AD logon problems if site link is down

We are using Active Directory – forest level is 2003. One of our sites is connected by T1. This site has a domain controller which is also a DNS server and global catalog svr. DNS zones are AD integrated. This DC has no FSMO roles, it is only there to facilitate logons and provide file and print services to local users at the site. If T1 link is up, everything works as it should. If T1 is down, local users can’t access file shares on the local DC nor can they log on to their workstations if their user is not cached. What do I need to do to enable local network domain functionality even if network link is down.