Wireless local area networks ( W L A N ) are expected to be a major growth factor for communication networks in the up-coming years. They are expected to provide a transparent connection f o r mobile hosts to communicate with other mobile hosts, and wired hosts o n the wired L A N and broadband networks. Recently there have been two W L A N projects u ndergo standardization process: the I E E E 802.11 and the E T S I H I P E R L A N . Most of the existing study of the two M A C protocols focused o n simulation results, and none of t h e m has formally analyzed the hiddenterminal effect, which is both crucial and unavoidable in wireless/mobile environment. I n the first part of this paper, we formally analyze the hidden-terminal effect o n H I P E R L A N . Through mathematical analysis, we formulate network throughput under hiddenterminal influence in terms of the original (clearchannel) throughput, hidden-terminal probability, and other protocol parameters. W e show that when hidden probability is greater than zero, the achievable throughput is reduced b y more than the percentage of hidden probability. I n the second part of the paper, we evaluate and compare the two W L A N M A C protocols by simulation o n the effect of hidden terminals o n (1) network throughput, (2) real-time voice delay, and (3) number of voice and data stations supported while guaranteeing delay f o r voice. W e also evaluate how well the two M A C protocols support real-time trafic while considering the effects of frame size and other network parameters, and measure (1) the distribution of voice *and ENH-TR-95. delay and (2) number of voice and data stations supported while guaranteeing their quality of service. W e found that, comparing with IEEE 802.11, H I P E R L A N provides real-time packet voice trafic with shorter delay, and at the same time provides the non-real-time packet data with higher bandwidth.

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The major challenges of designing multicast ratecontrol protocols f o r a combined wired/wireless network are the varying transmission characteristics (bandwidth, error, and propagation delay) of the wireless and wired media, and the different, possibly conflicting flow control requests from multiple receivers. To address these issues, in this paper we study multicasting rate-control ABR algorithms for a combined wired/wireless network with unreliable links and irregular network feedback. W e propose a new ABR multicast extension algorithm that can readily extend any unicast ABR rate control scheme for multicast services. By formal analysis, we show that it is max-min fair, and that its maximum cell loss is less than or equal to that of a n existing algorithm proposed by Siu and Tseng [15]. W e also extend the definition of global feasibility t o multicast flows, and propose a dekayedincrease policy t o ensure global feasibility. Both the waiting time of the delayed-increase policy, and the maximum cell loss in the absence of the policy are formally analyzed. The new algorithm requires a waiting time n o longer than, and has a maximum cell loss less than or equal to, that of the existing algorithm. The significance of our approach i s illustrated by the formal analysis, which allows u s t o design a new multicast extension algorithm that is max-min fair, results in a small cell-loss bound, and achieves global feasibility. The analytical method m a y also assist the design and analysis of other multicasting flow algorithms over A X M and wireless A T M , and other network: protocols such as multicast IP and mobile IP.

Multipoint communication has been an increasingly focused topic in computer communication networks, including both the Internet and the ATM networks. We have previously presented, analyzed, and evaluated new point-tomultipoint ABR flow control algorithms. In this paper, we focus on multipoint-to-point flow control. As the major objective of ABR service is to provide minimum-loss, fair service to data traffic, an effective merge-point scheme for multipoint-to-point flow control should guarantee some suitable fairness. In this paper, we first examine the "essential fairness" concept proposed by Wang and Schwartz for point-to-multipoint flow control in the Internet. We extend and enhance the concept to the multipoint-to-point ABR flow control. A general algorithm guaranteeing essential fairness is presented, with a detailed implementation on top of the ERICA unicast algorithm proposed by Jam, et. al. The general algorithm may be used for a wide range of fairness specifications to accommodate various bandwidth requirement from unicast or multicast sources of different application streams.Three major variations of the general algorithm are presented. These three schemes are simulated and evaluated, and compared with an existing scheme proposed by Ren, Siu, and Suzuki. Simulation results show that the proposed merge-point algorithm achieves, within short transient time, max-mm fairness based on different weights given to individual sources or sessions, or according to various specifications of fairness. The fairness concept and the general algorithm presented here may be readily applied to other high-speed networks such as the Next Generation Internet and Wireless ATM, and to different multicast settings such as point-to-multipoint and multipoint-to-multipoint.

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