1,721,034 research outputs found
A bandwidth request reiteration mechanism for IEEE 802.16 wireless networks
No full textThe IEEE 802.16 is a leading technology for Broadband Wireless Access (BWA), where
a Base Station (BS) provides a set of Subscriber Stations (SSs) with first-mile network access. Each SS
has multiple connections directed to the BS, which are assigned bandwidth on a demand basis. Specifically,
the BS allocates part of the channel as request slots, which are accessed by best-effort connections
in a random access manner to transmit bandwidth requests. Although bandwidth requests sent
by different SSs may collide the standard does not specify an explicit acknowledgment mechanism.
This, and the bandwidth being assigned by the BS to each SS as a whole, may lead to critical inconsistencies
between the perception of the SSs’ requirements at the BS and the actual SSs’ requirements,
which in turn may entail SS service disruption. While the standard suggests that an SS should regularly
update the BS about the backlog of its connections, the algorithm to do so is left unspecified. In
this paper we propose a simple, yet effective, mechanism to be employed by the SSs, called Bandwidth
Request Reiteration (BR2), which prevents deadlock from occurring. Using detailed packet-level simulation,
we compare BR2 to an alternative approach based on timeout, and show that BR2 achieves better
performance, in terms of the average transfer delay, while it does not incur a significant additional
overhead, in terms of MAC signalin
User level performance evaluation of VoIP using ns-2
No full textVoice over IP (VoIP) is gaining an ever increasing popularity. As such, it nowadays represents one of the most studied test applications in the performance evaluation of wireline and wireless networks. However, a sound performance analysis of VoIP communications should be carried out at the user level, by computing perceptive metrics like the Mean Opinion Score (MOS) or the EModel.
In this paper, we present enhancements to the popular Network Simulator 2 (ns-2) that allow a reliable VoIP user-level performance analysis to be carried out through simulation. We show that computing performance measures at the IP level, which is usually done in ns-2, often leads to inaccurate results. Our code is publicly available at http://info.iet.unipi.it/~cng/ns2voip/
Reducing Power Consumption with QoS Constraints in IEEE 802.16e Wireless Networks
No full textMobile Broadband Wireless Access (BWA) networks will offer in the forthcoming years multiple and differentiated services to users with high mobility requirements, connecting via portable or wearable devices which rely on the use of batteries by necessity. Since a relatively large fraction of energy is consumed by such devices for transmitting/receiving data over-the-air, mechanisms are needed to reduce power consumption, in order to increase the lifetime of devices and hence improve user’s satisfaction. The IEEE 802.16, which supports mobile BWA since its ‘e’ amendment in 2005, defined power saving functions at the Medium Access Control (MAC) layer, which are designed to be operated during open traffic sessions for greatest energy consumption reduction. However, enabling power saving usually increases the transmission latency, which can negatively affect the Quality of Service (QoS) experienced by users. On the other hand, imposing stringent QoS requirements may limit the amount of energy that can be saved. In this paper, an extensive study of the mutual interaction between power saving mechanisms and QoS support is carried out in the context of IEEE 802.16e. In particular, two types of delay-constrained applications with different requirements are considered, i.e., Web and Voice over IP (VoIP), for which the IEEE 802.16e standard specifies two different power saving classes. The performance is assessed via detailed packet-level simulation, with respect to several system parameters. To capture the relative contribution of all the factors on the energy- and QoS-related metrics, part of the evaluation is carried out by means of 2k • r! analysis
Measurement-driven design and runtime optimization in edge computing: Methodology and tools
No full textEdge computing is projected to become the dominant form of cloud computing in the future because of the significant advantages it brings to both users (less latency, higher throughput) and telecom operators (less Internet traffic, more local management). However, to fully unlock its potential at scale, system designers and automated optimization systems alike will have to monitor closely the dynamics of both processing and communication facilities. Especially the latter is often neglected in current systems since network performance in cloud computing plays only a minor role. In this paper, we propose the architecture of MECPerf, which is a solution to collect network measurements in a live edge computing domain, to be collected for offline provisioning analysis and simulations, or to be provided in real-time for on-line system optimization. MECPerf has been validated in a realistic testbed funded by the European Commission (Fed4Fire+), and we describe here a summary of the results, which are fully available as open data and through a Python library to expedite their utilization. This is demonstrated via a use case involving the optimization of a system parameter for migrating clients in a federated edge computing system adopting the GSMA platform operator concept
Quality of service support in IEEE 802.16 networks
No full textDuring the last few years, users all over the world have become more and more accustomed to the availability of broadband access. This has boosted the use of a wide variety both of established and recent multimedia applications. However, there are cases where it is too expensive for network providers to serve a community of users. This is typically the case in rural and suburban areas, where there is slow deployment (or no deployment at all) of traditional wired technologies for broadband access (e.g., cable modems, xDSL). In those cases, the most promising opportunity rests with Broadband Wireless Access technologies, such as the IEEE 802.16, also known as WiMAX. One of the features of the MAC layer of 802.16 is that it is designed to differentiate service among traffic categories with different multimedia requirements. This article focuses on mechanisms that are available in an 802.16 system to support quality of service (QoS) and whose effectiveness is evaluated through simulation
WTTP: A Scheduling Algorithm for Supporting QoS in IEEE 802.11e
No full textThis paper proposes a scheduling algo-rithm, the Wireless Timed Token Protocol (WTTP) for the Access Point of an IEEE 802.11e wireless network, to serve traffic streams with QoS guaran-tees. WTTP provides the established streams with rate-based guarantees. Furthermore, it makes the capacity not used by those streams available to con-tention-based access. The performance of WTTP is compared to that of a reference scheduler defined in the 802.11e draft standard using the ns2 simulator. The results show that WTTP outperforms the refer-ence scheduler with VBR traffic, both in terms of resource utilization and maximum number of ad-mitted flows
End-to-End Bandwidth Reservation in IEEE 802.16 Mesh Networks
No full textIEEE 802.16 mesh does not include support to traffic flows with strict Quality of Service requirements. In this paper, we propose an End-to-end Bandwidth Reservation Protocol (EBRP) in the backhaul of a Wireless Mesh Network using IEEE 802.16 mesh. The distinctive feature of EBRP is that it is carried out at the Medium Access Control (MAC) layer. Therefore, EBRP not only makes the resource reservation process extremely rapid, it also allows the available resources to be allocated efficiently by exploiting technology specific iinformation available at the MAC. We present EBRP as part of a framework which also includes the support for performing distributed Call Admission Control (CAC). Preliminary simulations results obtained
with VoIP traffic and nodes arranged in a grid topology are presented to show the effectiveness of EBRP, with ideal CAC computation
Bandwidth Allocation with Half-Duplex Stations in IEEE 802.16 Wireless Networks
No full textIEEE 802.16 is a recent IEEE standard for broadband wireless access networks. In IEEE 802.16 networks, the Medium Access Control ( MAC) protocol is centralized and explicitly supports quality of service ( QoS). That is to say, access to the medium by a number of Subscriber Stations ( SSs) is centrally controlled by one Base Station ( BS), which is responsible for allocating bandwidth to several MAC connections in order to provide them with the negotiated QoS guarantees. However, although the network can be operated in Frequency Division Duplex ( FDD) mode ( that is, transmissions from the BS ( downlink) and SSs ( uplink) occur on separate frequency channels), the standard supports SSs with half- duplex capabilities. This means that they are equipped with a single radio transceiver which can be used either to transmit in the uplink direction or to receive in the downlink direction. This may severely hamper the capacity to support QoS. Therefore, in order to allocate bandwidth, an IEEE 802.16 BS has to solve two related issues: 1) how it can schedule bandwidth grants to SSs in order to meet the QoS requirements of their connections and 2) how it can coordinate the uplink and downlink scheduled grants so as to support half- duplex capabilities. In this paper, we derive sufficient conditions for a set of scheduled grants to be allocated so that the transmission of each half- duplex SS does not overlap with its reception. Based on this, we propose a grant allocation algorithm, namely, the Half- Duplex Allocation ( HDA) algorithm, which always produces a feasible grant allocation provided that the sufficient conditions are met. HDA has a computation complexity of O(n), where n is the number of grants to be allocated. Finally, we show that the definition of HDA allows us to address the two issues mentioned above by following a pipeline approach. This is when scheduling and allocation are implemented by separate and independently running algorithms, which are just loosely coupled with each other. We show via extensive simulations that the performance of SSs with half- duplex capabilities, in terms of the delay of real- time and non- real- time interactive traffic, using HDA almost perfectly matches that of full- duplex SSs, whereas an alternative approach, based on the static partitioning of half- duplex SSs into separate groups, which are allocated alternately, is shown to degrade the performance
Design and Performance Analysis of the Real-Time HCCA Scheduler for IEEE 802.11e WLANs
No full textThis paper presents a new scheduling algorithm, called Real-Time HCCA (RTH), devised to support Quality of Service (QoS) at the flow level in an IEEE 802.11e network using the Hybrid Coordinator Function (HCF) Controlled Channel Access (HCCA) function. RTH separates online activities which take place at the frame transmission timescale, from offline activities which take place at the flow lifetime timescale. Complex computations are relegated to offline activities, while online tasks are kept as simple as possible. More specifically, at admission control time, RTH computes a periodic schedule based on the well-known Earliest Deadline First algorithm for 802.11e Traffic Streams (TSs). In doing so, the Stack Resource Policy is applied to account for non-pre-emptability of frame transmissions. Furthermore, the parameters are configured so as to reduce the MAC overhead due to polling uplink TSs. On the other hand, online scheduling is enforced simply by reading the pre-computed schedule, at little or no computational cost. RTH performance is assessed in terms of the admission control limit and of the amount of channel capacity that is left for contention-based access. Under both criteria, RTH is shown to outperform the sample scheduler proposed in IEEE 802.11e
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