Many types of signaling on FiberOptic? cables are serial
<add examples here>
Only one or 2 wires (definitely not parallel, but not one-bit-at-a-time either):
100Base-T Ethernet: 3-level modulation (100BASE-T4 uses 8B/6T) (100BASE-TX and 100BASE-FX use ... something else ?)
1000Base-T Ethernet (GigaBitEthernet?): 5-level modulation on each pair of wires
1200 bit/s and faster dial-up modems: up to 255-level modulation (limited by the telephone network)
Constellation diagrams show all the possible symbols that may be transmitted at any instant, using phase-amplitude modulation.
The first group has exactly 2 symbols in their constellation diagram ("2-level modulation"), so they transmit one bit at a time.
The second group has more than 2 symbols, so at any instant, they are transmitting one "symbol" that conveys more than one bit of information.
Doesn't 100 Base-T Ethernet also combine bits in a more complex manner? (using phase and amplitude changes, just as are used by modern modems)
Yes, but not quite as complicated.
See also: http://en.wikibooks.org/wiki/Programming:Serial_Data_Communicationshttp://en.wikipedia.org/wiki/Serial_communicationsCategoryHardware