- Fact:
- There are different kinds
of informations
carried in
frames
- Different kinds of informations will be sent using a different type of frame
- There are different kinds
of informations
carried in
frames
- The 3 types of
frames used in
HDLC:
- Information frame
- Information frames contain user data
- Supervisory frame
- Supervisory frames contains indications about whether a frame was received correctly or cantains bit error(s)
- "Unnumbered" frame
- Unnumbered frames contain link management information
- Information frame
- ACK frame:
- ACK frame = a frame used to aknowledge the correct receiption of some data
- Positive/negative
acknowledgements:
- Possitive acknowledgement = indication that the data was correctly received
- Negative acknowledgement = indication that the data contains bit errors (and was discarded)
Communication protocols always use positive acknowledgements (because if something is received in error, you can't trust what you has received)
- The value of some
control bits
indicates the
frame type
as follows:
