Link layer (LAPB on the B-channel or LAPD on the D-channel) establishment shall be initiated by:
- the calling terminal in the case of outgoing calls;
- the AU in the case of incoming calls in Case A; or
- the PH in the case of incoming calls in Case B.
Link layer release may be initiated by:
- the terminal;
- the AU in Case A; or
- the PH in Case B.