DEC-TR-553: Error Characteristics of FDDI. Report Available.


Raj Jain, DEC, 550 King St., Littleton, MA 01460, USA (jain%erlang.DEC@decwrl.dec.com)
24 Jun 88 20:40


BAD MSG:
802 LAN protocols, are discussed.
The standard uses a ``non-return to zero invert on ones'' (NRZI) signal
encoding and a 4 bit-to-5 bit (4B/5B) symbol encoding in the physical
layer. Due to the combination of NRZI and 4B/5B encoding, many noise
events are detected by code (or symbol) violations. A large percentage of
errors is also detected by framing violations. Some of the remaining
errors are detected by FCS violations. The errors that escape these three
violations remain undetected. The probability of undetected errors due to
creation of false starting delimiters, false ending delimiters, or merging
of two frames is analyzed.

It is shown that every noise event results in two code-bit errors, which in
turn may result in up to four data-bit errors. The FCS can detect up to
two noise events. Creation of a false starting delimiter or ending
delimiter on a symbol boundary also requires two noise events. This
assumes enhanced frame validity criteria. We justify the enhancements by
quantifying their effect.

This analysis here is limited to noise events not resulting in a change of
symbol boundaries. Extensions to the case of changed symbol boundaries is
continuing and will be presented at a later time.

                            Version: June 1988



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