Multiple access and full/half duplex point-to-point links

Question

1. In en.wikipedia.org/wiki/Channel_access_method,

   A channel-access scheme is based on a multiplexing method, that allows several data streams or signals to share the same communication channel or physical medium. Multiplexing is in this context provided by the physical layer.

   multiplexing also may be used in full-duplex point-to-point communication between nodes in a switched network, which should not be considered as multiple access

   Why "multiplexing also may be used in full-duplex point-to-point communication between nodes in a switched network, which should not be considered as multiple access"?

2. In en.wikipedia.org/wiki/Media_access_control,

   Examples of shared physical media are ..., and half-duplex point-to-point links.

   Are "shared physical media" the same as "multiple access media"? Why are "half-duplex point-to-point links" "shared physical media"?

Thanks.

Answer 1

Shared physical media: only one device on the shared media can access it at any given time, the rest has to wait.

Halfduplex point to point links, uses the same physical media in both directions. It is the same frequency and point to point electromagnetic wave/channel. It is halfduplex as a radio can only transmit or receive at a given point in time. The two sides of the point to point link can not transmit at the same time they share the physical media

Multiplexing: is the interleaving of multiple data streams, the resulting multiplexed stream can then be sent over a full or half duplex link.

Answer 2

1. Why "multiplexing also may be used in full-duplex point-to-point communication between nodes in a switched network, which should not be considered as multiple access"?

   • Because you want to send traffic from more than one host over the link, e.g. a trunk.

   • The actual link (e.g. Fiber) is not multiple access,only one device on each side with nothing else that has access to the link.

2. Are "shared physical media" the same as "multiple access media"? Why are "half-duplex point-to-point links" "shared physical media"?

   Yes.

   Because they share the physical channel with other devices.

   • e.g Wifi - links operating on the same frequency in the same area interfere with each other and reduces capacity.

   • e.g. Ethernet-hub , host have to check if media is available before sending.