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

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

In order to support multimedia applications such as voice and video over the wireless medium, a contention-based channel access function, called enhanced distributed coordination function (EDCF), is being developed in the emerging standard IEEE 802.11e. In EDCF, differentiated services are provided for different traffic classes. In this paper, we propose a two-level protection and guarantee mechanism for voice and video traffic in IEEE 802.11e wireless LANs. In the first-level protection, the existing voice and video flows are protected from the new and other existing voice and video flows. In the second-level protection, the voice and video flows are protected from the best-effort data traffic. For each protection level, a couple of protection mechanisms are proposed. Extensive simulation results show that the proposed two-level protection and guarantee mechanism is very effective in terms of protecting and guaranteeing existing voice and video flows as well as fully utilizing the channel capacity

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Protection and guarantee for voice and video traffic in IEEE 802.11e wireless LANs

We describe three attacks on the Wi-Fi Protected Access Temporal Key Integrity Protocol (WPA-TKIP). The first attack is a Denial of Service attack that can be executed by injecting only two frames every minute. The second attack demonstrates how fragmentation of 802.11 frames can be used to inject an arbitrary amount of packets, and we show that this can be used to perform a portscan on any client. The third attack enables an attacker to reset the internal state of the Michael algorithm. We show that this can be used to efficiently decrypt arbitrary packets sent towards a client. We also report on implementation vulnerabilities discovered in some wireless devices. Finally we demonstrate that our attacks can be executed in realistic environments.

Practical verification of WPA-TKIP vulnerabilities

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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Sangjin Hong

Papers

Collaborative QoS architecture between DiffServ and 802.11e wireless LAN