of video i at ONU j j The counter of ONUs k The number of video segments L i The length of video i in minutes l The counter of patching channels M Total number of video titles in video server N Total number of ONUs
IEEE Communications Surveys & Tutorials, 2012
Since light-paths are the basic connections in wavelength routed networks, their effective establ... more Since light-paths are the basic connections in wavelength routed networks, their effective establishment is very important. Routing and Wavelength Assignment (RWA) techniques can be divided into two categories. The first category (pure RWA) concentrates on setting up light-paths under the assumption of an ideal physical layer. However, this assumption could be suitable for opaque networks, where a signal is regenerated at each optical switch along its path. On the other hand, as an optical signal propagates along a light-path to its destination in a transparent (all-optical) network, the signal's quality degrades because there is no signal regeneration, thus increasing Bit-Error-Rate (BER) of the signal. However, users would not accept a light-path with a high BER. Even it is not acceptable if the establishment of a light-path causes the BER of other existing light-paths to become unacceptably high. Therefore, considering physical layer impairments, the quality of a light-path must be checked during the light-path setup in the second category. In this article, the operations of dynamic RWA techniques proposed in transparent networks for the second category are reviewed in detail. These techniques are called Quality of Transmission Aware (QoT-aware) RWA and are grouped in two groups: integrated QoT and RWA, and QoT after Pure RWA. Each group can be further divided into direct modelling and indirect modelling subgroups. A comprehensive discussion is also provided to compare dynamic QoT-aware RWA techniques based on different network and physical layer parameters. Index Terms-All-optical wavelength routed networks; Dynamic Routing and Wavelength Assignment (RWA), Quality of Transmission-aware (QoT-aware) RWA; Integrated QoT and RWA; QoT after a pure RWA.
The spectrally and spatially flexible optical networks (SS-FON) are the promising solution for fu... more The spectrally and spatially flexible optical networks (SS-FON) are the promising solution for future optical transport networks. The joint switching (J-Sw) paradigm is one of the possible switching schemes for SS-FON that brings optical component integration alongside with acceptable networking performance. The network planning of J-Sw is investigated in this paper by introducing new sorting policy of connections called descending frequency width (DFW) policy. Moreover, heuristic algorithm called joint switching resource allocation (JSRA) algorithm is introduced. The JSRA performance initiated with DFW is evaluated to find the near optimal solution of resource allocation thorough simulation for small size network and one topology of real network. The obtained results indicate that DFW shows better performance than other sorting policies.
Abstract—Reducing the traffic volume of location updating is a critical issue for tracking mobile... more Abstract—Reducing the traffic volume of location updating is a critical issue for tracking mobile users in a cellular network. Besides, when user x wants to communicate with user y, the location of user y must be extracted from databases. There-fore, one or more databases must be accessed for updating, recording, deleting, and searching. Thus, the most important criterion of a location tracking algorithm is to provide a small database access time. In this paper, we propose a new loca-tion tracking scheme, called Virtual Overlap Region with For-warding Pointer (VF), and compare the number of database accesses required for updating, deleting, and searching opera-tions for the proposed scheme and other approaches proposed for cellular networks. Our VF scheme like Overlap Region scheme reduces the updating information when a user fre-quently moves in boundaries of LAs. Unlike Overlap Region, the VF can reduce number of database accesses for searching users ’ information. Keywords—Cellul...
Journal of telecommunications and information technology, 2012
Reducing the traffic volume of location updating is a critical issue for tracking mobile users in... more Reducing the traffic volume of location updating is a critical issue for tracking mobile users in a cellular network. Besides, when user x wants to communicate with user y, the location of user y must be extracted from databases. Therefore, one or more databases must be accessed for updating, recording, deleting, and searching. Thus, the most important criterion of a location tracking algorithm is to provide a small database access time. In this paper, we propose a new location tracking scheme, called Virtual Overlap Region with Forwarding Pointer (VF), and compare the number of database accesses required for updating, deleting, and searching operations for the proposed scheme and other approaches proposed for cellular networks. Our VF scheme like Overlap Region scheme reduces the updating information when a user frequently moves in boundaries of LAs. Unlike Overlap Region, the VF can reduce number of database accesses for searching users’ information. Keywords—Cellular networks, de...
2007 International Symposium on High Capacity Optical Networks and Enabling Technologies
... Long-hop Connections in Bufferless OPS Networks Akbar Ghaffar Pour Rahbar ... [17] L.Wang, M.... more ... Long-hop Connections in Bufferless OPS Networks Akbar Ghaffar Pour Rahbar ... [17] L.Wang, M.Ma, and M.Hamdi, "Efficient protocols for multimedia streams on WDMA networks", J. of Lightwave Technology, 21(10), Oct.2003, 21232144. ...
Journal of telecommunications and information technology, 2015
The efficiency of cellular networks can be improved in various aspects such as energy consumption... more The efficiency of cellular networks can be improved in various aspects such as energy consumption, network capacity and interference between neighboring cells. This paper proposes a high capacity energy efficient scheme (HCEE) for data transmission in cellular networks in a country area. In this paper, the authors obtain a new equation to characterize the minimal required output power for traffic transmission between a base station (BS) and a mobile user (MU) based on the MU distance from the BS. Also, the cells boundaries (the boundary of overlapping areas of neighboring cells) by two static and dynamic approaches are specified. This work helps for better frequency allocation to MUs and allows increasing network capacity. In this paper, the analytical modeling in order to formulate the HCEE algorithm and evaluate its performance is used. The performance evaluation results show the simplicity of the HCEE algorithm and its effect on energy consumption decline, network capacity enhanc...
Optical Fiber Technology
Abstract Space Division Multiplexing Elastic Optical Networks (SDM-EONs) has been presented to pr... more Abstract Space Division Multiplexing Elastic Optical Networks (SDM-EONs) has been presented to provide flexibility and high speed transmission to increase network capacity and optimal use of network resources. Dynamic establishment and release of connections causes fragmentation in EONs, thus increasing blocking probability as a result of increased fragmentation. In this paper, we present three novel algorithms that focus on how to allocate resources in SDM-EONs under Multi-Core Fiber (MCF) in order to reduce blocking probability by reducing bandwidth fragmentation. The Core Classification Aware of Fragmentation (CCAF) is a method based on the core classification mechanism that uses the concept of demand splitting and a cost function to determine the appropriate spectral space for a new request. The Fragmentation Aware Spectrum and Core Assignment (FASCA-without priority) is a routing and spectrum allocation method that uses a cost function to specify the appropriate spectral space to improve spectrum efficiency and reduce fragmentation. The Fragmentation Aware Spectrum and Core Assignment (FASCA-with priority) is a routing and spectrum allocation method that considers priority of requests to improve spectrum efficiency and reduce fragmentation. Simulation results show that the proposed CCAF algorithm can achieve better performance compared with the FASCA-without priority and FASCA-with priority in terms of blocking probability and spectrum utilization. Moreover, FASCA-without priority can provide better performance than FASCA-with priority.
Computer Networks
Abstract Elastic optical networks are extremely effective networks for high speed optical communi... more Abstract Elastic optical networks are extremely effective networks for high speed optical communication owing to excessive data rate requirements in future years. Applying the space division multiplexing (SDM) technology with multi-core fibers (MCFs) provides possibility to increase the network capacity and data transmission rate as a consequence. One of the main issues in these types of networks is bandwidth fragmentation due to dynamic spectrum allocation and releasing. Management of this problem would lead to optimal use of network bandwidth. As a result, more connection demands can be accommodated. In this paper, two novel algorithms of multi-path routing are presented to improve fragmentation, where both algorithms are fragmentation-aware. The first algorithm, named Fragmentation-aware Best Splits (FABS), exploits fragmentation criteria as well as a new split technique called Best Split. In addition to these features, the second algorithm called Crosstalk-aware Best Split (CABS) considers inter-core crosstalk (XT) which is a significant issue in SDM. By employing these two algorithms and considering distance-adaptive modulation, our performance evaluation results illustrate a remarkable improvement in reducing blocking rate and enhancement of spectrum utilization.
Computer Networks
Diego (UCSD) em 2017. Pesquisador de identidades, narrativas e mitos políticos, foi orientado em ... more Diego (UCSD) em 2017. Pesquisador de identidades, narrativas e mitos políticos, foi orientado em seu doutorado por Jacques Wainberg (PUCRS) e Daniel Hallin (UCSD), quando trabalhou com o discurso do ódio e polarização em campanhas políticas. Membro do Grupo de Pesquisa em Comunicação, Emoção e Conflito (PUCRS/CNPq), tem apresentado e publicado trabalhos no Brasil e no exterior, participando de Congressos e Seminários internacionais como
Optical Switching and Networking
Abstract One of the newest technologies to qualify transmission capacity of optical backbone netw... more Abstract One of the newest technologies to qualify transmission capacity of optical backbone networks is Space Division Multiplexing with Elastic Optical Networks (SDM-EONs). SDM-EON has the feasibility to add flexibility to Wavelength division Multiplexing (WDM) networks. In SDM-EON, connections can be setup more efficiently than WDM networks and EON without SDM. There are challenging issues in SDM-EON as fragmentation (created due to dynamically allocating and releasing allocated bandwidth of connections over time), impairments and physical layer security vulnerabilities caused by inter-core crosstalk. In this article, we introduce three novel algorithms to resolve crosstalk and maintain physical layer security level and reduce blocking probability in SDM-EON as called Minimum Crosstalk by fragmentation per cores (Min_Cross), Minimum Fragmentation by Crosstalk per cores (Min_Frag), and Moderate fragmentation and crosstalk (Mod_Frag_Cross). We consider multi-core fibers (MCFs) in EON and study how to setup lightpaths by considering the impairments and physical layer security leaks and attacks caused by inter-core crosstalk. We investigate spectrum, and core assignment algorithms to control physical-layer security attacks in order to reduce inter-crosstalk impairments as well as reducing Blocking Probability (BP) as our performance evaluation results show.
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Papers by Akbar Ghaffarpour Rahbar