Does Wi-Fi MultiMedia (WMM) Really Do Anything?

[mgraves]

This is very interesting. My first exposure to WMM was a year ago when undertaking the review of the Polycom/SpectraLink 8002 Wifi SIP handset (http://www.smallnetbuilder.com/content/view/30498/80/)

My old Wifi AP (Linksys WAP-54G) was adequate to make/receive calls while there was little else using the WLAN. If I started up Outlook on a laptop logged into Exchange via PPTP VPN the traffic it generated by checking mail and synchronizing folders would cause calls to break-up.

When I changed to a Netgear WRT-2000 router (used just as an AP) capable of WMM the problem disappeared.

Michael

[rogerbinns]

It may be covered in part two or not. In order to implement QOS the hardware has to have the ability to store a queue of packets, and then be able to transmit them in a different order than received. This is obviously more complex than a simple no buffering transmit as you receive.

The part of WMM that is really important to me is power saving with my wifi enabled cell phone which allows me to make and receive cell phone calls over wifi. (Under the hood the data packets that would go over the cellular network are wrapped up and sent over wifi. It works very well.)

The power saving part of WMM comes in because it allows the phone to turn off its radio while the access point queues any packets for the phone. The phone can then briefly turn the radio on once every second or two to ask if the access point has anything for it and then power back off. This saves a considerable amount of power versus having the radio on all the time. I get slightly better battery life than using the cellular network! With a previous access point that didn't have WMM, the cell phone battery would be almost dead after about 6 hours.

[thiggins]

Thanks for the comments, Roger. I'm only focusing on the QoS aspects of WMM in this series, not WMM Power Save, which is a separate Wi-Fi Certification.

[harsh3090416]

well i always have problems with watching streaming sports game on my laptop
on my desktop it works perfect doesn't buffer and the quality also looks better than my laptop. I always wondered what the problem is but i never actually found my answer. i have used many different routers from linksys to d-link and right now i am with verizon fios so i have the actiontec router i think that the problem is that the wireless routers have some problem with streaming video's.

I don't maybe it might be this WMM that could change my world around and i would finally be able to connect my laptop to my HDTV and watch my favorite sports on tv that i don't get here USA.

I own several Roku Soundbridge players that I use to stream WMA lossless music files from a Windows Home Server. I have had re-buffering problems that would appear regularly and completely ruin the listening experience.

I have a DIR-655 A4 with 1.21 firmware and I don't believe that there is a better router on the market today at this price point.

I believe that I have solved the re-buffering issue by disabling the WMM feature on the DIR-655. I believe that it may have been de-prioritizing my music streams and limiting the bandwidth, causing the re-buffering.

I hope this helps other Roku users who are experiencing the same issue.

Regards,

Pete

[mgraves]

That makes me wonder of WMM is acting in a UDP specific fashion. Would a WMM implementation prioritize UDP streams like voice over a TCP stream?

[thiggins]

Originally Posted by mgraves

Would a WMM implementation prioritize UDP streams like voice over a TCP stream?

No. WMM is protocol agnostic and only processes DSCP and 802.1p priority information in the stream.

Remember that the DIR-655 and other D-Link products use Ubicom auto-QoS technology, including its WISH wireless form. There could have been some interaction between WMM and WISH.

It would also be interesting if the same effect were seen by disabling WMM in the Soundbridge.

Hi Tim,

Thanks - interesting article. I work for the Media Center team at Microsoft and must clarify an important point -

1. A PC running Windows Vista Media Center SKU (Home Premium/Ultimate) doesnt become a Media Center server for all client end points. specifically - when you stream video from a Media Center PC to another client PC using Windows Media Player -this uses WMP technology (and whether the source PC is a Media Center PC or not doesn't matter).

2. However if you stream a video (limited to some codecs, TV content or WMV for example) from Media Center to Media Center Extender such as Xbox 360 - media is streamed over RTP/UDP and the 802.1p tags are set correctly to take advantage of WMM/QoS prioritization.

Great point about the lack of awareness amongst media server applications setting the QoS prioritization tags incorrectly.

Highly recommend you to get hold of a Xbox 360 and use it as a Media Center Extender in your experiments.

Thx,
Sidd

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