VoIP over Wireless

Unanswered Question
Apr 10th, 2008

I am working on a study and feasability project to implemnet a VoIP solution to an existing LAN/WAN infrastructure.

Currently, we have a campus LAN; multiple buildings each with 3 cascaded switches linked to a central building ( Bldg A), where the core switch is and connected to the gateway router. A wireless bridge is linked to the core switch and wirelessly connecting a remote building (Bldg B) to the core switch. So, the question is if I were to move the core switch and gateway router(WAN link is DS3 to headquarters) to building (B), link Bldg (A) and Bldg (B) wirelessly, and implement VoIP, would this design create any performance issues? My concern is if VoIP and data would suffer throughput issues due to the 54Mbps Wi-Fi speed. Any thoughts or feedback?

Thanks in advance,

sK

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Paolo Bevilacqua Thu, 04/10/2008 - 09:40

Hi, I've seen VoIP over wireless in many installations and always without any issue.

Then if you want to do things the proper and careful way, you would use cisco or other brand wireless devices with support of QoS to give preferential treatment to voice.

Hope this helps, please rate post if it does!

skhirbash Thu, 04/10/2008 - 10:36

Thank you P.

Yes, we are a Cisco shop, so all networking devices are Cisco.

Thanks,

sK

Joseph W. Doherty Thu, 04/10/2008 - 10:36

With VoIP, always important to keep in mind it's much more sensitive to delay, jitter and drops. Most of these are often not issues on LANs, whether it might be on your 54 Mbps WiFi link depends on how much traffic you will pass across the link. If this link, or other links, have congestion, CoS/QoS often provides the solution, as also mentioned by Paolo.

Also keep in mind for your 54 Mbps, it's often difficult to get anywhere near "full" bandwidth if using wireless encryption and/or multiple hosts on wireless AP. Hopefully you'll get much better on a dedicated wireless bridge (directional antennas?). Other issue with wireless, often many more corrupted frames (especially bad for traffic like VoIP), again, hopefully, a dedicated wireless bridge will be much better.

skhirbash Thu, 04/10/2008 - 11:11

Yes, wireless link is on dedicated wirless bridge (directional antennas). However, what did you mean by multiple hosts on wireless AP?

Thanks,

sK

Joseph W. Doherty Thu, 04/10/2008 - 11:54

Since you described 54 Mbps, I thought you might be using a device like a Cisco Aironet 1300/1400 Series Wireless Bridge that uses 802.11 "g" or "a" channels. Wireless 802.11a/b/g APs share the "air" much as Ethernet hubs shared the wire. I would be concerned if multiple wireless AP clients where using the same channel or near by channel as your bridge. Such interference can reduce wireless throughput; the directional antennas should help.

skhirbash Thu, 04/10/2008 - 13:41

Yes, I was considering using the 1400s; however, since you brought up these points, which Cisco wireless bridges would you recommend in this situation. I would like to connect 2 bldgs to the central bldg via wireless and implement VoIP.

Joseph W. Doherty Thu, 04/10/2008 - 17:41

I don't really have enough expertise in this area to make a recommendation. However, since the 1400 uses "a" channels, less likely to have interference from typical wireless clients that use "b/g" channels.

For further suggestions or recommendations on the wireless aspect, you might post a question within the wireless forum.

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