Polycom601 peer unreachable

I have a Polycom remote registered to a server (Asterisk 1.4.29.1 connected to MetroE) through my home DSL line. When booted the phone connects I can make calls in and out, eveything is fine but after being left alone for a while calls go directly to voicemail. When I look at the Asterisk console “show peers” its status is unreachable. If i make a call out it works fine and susequent status is then reachable. I have changed the qualify= setting to several different values to no avail.
My sip.conf:

[7085]
type=friend
secret=xxxxxxxx
host=dynamic
qualify=6000
callerid=“XXXXXX”
mailbox=7085@default