jain@erlang.DEC.COM (Raj Jain, DEC, 550 King St., Littleton, MA 01460, USA) (06/25/88)
The following DEC Technical Report DEC-TR-553 is now available for
distribution:
Title: Error Characteristics of Fiber Distributed Data Interface (FDDI)
[32 pages]
Author: Raj Jain
Digital Equipment Corp.
550 King St. (LKG1-2/A19)
Littleton, MA 01460
If you would like a hard copy of the report mailed to you, please send me
your U.S. (or foreign) Mail address. Soft copies of the report are also
available for LN03 and postscript printers. If you like a soft copy,
please specify LN3 or PS. My network address on ARPAnet is
Jain%Erlang.dec@decwrl.dec.com
ABSTRACT
Fiber Distributed Data Interface (FDDI) is a 100 megabits per second fiber
optic local area network (LAN) standard being developed by the American
National Standard Institute (ANSI).
We analyze the impact of various design decisions on the error detection
capability of the protocol. In particular, we quantify frame error rate,
token loss rate, and undetected error rate. Several characteristics of the
32-bit frame check sequence (FCS) polynomial, which is also used in IEEE
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