These are all ways that multiple logical channels can coexist over a period of time. Some of these will be mentioned here, as appropriate. The entire bandwidth of both physical channels may be used simultaneously. A standard example of this is the multiple wires used in a bus, or ribbon cable, or telephones, etc. In this case, there is not a need for a central mux, except to act as a switch.
Circuit switching is considered in the next page.
There are two main ways of doing this. I include CDM under FDM since the stations do transmit simultaneously and matched filters are used to extract the desired signals. FDM is used for both centrally combined signals and for distributed multiple access systems, which CDM is only used for distributed multiple access systems. Here, a band-limited signal is shifted to a frequency band that is not shared with any other signal. Several such signals may be combined in a channel having larger bandwidth available, with the total spectrum of the channel divided into smaller bands, one per logical channel, with guard bands between them.