In news that is huge for VoWi-Fi, the Wi-Fi Alliance announced on June 30th a new certification program, “Voice-Personal.” Eight devices have already been certified under this program, including enterprise access points from Cisco and Meru, a residential access point from Broadcom, and client adapters from Intel and Redpine Signals.

Why is this huge news? Well, as the press release points out, by 2011 annual shipments of cell phones with Wi-Fi will be running at roughly 300 million units. The Wi-Fi in these phones will be used for Internet browsing, for syncing photos and music with PCs, and for cheap or free voice calls.

The certification requirements for Voice-Personal are not aggressive: only four simultaneous voice calls in the presence of data traffic, with a latency of less than 50 milliseconds and a maximum jitter of less than 50 milliseconds. These numbers will produce an acceptable call under most conditions, but a network round-trip delay of 300 ms is generally considered to approach the limit of acceptability, and with a Wi-Fi hop at each end running at the limit of these specifications there would be no room in the latency budget for any additional delays in the voice path. The packet loss requirement, 1% with no burst losses, is a very good number considering that modern voice codecs from companies like GIPS can yield excellent sound quality in the presence of much higher packet loss. This number is hard to achieve in the real world, as phones encounter microwave ovens, move through spots of poor coverage and transition between access points.

Since this certification is termed “Voice-Personal,” four active calls per access point is acceptable; a residence is unlikely to need more than that. Three of the four access points submitted for this certification are enterprise access points. They should be able to handle many more calls, and probably can. The Wi-Fi Alliance is planning a “Voice-Enterprise” certification for 2009.

There are several things that are good about this certification. First, the WFA has seen fit to highlight voice as a primary use for Wi-Fi, and has set a performance baseline. Second, this certification requires some other certifications as well, like WMM power save and WMM QoS. So far in 2008, of 99 residential access points certified only 6 support WMM power save, and of 52 enterprise access points only 13 support WMM power save. One of the biggest criticisms of Wi-Fi in handsets is that it draws too much power. WMM power save yields radical improvements in battery life - better than doubling talk time and increasing standby time by over 30%, according to numbers in the WFA promotional materials.

Today’s Wall Street Journal has a good article about T-Mobile’s UMA trial in Seattle. It says that T-Mobile may be rolling it out nationally as early as next month, despite some trial particpants’ complaints about handoff and battery life issues. T-Mobile will be offering a home router to help with QoS and battery life. I presume that for the battery life this is just WMM Power Save (802.11e APSD) since that is what the phones in the trial (Samsung T709 and Nokia 6136) support. For QoS side I expect these APs will support WMM (802.11e EDCF), but they could also support some proprietary QoS on the WAN access link, the way that the AT&T CallVantage routers do, which would be interesting.

There is some background on the trial here.

The article goes on to put the trial into the context of other FMC deployments, from BT Fusion, Telecom Italia and Orange. The article quotes a Verizon Wireless spokesman saying that they aren’t convinced that Wi-Fi can deliver high enough voice quality to carry Verizon branded calls. This is amusing bearing in mind the usual quality of a cellular call in a residence.

The article also quotes Frank Hanzlik, the head of the Wi-Fi Alliance as saying that business FMC may have more potential than consumer. I agree.

Interesting new series of white papers on Wi-Fi interference from Craig Mathias of the Farpoint Group. He set up a couple of clients and attempted various activities (file transfer, VoIP, video streaming) in the presence of interference from various sources (microwave oven, cordless phone, DECT phone, another AP, a Bluetooth headset) and characterized the impairments. His conclusions were that some interference sources can completely shut down some uses (almost all of them shut down video), but that interference can be managed and does not present a long term stopper to Wi-Fi.

Missing from the tests was 802.11n. This should make a huge difference, for several reasons. First, its MIMO operation is intrinsically more resistant to interference, second 11n operates both in the 2.4 GHz frequency range (like 11b/g) and in the 5 GHz frequency range (like 11a) . The 5 GHz waveband is immune from microwave oven interference, and most of the cordless phone interference. Its disadvantage of shorter range is mitigated by the multi-path amplification effect of MIMO.