Linksys / Cisco Devices and RTP Packet Size
Copied from: https://teliax.zendesk.com/entries/167685-linksys-devices-and-rtp-packet-size
Having trouble with poor one-way audio quality on your Linksys device? There is a quick and easy fix. Linksys ships their devices with a non-standard RTP Packet Size, or 'ptime' of .030 (30 millisecond packet size) when the standard is .020 (20 millisecond packet size).
To change this, log on to your Linksys device, access the SIP settings, then enable the Advanced Settings. Search for RTP Packet Size and change from the default of .030 to .020. This will fix your audio issues!