One more OSI layer

amtt81amtt81 Member Posts: 48 ■■□□□□□□□□
what layer is half/full duplexing take place?



  • skrpuneskrpune Member Posts: 1,409
    It's the session layer - which has to do with session connections. Presentation layer is more associated with translation.
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  • skrpuneskrpune Member Posts: 1,409
    Just some clarification now that I'm home and have a Network+ book in front of me with the details....the upper layers 5-7 often get lumped together, so here's a quick rundown:

    The session layer establishes a communication session between hosts. The three options for communication are simplex (simply sending out a signal, like a TV broadcast) & half-duplex (ala walkie-talkies) & full-duplex (like a phone conversation).

    Presentation layer translates/presents/formats data into a readable format for the recipient. It also performs encryption & compression.

    It's a little late and I'm a little fuzzy on how to properly explain this next one, so forgive me but I'll pretty much quote one of my N+ books here: Application layer is involved with services (file transfer services, printing service, etc) & interfaces that support applications that need network resources. One of the examples the book gives is that the application layer isn't involved with the writing of an email to another person, but it IS involved when the user clicks on "send message" - at that point, it's in the application layer for processing.
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  • dynamikdynamik Banned Posts: 12,312 ■■■■■■■■■□
    It seems like there's a bit of confusion when it comes to the terminology here, and it's important to make the distinction in what you're talking about.

    My initial reaction was that it wasn't the session layer, but rather the physical layer since duplex settings refer to the transmission of electrical signals, collisions, etc. If you're talking about hubs (layer 1 devices) and switches (typically layer 2, occasionally layer 3 devices), they clearly aren't using a layer 5 (session) protocol for their duplex settings.

    However, this terminology is also used in regards to session-layer protocols. I think those would be better labeled as "synchronous" and "asynchronous" in order to avoid confusion, but Skrpune explained the logic in her second post. This seems to refer to the logical flow of data, rather than the physical flow.

    If you get a question about this, hopefully you'll be given some context, so you can determine what they're looking for.
  • PaperclipPaperclip Member Posts: 59 ■■□□□□□□□□
    Right. Application layer is HTTP, FTP, SMTP, etc. The user is using an application to accomplish communicating with these services so really there are like, a bunch of layers on top of the OSI model, but this is as high as the OSI model goes.
  • Met44Met44 Member Posts: 194
    In the networking world, full or half duplex will usually refer to layer 2, but the idea may also apply at layer 5.

    This is why there are Ethernet specifications for half and full duplex communication and auto-negotiation of those settings, and why you can set Ethernet interfaces on switches, routers, and PCs to particular duplex settings. In Ciscoland, if your duplex settings are wrong on an ethernet interface, it will show that layer 2 is down.
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