Retry Limit Adaptation Research Articles

Joint Voice/Video Retry Limit Adaptation for On-Demand Streaming Over WiFi Networks

This letter proposes a fast retry limit adaptation algorithm for the 802.11e distributed networks. Different from existing solutions, which manage a unique access category, the presented method jointly estimates the retry limits associated with both voice and video packets. The algorithm that operates in saturated and non-saturated traffic conditions is validated adopting an 802.11n physical layer and comparing its performance with a proper extension of an existing solution.

Fast retry limit adaptation for video distortion/delay control in IEEE 802.11e distributed networks

This paper presents a fast retry limit adaptation method for video streaming applications over IEEE 802.11e distributed networks. The method enables each source to adapt the number of retransmissions associated to each video packet by relating the perceived distortion to the drop probability and the acceptable delay to the expiration time, without asking the destination for feedback distortion/delay information. The resulting framework, which is based on a simplified but accurate evaluation of the network statistics and of the distortion introduced by the loss of a specific packet, provides a closed-form, and hence computationally cheap, estimation of the retry limit. Furthermore, with respect to most of the existing solutions, the proposed strategy accounts for the impact of the higher priority voice access category (AC), in order to improve the reliability of the retry limit adaptation in the presence of contending ACs. The method is validated by a simulation platform including the physical communication chain and the 802.11e medium access control layer, and its performance is compared to that obtained from an existing solution and from the optimum theoretical settings.

Analytical Modeling for Delay-Sensitive Video Over WLAN

Delay-sensitive video transmission over IEEE 802.11 wireless local area networks (WLANs) is analyzed in a cross-layer optimization framework. The effect of delay constraint on the quality of received packets is studied by analyzing “expired-time packet discard rate”. Three analytical models are examined and it is shown that M/M/1 model is quite an adequate model for analyzing delay-limited applications such as live video transmission over WLAN. The optimal MAC retry limit corresponding to the minimum “total packet loss rate” is derived by exploiting both mathematical analysis and NS-2 simulations. We have shown that there is an interaction between "packet overflow drop" and "expired-time packet discard" processes in the queue. Subsequently, by introducing the concept of virtual buffer size, we will obtain the optimal buffer size in order to avoid "packet overflow drop". We finally introduced a simple and yet effective real-time algorithm for retry-limit adaptation over IEEE 802.11 MAC in order to maintain a loss protection for delay-critical video traffic transmission, and showed that the average link-layer throughput can be improved by using our adaptive scheme.

Cross-Layer Packet Retry Limit Adaptation for Video Transport Over Wireless LANs

Video transport over wireless networks requires retransmissions to successfully deliver video data to a receiver in case of packet loss, leading to increased delay time for the data to arrive at the receiver. Delay constraint is one of the most important requirements in real-time applications. A video packet arriving later than the presentation time will become useless for the client. In this paper, we propose a cross-layer content-aware retry limit adaptation scheme for video streaming over IEEE 802.11 wireless LANs. Video packets of different importance are unequally protected with different retry limits at the media access control (MAC) layer. The error propagation effect of each packet is estimated to guide the determination of its retry limit. More retry numbers are allocated to packets of higher loss impact to achieve unequal error protection. Our scheme also analyzes the backoff time for each retry and then takes into account the estimated backoff time for retransmission scheduling. Experimental results show that the proposed adaptation scheme can effectively mitigate the error propagation due to packet loss and assure the on-time arrival of packets for presentation, so as to improve video quality significantly.

Providing forwarding assurance in multi-hop wireless networks

The Assured Forwarding (AF) service in a differentiated services network offers different levels of forwarding assurance for IP packets. In the wired Internet, the AF service is implemented as a queue management scheme associated with a drop policy in each router. In multi-hop wireless networks, however, queue management in each node is not enough to provide service differentiation globally since resource is shared among neighboring nodes. Hence, several studies for the AF service in wireless networks have proposed to manipulate the contention window size to provide service differentiation. The contention window size based differentiation scheme provides the AF service by transmitting packets in a higher class with a smaller contention window. However, since network congestion in multi-hop wireless networks causes packet losses at the link layer, the contention window size based differentiation scheme is not sufficient to provide the AF service. In this paper, we propose a rate control scheme to control load on the shared channel by adjusting sending rate according to the estimated channel state and the amount of AF traffic. We further propose a RTS retry limit adaptation scheme for loss rate differentiation at the link layer. Through extensive simulations, we show that proposed schemes are effective to differentiate forwarding assurance in multi-hop wireless networks.

Providing Adaptive QoS to Layered Video Over Wireless Local Area Networks Through Real-Time Retry Limit Adaptation

Robust streaming of video over 802.11 wireless LANs (WLANs) poses many challenges, including coping with packets losses caused by network buffer overflow or link erasures. In this paper, we propose a novel error protection method that can provide adaptive quality-of-service (QoS) to layered coded video by utilizing priority queueing at the network layer and retry-limit adaptation at the link layer. The design of our method is motivated by the observation that the retry limit settings of the MAC layer can be optimized in such a way that the overall packet losses that are caused by either link erasure or buffer overflow are minimized. We developed a real-time retry limit adaptation algorithm to trace the optimal retry limit for both the single-queue (or single-layer) and multiqueue (or multilayer) cases. The video layers are unequally protected over the wireless link by the MAC with different retry limits. In our proposed transmission framework, these retry limits are dynamically adapted depending on the wireless channel conditions and traffic characteristics. Furthermore, the proposed priority queueing discipline is enhanced with packet filtering and purging functionalities that can significantly save bandwidth by discarding obsolete or un-decodable packets from the buffer. Simulations show that the proposed cross-layer protection mechanism can significantly improve the received video quality.