PPP times out after 1min and disconnects session

I have setup my RB750 running 6.27 with a ppp session , I can authenticate fine and access my internal resources , but the session only stays up for about 60 seconds when i use my work internet connection , when i use my phone’s 3G connection it stays up for , i have enbled debug and ppp logs on the device but cant see any reason for the timeout

any idea where to look to diagnose the problem ?


Rgds
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