Review:

1

• Review
• Hamming distance of a code.
• Relation between the Hamming distance (N) of a
  code and the number of errors that can be
  detected/corrected?
• Error correction code and error detection code,
  which one is more efficient?
• How do sender and receiver work when the CRC code
  is used to do error detection?
• How to generate (and verify) CRC code
• E.g G(x) x21, data 100001, final message?

2

• Example of a data link layer protocol HDLC
  (High-level Data link Control).
• Frame
• 01111110 Address Control Data Checksum
  01111110
• 8 8 8
  gt0 16 8
• Framing bit oriented framing with bit stuffing
• Error detection CRC code with CRC-CCITT as the
  generator polynomial.
• Flow control and Error control Sliding window
  protocol with 3 bits sequence number and
  piggybacking.
• Sequence number in the control field.
• Control frames to do line maintenance.

3

• Three kind of frames
• information frame
• control field 0 seq P/F
  next
• 3
  1 3
• Supervisory frame
• control field 1 0 Type P/F
  next
• Type ACK, NACK, RECEIVE NOT READY, SELECTIVE
  REJECT.
• Unnumbered
• use a control frame, or sending unacknowledged
  data.
• Control field 1 1 Type P/F Modifier