Client RSSI suggestion for VoIP over Wireless

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hi, i need some suggestion here on what client RSSI should be when am gone deploy VoIP over the wireless Network. anyone has done any VoIP deployment using aerohive wireless with using a smart phone (SIP function). any suggestion on the client RSSI requirement when roaming. e.g -60dbm. 

i have a current aerohive wireless client whom now wana deploy the VoIP using their smart phone. any suggestion or advice or guide line to follow. 

Regards, 
Mohan 
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Mohanantass

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Posted 4 years ago

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Crowdie, Champ

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We have done deployments with Cisco and Ascom VoIP phones.  The RSSI values we designed for was a -65 dBm primary access point and -67 dBm secondary access point.  From our experience, your biggest issue is going to be roaming and voice quality particularly if the wireless network was designed for data and is now having VoIP phones deployed.

At some sites we just got a VoIP phones and held conversations with a landline or stationary VoIP phone.  This enabled us to identify areas with roaming and/or voice quality issues.

If you have a spectrum that is flooded with wireless signal from access points then the VoIP phones will show it up very quickly:

  • The co-channel contention (wait states caused by multiple adjacent access points being configured on the same channel - this includes access points on different floors) will quality call quality loss and "popping".
  • Too much signal (commonly caused by multiple access points in corridors) will cause the VoIP phone to become "sticky" (not want to roam between access points) and this will adversely affect call quality and, possibly, cause periods of no sound during a roam or disconnection.
(Edited)
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Mohanantass

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Yes the network was designed for data and now they wanted to use for Voice as well. I will do a necessary study on the coverage holes, my challenge here would be, when the customer wanted to use their smart phones instead of VoIP phones. what would be your suggestion. as the smart phones now days are power crazy and when the smartphone battery is low the tx power for wireless connection will be low as well. will that interrupt the voice calls and what would be the advice. 
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Crowdie, Champ

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I would be more worried about too much signal than too little.  The VoIP phones I have used worked well when the RSSI dropped down to around -75 dBm, which is a reasonable fade amount from the target of -65 dBm.  If you get the manufacturer's specifications for the VoIP phone it should tell you what data rates can be achieved at what RSSI value and I am sure that you will see that the VoIP phone's maximum data rate can be achieved with a RSSI value below -65 dBm.

If the wireless engineer who configured the wireless network has utilised omni-directional antennas and set the 2.4 GHz transmit power to auto you are, most likely, going to have CCC issues.

A couple of other pointers:

  • Enable Call Admission Control (CAC) when the VoIP phones are deployed. CAC reserves capacity for VoIP phones and is a mandatory requirement for VoIP.
  • Check the power save requirements for the VoIP phone as Unscheduled Automatic Power Save Delivery (UAPSD) may need to be enabled in the wireless network.
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Mohanantass

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Thanks for your advice on the VoIP phones, how if smart phone (samsung G4, Iphones and such). how would that will help.. 
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Crowdie, Champ

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Modern smartphones have the advantage of being 802.11n devices, rather than VoIP phones which tend to be 802.11b/g or 802.11a/b/g, so perform better.  If the smartphone is running Android then there is a large selection of wireless tools that can help you with fault finding and performance validation.
(Edited)
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Crowdie, Champ

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Mohanantass

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ok .. will do necessary things and will come back here for advice. thank you for your time and advice.