HP Labs Technical Reports

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The Use of Scramblers With an Anti-Locking Circuit

Spratt, Michael P.



Abstract: The Fiber Distributed Data Interface (FDDI) was originally designed as a fiber optical Local Area Network. Recently, attempts have been made to transmit FDDI over copper cables, reducing costs. HPLB was part of a consortium of companies looking at the transmission of FDDI over Category 3 (voice-grade) unshielded twisted pair cable. In the operation of the FDDI Media Access Control protocol, long sequences of the Idle symbol will occur, and too reduce radio frequency emission, the use of scrambling is required. This paper was presented to the December 1991 meeting of FDDI in San Diego. It discusses the error propagation, which occurs in the decoding of line codes, and in descrambling of self-synchronized scramblers. It describes the locking of scramblers, and describes Anti-Locking Circuit. It discusses the advantages of using primitive polynomials with even numbers of taps to implement the scrambler, and proposes a suitable trinomial.

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