Controller Based WLANs

How does multicast rate optimization work and at what rate are the multicast packets sent on wireless?

Product and Software: This article applies to ArubaOS 3.2 and later.

 

Broadcast and multicast rate optimization helps choose the optimal rate for broadcast and multicast frames. When enabled, a timer scans the station table and picks the lowest unicast rate across the set of associated stations. This rate is used for transmitting broadcast and multicast data frames until the timer gets triggered again in 1 second.

Broadcast and multicast rate optimization does not change the behavior of 802.11 management frames.

Starting with ArubaOS 3.3.2.11, the rate at which broadcast and multicast data is sent is controlled and is known as the control rate.

 

These tables list the different transmit rates and associated control rates.

 

Control Rates for 802.11a

Tx Rate(in Mb/s)

Ctrl Rate*(in Mb/s)

6

6

9

6

12

12

18

12

24

24

36

24

48

24

54

24

 

Note: Ctrl rate is control rate.

 

Control Rates for 802.11 b/g

 

Tx Rate (in Mb/s)

Ctrl Rate* (in Mb/s)

1

1

2

2

5.5

5.5

11

11

6

6

9

6

12

12

18

24

24

24

36

24

48

24

54

24

 

Note: Ctrl rate is control rate.

 

Control Rates for 802.11n are 6, 12, and 24 Mb/s.

 

How does multicast rate optimization work?

 

Currently, the broadcast and multicast packet is sent at basic rate. In b/g band, the default basic rate is 1/2 mb/s. This is not sufficient for some multicast applications like video streaming.

 

Starting with ArubaOS 3.2, a new knob had been introduced under the ssid profile.

 

(Aruba) (config) #wlan ssid-profile default


(Aruba) (SSID Profile "default") #?
...
mcast-rate-opt à Choose the optimal rate for broadcast/multicast frames
...

When "mcast_rate_opt" is turned on, a periodic timer fires every second. The controller scans the list of all associated stations in that BSS and finds the lowest tx rate for each station. The controller uses that rate as the tx rate for multicast and broadcast traffic.

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Last update:
‎07-01-2014 04:02 PM
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