Establishing data link connections identified by
the Data Link Connection Identifier (DLCI = SAPI +
TEI)
Frame delimiting, alignment and transparency, allowing recognition of
frames transmitted over the D-channel
Flow control: (a) to maintain the
sequential order of frames across a data link connection, (b)
temporarily stopping transmission
Error Control: detection of errors on
a data link connection, recovery from errors, and notification to the management entity of
unrecoverable errors