Are the channels mentioned here physical or logical in duplex and multiplex?

Question

1. https://en.wikipedia.org/wiki/Duplex_(telecommunications)

   In a half-duplex system, there are still two clearly defined paths/channels, and each party can communicate with the other but not simultaneously

   Are the "two clearly defined paths/channels" physical channels?

2. https://en.wikipedia.org/wiki/Multiplexing

   The multiplexed signal is transmitted over a communication channel, such as a cable. The multiplexing divides the capacity of the communication channel into several logical channels, one for each message signal or data stream to be transferred.

   Is "a communication channel" a physical channel?

3. Is it correct that

   • a physical channel can only allow at most one transmission at a time?
   • a medium can have multiple physical channels? E.g. a duplex medium has two channels for opposite directional transmissions (see the quote in part 1)?

Thanks.

Answer 1

1. No, they do not have to be physical. They can be a logical, virtual, etc.

2. Same as answer 1

3a. No. A physical channel can be half or full duplex. It can also support multiple simultaneous transmissions. Actually, it depends more upon the capabilities of the endpoints.

3b. Again, they don't have to be physical.

Consider the "aether" (space-time) as a medium. You can transmit radio energy through it, and you can do it half duplex or full duplex. You can divide it up into "channels". Many transmitters can operate simultaneously. You can (but you don't have to) multiplex. Depending on how you want to define it, it can fit any of your definitions.