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VOIP Handset woes

Last Modified: 2016-03-07
Have a Comcast business account with 50Mbps/10Mbps service using CISCO DPC3939B Gateway.  Not using Comcast's VOIP XFINITY service.

VOIP Handset and PC are hardwired to amped|wireless AC750 Range Extender TAP-EX2 configured to use dual band.

VOIP handset drops calls.  On one instance, call was dropped and couldn't get dialtone without rebooting the AC750.  Before reboot, the 5GHz signal was at 0% (per AC750 panel display) whereas the 2.4GHz signal was at 97%.  I'm not sure of the relevance since the AC750 is configured to route hardwired connections through the 2.4GHz connection.

Wanting to know best practices for configuring the AC750 and CISCO DPC3939B for VOIP.  Also, whether AC750 is a satisfactory choice: I need a wireless connection between (a) the pc and VOIP handset  and (b) the Gateway.  

I don't see QoS settings on the AC750 nor in user manual for the Gateway.  I also saw a post here saying that known problems with CISCO DPC3939B Gateway include:
SIP ALG is enabled by default and cannot be disabled, causing intermittent phone call and feature failures.

Any thoughts on that?

Is resolving the dropped VOIP calls likely going to chew up a lot of time diagnosing and might it be better to subscribe to Comcast's VOIP/XFinity -- although it seems I would still have the need for a wireless hop between the handset and the Gateway's Line 1/2 ports...?

Appreciate any help -- thanks.

edit: Seems Comcast's VOIP/Xfinity is for use with analog handsets...
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