HDLC-High Level Data Link Control-ISO 3309
Three stations types:
- primary - issues command frames
- secondary - response frames
- combined - primary & secondary fcns
Two Link configurations
- unbalanced - 1 primary & full/half duplex
- balanced - only point to point combined
Three Data Transfer Modes
- normal response mode (NRM) - unbalanced
- asynchronous balanced mode (ABM)
- asynchronoous response mode (ARM) -unbal.