Multicast video traffic

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How many sets of simultaneous multicast video traffic can ruckus AP handle?
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Posted 2 months ago

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Albert Pierson, Employee

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Hi Huge,

There are no specific limits to the number of multicast video streams a Ruckus AP can handle.

Ruckus has a robust QOS implementation that is part if it's DNA as Ruckus started as a IPTV over WiFi company (Media Cast product line) - the QOS features are known as Smart Cast and are still part of the latest versions of code and products.

For IGMP subscription based multicast as used in IPTV video streams, Ruckus has a multicast to unicast feature called Directed Multicast.  Since multicast messages must usually be sent to all connected clients at different distances and capabilities, generally multicast messages are sent at the lowest common data rate.  Originally this was 1Mbps for 802.11b, 6mbps for 802.11g and above. 

Directed Multicast will sniff for IGMP messages, build a table of devices connected to a given IGMP group and then convert inbound multicast packets into separate unicast packets sent to each client at the highest data rate that particular client can receive (verified by acknowledgment success)

Directed Multicast is enabled by default on all interfaces and can be disabled, but this can be detrimental for high speed transmission of IGMP multicast traffic.

The limit to the number of Directed Multicast streams is the limit of the AP throughput, as in all traffic.  AP's that support higher data rates (802.11ac, 802.11ax) will be able to handle many more streams then older 802.11n or even 802.11g AP's and clients.

The answer on the number of streams supported per AP gets complex, especially if the AP is providing other WLAN services

There is no simple answer to how many clients ... Testing with Ruckus original 802.11g ZF 2942 began to have issues after about 24 streaming clients. 

Monitoring Airtime statistics for the AP can indicate if a limit is being reached for a given model AP and client mix. 

You can always limit the number of clients per WLAN to prevent over subscribing an AP capacity.

With a general best practice allowing more clients on 5GHz than 2.4GHz, assuming the proper conditions exist (clients support 40MHz channels, clean environment, etc).

This information should be visible in the Monitor Access Point section for AP's managed by a controller.  The Airtime usage is also visible in the AP support info file under "athstats" section for each AP.  A histogram of Airtime shows if the AP radio is getting saturated.

------------ Airtime Stats ------------
Airtime utilized (percent) since clearing delta stats (1 sec)
   Busy:  0    RX: 43    TX: 17    Total: 60
Histograms of airtime (pcttime in each range) since clearing all stats
        0  0-10  ..20  ..30  ..40  ..50  ..60  ..70  ..80  ..90 ..100
busy:  79    21     0     0     0     0     0     0     0     0     0
rx:     0     0     1     3    24    52    16     2     1     1     0
tx:     0    92     6     1     0     0     0     0     0     0     0
tot:    0     0     0     1    13    47    28     6     2     1     1

In this case (a 2.4GHz or WiFi0 radio) we see 1% of the samples are hitting 100% utilization.  This looks like it i due to overlapping radios since rx is higher then rx utilization.  Issues with saturation of video streams would show up under tx since this traffic is coming from the AP to the Client device.

I hope this information is helpful

Thank you for choosing Ruckus Networks