A WLAN system adapted to apply QoS differentiation to a media stream to be transmitted from a transmitting station (STA) to a receiving STA of that system. The transmitting STA processes the media stream to generate a base sub-stream and one or more enhancement sub-streams for subsequent transmission over a wireless communication channel and assigns different priorities to different sub-streams. Depending on the channel conditions, the transmitting STA may select to discard, without transmission, portions of data from enhancement sub-streams. The selection process is based on the assigned priority and operates to preserve as much of relatively high-priority data as possible. The receiving STA then processes the received data to generate a reconstructed media stream, which provides signal quality equal to or better than the signal quality supported by the base sub-stream. Advantageously, a WLAN system of the invention is adapted to change signal quality dynamically and incrementally in a manner commensurate with current channel conditions without the need for communication between the higher and lower network layers. In addition, it provides gradual and graceful degradation of signal quality when channel conditions deteriorate as opposed to abrupt degradation inherent in analogous prior art systems.

Media delivery using quality of service differentiation within a media stream

High oxygen solubility at cold-water temperature is frequently considered to be responsible for an apparently elevated level of antioxidant protection in marine ectotherms from polar environments. However, tissue oxidative stress is in most cases a function of elevated or variable pO2, rather than of an elevated tissue oxygen concentration. This review summarizes current knowledge on pro- and antioxidant processes in marine invertebrates and fish, and relates reactive oxygen species (ROS) formation in polar ectotherms to homeoviscous adaptations of membrane and storage lipids, as well as to tissue hypoxia and re-oxygenation during physiological stress.

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Formation of reactive species and induction of antioxidant defence systems in polar and temperate marine invertebrates and fish

Developed as a simple and cost-effective wireless technology for best effort services, IEEE 802.11 has gained popularity at an unprecedented rate. However, due to the lack of built-in quality of service support, IEEE 802.11 experiences serious challenges in meeting the demands of multimedia services and applications. This article surveys 802.11 QoS schemes, including service differentiation in the MAC layer, admission control and bandwidth reservation in MAC and higher layers, and link adaptation in the physical layer, designed to meet these challenges by providing the necessary enhancements for the required QoS. Furthermore, the article addresses issues that arise when end-to-end QoS has to be guaranteed in today's pervasive heterogeneous wired-cum-wireless networks. Among these challenges, protocol interoperability, multihop scheduling, full mobility support, and seamless vertical handoff among multiple mobile/wireless interfaces are specifically addressed.

A survey of quality of service in IEEE 802.11 networks

In this paper, we provide a saturation throughput analysis of the IEEE 802.11 protocol at the data link layer by including the impact of both transmission channel and capture effects in Rayleigh fading environment. Impacts of both non-ideal channel and capture effects, specially in an environment of high interference, become important in terms of the actual observed throughput. As far as the 4-way handshaking mechanism is concerned, we extend the multi-dimensional Markovian state transition model characterizing the behavior at the MAC layer by including transmission states that account for packet transmission failures due to errors caused by propagation through the channel. This way, any channel model characterizing the physical transmission medium can be accommodated, including AWGN and fading channels. We also extend the Markov model in order to consider the behavior of the contention window when employing the basic 2-way handshaking mechanism. Under the usual assumptions regarding the traffic generated per node and independence of packet collisions, we solve for the stationary probabilities of the Markov chain and develop expressions for the saturation throughput as a function of the number of terminals, packet sizes, raw channel error rates, capture probability, and other key system parameters. The theoretical derivations are then compared to simulation results confirming the effectiveness of the proposed models.

Saturation throughput analysis of IEEE 802.11 in the presence of non ideal transmission channel and capture effects

Heavy metal contamination in coastal sediments and soils near the Brazilian Antarctic Station, King George Island

Baseline heavy metal concentrations in the Antarctic clam, Laternula elliptica in Maxwell Bay, King George Island, Antarctica

As the multimedia applications such as voice over IP (VoIP) and audio/visual (AV) streaming across the Internet emerge, many are working on the network architecture to extend such applications to the wireless networking domain. The emerging IEEE 802.11e quality-of-service (QoS)-enabled wireless LAN (WLAN) is considered a strong candidate for the air interface for such multimedia applications thanks to the IP-centric network paradigm along with its inherent high-speed transmission capability. This paper provides an integrated wired/wireless network architecture interfacing QoS between user level traffic over IP using differentiated service (Diffserv) and transport level traffic using IEEE 802.11e WLAN. Our study investigates the correlations in end-to-end traffic management between Diffserv and 802.11e, and presents the hierarchical QoS signaling interface between Diffserv and 802.11e, in terms of traffic classifying, shaping and policing.

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Collaborative QoS architecture between DiffServ and 802.11e wireless LAN

A Preliminary Study on Heavy Metals in the Antarctic Limpet, Nacella concinna (Strebel, 1908) (Gastropoda: Patellidae) in an Intertidal Habitat on King George Island

Dong-Yup Kim

Papers

Baseline heavy metal concentrations in the Antarctic clam, Laternula elliptica in Maxwell Bay, King George Island, Antarctica

Collaborative QoS architecture between DiffServ and 802.11e wireless LAN

A Preliminary Study on Heavy Metals in the Antarctic Limpet, Nacella concinna (Strebel, 1908) (Gastropoda: Patellidae) in an Intertidal Habitat on King George Island

Photosynthetic Parameters of Phytoplankton Assemblages in the Surface Water of Maxwell Bay and the Weddell Sea during the 1996/97 Austral Summer