If you are using a Grandstream unit with QoS (Quality Of Service) on your router you may find the following information useful
By default, the GS2000 units use a value of "48" to tag/weight
DiffServ/QoS packets which does not actually tie in with the QoS support
of the Draytek 3100.
On checking the website http://www.rhyshaden.com/qos.htm it would seem the correct value for EF tagged DiffServ packets should actually be 46, and not 48 which is supplied or set as default.