Multicast transmission optimization

Multicast transmission optimization (MTO) is a HPE Aruba Networking innovation that when used can forward specific multicast frames at higher transmit data rate than other 802.11 broadcast multicast frames. When MTO is enabled in a WLAN profile, IP multicast frames that are marked with a differentiated services code point (DSCP) value that maps to the WMM video access category (VI_AC) are forwarded at the higher transmit data rate. By default, the following DSCP values map to the VI_AC:

• CS4 (32)
• AF41 (34)
• AF42 (36)
• AF43 (38)
• CS5 (40)
• EF (46)

By default, MTO forwards marked multicast frames at 24 Mbps with a configurable maximum transmit data rate of MCS15. When MTO is enabled, only IP multicast frames assigned to the VI_AC WMM transmit queue are transmitted at the higher data rate. All other 802.11 broadcast multicast frames are transmitted by each radio at their minimum configured transmit data rate.

Recommendation

MTO is a unique feature designed to support IP multicast video distribution for specific use cases. This feature should only be enabled when advised by your HPE Aruba Networking account team.

Configuration

MTO is enabled within each WLAN profile and by default will transmit multicast frames placed into the VI_AC WMM transmit queue at a 24 Mbps transmit data rate. The transmit data rate for MTO is configurable between 6Mbps and MCS15 but is only customizable using an API. In classic Central, MTO is enabled for each WLAN under Broadcast/Multicast and on New Central, MTO is enabled for each WLAN profile under Broadcast/Multicast

Before and after

The following packet capture depicts an IP multicast video stream transmitted to wireless stations when MTO is disabled. The IP multicast video stream is transmitted at lowest configured transmit data rate, in this example 24 Mbps:

The following packet capture depicts an IP multicast video stream transmitted to wireless stations when MTO is enabled. The IP multicast video stream is marked with a DSCP value assured forwarding 41 that maps to the WMM VI_AC transmit queue. The IP multicast video frames are transmitted by the radio at the configured MTO rate, in this example 54 Mbps: