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Frame aggregation is the most important medium access control (MAC) enhancement of IEEE 802.11n. In frame aggregation, multiple frames are encapsulated into a single frame. In the analysis of 802.11n performance, the existing researches assumed that each station always had a packet for transmission. But actually, sometimes stations may have no packet to transmit. In this paper, we develop an analytical model for IEEE 802.11n in unsaturated conditions. Therefore, the transmission of the station is assumed to be a bulk service queue system. Bulk size is aggregation size. According to the 802.11n standard, when the number of packets in the buffer is smaller than the aggregation size, we can also transmit all the packets in the buffer using A-MPDU. Therefore, bulk size is variable. The throughput and mean access delay are achieved. Numerical results show that the proposed algorithm can effectively increase the throughput and lower the access delay.

In queueing systems with multi-server models, every server goes on vacation irrespective of the availability of the server in the system. This creates inconvenience to the customers in places like computer network, communication network, hospitals, telegraph offices and telephone booths, etc., where at least one server must be available in the system for service. In this paper, an analysis has been carried out on a bulk service queueing system with two servers in which at least one server is available for service in the system always.