WiFi bridging reliable solution for business VoIP?

Hello all,

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.

Charlie

On 15 Aug 2006 08:58:37 -0700, "Charles Kerekes" <(E-Mail Removed)>
wrote in <(E-Mail Removed) .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>

Thank you, John--your feedback has been very helpful.

I also spoke to Proxim tech support. According to them, a link carying
5 VoIP lines over a 5054 wireless bridge is a typical setup, and
provides good quality phone converstations. I assume this is also true
on a similar setup with other products, such as the Cisco wireless
bridge.

Charlie

On 15 Aug 2006 10:37:44 -0700, "Charles Kerekes" <(E-Mail Removed)> wrote:

~ Thank you, John--your feedback has been very helpful.
~
~ I also spoke to Proxim tech support. According to them, a link carying
~ 5 VoIP lines over a 5054 wireless bridge is a typical setup, and
~ provides good quality phone converstations. I assume this is also true
~ on a similar setup with other products, such as the Cisco wireless
~ bridge.
~
~ Charlie

Yes, we would certainly support 5 G.711 VoIP calls over a 54Mbps point to
point link between two BR1310s (assuming good RF.)

In my experience, the main concern would be interference in the 2.4GHz
band from other devices in the vicinity.

Regards,

Aaron

Aaron,

> Yes, we would certainly support 5 G.711 VoIP calls over a 54Mbps point to
> point link between two BR1310s (assuming good RF.)

Thanks for the reply, Aaron. Since you have a Cisco email address, can
I assume that "we" means Cisco?

Charlie

~ > Yes, we would certainly support 5 G.711 VoIP calls over a 54Mbps point to
~ > point link between two BR1310s (assuming good RF.)
~
~ Thanks for the reply, Aaron. Since you have a Cisco email address, can
~ I assume that "we" means Cisco?
~
~ Charlie

That would be a reasonable inference.

Aaron