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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.

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    What is your WAP model and configuration? Also, broadcast, including multicast, on Wi-Fi uses the slowest available speed on a WAP, which.is why many WAPs give you the option to convert multicast to unicast.
    – Ron Maupin ♦
    Nov 27, 2016 at 2:03
  • i'm using various engenius 2x2 and 3x3 APs. All packets are multicast. i'd rather turn off any lower speeds, force multicast to go at fastest options avialable, and configure it to send true multicast/broadcast (transmit 1x to ALL clients, not 1x to each client). i've turned OFF 2.4ghz, only running on 5ghz, 80mhz, mcs9.. is there a way to 'up the speed' so multicast will run faster? how would i do this?
    – frank ankersly
    Nov 27, 2016 at 3:21
  • i have no desire for this network to do ANYTHING BUT do super high speed multicast. I do not care about unicast other than for basic association & dhcp. The AP handles only connections - DHCP is handled elsewhere.
    – frank ankersly
    Nov 27, 2016 at 3:25
  • You can "up the speed" for Wi-Fi multicast by converting it to unicast. This whitepaper explains the the IEEE 802.11 standard for multicast only supports the lowest available speed, and the proposal is to convert multicast to unicast. There is also the new 802.11aa standard, but it may be a while before it is common for both WAPs and hosts. You don't have much in the way of options right now.
    – Ron Maupin ♦
    Nov 27, 2016 at 3:31
  • "EEE 802.11 standard for multicast only supports the lowest available speed" When you say this, does it mean the lowest available speed ON THIS PARTICULAR AP?? Is there a way to force a particular AP to run at a much higher speed? would it be possible to force multicast to run at the same speed/highest speed that an AP can handle? in many networks this would not be optimal. BUT the clients on this network will only be high speed - and we want them to run ONLY high speeds (this is in a backhaul process for transferring this multicast to remote locations using fixed equipment).
    – frank ankersly
    Nov 27, 2016 at 3:42

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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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