the port you are specking about called controller and for 30 it will be E1 . its format will be something like E1 0/0/0 .
so by issue sh controllers E1 you will get some thing like
E1 0/0/0 is up.
E1 0/0/1 is down.
the UP one is the CONNECTED one
to check the status of the ISDN ,issue the command sh isdn status
Global ISDN Switchtype = primary-net5
ISDN Serial0/0/0:15 interface
dsl 0, interface ISDN Switchtype = primary-net5
Layer 1 Status:
Layer 2 Status:
TEI = 0, Ces = 1, SAPI = 0, State = MULTIPLE_FRAME_ESTABLISHED
Layer 3 Status:
0 Active Layer 3 Call(s)
Active dsl 0 CCBs = 0
The Free Channel Mask: 0xFFFF7FFF
Number of L2 Discards = 0, L2 Session ID = 6
Total Allocated ISDN CCBs = 0
the most importunate here ,the status of layer 1 which active indicating that connection is establish and every thing going well