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Iqbal, Z., Almeida, L. & Ashjaei, S. M. (2017). Analyzing the Efficiency of Sporadic Reservations on Ethernet with FTT-SE. In: International Conference on Emerging Technologies And Factory Automation ETFA'17: . Paper presented at International Conference on Emerging Technologies And Factory Automation ETFA'17, 12 Aug 2017, Limassol, Cyprus.
Öppna denna publikation i ny flik eller fönster >>Analyzing the Efficiency of Sporadic Reservations on Ethernet with FTT-SE
2017 (Engelska)Ingår i: International Conference on Emerging Technologies And Factory Automation ETFA'17, 2017Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

Ethernet is a promising candidate for networking real-time embedded systems such as automobiles, and it is already used in several embedded scopes, such as airplanes and trains. Moreover, its higher bandwidth enables applications made of dispersed embedded systems that exchange large amounts of data through the so-called Internet-of-Things, such as wide-area video sensing. In this realm, network reservations are an important design element that favor composability in the time domain thereby supporting the design of complex systems. However, reservations may impact negatively on the network bandwidth efficiency due to over-specification, particularly when they are designed to meet worst-case delay constraints. In this work, we use a specific Ethernet protocol that provides real-time reservations, namely FTT-SE, and we assess through extensive simulations the efficiency of a worst-case network delay analysis for sporadic reservations associated to asynchronous messages. Essentially, we compare the analytical worst-case delay with the one observed in the simulations using two data sets comprising up to 20000 and 100000 message sets, respectively, and we change the system configuration, namely properties of the message sets and network and protocol configuration parameters. We find that the analysis is accurate, i.e. matches observations, for a significant percentage of messages in the message sets (up to 60% on average). Conversely, we found that a small percentage of message sets (below 6%) generated rather pessimistic analytic estimates exceeding the observations by 6 times, thus with a negative impact on efficiency. The results we present in the paper, particularly their distributions, inform system designers of how to tune their designs to improve network bandwidth efficiency under strict timing constraints.

Nationell ämneskategori
Datorsystem
Identifikatorer
urn:nbn:se:mdh:diva-35515 (URN)10.1109/ETFA.2017.8247607 (DOI)000427812000042 ()2-s2.0-85044444451 (Scopus ID)9781509065059 (ISBN)
Konferens
International Conference on Emerging Technologies And Factory Automation ETFA'17, 12 Aug 2017, Limassol, Cyprus
Projekt
PRESS - Predictable Embedded Software Systems
Tillgänglig från: 2017-06-01 Skapad: 2017-06-01 Senast uppdaterad: 2019-06-25Bibliografiskt granskad
Ashjaei, M., Khalilzad, N., Mubeen, S., Behnam, M., Sander, I., Almeida, L. & Nolte, T. (2017). Designing End-to-end Resource Reservations in Predictable Distributed Embedded Systems. Real-time systems, 53(6), 916-956
Öppna denna publikation i ny flik eller fönster >>Designing End-to-end Resource Reservations in Predictable Distributed Embedded Systems
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2017 (Engelska)Ingår i: Real-time systems, ISSN 0922-6443, E-ISSN 1573-1383, Vol. 53, nr 6, s. 916-956Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Contemporary distributed embedded systems in many domains have become highly complex due to ever-increasing demand on advanced computer controlled functionality. The resource reservation techniques can be effective in lowering the software complexity, ensuring predictability and allowing flexibility during the development and execution of these systems. This paper proposes a novel end-to-end resource reservation model for distributed embedded systems. In order to support the development of predictable systems using the proposed model, the paper provides a method to design resource reservations and an end-to-end timing analysis. The reservation design can be subjected to different optimization criteria with respect to runtime footprint, overhead or performance. The paper also presents and evaluates a case study to show the usability of the proposed model, reservation design method and end-to-end timing analysis. 

Nationell ämneskategori
Datorsystem
Identifikatorer
urn:nbn:se:mdh:diva-35506 (URN)10.1007/s11241-017-9283-6 (DOI)000412536700004 ()2-s2.0-85020515685 (Scopus ID)
Projekt
PRESS - Predictable Embedded Software SystemsFuture factories in the CloudPreView: Developing Predictable Vehicle Software on Multi-core
Tillgänglig från: 2017-05-31 Skapad: 2017-05-31 Senast uppdaterad: 2018-07-25Bibliografiskt granskad
Aisa, J., Fotouhi, H., Almeida, L. & Villarroel, J. L. (2016). DoTHa - A Double-threshold Hand-off Algorithm for Managing Mobility in Wireless Mesh Networks. In: 21st IEEE Conference on Emerging Technologies and Factory Automation ETFA'16: . Paper presented at 21st IEEE Conference on Emerging Technologies and Factory Automation ETFA'16, 6-9 Sep 2016, Berlin, Germany. , Article ID 7733511.
Öppna denna publikation i ny flik eller fönster >>DoTHa - A Double-threshold Hand-off Algorithm for Managing Mobility in Wireless Mesh Networks
2016 (Engelska)Ingår i: 21st IEEE Conference on Emerging Technologies and Factory Automation ETFA'16, 2016, artikel-id 7733511Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

Wireless communication will play an increasingly important role in future factory automation and process control, where the presence of mobile autonomous devices is expected to grow. However, wireless links are prone to errors due to shadowing and multi-path fading, which is even more severe in dynamic environments. These problems can be attenuated by using a mesh backbone to which mobile node connect to, using a hand-off algorithm. This solution is particularly important under real-time requirements typically found in factory automation. In this paper, we devise the Double-Threshold Hand-off (DoTHa) algorithm, a novel hand-off mechanism that triggers a hand-off in various environmental conditions. As a case study, we carry out the tele-operation of a mobile robot through a wireless mesh network in an indoor setting, using a wireless chain network protocol (WICKPro-SRT) that supports soft real-time traffic. We empirically compared DoTHa with two existing hand-off algorithms based on single and double hysteresis margin. The results revealed that DoTHa achieves Data Delivery Ratio (DDR) close to 100% whereas the single hysteresis-based hand-off suffers from frequent disconnections, dropping DDR to 88%. The double hysteresis-based hand-off shows higher ping-pong effect than DoTHa, doubling the number of hand-offs in some scenarios.

Nyckelord
Wireless mesh networks, mobility, hand-off, chain topology, soft real-time, token passing, IEEE 802.11
Nationell ämneskategori
Datorsystem
Identifikatorer
urn:nbn:se:mdh:diva-32888 (URN)10.1109/ETFA.2016.7733511 (DOI)000389524200019 ()2-s2.0-84996522079 (Scopus ID)978-1-5090-1314-2 (ISBN)
Konferens
21st IEEE Conference on Emerging Technologies and Factory Automation ETFA'16, 6-9 Sep 2016, Berlin, Germany
Projekt
READY - Research Environment for Advancing Low Latency Internet
Tillgänglig från: 2016-08-26 Skapad: 2016-08-24 Senast uppdaterad: 2017-01-05Bibliografiskt granskad
Ashjaei, M., Silva, L., Behnam, M., Pedreiras, P., Bril, R. J., Almeida, L. & Nolte, T. (2016). Improved Message Forwarding for Multi-Hop HaRTES Real-Time Ethernet Networks. Journal of Signal Processing Systems, 84(1), 47-67
Öppna denna publikation i ny flik eller fönster >>Improved Message Forwarding for Multi-Hop HaRTES Real-Time Ethernet Networks
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2016 (Engelska)Ingår i: Journal of Signal Processing Systems, ISSN 1939-8018, E-ISSN 1939-8115, Vol. 84, nr 1, s. 47-67Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Nowadays, switched Ethernet networks are used in complex systems that encompass tens to hundreds of nodes and thousands of signals. Such scenarios require multi-switch architectures where communications frequently occur in multiple hops. In this paper we investigate techniques to allow efficient multi-hop communication using HaRTES switches. These are modified Ethernet switches that provide real-time traffic scheduling, dynamic bandwidth management and temporal isolation between real-time and non-real-time traffic. This paper addresses the problem of forwarding traffic in HaRTES networks. Two methods have been recently proposed, namely Distributed Global Scheduling (DGS) that buffers traffic between switches, and Reduced Buffering Scheme (RBS), that uses immediate forwarding. In this paper, we discuss the design and implementation of RBS within HaRTES and we carry out an experimental validation with a prototype implementation. Then, we carry out a comparison between RBS and DGS using worst-case response time analysis and simulation. The comparison clearly establishes the superiority of RBS concerning end-to-end response times. In fact, with sample message sets, we achieved reductions in end-to-end delay that were as high as 80 %.

Nyckelord
Switched Ethernet, HaRTES architecture, Real-time communication, Real-time Ethernet, Response time analysis, Simulation
Nationell ämneskategori
Elektroteknik och elektronik
Identifikatorer
urn:nbn:se:mdh:diva-32178 (URN)10.1007/s11265-015-1010-8 (DOI)000376617700004 ()2-s2.0-84929118870 (Scopus ID)
Tillgänglig från: 2016-06-23 Skapad: 2016-06-23 Senast uppdaterad: 2017-11-28Bibliografiskt granskad
Ashjaei, M., Behnam, M., Almeida, L. & Nolte, T. (2016). MTU Configuration for Real-Time Switched Ethernet Networks. Journal of systems architecture, 70, 15-25
Öppna denna publikation i ny flik eller fönster >>MTU Configuration for Real-Time Switched Ethernet Networks
2016 (Engelska)Ingår i: Journal of systems architecture, ISSN 1383-7621, E-ISSN 1873-6165, Vol. 70, s. 15-25Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

In this paper, we show that in real-time switched Ethernet networks reducing the Maximum Transmission Unit (MTU) size may cause an increase or decrease in the response time of messages. This contradicting behavior arises an optimization problem for configuring the MTU size. We formulate the optimization problem in the context of the multi-hop HaRTES architecture, which is a hard real-time Ethernet protocol. As part of the solution, we propose a search-based algorithm to achieve optimum solutions. We modify the algorithm by presenting two techniques to reduce the search space. Then, we propose a heuristic algorithm with a pseudo-polynomial time complexity based on the search-based algorithm. We perform several experiments, and we show that the proposed heuristic results in an improvement regarding messages response times, compared with configuring the MTU to the maximum or minimum values. Moreover, we show in small network configurations that the heuristic performs as good as the search-based algorithm in many cases.

Nyckelord
Switched Ethernet, HaRTES, Response time analysis, MTU, Optimization
Nationell ämneskategori
Datorsystem
Identifikatorer
urn:nbn:se:mdh:diva-32840 (URN)10.1016/j.sysarc.2016.04.009 (DOI)000388061000003 ()2-s2.0-84964575162 (Scopus ID)
Projekt
PRESS - Predictable Embedded Software Systems
Tillgänglig från: 2016-08-25 Skapad: 2016-08-24 Senast uppdaterad: 2017-11-28Bibliografiskt granskad
Khalilzad, N., Ashjaei, M., Almeida, L., Behnam, M. & Nolte, T. (2015). Adaptive Multi-Resource End-to-End Reservations for Component-Based Distributed Real-Time Systems. In: ESTIMedia 2015 - 13th IEEE Symposium on Embedded Systems for Real-Time Multimedia: . Paper presented at IEEE Symposium on Embedded Systems for Real-Time Multimedia. October 8-9, 2015. Amsterdam, The Netherlands. (pp. Article number 7351772).
Öppna denna publikation i ny flik eller fönster >>Adaptive Multi-Resource End-to-End Reservations for Component-Based Distributed Real-Time Systems
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2015 (Engelska)Ingår i: ESTIMedia 2015 - 13th IEEE Symposium on Embedded Systems for Real-Time Multimedia, 2015, s. Article number 7351772-Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

Complexity in the real-time embedded softwaredomain has been growing rapidly. The component-based softwaredevelopment approach facilitates the development process of suchsoftware systems by dividing a complex system into a numberof simpler components. Resource reservation techniques havebeen widely used for providing resources to real-time softwarecomponents. In this paper we target real-time components operatingon a distributed resource infrastructure. Furthermore,we target a class of software components which demonstratedynamic resource consumption behavior. A prime example ofsuch components is a multimedia software component. In thepaper, we present a framework supporting multi-resource endto-end resource reservations. We reserve resource bandwidths onboth processor resources as well as on the network resources. Theproposed framework utilizes a Multiple Input Multiple Output(MIMO) controller which adjusts the sizes of reservations trackingthe dynamic resource demands of the software components. Finally, we present a case study using a multimedia component todemonstrate the performance and efficiency of our framework.

Nationell ämneskategori
Datorteknik
Identifikatorer
urn:nbn:se:mdh:diva-29106 (URN)10.1109/ESTIMedia.2015.7351772 (DOI)000377587200013 ()2-s2.0-84962285268 (Scopus ID)978-146738164-2 (ISBN)
Konferens
IEEE Symposium on Embedded Systems for Real-Time Multimedia. October 8-9, 2015. Amsterdam, The Netherlands.
Tillgänglig från: 2015-09-23 Skapad: 2015-09-23 Senast uppdaterad: 2018-01-11Bibliografiskt granskad
Iqbal, Z., Almeida, L. & Behnam, M. (2015). Designing Network Servers within a Hierarchical Scheduling Framework. In: Proceedings of the ACM Symposium on Applied Computing: . Paper presented at The 30th ACM/SIGAPP Symposium On Applied Computing SAC'15, 13-17 Apr 2015, Salamanca, Spain (pp. 653-658).
Öppna denna publikation i ny flik eller fönster >>Designing Network Servers within a Hierarchical Scheduling Framework
2015 (Engelska)Ingår i: Proceedings of the ACM Symposium on Applied Computing, 2015, s. 653-658Konferensbidrag, Publicerat paper (Refereegranskat)
Nationell ämneskategori
Data- och informationsvetenskap
Identifikatorer
urn:nbn:se:mdh:diva-28114 (URN)10.1145/2695664.2695919 (DOI)000381029800102 ()2-s2.0-84955502560 (Scopus ID)
Konferens
The 30th ACM/SIGAPP Symposium On Applied Computing SAC'15, 13-17 Apr 2015, Salamanca, Spain
Projekt
RV-REDS - Resource Virtualization for Real-Time Embedded Distributed Systems
Tillgänglig från: 2015-06-11 Skapad: 2015-06-08 Senast uppdaterad: 2018-01-11Bibliografiskt granskad
Cano, J. & Almeida, L. (2015). Feedback Management for Scaling Clients in Streaming Multicast. In: Proceedings of the 30th Annual ACM Symposium on Applied Computing: . Paper presented at 30th Annual ACM Symposium on Applied Computing, SAC 2015; Salamanca; Spain; 13 April 2015 through 17 April 2015 (pp. 669-671).
Öppna denna publikation i ny flik eller fönster >>Feedback Management for Scaling Clients in Streaming Multicast
2015 (Engelska)Ingår i: Proceedings of the 30th Annual ACM Symposium on Applied Computing, 2015, s. 669-671Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

The increase in the number of mobile devices accessing the Internet creates new problems. A specific case is when a large number of wirelessclients try to access the same video stream in the same hot spot, which requires multicast transmission. However, multicast packets are unconfirmed and to compensate their higher loss rate we propose using a feedback repeat request mechanism per client. Then, the number ofclients is scaled up by adequately scheduling their feedback in the streaming server. This mechanism also allows managing the QoS provided to the clients controlling their feedback rate independently. Our preliminary results confirm the desired scalability with reliable streaming.

Nationell ämneskategori
Datorsystem
Identifikatorer
urn:nbn:se:mdh:diva-31514 (URN)10.1145/2695664.2696036 (DOI)000381029800106 ()2-s2.0-84955499021 (Scopus ID)9781450331968 (ISBN)
Konferens
30th Annual ACM Symposium on Applied Computing, SAC 2015; Salamanca; Spain; 13 April 2015 through 17 April 2015
Tillgänglig från: 2016-05-04 Skapad: 2016-05-04 Senast uppdaterad: 2016-09-22Bibliografiskt granskad
Oliveira, L., Graca, R., Martins, J. & Almeida, L. (2015). Managing high loads in WiFi with automatic synchronization and bandwidth control. In: Proceeding - 2015 IEEE International Conference on Industrial Informatics, INDIN 2015: . Paper presented at 13th International Conference on Industrial Informatics, INDIN 2015, 22 July 2015 through 24 July 2015 (pp. 937-942).
Öppna denna publikation i ny flik eller fönster >>Managing high loads in WiFi with automatic synchronization and bandwidth control
2015 (Engelska)Ingår i: Proceeding - 2015 IEEE International Conference on Industrial Informatics, INDIN 2015, 2015, s. 937-942Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

Mobile devices in industrial settings became commonplace with different handheld equipment and mobile robots using COTS WiFi interfaces for communication. This growth in the use of the wireless medium increases the potential for overload and consequent long delays and high losses. Traffic segregation with different Quality of Service (QoS) classes can attenuate the problem but does not solve it within each class. In this paper we propose an extension to the Reconfigurable and Adaptive TDMA protocol to cope with generic traffic and improve the performance of highly loaded WiFi networks. We benefit from the self-synchronization feature of the protocol to create disjoint slots without clock synchronization which are then made available to the protocol stack through a TUN/TAP virtual interface. Then we propose a cooperative bandwidth management to adjust the traffic generated by each node through the virtual interface to match the available bandwidth, granting high bandwidth utilization while avoiding overload. We validate our approach with several practical experiments that confirm the capacity to measure and track the actual bandwidth available for communication through the protocol, removing the bandwidth consumed by interference.

Nyckelord
adaptation, overload management, synchronization, TDMA, WiFi, Wireless communication, Bandwidth, Information science, Mobile devices, Quality of service, Wi-Fi, Wireless telecommunication systems, Automatic synchronization, Bandwidth management, Clock Synchronization, Hand-held equipment, Self synchronization, Wireless communications, Time division multiple access
Nationell ämneskategori
Datorsystem
Identifikatorer
urn:nbn:se:mdh:diva-30601 (URN)10.1109/INDIN.2015.7281861 (DOI)000380453900137 ()2-s2.0-84949504852 (Scopus ID)9781479966493 (ISBN)
Externt samarbete:
Konferens
13th International Conference on Industrial Informatics, INDIN 2015, 22 July 2015 through 24 July 2015
Tillgänglig från: 2015-12-23 Skapad: 2015-12-23 Senast uppdaterad: 2016-09-01Bibliografiskt granskad
Moreira, A., Almeida, L. & Lucani, D. E. (2015). Merging Network Coding with Feedback Management in Multicast Streaming. SIGBED Review, 12(3), 49-52
Öppna denna publikation i ny flik eller fönster >>Merging Network Coding with Feedback Management in Multicast Streaming
2015 (Engelska)Ingår i: SIGBED Review, ISSN 1551-3688, Vol. 12, nr 3, s. 49-52Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Reliable multicast over wireless poses interesting challenges arising from the unreliable nature of the wireless medium. Recovering lost packets is particularly challenging in multicast scenarios since different receivers lose different packets. For this reason, simply retransmitting packets does not scale well with the number of receivers and particularly with the packet loss rate. A more efficient alternative is to use erasure codes to generate packets that can help many receivers at the same time. In this paper, we propose using online network coding to send coded packets that repair losses according to feedback reports sent by the clients. In particular, we propose using a recently developed scheduler for controlling feedback reports, which also allows differentiating the QoS provided to clients, and combine it with an online coding approach to provide novel stochastic guarantees of worst-case delay as required for QoS sensitive applications. We show preliminary simulation results that confirm the bounded decoding delay of our approach in a streaming application.

Nationell ämneskategori
Datorsystem
Identifikatorer
urn:nbn:se:mdh:diva-31521 (URN)10.1145/2815482.2815492 (DOI)
Tillgänglig från: 2016-05-04 Skapad: 2016-05-04 Senast uppdaterad: 2016-05-04Bibliografiskt granskad
Organisationer
Identifikatorer
ORCID-id: ORCID iD iconorcid.org/0000-0002-9544-3028

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