Figuring out A-DSL link uptime on a Cisco 877W

There is an SNM MIB that may help you.

.iso.org.dod.internet.mgmt.mib-2.interfaces.ifTable.ifEntry.ifLastChange .1.3.6.1.2.1.2.2.1.9

The value of sysUpTime at the time the interface entered its current operational state. If the current state was entered prior to the last re- initialization of the local network management subsystem, then this object contains a zero value.

Otherwise use logs.

Thing is that the dialer is always UP and so you will not see ppp restarts but the ATM of course does go down if it loses the signal.

Depends what you want.