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I have an Apple AirPort Extreme Rev C (2011) and I need to set a manual multicast rate. While I can set a manual multicast rate, I only have the option between low, medium and high.

In the previous versions of the Apple AirPort Extreme you had the option of 1mbps, 2mbps, 4mbps, 6mbps and 12mbps.

How do you get these options back? I need to set the multicast rate at 6mbps, not a vague range of low, medium and high...

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2 Answers 2

up vote 4 down vote accepted

For simultaneous dual-band APs, the AirPort Utility displays Low/Medium/High instead of numeric rates in the multicast rate pop-up menu because it means different things in the different bands.

Here's what those settings mean, per band:

   Low:  2   mbps in 2.4GHz,  6 mbps in 5GHz  
Medium:  5.5 mbps in 2.4GHz, 12 mbps in 5GHz  
  High: 11   mbps in 2.4GHz, 24 mbps in 5GHz  

Note that the AirPort Extreme's default "Automatic" radio mode supports 802.11b clients in 2.4GHz, so the multicast rates for that band in this table are 802.11b CCK and 802.11-1997 DSSS D[B|Q]PSK rates. In contrast, 802.11 in 5GHz started with 802.11a OFDM rates, so there are no 1/2/5.5/11 rates in that band.

If you change your radio mode on the 2.4GHz radio to G-only or N-only, the 2.4GHz band "Low/Med/High" multicast rates match the 5GHz values in the chart above. Note that to see some of these options, you'll need to hold option on the Mac or alt on Windows while clicking the Radio Mode pop-up menu. Also note that "N-only" requires clients to be N-capable to join, but it doesn't force clients to use only N-style MCS-based rates; it still enables the A/G OFDM rates so that clients can choose those rates for possibly greater range or power savings.

Contrary to what you said in your Question, there was never an option for a 4mbps multicast rate because there is no such thing as a 4mbps data rate in 802.11, a, b, g or n.

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Thanks, that makes sense. Now that I know what the low, med, high options means in both bands, I changed my settings from high to medium (since I only need around a 6mbps multicast rate in both bands)... and now my IPTV stream from ISP is streaming uninterrupted. The high option was overkill. –  cappuccino Mar 10 '11 at 15:52

I don't believe you can get these options back. That said, the exact amount really should not matter.

The Multicast Rate option sets the threshold throughput level a wireless client must meet in order to be "accepted" by the base station. The lower this value, theoretically, the greater number of clients that can connect, especially those at greater distances from the base station.

At the opposite end, the higher this number, only those wireless clients that can achieve the higher throughput value will be able to connect.

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In my case the exact amount does matter because my IPTV stream from my ISP does not work with a multicast lower than 6mbps. The low medium and high options is vague, I mean, what does low medium and high mean???? I have it set to high, and the IPTV stream is always breaking, even when i'm next to the router. I have it set on 5ghz N only... Pretty crap considering my old G router could maintain a stream... What to do?... –  cappuccino Mar 10 '11 at 8:04

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