VOIP implementation problems for Wi-Fi

TIPPINST – Having attended the one day National Communications Network Research Centre (NCNRC) wireless workshop at UL yesterday I am now viewing Wi-Fi in a different light. The workshop reviewed the ongoing work of the Intel directed NCNRC project, in particular on Quality of Service control for 802.11 based networks, VOIP and Video, and introduced the range of test beds developed.
What was immediately evident is that the current implementation of 802.11 i.e b/g is not capable of supporting VOIP and in the future Video stream such as HDTV. I will now have to keep an eye out for 802.11e compliant devices that support QoS. The current implementations have no notion of prioritised or delay sensitive traffic. At the moment if you want an 802.11e access point you may want to consider the cisco 1200 AP and IOS 12.3(7)JA2 ) on Channel 6 which is capable of 802.11e EDCA operation
Mark Davis and his team in DIT are doing some interesting work to address this issue. As he stated in his presentation “If you can’t measure it you can’t control it” its this lack of measurement that really surprised me and I was to learn that it a common problem with Wi-Fi. There is requirement for funcionality to allow the codecs for VOIP to have a detailed picture of the current network so as they can be fine tuned. This would allow:
– Proper tuning of the playout buffer settings to compensate for jitte iin wireless networks
– Proper tuning of various MAC layer parameters (CWmin, CWmax, AIFS) to maximize capacity of the WLAN in terms of number of VoIP calls that can be supported
To this end DIT have been investigating the problems associated with how to figure out what bandwidth is available. Most laptops etc will tell you about the signal strength but have no way of indicating the available bandwidth. This is because:
– Bandwidth is shared rather than reserved
– Users must compete for bandwidth
– Network capacity is not fixed
– Users perceive different capacities
What they have produced is a Unified and tractable framework for characterising bandwidth usage on IEEE 802.11 WLANs.
Their radio resource monitor Non-intrusively measures bandwidth availability and utilisation, Operates in real-time and on a per-station basis in a variety of modes that includes 802.11b/g/a and e modes.
If you want to see the bw monitor in action you can visit http://probe.cnri.dit.ie
Visit www.cnri.dit.ie for more details
To summarise if you are considering a multimedia box to sit under the TV that will connect to the Internet and download programmes etc as well as VOIP you better ensure that you have structured cabling in place. Othewise you will have to wait for 802.11e compliant kit to come out on the market place.

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