-In this work, we measure Wireless Local Area Network (WLAN) voice performance and capacity. While most WLAN applications today are data centric, the growing popularity of Voice over IP (VoIP) applications and the trend towards convergence with cellular networks will catalyze increased voice traffic. Since voice applications compete not only with each other, but also with data applications for WLAN bandwidth, quantifying voice performance and capacity in the presence of simultaneous data traffic is an important issue. We offer a practical investigation of the 802.11b MAC layer's ability to support simultaneous voice and data applications. We quantify VoIP capacity for standard WLAN networks, indicative of those already in the field, as well as evaluate the practical benefits of implementing backoff control and priority queuing at the access point. Conclusions are drawn based on an extensive set of real-world measurements conducted using off-theshelf equipment in an experimental testbed. I INTRODUCTIONOnce only seen within the enterprise, Wireless Local Area Networks (WLANs) are increasingly making their way into residential, commercial, industrial and public areas. Examples of such environments are hotels, airports and coffee shops, which typically have a floating end user population. University campuses and conference settings also benefit from WLANs since they provide flexible connectivity and network access at reduced costs. While the majority of traffic in WLAN deployments is data, we expect that voice will be an increasingly important application and a significant driver for WLAN adoption and integration, particularly as voice over IP (VoIP) applications flourish. Additionally, voice will be especially important in vertical industries such as construction, healthcare, and banking, etc. Therefore it is crucial to understand voice performance in WLANs. Furthermore, since WLAN endpoints share a common transmission medium, voice applications must compete with data applications for access and bandwidth. As such, voice quality and capacity can be significantly affected by the simultaneous transmission of data traffic in these networks. So it is also critical to understand the effects of data transmissions on voice performance and capacity.We focus exclusively on IEEE 802.11b [1], the most popular and prominently deployed WLAN standard. We measure the achievable voice performance and capacity using an experimental testbed consisting of commercially available, off-the-shelf components indicative of those that have already been deployed. With such a large legacy base for 802.11b equipment, especially among residential and enterprise customers, we believe that this approach provides the most immediately relevant results.In addition to standard 802.11b, we investigate MAClayer and queuing mechanisms , which can be easily implemented and can improve voice performance. Specifically, we measure the effects of backoff control and priority queuing (BC-PQ), as provided by [2]. Using both the standard and additional...

The growing Ldmand for mobility has increased the need to develop more efficient, reliable and cost effective services for data transmission over the air interface. The air interface, as compared to the wired domain, is characterized by a high bit-error-rate, limited bandwidth, and intermittent connectivity. In addition, power in the hand-held devices and laptops is limited by the battery technology. In this paper, we present AFEC, an Adaptive Forward Error-Correction scheme, which makes effective use of the air interface by minimizing the number of data bits transmitted to convey message packets in a real time stream over an air interface. Through simulations, we show that AFEC outperforms the traditional single forward-error-correction scheme.

In a Code Division Multiple Access (CDMA) network, multiple mobile hosts (MHs) can simultaneously transmit over the wireless channel by using different codes. To assure an acceptable quality of service for all users' flows, the network usually tunes the transmit powers of all MHs to achieve a certain level of signal strength as compared to the noise and the interference (SINR) for each user. The traditional assumption in power control schemes is that the SINR requirement is statically determined for each user flow.In contrast, in this paper, we propose a scheme that dynamically adapts the SINR requirements of user flows based on its quality of service (QoS) requirements and the conditions of the wireless channel between the MHs and the base station. As a result of this adaptation, we show that network-level QoS measures such as fraction of packets meeting their delay requirements and energy consumed per packet transmission are significantly better than in a scheme that statically fixes the SINR requirements.Our scheme uses a simple table-driven approach for optimally selecting the target SINR requirement for each MH at run time. The entries in the table are computed otttine using a dynamic programming algorithm with the objective of maximizing a profit function that balances the need for meeting the network-level QoS requirements and the cost of using a particular target SINR for a given transmission.

The use of IPSec for securing communication between nodes of wireless and mobile ad hoc networks has traditionally been considered difficult. We describe an IPSec-based architecture and implementation for ad hoc networks that can seamlessly handle node mobility and IP address change. The approach can be used for securing application traffic as well as configuration and mobility management protocol traffic. A certificate-based approach that aids dynamic key generation and distribution is used for creating security associations between nodes. Simple and backward compatible extensions to the IPSec and PKIX protocols that do not violate existing and proposed standards are described, and an existing implementation is discussed. Initial experimental evaluation reveals that the perpacket latency overhead at the end-host for using our proposed mechanisms is tolerable.

Abstract-In an effort to realize wireless Internet telephony and multimedia streaming in a highly mobile environment a testbed emulating a wireless Internet has been built. This would allow setting up multi-media calls between IP mobiles and integration between IP and PSTN end-points in a wireless environment. Different functionalities and components involved with the wireless Internet streaming multimedia have been prototyped and experimented in the testbed. These include signaling, registration, dynamic binding, location mangamenet as well as supporting the QoS features for the mobile users. This paper describes some of the components of the testbed and highlights the experiences while building this testbed which could be beneficial to some who plan to build a similar testbed to realize several features and capabilities of Mobile Wireless Internet, before actually bringing to the market.