MAC – Multiaccess with Duplex and Multiplexing

mac

If I am correct (correct me if I am wrong):

  • MAC sublayer is all about how to use a multiaccess medium.

  • A multiaccess medium is a medium with multiple communication entities attached to its end(s), which has conflict issue between senders and addressing issue between receivers.

But I am not very clear about it yet, especially related it to duplex and multiplexing:

  1. Relation between multiaccess and full-duplex

    For a full-duplex medium, with only one communication entity
    at each end,

    • will it cause conflict when the two entities try to communicate with each other at the same time?

    • Is this medium a multiaccess medium? Does a multiaccess medium require multiple entities attach to at least one of its ends? When
      people talking about a multiaccess medium in general, do they assume
      the medium to be unidirectional instead of full-duplex?

  2. Relation between multiaccess and multiplexing

    For a multiaccess medium,
    when there are multiple entities attaching to one end of the medium
    and they want to send out signals/messages at the same time, is
    multiplexing a solution to solve the conflict problem?

    Wikipedia says:

    A multiplexing technique may be further extended into a multiple access method or channel access method, for example, TDM into time division multiple access (TDMA) and statistical multiplexing into carrier sense multiple access (CSMA). A multiple access method makes it possible for several transmitters connected to the same physical medium to share its capacity.

    Multiplexing is provided by the Physical Layer of the OSI model, while multiple access also involves a media access control protocol, which is part of the Data Link Layer.

    What does it mean by saying "A multiplexing technique may be further extended into a multiple access method"?

  3. Relation between duplex and multiplex,

    Is it correct that although the two words end with the same suffix "-plex", multiplex isn't an extension of duplex, in that duplex means bi-directional with only one communication entity at each end, while multiplex is uni-directional with multiple communication sending entities at one end?

Thanks.

Best Answer

Remember that you're talking about abstract concepts, so exact definitions can be a bit squishy.

  1. Full duplex means that an endpoint can send and receive at the same time. A telephone is a good example of that.

1a. No, depending on how you define "the medium," there will not be a conflict.

1b. Maybe. It doesn't have to be.

  1. When actually implementing a "multiaccess medium" in real life, multiplexing is one strategy to make it work.

  2. Again, I think you're trying to pin down an abstract term. Multiplex could mean everyone can talk and hear at the same time, but then again, maybe not. Multiplex could be either half or full duplex.

Related Topic