Synch Cisco Router with NTP server

I have existing NTP server (timesource 3100) which is connected to the GPS and I want to connect it to the router 3800 series, but when I read URL below, it is mentioned that only router series 7200 can connect to external NTP server as stratum 2 and router 3800 can be synchronized from external NTP server as stratum 4E.

http://www.cisco.com/en/US/docs/ios/12_1t/12_1t1/feature/guide/dtrimble.html

Could you please advice me whether I could use router 3800 as stratum 2 (direct connect to the external NTP server (timesource 3100)? If yes, what is the interface required at the router side?

thanks
lington