One of the major features proposed in the IEEE 802.11n amendment is the use of frame aggregation. Thus, two types of frame aggregations are defined: MAC Service Data Unit Aggregation (A-MSDU) and MAC Protocol Data Unit Aggregation (A-MPDU). As frame aggregation is mainly defined to increase the efficiency of the MAC layer, this feature is very needed to support multimedia traffic such as High Definition TV (HDTV). The multicast transport is another way to increase the MAC layer efficiency by transmitting the same information only once to many receivers. However, the 802.11 standard does not define a reliable multicast and consequently the 802.11n is unable to provide a reliable transport for multicast streams. The 802.11aa remains the only draft to handle the unreliability issue of the multicast, but the proposed solution is defined only for the legacy 802.11 standard and does not consider the aggregation feature of the 802.11n. In this paper we design a new extension for the 802.11aa in order to take a full advantage of the 802.11n capabilities and we provide a new analytical model to evaluate the performance of the MAC layer. We particularly study the impact of the frame aggregation type on the MAC throughput for the multicast transport. Our results show that in an ideal channel (no losses), A-MSDU slightly outperforms A-MPDU when using the data rate of 6.5Mbps and both schemes have the same performance with rates of 130 and 300 Mbps. However the use of A-MPDU aggregation becomes more efficient in a noisy channel.
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