Wireless VoIP network architecture

Wireless VoIP network architecture requires carefull planning and configuration. In IP telephony, wired and wireless, data and voice should be separated.

Following issues are key in Wireless VoIP network architecture:

1) VLANs
Virtual LANs – VLANs are mechanism to separate network in more than one segment – broadcast domains. With VLANs you could separate traffic into voice and data. This gives you possibility that you can give voice greater priority than data. More on this in QoS.

You could use VLANs, also to provide different security standards for different parts of your network. You could create one VLAN for everyone with low security level, and other VLAN that have access to sensible data with big security level.

My recommendation is to divide your network on data and voice VLAN. This gives you opportunity to give bigger priority to voice. This is also very useful in troubleshooting. You could much faster locate problem and realize is it up to telephony equipment or data.

Most of access points have possibility to have VLANs and each VLAN is mapped to specific SSID. So you need to configure your wireless telephony to use SSID which is on voice VLAN.

2) Network Sizing
In IP telephony network sizing is key issue. You need to provide enough resources for each voice channel. The bandwidth of voice channel depends on codec you are using. My recommendation is to use 7 G.711 calls per one AP, or 8 G.729 calls per AP.

It is also very important to limit number of stations (wireless phones and wireless stations). It is good to have 20, maximum 25 stations per one AP.



3) Multicast
Multicast traffic can be problem for wireless networks, especially wireless telephony. There are several reasons for that:
- multicast packets are unacknowledged.
- multicast traffic has lower bit rates and this decrease speed of overall traffic.
- when devices enters in power-save mode, AP buffers multicast traffic and waits until stations leave this mode and then they sends all buffered traffic.

This is reason for you to reduce number of wireless IP phones in your network that supports multicast traffic.

4) Server recommendation
Voice network requires servers that offer you telephony capabilities. Now you have even free VoIP servers. It is good to have server over wired link to ensure greater availability.

5) Switch recommendation Do not use hub to connect AP, use switch instead. Hub adds delays. Use dedicated VLAN for voice traffic on switch.

So as you can see, Wireless VoIP network architecture includes lots of things. You need to watch carefully and include them all in your network planning.



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