Proceedings of the 1st international conference on Performance evaluation methodolgies and tools - valuetools '06, 2006
ABSTRACT Deficit Round Robin (DRR) is a scheduling algorithm which provides fair queuing at O(1) ... more ABSTRACT Deficit Round Robin (DRR) is a scheduling algorithm which provides fair queuing at O(1) complexity. However, due to its round robin structure, its latency properties are not adequate for latency-critical applications, such as voice. For this reason, router manufacturers implement variants of the DRR algorithm which guarantee lower latencies to one (or a subset of) queue(s). In this paper we evaluate the performance of two such variants, both of which are known as Modified Deficit Round Robin, currently implemented in commercial routers. The comparison is carried out analytically, by deriving the latency and bandwidth sharing properties of both algorithms, and by simulation.
Proceedings of the Second International ICST Conference on Simulation Tools and Techniques, 2009
Stochastic simulation is an important aid for the design and performance engineering of computer ... more Stochastic simulation is an important aid for the design and performance engineering of computer networks. The credibility of simulative results can, however, be seriously affected by human errors (e.g., inconsistencies in the parameter selection, poor initialization of random generators, bugs in the scripts used for post-processing), which become more and more likely and numerous as the dimension of the set of simulated scenarios (simulation campaign) increases. The occurrence of such errors can be limited by using reliable automation tools, i.e. tools which take care of the above mentioned tasks by using state-of-the-art methodologies. This work describes ANSWER (Automated NS-2 Workflow managER), a simulation workflow automation tool for the Network Simulator (ns-2), explicitly designed for facilitating large-scale simulation campaigns, i.e. those involving many factors. Our framework reduces the space for errors when defining scenarios, controls the execution of a large number of scenarios, and reduces the time overhead required for output data analysis.
In this paper we compute the actual worst-case endto-end delay for a flow in a feed-forward netwo... more In this paper we compute the actual worst-case endto-end delay for a flow in a feed-forward network of FIFOmultiplexing service curve nodes, where flows are shaped by piecewise-affine concave arrival curves, and service curves are piecewise affine and convex. We show that the worst-case delay problem can be formulated as a mixed integer-linear programming problem, whose size grows exponentially with the number of nodes involved. Furthermore, we present approximate solution schemes to find upper and lower delay bounds on the worst-case delay. Both only require to solve just one linear programming problem, and yield bounds which are generally more accurate than those found in the previous work, which are computed under more restrictive assumptions.
IEEE Transactions on Parallel and Distributed Systems, 2004
Interconnection networks of parallel systems are used for servicing traffic generated by differen... more Interconnection networks of parallel systems are used for servicing traffic generated by different applications, often belonging to different users. When multiple users contend for channel bandwidth, fairness in bandwidth sharing becomes a key requirement. In fact, enforcing a fair sharing of channel bandwidth improves flow isolation, thus preventing misbehaving flows from affecting the performance of other flows. We present a novel packet scheduling algorithm, called eligibility-based round robin (EBRR), devised to provide fair queueing in interconnection networks. In fact, EBRR meets the constraints imposed by wormhole switching, which is the most popular switching technique in interconnection networks of parallel systems. It can also be applied to packet switching wide area networks (WANs), such as IP and ATM. We show that EBRR has O(1) complexity and better delay and fairness properties than existing algorithms of comparable complexity. Here, we also investigate the means for assessing the fairness of a scheduler: we show that using the relative fairness bound as a fairness measure may lead to erroneous results. We then propose an alternative measure, called the generalized relative fairness bound, that allows fairness to be assessed more precisely.
Multiservice networks face the challenge of managing several traffic classes simultaneously. Serv... more Multiservice networks face the challenge of managing several traffic classes simultaneously. Service disciplines devised for multiservice networks therefore need to be flexible, i.e., able to provide different types of service, in order to accommodate different traffic classes efficiently. In this paper, we present and analyze an innovative Timed Token Service Discipline (TTSD, which has been given Patent Application No. TO2000A001000) which is able to schedule both rate-guaranteed and best-effort traffic simultaneously at a feasible computational complexity. The service paradigm approximated by TTSD is unveiled by means of a fluid-flow analysis and proven to be different from the well-known Generalized Processor Sharing. We then describe the TTSD properties, deriving minimum rate guarantees and delay bounds for leaky-bucket constrained traffic, both in a single node and in a multinode environment. Furthermore, algorithms for selecting the TTSD parameters in order to achieve a prespecified rate and delay guarantees are proposed.
Multiservice networks will host heterogeneous applications, requiring different qualities of serv... more Multiservice networks will host heterogeneous applications, requiring different qualities of service (QoS), the coexistence of which can be efficiently accounted by employing scheduling algorithms which are capable of providing different QoS simultaneously. In a previous work, we defined a reference Dual-Class (DC) paradigm, according to which rate-guaranteed flows are restrained from using more than their minimum guaranteed rate in the presence of backlogged best-effort flows and the latter share all the remaining capacity according to predetermined weights. The Timed Token Service Discipline (TTSD), which applies at the output link of a switch the same rules used to control medium access by the Timed Token Protocol, was also introduced and analyzed therein. It was proven that TTSD shares most of the capacity which is not strictly needed by the rate-guaranteed flows among the best-effort ones, thus achieving one of the goals of the DC paradigm. However, in TTSD, best-effort flows can only share the available capacity equally. In this paper, we take into account the issue of differentiating the capacity sharing among the best-effort flows: We define a Generalized TTSD (GTTSD) in which the latter actually share capacity according to predefined weights in a weighted fair queuing service discipline. Formal analysis and simulation results show that GTTSD closely approximates the DC paradigm.
Deficit Round-Robin (DRR) is a scheduling algorithm devised for providing fair queueing in the pr... more Deficit Round-Robin (DRR) is a scheduling algorithm devised for providing fair queueing in the presence of variable length packets. The main attractive feature of DRR is its simplicity of implementation: in fact, it can exhibit O(1) complexity, provided that specific allocation constraints are met. However, according to the original DRR implementation, meeting such constraints often implies tolerating high latency and poor fairness. In this paper, we first derive new and exact bounds for DRR latency and fairness. On the basis of these results, we then propose a novel implementation technique, called Active List Queue Method (Aliquem), which allows a remarkable gain in latency and fairness to be achieved, while still preserving O(1) complexity. We show that DRR achieves better performance metrics than those of other round-robin algorithms such as Pre-Order Deficit Round-Robin and Smoothed Round-Robin. We also show by simulation that the proposed implementation allows the average delay and the jitter to be reduced.
ABSTRACT Integrated services networks face the challenge of managing several traffic classes at t... more ABSTRACT Integrated services networks face the challenge of managing several traffic classes at the same time. Service disciplines devised for integrated services networks therefore need to be flexible, i.e. able to provide different types of service, in order to accommodate different traffic classes efficiently. In this paper we focus on the integration of rate-guaranteed and best-effort traffic, and we argue that service disciplines based on the generalized processor sharing paradigm, which schedule flows according to their weights, lack the flexibility needed to efficiently manage both classes at the same time. We propose that a different service paradigm, the dual-class paradigm, which considers the two traffic classes at the same time, be used as a reference to devise flexible and efficient service disciplines for integrated services networks. We then present and analyze an innovative packet timed token service discipline, which approximates a dual-class paradigm at a low computational complexity. PTTSD properties are described analytically: we derive minimum rate guarantees for rate-guaranteed traffic and propose rules to select the system parameters in order to achieve pre-specified guarantees. Finally, we show some of the PTTSD properties by means of simulation.
The EuQoS (End-to-End QoS over Heterogeneous Networks) IST Integrated European Project aimed to d... more The EuQoS (End-to-End QoS over Heterogeneous Networks) IST Integrated European Project aimed to define a Next Generation Network architecture that builds, uses and manages end-to-end QoS across different administrative domains and heterogeneous networks (UMTS, xDSL, Ethernet, WiFi, Satellite and IP/ MPLS). The EuQoS architecture preserves the openness and the decentralized decision model of the actual Internet, runs on off-the-shelf hardware and network equipment, and allows end users to request various services without changing the Application Signaling protocol, while meeting regulators' and users' Net Neutrality requirements. This paper presents the key elements of the EuQoS architecture and describes the main results obtained in field trials performed on a fully-functional EuQoS system prototype developed over a pan-European testbed. Furthermore, the paper discusses the main strengths of the system and the issues related to its actually deployment on a large scale, from both technical and market points of view.
In a DiffServ architecture, packets with the same marking are treated as an aggregate at core rou... more In a DiffServ architecture, packets with the same marking are treated as an aggregate at core routers, independently of the flow they belong to. Nevertheless, for the purpose of QoS provisioning, derivation of upper bounds on the delay of individual flows is of great importance. In this paper, we consider a case study network, composed by a tandem of rate-latency
Deficit Round Robin (DRR) is a scheduling algorithm devised for providing fair queueing in the pr... more Deficit Round Robin (DRR) is a scheduling algorithm devised for providing fair queueing in the presence of variable length packets. The main attractive feature of DRR is its simplicity of implementation: in fact, it can exhibit (1) O complexity, provided that specific allocation constraints are met. However, according to the DRR implementation proposed in [7], meeting such constraints often implies tolerating high latency and poor fairness. In this paper, we first derive new and exact bounds for DRR latency and fairness. On the basis of these results, we then propose a novel implementation technique, called Active List Queue Method (Aliquem), which allows a remarkable gain in latency and fairness to be achieved, while still preserving (1) O complexity. We show that DRR achieves better performance metrics than those of other round robin algorithms such as Pre-Order Deficit Round Robin and Smoothed Round Robin. We also show by simulation that the proposed implementation allows the average delay and the jitter to be reduced.
2010 IEEE International Symposium on "A World of Wireless, Mobile and Multimedia Networks" (WoWMoM), 2010
Abstract In this paper we investigate link scheduling for Wireless Mesh Networks (WMNs) carrying ... more Abstract In this paper we investigate link scheduling for Wireless Mesh Networks (WMNs) carrying real-time (ie, delay-constrained) traffic. We show that the problem of computing a conflict-free link schedule with end-to-end delay constraints can be formulated as a mixed-...
We discuss the issue of computing resource-optimal routing plans in a network domain. Given a num... more We discuss the issue of computing resource-optimal routing plans in a network domain. Given a number of known traffic demands, with associated required delays, we discuss how to route them and allocate resources for them at each node so that the demands are ...
Real-time systems are increasingly becoming communication intensive, where different functions ar... more Real-time systems are increasingly becoming communication intensive, where different functions are implemented using distributed real-time tasks mapped onto different physical systems (sensors, processors, and actuators). To ensure global correctness, one has to ensure the correctness of each task, schedulability of the tasks on each system, and finally also bound the communication time, i.e., the worst case (network) traversal time (WCTT).
Proceedings of the First International ICST Conference on Simulation Tools and Techniques for Communications Networks and Systems, 2008
... Silva Lab. of Communications and Telematics CISUC-DEI, University of Coimbra, Portugal sasilv... more ... Silva Lab. of Communications and Telematics CISUC-DEI, University of Coimbra, Portugal [email protected] G. García-de Blas, FJ Ramón Salguero Telefónica I+D, Madrid, Spain {ggdb; fjrs}@tid.es ABSTRACT The EuQoS ...
ABSTRACT In an LTE cell, Discontinuous Reception (DRX) allows the central base station to configu... more ABSTRACT In an LTE cell, Discontinuous Reception (DRX) allows the central base station to configure User Equipments for periodic wake/sleep cycles, so as to save energy. DRX operations depend on several parameters, which can be tuned to achieve optimal performance with different traffic profiles (i.e., CBR vs. bursty, periodic vs. sporadic, etc.). This work investigates how to configure these parameters and explores the trade-off between power saving, on one side, and per-user QoS, on the other. Unlike previous work, chiefly based on analytical models neglecting key aspects of LTE, our evaluation is carried out via simulation. We use a fully-fledged packet simulator, which includes models of all the protocol stack, the applications and the relevant QoS metrics, and employ factorial analysis to assess the impact of the many simulation factors in a statistically rigorous way. This allows us to analyze a wider spectrum of scenarios, assessing the interplay of the LTE mechanisms and DRX, and to derive configuration guidelines.
Proceedings of the 3rd International Conference on Performance Evaluation Methodologies and Tools, 2008
This paper addresses the problem of estimating the worst-case endto-end delay for a flow in a tan... more This paper addresses the problem of estimating the worst-case endto-end delay for a flow in a tandem of FIFO multiplexing nodes, following up our previous work . We show that, contrary to the expectations, the state-of-the-art method for computing delay bounds, i.e. upper bounds on the worst-case delay, called the Least Upper Delay Bound (LUDB) methodology, may actually be larger than the worst-case delay even in simple cases. Thus, we first devise a method to compute improved delay bounds. Then, in order to assess how close the derived bounds are to the actual, still unknown, worst-case delays, we devise a method to compute lower bounds on the worst-case delay. Our analysis shows that the gap between the upper and lower bounds is quite small in many practical cases, which implicitly validates the upper bounds themselves.
ABSTRACT Computing network paths under worst-case delay constraints has been the subject of abund... more ABSTRACT Computing network paths under worst-case delay constraints has been the subject of abundant literature in the past two decades. As-suming Weighted Fair Queueing scheduling at the nodes, this translates to computing paths and reserving rates at each link. The problem is N P-hard in general, even for a single path; hence polynomial-time heuristics have been proposed in the past, that either assume equal rates at each node, or compute the path heuristically and then allocate the rates optimally on the given path. In this paper we show that the above heuristics, albeit finding optimal solutions quite often, can lead to failing of paths at very low loads, and that this could be avoided by solving the problem, i.e., path computation and rate allocation, jointly at optimality. This is possible by modeling the problem as a mixed-integer second-order cone program and solving it optimally in split-second times for relatively large networks on commodity hardware; this approach can also be easily turned into a heuristic one, trading a negligible increase in blocking probability for one order of magnitude of computation time. Extensive simulations show that these methods are feasible in today's ISPs networks and they significantly outperform the existing schemes in terms of blocking probability.
Proceedings of the 1st international conference on Performance evaluation methodolgies and tools - valuetools '06, 2006
ABSTRACT Deficit Round Robin (DRR) is a scheduling algorithm which provides fair queuing at O(1) ... more ABSTRACT Deficit Round Robin (DRR) is a scheduling algorithm which provides fair queuing at O(1) complexity. However, due to its round robin structure, its latency properties are not adequate for latency-critical applications, such as voice. For this reason, router manufacturers implement variants of the DRR algorithm which guarantee lower latencies to one (or a subset of) queue(s). In this paper we evaluate the performance of two such variants, both of which are known as Modified Deficit Round Robin, currently implemented in commercial routers. The comparison is carried out analytically, by deriving the latency and bandwidth sharing properties of both algorithms, and by simulation.
Proceedings of the Second International ICST Conference on Simulation Tools and Techniques, 2009
Stochastic simulation is an important aid for the design and performance engineering of computer ... more Stochastic simulation is an important aid for the design and performance engineering of computer networks. The credibility of simulative results can, however, be seriously affected by human errors (e.g., inconsistencies in the parameter selection, poor initialization of random generators, bugs in the scripts used for post-processing), which become more and more likely and numerous as the dimension of the set of simulated scenarios (simulation campaign) increases. The occurrence of such errors can be limited by using reliable automation tools, i.e. tools which take care of the above mentioned tasks by using state-of-the-art methodologies. This work describes ANSWER (Automated NS-2 Workflow managER), a simulation workflow automation tool for the Network Simulator (ns-2), explicitly designed for facilitating large-scale simulation campaigns, i.e. those involving many factors. Our framework reduces the space for errors when defining scenarios, controls the execution of a large number of scenarios, and reduces the time overhead required for output data analysis.
In this paper we compute the actual worst-case endto-end delay for a flow in a feed-forward netwo... more In this paper we compute the actual worst-case endto-end delay for a flow in a feed-forward network of FIFOmultiplexing service curve nodes, where flows are shaped by piecewise-affine concave arrival curves, and service curves are piecewise affine and convex. We show that the worst-case delay problem can be formulated as a mixed integer-linear programming problem, whose size grows exponentially with the number of nodes involved. Furthermore, we present approximate solution schemes to find upper and lower delay bounds on the worst-case delay. Both only require to solve just one linear programming problem, and yield bounds which are generally more accurate than those found in the previous work, which are computed under more restrictive assumptions.
IEEE Transactions on Parallel and Distributed Systems, 2004
Interconnection networks of parallel systems are used for servicing traffic generated by differen... more Interconnection networks of parallel systems are used for servicing traffic generated by different applications, often belonging to different users. When multiple users contend for channel bandwidth, fairness in bandwidth sharing becomes a key requirement. In fact, enforcing a fair sharing of channel bandwidth improves flow isolation, thus preventing misbehaving flows from affecting the performance of other flows. We present a novel packet scheduling algorithm, called eligibility-based round robin (EBRR), devised to provide fair queueing in interconnection networks. In fact, EBRR meets the constraints imposed by wormhole switching, which is the most popular switching technique in interconnection networks of parallel systems. It can also be applied to packet switching wide area networks (WANs), such as IP and ATM. We show that EBRR has O(1) complexity and better delay and fairness properties than existing algorithms of comparable complexity. Here, we also investigate the means for assessing the fairness of a scheduler: we show that using the relative fairness bound as a fairness measure may lead to erroneous results. We then propose an alternative measure, called the generalized relative fairness bound, that allows fairness to be assessed more precisely.
Multiservice networks face the challenge of managing several traffic classes simultaneously. Serv... more Multiservice networks face the challenge of managing several traffic classes simultaneously. Service disciplines devised for multiservice networks therefore need to be flexible, i.e., able to provide different types of service, in order to accommodate different traffic classes efficiently. In this paper, we present and analyze an innovative Timed Token Service Discipline (TTSD, which has been given Patent Application No. TO2000A001000) which is able to schedule both rate-guaranteed and best-effort traffic simultaneously at a feasible computational complexity. The service paradigm approximated by TTSD is unveiled by means of a fluid-flow analysis and proven to be different from the well-known Generalized Processor Sharing. We then describe the TTSD properties, deriving minimum rate guarantees and delay bounds for leaky-bucket constrained traffic, both in a single node and in a multinode environment. Furthermore, algorithms for selecting the TTSD parameters in order to achieve a prespecified rate and delay guarantees are proposed.
Multiservice networks will host heterogeneous applications, requiring different qualities of serv... more Multiservice networks will host heterogeneous applications, requiring different qualities of service (QoS), the coexistence of which can be efficiently accounted by employing scheduling algorithms which are capable of providing different QoS simultaneously. In a previous work, we defined a reference Dual-Class (DC) paradigm, according to which rate-guaranteed flows are restrained from using more than their minimum guaranteed rate in the presence of backlogged best-effort flows and the latter share all the remaining capacity according to predetermined weights. The Timed Token Service Discipline (TTSD), which applies at the output link of a switch the same rules used to control medium access by the Timed Token Protocol, was also introduced and analyzed therein. It was proven that TTSD shares most of the capacity which is not strictly needed by the rate-guaranteed flows among the best-effort ones, thus achieving one of the goals of the DC paradigm. However, in TTSD, best-effort flows can only share the available capacity equally. In this paper, we take into account the issue of differentiating the capacity sharing among the best-effort flows: We define a Generalized TTSD (GTTSD) in which the latter actually share capacity according to predefined weights in a weighted fair queuing service discipline. Formal analysis and simulation results show that GTTSD closely approximates the DC paradigm.
Deficit Round-Robin (DRR) is a scheduling algorithm devised for providing fair queueing in the pr... more Deficit Round-Robin (DRR) is a scheduling algorithm devised for providing fair queueing in the presence of variable length packets. The main attractive feature of DRR is its simplicity of implementation: in fact, it can exhibit O(1) complexity, provided that specific allocation constraints are met. However, according to the original DRR implementation, meeting such constraints often implies tolerating high latency and poor fairness. In this paper, we first derive new and exact bounds for DRR latency and fairness. On the basis of these results, we then propose a novel implementation technique, called Active List Queue Method (Aliquem), which allows a remarkable gain in latency and fairness to be achieved, while still preserving O(1) complexity. We show that DRR achieves better performance metrics than those of other round-robin algorithms such as Pre-Order Deficit Round-Robin and Smoothed Round-Robin. We also show by simulation that the proposed implementation allows the average delay and the jitter to be reduced.
ABSTRACT Integrated services networks face the challenge of managing several traffic classes at t... more ABSTRACT Integrated services networks face the challenge of managing several traffic classes at the same time. Service disciplines devised for integrated services networks therefore need to be flexible, i.e. able to provide different types of service, in order to accommodate different traffic classes efficiently. In this paper we focus on the integration of rate-guaranteed and best-effort traffic, and we argue that service disciplines based on the generalized processor sharing paradigm, which schedule flows according to their weights, lack the flexibility needed to efficiently manage both classes at the same time. We propose that a different service paradigm, the dual-class paradigm, which considers the two traffic classes at the same time, be used as a reference to devise flexible and efficient service disciplines for integrated services networks. We then present and analyze an innovative packet timed token service discipline, which approximates a dual-class paradigm at a low computational complexity. PTTSD properties are described analytically: we derive minimum rate guarantees for rate-guaranteed traffic and propose rules to select the system parameters in order to achieve pre-specified guarantees. Finally, we show some of the PTTSD properties by means of simulation.
The EuQoS (End-to-End QoS over Heterogeneous Networks) IST Integrated European Project aimed to d... more The EuQoS (End-to-End QoS over Heterogeneous Networks) IST Integrated European Project aimed to define a Next Generation Network architecture that builds, uses and manages end-to-end QoS across different administrative domains and heterogeneous networks (UMTS, xDSL, Ethernet, WiFi, Satellite and IP/ MPLS). The EuQoS architecture preserves the openness and the decentralized decision model of the actual Internet, runs on off-the-shelf hardware and network equipment, and allows end users to request various services without changing the Application Signaling protocol, while meeting regulators' and users' Net Neutrality requirements. This paper presents the key elements of the EuQoS architecture and describes the main results obtained in field trials performed on a fully-functional EuQoS system prototype developed over a pan-European testbed. Furthermore, the paper discusses the main strengths of the system and the issues related to its actually deployment on a large scale, from both technical and market points of view.
In a DiffServ architecture, packets with the same marking are treated as an aggregate at core rou... more In a DiffServ architecture, packets with the same marking are treated as an aggregate at core routers, independently of the flow they belong to. Nevertheless, for the purpose of QoS provisioning, derivation of upper bounds on the delay of individual flows is of great importance. In this paper, we consider a case study network, composed by a tandem of rate-latency
Deficit Round Robin (DRR) is a scheduling algorithm devised for providing fair queueing in the pr... more Deficit Round Robin (DRR) is a scheduling algorithm devised for providing fair queueing in the presence of variable length packets. The main attractive feature of DRR is its simplicity of implementation: in fact, it can exhibit (1) O complexity, provided that specific allocation constraints are met. However, according to the DRR implementation proposed in [7], meeting such constraints often implies tolerating high latency and poor fairness. In this paper, we first derive new and exact bounds for DRR latency and fairness. On the basis of these results, we then propose a novel implementation technique, called Active List Queue Method (Aliquem), which allows a remarkable gain in latency and fairness to be achieved, while still preserving (1) O complexity. We show that DRR achieves better performance metrics than those of other round robin algorithms such as Pre-Order Deficit Round Robin and Smoothed Round Robin. We also show by simulation that the proposed implementation allows the average delay and the jitter to be reduced.
2010 IEEE International Symposium on "A World of Wireless, Mobile and Multimedia Networks" (WoWMoM), 2010
Abstract In this paper we investigate link scheduling for Wireless Mesh Networks (WMNs) carrying ... more Abstract In this paper we investigate link scheduling for Wireless Mesh Networks (WMNs) carrying real-time (ie, delay-constrained) traffic. We show that the problem of computing a conflict-free link schedule with end-to-end delay constraints can be formulated as a mixed-...
We discuss the issue of computing resource-optimal routing plans in a network domain. Given a num... more We discuss the issue of computing resource-optimal routing plans in a network domain. Given a number of known traffic demands, with associated required delays, we discuss how to route them and allocate resources for them at each node so that the demands are ...
Real-time systems are increasingly becoming communication intensive, where different functions ar... more Real-time systems are increasingly becoming communication intensive, where different functions are implemented using distributed real-time tasks mapped onto different physical systems (sensors, processors, and actuators). To ensure global correctness, one has to ensure the correctness of each task, schedulability of the tasks on each system, and finally also bound the communication time, i.e., the worst case (network) traversal time (WCTT).
Proceedings of the First International ICST Conference on Simulation Tools and Techniques for Communications Networks and Systems, 2008
... Silva Lab. of Communications and Telematics CISUC-DEI, University of Coimbra, Portugal sasilv... more ... Silva Lab. of Communications and Telematics CISUC-DEI, University of Coimbra, Portugal [email protected] G. García-de Blas, FJ Ramón Salguero Telefónica I+D, Madrid, Spain {ggdb; fjrs}@tid.es ABSTRACT The EuQoS ...
ABSTRACT In an LTE cell, Discontinuous Reception (DRX) allows the central base station to configu... more ABSTRACT In an LTE cell, Discontinuous Reception (DRX) allows the central base station to configure User Equipments for periodic wake/sleep cycles, so as to save energy. DRX operations depend on several parameters, which can be tuned to achieve optimal performance with different traffic profiles (i.e., CBR vs. bursty, periodic vs. sporadic, etc.). This work investigates how to configure these parameters and explores the trade-off between power saving, on one side, and per-user QoS, on the other. Unlike previous work, chiefly based on analytical models neglecting key aspects of LTE, our evaluation is carried out via simulation. We use a fully-fledged packet simulator, which includes models of all the protocol stack, the applications and the relevant QoS metrics, and employ factorial analysis to assess the impact of the many simulation factors in a statistically rigorous way. This allows us to analyze a wider spectrum of scenarios, assessing the interplay of the LTE mechanisms and DRX, and to derive configuration guidelines.
Proceedings of the 3rd International Conference on Performance Evaluation Methodologies and Tools, 2008
This paper addresses the problem of estimating the worst-case endto-end delay for a flow in a tan... more This paper addresses the problem of estimating the worst-case endto-end delay for a flow in a tandem of FIFO multiplexing nodes, following up our previous work . We show that, contrary to the expectations, the state-of-the-art method for computing delay bounds, i.e. upper bounds on the worst-case delay, called the Least Upper Delay Bound (LUDB) methodology, may actually be larger than the worst-case delay even in simple cases. Thus, we first devise a method to compute improved delay bounds. Then, in order to assess how close the derived bounds are to the actual, still unknown, worst-case delays, we devise a method to compute lower bounds on the worst-case delay. Our analysis shows that the gap between the upper and lower bounds is quite small in many practical cases, which implicitly validates the upper bounds themselves.
ABSTRACT Computing network paths under worst-case delay constraints has been the subject of abund... more ABSTRACT Computing network paths under worst-case delay constraints has been the subject of abundant literature in the past two decades. As-suming Weighted Fair Queueing scheduling at the nodes, this translates to computing paths and reserving rates at each link. The problem is N P-hard in general, even for a single path; hence polynomial-time heuristics have been proposed in the past, that either assume equal rates at each node, or compute the path heuristically and then allocate the rates optimally on the given path. In this paper we show that the above heuristics, albeit finding optimal solutions quite often, can lead to failing of paths at very low loads, and that this could be avoided by solving the problem, i.e., path computation and rate allocation, jointly at optimality. This is possible by modeling the problem as a mixed-integer second-order cone program and solving it optimally in split-second times for relatively large networks on commodity hardware; this approach can also be easily turned into a heuristic one, trading a negligible increase in blocking probability for one order of magnitude of computation time. Extensive simulations show that these methods are feasible in today's ISPs networks and they significantly outperform the existing schemes in terms of blocking probability.
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