As per Cisco:
router#debug cdp events
CDP events debugging is on
*Mar 3 00:14:13: CDP-EV: Encapsulation on interface Dialer0 failed
In this example, the device did not send the CDP packet because the dialer map did not view the CDP packets as interesting traffic and did not bring up the line. Note that basic rate interfaces (BRIs) do not support CDP. Enhancement request CSCdu20683 has been opened against this. As a workaround, you can configure a dialer map to send the CDP packets. CDP is supported on dialer interfaces.
Debug CDP packets on the other end will show it arriving.
Hope it helps.
Steve