Error Characteristics of Fiber Distributed Data Interface (FDDI)

FiberDistributed DataInterface (FDDI) is a100megabits per second ber optic local area network (LAN) standardbeing developed by the AmericanNational Standard Institute (ANSI). We analyze the impact of various designdecisions onthe error detectioncapabilityof the protocol. Inparticular, we quantifyframe error rate, tokenloss rate, andundetectederror rate. Several characteristics of the 32-bit frame check sequence (FCS) polynomial, which is also usedinIEEE802LANprotocols, are discussed. The standarduses a \non-return to zero invert on ones" (NRZI) signal encoding and a 4 bit-to-5 bit (4B/5B) symbol encoding inthe physical layer. Due to the combinationof NRZI and4B/5Bencoding, manynoise events are detectedbycode (or symbol) violations. Alarge percentage of errors is also detected by framing violations. Some of the remaining errors are detected by FCSviolations. The errors that escape these three violations remainundetected. The probability of undetected errors due to creationof false starting delimiters, false ending delimiters, or merging of two frames is analyzed. It is shownthat every noise event results intwo code-bit errors, whichinturnmayresult inup to four data-bit errors. The FCScandetect up to two noise events. Creationof a false starting delimiter or ending delimiter ona symbol boundaryalso requires two noise events. This assumes enhanced frame validity criteria. We justify the enhancements by quantifying their e ect. This analysis here is limitedtonoise events not resultinginachange of symbol boundaries. Extensions to the case of changedsymbol boundaries is continuingandwill be presented at a later time. Version: July25, 1990