Example 8: Ip Multicast Enhancements - Black Box SmartPath LWN602A User Manual

Chapter 8: Basic Configuration Examples
You can also create these lists through the CLI. To create a whitelist for selective multicast forwarding through GRE tunnels except
for a single IP address (for example, 224.1.1.10), make an SSH connection to the SmartPath AP where you want to create the
whitelist, and then enter the following command:
forwarding-engine tunnel selective-multicast-forward block-all except 224.1.1.10
To create a whitelist for selective multicast forwarding except for a range of IP addresses (e.g., 224.1.1.0/24), enter the following
command:
forwarding-engine tunnel selective-multicast-forward block-all except 224.1.1.0/30

8.8 Example 8: IP Multicast Enhancements

IP Multicast Enhancements: To minimize airtime consumption caused by multicast frame transmissions, SmartPath APs can convert
multicast to unicast frames when channel utilization is high or multicast group membership is low. Furthermore, when SmartPath
APs cannot detect any multicast group members among their active clients, they can automatically suppress multicast frame
transmissions completely.
Video streaming typically makes use of multicasting as its transport. With multicasting, a data stream from a single source reaches
multiple subscribers identified by their multicast group IP address. These subscribers notify their network routers and switches
when they belong to a particular group and are interested in receiving data. When a router or switch receives such a notification,
it then forwards any multicast stream for that group onto the network segment from which it received the notification. If there
are no subscribers on a particular segment, the forwarding device stops transmitting the stream to conserve bandwidth.
On a wireless network, data transmitted by multiple stations on the same RF channel in an overlapping area must share the same
physical transportation resource: the available airtime. When an access point transmits unicast traffic, it uses a rate-adaptation
algorithm to determine the fastest data rate at which it can communicate with each station. When transmitting multicast traffic,
the access point must choose the best data rate all the group members can support. If one group member has a slow
connection, the access point must transmit at that speed to all group members. This not only slows down data transmissions to
other members with stronger connections, it also uses up more airtime that otherwise would be available for use by other
wireless stations in the area.
To reduce unnecessary airtime usage for multicast transmissions, a SmartPath AP can convert multicast frames to unicast frames
under certain conditions or at all times, and it can also drop multicast frames when there are no group members present to
receive them. In addition to reducing airtime usage, another benefit of using unicast traffic is the increased reliability of video
delivery. If a wireless client does not receive a unicast frame and does not reply with an ACK, the access point will retransmit it.
However, multicast traffic does not support wireless frame delivery confirmation as unicast traffic does.
When a SmartPath AP is enabled to convert multicast frames to unicast, it performs the conversion when the percent of channel
usage exceeds a specified threshold or when the number of multicast group members drops below a specified threshold. By
default, the channel utilization threshold is 60% and the membership count threshold is 10. You can change the channel utiliza-
tion threshold from 1 to 100 % and the membership count threshold from 1 to 30 on a per-SSID basis. These settings are on the
Configuration > SSIDs > New page in the IP Multicast subsection within the Advanced section.
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