I have tried to set the wifi multicast rates and find that all the multicast packets are send by 80211g, so that the max rate is 54M. Can I use the 80211n to achieve higher rate?
The 802.11 standard calls for broadcasts and multicasts to be sent at the lowest possible rate. That is because there may be receivers too far from the WAP to receive at a higher rate, and multicasts and broadcasts must reach all the receivers.
The original way to overcome this is to convert multicast to unicast at the WAP.
In multicast, a single sender transmits data packet to multiple recipients at the same time. The multicast is an efficient way to transmit data packets to multiple stations that need them. However, unlike unicast, there is no feedback process, i.e., sending ACK, and therefore it does not guarantee reliability. On the other hand, assuring maximum reliability to multiple recipients causes multicast data to be transmitted at the lowest data transmission speed.
Although sending multiple unicast frames in place of a single multicast or broadcast frame may be even slower, depending on how many receivers and the unicast rate.
There is now the 802.11aa standard, but it will take some time before both WAPs and hosts are compliant with the standard.
The IEEE 802.11aa Task Group has recently standardized a set of mechanisms to efficiently support video multicasting, namely, the Group Addressed Transmission Service (GATS). In this article, we report the implementation of these mechanisms over commodity hardware, which we make publicly available, and conduct a study to assess their performance under a variety of real-life scenarios. To the best of our knowledge, this is the first experimental assessment of GATS, which is performed along three axes: we report their complexity in terms of lines of code, their effectiveness when delivering video traffic, and their efficiency when utilizing wireless resources. Our results provide key insights on the resulting trade-offs when using each mechanism, and paves the way for new enhancements to deliver video over 802.11 Wireless LANs.