Media for Cable Modem and Router or Phone Adapter Issues

Cable Modem and Router or Phone Adapter Issues

I have Cox Cable with a Motorola Surfboard Cable Modem. If I connect the cable modem direct to my PC I get speeds of about 2.2 Mbps as measured at:

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But when I connect either a GrandStream Phone Adapter (for AOL Total Talk VoIP) or a Linksys Wireless router BEFW11S4 v4 my connection speed drops to about 500 Kbps.

I've contacted AOL Total Talk and they said the decrease should be about 250 Kbps at max. They are sending me a new device - as this is when I noticed it.

But the Linksys router is much more puzzling - and the fact that anything connected to the Cable Modem causes issues is troubling.

I've tried different cables.

I'm guessing there is some setting for the cable modem that is having problems.

Cox Cable just tells me if I get good speeds from their modem - they are done.

Linksys has told me to upgrade the firmware - which I did and lower the MTU which I did - but since upgrading the firmware can no longer do. Any ideas?