How multiple telephones(Landline) transmit signals simultaneously? How the bandwidth is divided individually to make transmission happen individually?


1 Answer 1


Merging multiple individual signals/services/data paths together is called multiplexing. Depending how you actually do that there are several technologies:

  • time division multiplexing (TDM) - there are distinctive time slots that iterate over the services (e.g. most ISDN variants)
  • frequency division multiplexing (FDM) - each service uses a dedicated frequency band over copper (e.g. xDSL over POTS/ISDN)
  • wavelength division multiplexing (WDM) - each service uses one or more dedicated wavelengths/colors over fiber (e.g. for SONET or Ethernet WAN/MAN)

When it comes to packet switching, multiplexing a large number of data streams comes naturally (essentially a kind of dynamic TDM).

For POTS landlines, both TDM and FDM are (were) used. Both usually exclude the use of additional FDM for DSL.

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