Review of "MACAW: A Media Access Protocol for Wireless LAN's"

From: Michelle Liu (liujing@u.washington.edu)
Date: Sun Nov 21 2004 - 20:32:03 PST

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    Review of "MACAW: A Media Access Protocol for Wireless LAN's"

    Jing Liu

     

        This paper presents a media access protocol for wireless LAN; MACAW. The protocol is based on MACA and has some modification over MACA.

        The design of MACAW is based on several observations. First, the relevant contention is at the receiver, not the sender. This renders the carrier sense approach inappropriate. Second, congestion is location dependent. Third, to allocate media access fairly, learning about congestion levels must be a collective enterprise. Fourth, the media access protocol should propagate synchronization information about contention periods, so that all devices can contend effectively.

        RTS and CTS control signals are used to meet the requirement of first observation. The RTS-CTS exchange enables nearby stations to avoid collisions at the receiver, not the sender. Moreover, "hidden terminal" and "exposed terminal" scenarios are overcome. In contrast to MACA's binary exponential backoff algorithm, MACAW modifies the backoff algorithm by including in the packet header a field which contains the current value of the backoff counter. This makes a fairer allocation of resources possible and also in order to prevent a wild oscillations, multiplicative increase and linear decrease is proposed. The backoff algorithm is modified in the way that the transmission of RTS's are delayed for a random number of slots to reduce the probability of collision and to resolve collisions once they occur. ACK signal is used to schedule retransmission and DS signal is used to avoid collisions in exposed terminal scenarios.

        This paper also points out that there are still quite a lot of problems unsolved, such as multicast and the presumptions are pretty restrictive. In wireless networks, there are some key issues, such as security and energy consumption. This paper doesn't mention how to treat them. Those issues could be the future work.

        There are a lot of issues in wireless networks that haven't been well solved yet. Recently ad hoc wireless network is also a hot research topic. From wired to wireless, this is not only a trend, but also makes people's life more convenient.

        

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