Rechnernetze

Manchester-Kodierung in IEEE 802

Die als Manchester-Kodierung bezeichnete Kodierungsmethode wird im Ethernet verwendet, die differentielle Manchester-Kodierung im Token-Ring. Der Ethernet-Standard beschreibt diese folgendermaßen:

Manchester encoding is used for the transmission of data across the AUI. Manchester encoding is a binary signaling mechanism that combines data and clock into "bit-symbols." Each bit-symbol is split into two halves with the second half containing the binary inverse of the first half; a transition always occurs in the middle of each bit-symbol. During the first half of the bit-symbol, the encoded signal is the logical complement of the bit value being encoded. During the second half of the bit-symbol, the encoded signal is the uncomplemented value of the bit being encoded. Thus, a CD0 is encoded as a bit-symbol in which the first half is HI and the second half is LO. A CD1 is encoded as a bit-symbol in which the first half is LO and the second half is HI. Examples of Manchester waveforms are shown in Figure 7–10.

Offenbar entspricht die Manchester-Kodierung unserer Darstellung der Bi-Phase-Kodierung. In IEE 802.5 wird für das Token-Passing-Protokoll geschrieben:

1.3.22 differential Manchester encoding: A signaling method used to encode clock and data bit information into bit symbols. Each bit symbol is split into two halves, or signal elements, where the second half is the inverse of the first half. A 0 bit is represented by a polarity change at the start of the bit time. A 1 bit is represented by no polarity change at the start of the bit time. Differential Manchester encoding is polarity-independent.

Damit entspricht die differentielle Manchester-Kodierung unserer Darstellung von Differential Bi-Phase.