Block Negative Acknowledgement protocol for reliable multicast in IEEE 802.11

The default multicast transport of the IEEE 802.11 standard does not use any feedback policy to detect and retransmit missing packets. Consequently, it has a limited reliability. In this paper we introduce the Block Negative Acknowledgment (BNAK) protocol as a solution for a reliable multicast transport in wireless networks. Using BNAK, the Access Point (AP) transmits a block of multicast packets followed by a Block Negative acknowledgement Request (BNR). Upon the reception of a BNR, a multicast member sends a BNAK response, only if it has some missing packets. A BNAK is acknowledged and therefore is delivered reliably to the AP. Moreover it is transmitted after channel contention in order to avoid eventual collisions with other feedbacks. Under the assumption that (1) the receiver is located within the coverage area of the sender, (2) the multicast packets are delivered using the appropriate data rate and (3) the collisions are avoided, the Packet Error Rate (PER) of the network becomes very low. To guarantee a limited PER, BNAK requires the use of a collision prevention feature (such as CTS-to-Self), and defines a retirement/reactivation procedure. Thus few feedbacks are generated and the bandwidth is saved. We show that our protocol has very high scalability and outperforms the proposals defined by 802.11v and 802.11aa considerably. Particularly our protocol can achieve a throughput exceeding 10 times that of GCR-BACK.