Two important Quality-of-Service (QoS) measures for current cellular networks are the fractions of new and handoff "calls" that are blocked due to unavailabili t y of "channels" (radio and/or computing resources).Based on these QoS measures, we derive optimal admission control policies for three problems: minimizing a linear objective function of the new and handoff call blocking probabilities (MINOBJ), minimizing the new call blocking probability with a hard constraint on the handoff call blocking probability (MINBLOCK) and minimizing the number of channels with hard constraints on both of the blocking probabilities (MINC). We show that the well-known Guard Channel policy is optimal for the MINOBJ problem, while a new Fractional Guard Channel policy is optimal for the MINBLOCK and MINC problems. The Guard Channel policy reserves a set of channels for handoff calls while the Fractional Guard Channel policy eflectively reserves a non-integral number of guard channels for handoff calls by rejecting new calls with some probability that depends on the current channel occupancy.It is also shown that the Fractional policy results in significant savings (20-50%) in the new call blocking probability for the MINBLOCK problem and provides some, though small, gains over the Integral Guard Channel policy for the MINC problem. Further, we also develop computationally inezpensive algorithms for the determination of the parameters for the optimal policies.

Recent interest in supporting packet-audio applications over wide area networks has been fueled by the availability of low-cost, toll-quality workstation audio and the demonstration that limited amounts of interactive audio can be supported by today's Internet. In such applications, received audio packets are buffered, and their playout delayed at the destination host in order to compensate for the variable network delays. The authors investigate the performance of four different algorithms for adaptively adjusting the playout delay of audio packets in an interactive packet-audio terminal application, in the face of such varying network delays. They evaluate the playout algorithms using experimentally-obtained delay measurements of audio traffic between several different Internet sites. Their results indicate that an adaptive algorithm which explicitly adjusts to the sharp, spike-like increases in packet delay which were observed in the traces can achieve a lower rate of lost packets for both a given average playout delay and a given maximum buffer size

Abstract-As local area wireless networks based on the IEEE 802.11 standard see increasing public deployment, it is important to ensure that access to the network by different users remains fair. While fairness issues in 802.11 networks have been studied before, this paper is the first to focus on TCP fairness in 802.11 networks in the presence of both mobile senders and receivers. In this paper, we evaluate extensively through analysis, simulation, and experimentation the interaction between the 802.11 MAC protocol and TCP. We identify four different regions of TCP unfairness that depend on the buffer availability at the base station, with some regions exhibiting significant unfairness of over 10 in terms of throughput ratio between upstream and downstream TCP flows. We also propose a simple solution that can be implemented at the base station above the MAC layer that ensures that different TCP flows share the 802.11 bandwidth equitably irrespective of the buffer availability at the base station.

Mobile IP is the current standard for supporting macromobility of mobile hosts. However, in the case of micromobility support, there are several competing proposals. In this paper, we present the design, implementation, and performance evaluation of HAWAII: a domain-based approach for supporting mobility. HAWAII uses specialized path setup schemes which install host-based forwarding entries in specific routers to support intra-domain micro-mobility. These path setup schemes deliver excellent performance by reducing mobility related disruption to user applications. Also, mobile hosts retain their network address while moving within the domain, simplifying QoS support. Furthermore, reliability is achieved through maintaining soft-state forwarding entries for the mobile hosts and leveraging fault detection mechanisms built in existing intra-domain routing protocols. HAWAII defaults to using Mobile IP for macromobility, thus providing a comprehensive solution for mobility support in wide-area wireless networks.

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In third generation (3G) wireless data networks, multicast throughput decreases with the increase in multicast group size, since a conservative strategy for the base station is to use the lowest data rate of all the receivers so that the receiver with the worst downlink channel condition can decode the transmission correctly. This paper proposes ICAM, Integrated Cellular and Ad hoc Multicast, to increase 3G multicast throughput through opportunistic use of ad hoc relays. In ICAM, a 3G base station delivers packets to proxy mobile devices with better 3G channel quality. The proxy then forwards the packets to the receivers through an IEEE 802.11-based ad hoc network. In this paper, we first propose a localized greedy algorithm that discovers for each multicast receiver the proxy with the highest 3G downlink channel rate. We discover that due to capacity limitations and interference of the ad hoc relay network, maximizing the 3G downlink data rate of each multicast receiver's proxy does not lead to maximum throughput for the multicast group. We then show that the optimal ICAM problem is NP-hard, and derive a polynomial-time 4-approximation algorithm for the construction of the multicast forest. This bound holds when the underlying wireless MAC supports broadcast or unicast, single rate or multiple rates (4ð1 þ Þ approximation scheme for the latter), and even when there are multiple simultaneous multicast sessions. Through both analysis and simulations, we show that our algorithms achieve throughput gains up to 840 percent for 3G downlink multicast with modest overhead on the 3G uplink.