Abdelhamid Nafaa

Sliding contention window (SCW): towards backoff range-based service differentiation over IEEE 802.11 wireless LAN networks

A number of works have tried to adjust the contention window in order to provide differentiated quality of service in IEEE 802.11-based wireless networks. By giving different service classes different CWs, the distribution of backoff intervals (chosen randomly, on the interval [O, CW]) will reflect the desired service classes. However, these protocols cannot deliver firm service guarantees while maintaining high network utilization, particularly under congested network conditions. In this article we propose a new MAC protocol featuring a sliding CW (SCW) for each network flow. The SCW dynamically adjusts to changing network conditions, but remains within a per-class predefined range in order to maintain a separation between different service classes. Each flows SCW reacts based on the degree to which class-defined QoS metrics are satisfied. Simulation results show that compared to the enhanced distributed coordination function (EDCF) scheme of 802.11e, SCW consistently excels, in terms of network utilization, strict service separation, and service-level fairness.

FAFC: fast adaptive fuzzy AQM controller for TCP/IP networks

Recently, many active queue management (AQM) algorithms have been proposed to address performance degradations of end-to-end congestion control. However, these AQM algorithms present weaknesses for stabilizing delays in heavily loaded networks. In this paper, we describe a novel adaptive fuzzy control algorithm to improve best effort TCP/IP networks performance. Compared to traditional AQM algorithms (RED, PID and others), our proposal avoids buffer overflows/underflows, and minimizes packet dropping. We propose an on-line adaptation mechanism that captures fluctuating network conditions, while classical AQM algorithms require static tuning. The algorithm stability is mathematically proven. Simulation results show that for the same link utilization, our fast adaptive fuzzy controller provides better performance than RED and PID.

Determinist contention window algorithm for IEEE 802.11

With the widespread IEEE 802.11 networks use, strong needs to enhance quality of service (QoS) has appeared. The IEEE 802.11 medium access control (MAC) protocol provides a contention-based distributed channel access mechanism that allow for wireless medium sharing. This protocol involves a significant collision rate as the network gets fairly loaded. Although the contention window (CW) is doubled after each collision, active stations may randomly select a backoff timer value smaller than the preceding one. This is obviously sub-optimal since the backoff values should rather increase after each collision in order to further space between successive transmissions and thus absorbing the growing contending flows. In this paper, we propose a novel backoff mechanism, namely determinist contention window algorithm (DCWA), which further separates between the different backoff ranges associated to the different contention stages. Instead of just doubling the upper bound of the CW, DCWA increases both backoff range bounds (i.e., upper and lower bounds). On the other hand, after each successful transmission the backoff range is readjusted by taking into account current network load and past history. Simulation results show that DCWA outperforms both the distributed coordination function (DCF) and the slow decrease (SD) scheme in terms of responsiveness to network load fluctuations, network utilization, and fairness among active stations

Service-driven inter-domain QoS monitoring system for large-scale IP and DVB networks

There is a growing synergy between well-established Service Providers (SP), Content Providers (CP), and Network Providers (NP), to propose new value-added services, and hence opening new markets to generate further revenues. Meanwhile, the explosive increasing amount of multimedia content to be offered in the Internet and the heterogeneity of the underlying networking technologies demand the provision of new QoS-enabled mechanisms and architecture to efficiently control, manage and monitor the networks. Quality of service monitoring is becoming crucial to SPs for providing quantified QoS-based services and service assurance and to NPs for managing network resources. This paper proposes a framework for large scale inter-domain QoS monitoring in heterogeneous networks including IP and DVB networks that has been developed in the IST-ENTHRONE project of European Commission. One of the main aims is actually to allow high cooperation between different providers while keeping intact the authority, confidentiality, and full control of each provider over its underlying resources. The proposed monitoring framework consists of a layered architecture with two signaling protocols namely an inter-domain monitoring signaling protocol (EQoS-RM), and an intra-domain active measurement signaling protocol (Emon). The proposed QoS monitoring system is service-driven in the sense that it aimed at providing in service verification of QoS performance guarantees for the services offered to the users by the providers. To achieve this, it uses both QoS probes that perform both active and passive monitoring at different levels of abstraction employing node and network wide measurements and application-level perceived quality meters for detecting quality degradation. As such, this framework specifies three types of QoS monitoring components operating at different levels: at network element or node, at network and at service levels. This proposed system also provides monitoring information to NPs in order to assist in managing the operational status of their networks. Design and implementation of the proposed QoS monitoring system is described in this paper. Some experimental assessments of this service-driven QoS monitoring system prove its functioning in terms of accuracy and responsiveness in providing the necessary results.

SCW: sliding contention window for efficient service differentiation in IEEE 802.11 networks

Many works have recently addressed the IEEE 802.11 QoS issues by proposing different monitoring-based contention window (CW) differentiation techniques. In network saturation, however, it is difficult to guarantee firm services differentiation while achieving high network exploitation. Particularly, most existing QoS-capable MAC protocols rely on a backoff interval sampled from a dynamic range [0 CW/sub i/]. In order to ensure more deterministic service differentiation, we propose a new MAC protocol featuring a sliding contention window (SCW) for each network flow. The different flows are now able to select backoff intervals from different (separated) CW ranges. The SCW dynamically adjusts to changing network conditions, but remains within a per-class predefined range, in order to maintain a separation between different service classes. Simulation results show that compared to the EDCA scheme of 802.11e, SCW consistently excels, in terms of network utilization, strict service separation, and service-level fairness.

Unequal and interleaved FEC protocol for robust MPEG-4 multicasting over wireless LANs

Robust video streaming over wireless local area networks (IEEE 802.11) faces many challenges, including bandwidth channel variations, data errors/losses, and terminal capacity heterogeneity. This is worsen by the TCP/IP architecture that does not offer any quality of service QoS guarantees to demanding applications such as video streaming. In order to improve error resilience and user-perceived video quality, a novel error control protocol, called unequally interleaved forward error correction (UI-FEC), is proposed. UI-FEC is particularly efficient for adaptive MPEG-4 video multicast over wireless LAN. The proposed protocol is composed of (1) a coordinated unequal and interleaved MPEG-4 data protection mechanism, that gracefully degrades video quality at receivers while minimizing the overall link bandwidth consumption; (2) an adaptive MPEG-4 video fragmentation and encapsulation protocol for a higher wireless link utilization.

Meet In the Middle Cross-Layer Adaptation for Audiovisual Content Delivery

This paper describes a new architecture and implementation of an adaptive streaming system (e.g., television over IP, video on demand) based on cross-layer interactions. At the center of the proposed architecture is the meet in the middle concept involving both bottom-up and top-down cross layer interactions. Each streaming session is entirely controlled at the RTP layer where we maintain a rich context that centralizes the collection of (i) instantaneous network conditions measured at the underlying layers (i.e.: link, network, and transport layers) and (ii) user- and terminal-triggered events that impose new real-time QoS adaptation strategies. Thus, each active multimedia session is tied to a broad range of parameters, which enable it to coordinate the QoS adaptation throughout the protocol layers and thus eliminating the overhead and preventing counter-productiveness among separate mechanisms implemented at different layers. The MPEG-21 framework is used to provide a common support for implementing and managing the end-to-end QoS of audio/video streams. Performance evaluations using peak signal to noise ratio (PSNR) and structural similarity index (SSIM) objective video quality metrics show the benefits of using the proposed Meet In the Middle cross-layer design compared to traditional media delivery approaches.

On interaction between loss characterization and forward error correction in wireless multimedia communication

With the steadily growing synergy between existing heterogeneous networks, the wireless LAN appears as the de-facto wireless access network in the end-to-end multimedia services distribution chain. Unlike in the traditional wired multi-hop networks (Internet) where congestions increase persistently both delays and losses, wireless packet losses are often location- and time-varying. Particularly, WLAN communication is characterized by high bit error rates that translates into tight loss dependency. The loss process may rapidly shift between different loss correlations levels, resulting in poor forward error correction (FEC) recovery capabilities. In this paper, we address this issue by providing a combined loss model to accurately characterize the wireless loss distribution features. We use control theory guided parameter tuning in order to urge the convergence of the loss models towards seizing the instantaneous loss distribution trends. Finally, we derive a new loss-specific QoS metrics for new FEC block allocation scheme.

Joint loss pattern characterization and unequal interleaved FEC protection for robust H.264 video distribution over wireless LAN

The recently adopted H.264 standard achieves efficient video encoding and bandwidth savings. Thus, designing communication protocols and QoS control mechanisms for H.264 video distribution over wireless IP networks is a topic of intense research interest. Delivering video streams to terminals via a wireless last hop is indeed a challenging task due to the varying nature of the wireless link. While a common approach suggests exploiting the variations of the wireless channel, an alternative is to exploit characteristics of the video stream to improve the transmission. In this paper, we combine both approaches through an efficient wireless loss characterization and a low-delay unequal interleaved FEC protection. Besides deriving new QoS metrics for FEC block allocation, the wireless loss characterization is as well used to adjust the interleaving level depending on the loss correlation exhibited by the wireless channel. This novel unequal interleaved FEC (UI-FEC) protocol allows graceful video quality degradation over error-prone wireless links while minimizing the overall bandwidth consumption and the end-to-end latency.

An object-based MPEG-4 multimedia content classification model for IP QoS differentiation

In this article, we investigate efficient transmission of object-based MPEG-4 video over IP networks with QoS management capabilities. MPEG-4 audio visual objects (AVOs) are classified based on application-level QoS criteria and AVOs semantic descriptors according to MPEG-7 framework MPEG-4 AVOs requiring same QoS performance form the network are automatically classified and multiplexed within one of the IP DiffServ PHB (per hop behaviours). Object data-packets within the same class are then transmitted over the selected transport layer with the corresponding bearer capability and priority level. We propose to extend the MPEG-4 system architecture with a new media QoS classification layer. This layer provides automatic and accurate mapping between MPEG-4 application-level QoS metrics and underlying transport network with QoS mechanisms such as IP DiffServ. The media QoS classification layer makes use of a neural network classification model that is transparent to application and network layers. Implementation and performance evaluation of the proposal are also described.