Wireless – truly multicast over Wifi AP

ieee 802.11multicastqoswireless

I have a small dedicated wifi network setup specifically to carry a multicast multimedia package.. no other use (no web or other data on this network, due to the arrangement)..

The issue I've found is that clients are not receiving a true multicast transmission – they're actually receiving unicast from the AP.

Some APs have options to "convert Multicast to Unicast", as supposedly it raises the QoS of the packet to a faster delivery.when I turn this off, the packet delay is FAR higher for any device/all devices…

However, as I need to deliver the multicast to more clients (dozens), i need it to truly multicast (ie., 1 RF transmission transmitting the entire packet to dozens of clients).

My clients are listening for the multicast port, but i need the AP to actually multicast/broadcast the packet..

How can this be accomplished?
I've looked at various 'open source' options (OpenWRT etc), but am unsure how to actually configure APs to accomplish this.

Best Answer

Unfortunately, you really aren't going to get what you want with today's Wi-Fi implementations. Multicast over Wi-Fi performance is pretty abysmal, today, but there are things in the future which hope to change this situation. Multicast over Wi-Fi will use the lowest available speed for multicast. The original way to overcome this is to convert multicast to unicast at the WAP.

A Scheme Improving Performance of IEEE 802.11 Multicast Protocol:

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.

There is now the 802.11aa standard, but it will take some time before both WAPs and hosts are compliant with the standard.

A First Implementation and Evaluation of the IEEE 802.11aa Group Addressed Transmission Service:

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.

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