On 15 Aug 2006 08:58:37 -0700, "Charles Kerekes" <ckerekes@gmail.com>
wrote in <1155657517.329824.129260@b28g2000cwb.googlegroups .com>:

>I am experienced in networking, but new to WiFi and VoIP. In a previous
>posting about WiFi bridging equipment, someone pointed out that all
>WiFi technologies are half-duplex and _may_ cause issues with VoIP.
>
>I am researching equipment for a wireless bridge between two buildings
>and narrowed my choices down to the Proxim Trunami 5054 or the Cisco
>Aironet 1310G bridges. One pair of these bridges will be dedicated to
>VoIP traffic, which will have to carry a maximum of 5 simultaneous
>phone conversations. The lowest aggregate throughput for these
>solutions is 23 Mbps.
>
>Will the half-duplex nature of WiFi cause quality problems for VoIP? If
>yes, are there other wireless solutions more appropriate for this
>setup? Thanks in advance.

The duplex issue is way overblown IMnsHO -- Wi-Fi latency is quite low
(on the order of a millisecond), and unless Wi-Fi speed is very slow (in
which case reliability is probably a bigger issue), the fact that only
one radio can transmit at a time is pretty much irrelevant, since even
at only 11 Mbps, each packet takes less than 2 ms of air time. Typical
end-to-end latency of a long distance voice call is orders of magnitude
higher.

The real issue is QoS (Quality of Service) when a wireless network is
under heavy load. Without QoS, there may be annoying pauses due to
congestion and packet loss.

If you dedicate a wireless link to VoIP with sufficient capacity to
handle worst case traffic then there shouldn't be any significant
problems.

The throughput of a standard 802.11g Wi-Fi link will only approach 23
Mbps at maximum 54 Mbps link speed, with requires a strong clear signal,
greatly limiting range. As range increases, throughput drops off.

To calculate the necessary bandwidth for VoIP, see
<http://www.voip-calculator.com/calculator/lipb/>. 5 voice circuits
typically only need about 0.120 Mbps (120 Kbps), a small fraction of
even a slow Wi-Fi link.

--
Best regards, FAQ for Wireless Internet: <http://Wireless.wikia.com>
John Navas FAQ for Wi-Fi: <http://wireless.wikia.com/wiki/Wi-Fi>
Wi-Fi How To: <http://wireless.wikia.com/wiki/Wi-Fi_HowTo>
Fixes to Wi-Fi Problems: <http://wireless.wikia.com/wiki/Wi-Fi_Fixes>