SDLC and derivatives (3)
HDLC - High-level Data Link Control
- SDLC modified by ISO
- considered to be compatible with SDLC; the same frame format; does not support loop or hub go-around
- supports full-duplex, synchronous operation
- 3 transfer modes:
- Normal Transfer Mode (used also by SDLC) - secondary cannot communicate with primary without permission
- Asynchronous Response Mode (ARM) - can communicate
- Asynchronous Balanced Mode (ABM) - combine node: primary or secondary