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OSI Model - Which level is TCP/IP

Posted on 2004-10-29
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Where would TCP/IP  be In the 7 Layer OSI Model  ???
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Question by:pdoriley
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    by:NetworkArchitek
    Hi pdoriley,
    TCP is on layer 3 and IP is on layer 2

    Cheers!
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    by:NetworkArchitek
    I guess I could have clarified. TCP and UDP are the transport protocols and thus work on the Transport while IP, in very simple terms, deals with the addressing and so forth and thus works on the network layer. It is the same sort of comparison with Novell's IPX/SPX, although in reverse.
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    by:
    TCP is on layer 4
    IP is on layer 3

    -Justin
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    by:NetworkArchitek
    pdoriley,
    er I made a stupid mistake. Yes Trying to count down and I had just woken up, bad idea. He's right, but nevertheless TCP is on transport and IP is on network.
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    Expert Comment

    by:cmsJustin
    :)
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    by:pdoriley
    OK I understand that TCP is on layer 4 and IP is on layer 3

    Now I'm confused because this article below makes a big distinction between the OSI model and the TCP/IP model.  Hey, I thought that TCP/IP was part of the OSI ? Can someone please take a look at the URL and explain to me whats going on here?  

    http://www.uwsg.iu.edu/usail/network/nfs/network_layers.html
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    by:cmsJustin
    Basically, each layer of the TCP/IP model may overlap a few layers of the OSI model.

    http://www.gphmi.sk/pages/siete/images/osivstcp.gif

    Some of this pic is russian but you should still see what i mean.

    OSI was created a long time ago, and TCP/IP built its own model, sorta.

    Basically TCP/IP doesnt care about certain layers (namely application layer and layer 1). TCP/IP is exactly what it stands for (Transport control protocol/Internet Protocol). TCP/IP doesnt care what is sendind and what medium it is sending it over, just addressing and delivery)

    Hope that helped.

    -Justin
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    by:JFrederick29
    TCP/IP has it's own model, seperate from the OSI model.

    TCP/IP mapping to OSI:

    network interface layer (TCP/IP) = physical and data link layers of OSI
    internet layer (TCP/IP) = network layer of OSI
    transport layer (TCP/IP) = transport layer of OSI
    application layer (TCP/IP) = session, presentation, application layers of OSI

    IP corresponds to the internet layer of the TCP/IP model and network layer of the OSI model.  TCP and UDP correspond to the transport layer of both models.

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    by:stevemjp
    OSI (7 layers)

    From layer 7 downwards:

    Application
    Presentation
    Session
    Transport
    Network
    Data Link
    Physical

    TCP (4 layers)

    Application
    Transport
    Internetwork
    Network Interface

    The Network Interface on TCP maps to layers 1&2 of the OSI
    Internetwork - Network
    Transport - Transport
    The Application on TCP maps to layers 5, 6 and 7 of the OSI.
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    Author Comment

    by:pdoriley
    I just have a regular Windows PC, DSL modem, an connect to the internet.   Would this be:

    OSI Model
    TCP/IP Model

    or both?                
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    by:cmsJustin
    TCP/IP is in effect in this scenario, but you could still map everything to the OSI layer.

    -Justin
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    by:stevemjp
    Neither in practical terms.

    These are just models of how data passes form source to destination. Think of it an opertional guide for your network.
    It's more a set of principals/standards.

    You will probably be using TCP/IP which is designed as a protocol to conform to the TCP/IP model.

    The TCP model would have originated from the OSI model. This is an old model that all modern models use to reference which layer a particular operation is performed at.

    You don't really need to know.

    Can I ask why you need to know? I/we may be able to help further.


    Hope this helps.
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    Expert Comment

    by:JonSh
    Connection to the internet is Physical, Layer 1 (phone wiring).
    DSL is a signalling protocol on top of that physical layer...it's arguably Physical or Datalink (1 or 2)....on an ethernet cable, it is equivalent to Winchester encoding or NRZi, which is arguably layer 1 or 2 (but most engineers refer to it as layer 2)....the rest of your "stack" is software and doresn't really matter, but the model used is OSI.

    Let's be very clear: The Open Systems Interconnect (OSI) stacked/layered Model is an ISO invention, just like it's cousin GOSIP is an invention of the government.  TCP/IP was not conceived of as a layered model, so to speak (altho it works and maps remarkably well to one).  It just made sense at the time (still does).  There is no officlal TCP layered model that I'm aware of.  If there is, what RFC is it?

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    by:stevemjp
    JonSh

    You are correct in what you say, however most people refer to it as the TCP/IP model.

    Refer to RFC 793. This is mainly to do with only TCP but may fill in some gaps.
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    Expert Comment

    by:stevemjp
    Or RFC 1180 may also help.
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    by:JonSh
    LOL.... Stevemjp, that's my point exactly....those RFCs (I know them well) don't indicate a full protocol or the mapping that would be used as a full layered model.  But yes, I take your point, TCP is considered an unofficial layered suite.

    BTW, folkses, TCP/IP is a 5 layer model, not 4 (if we use the unoffical definitions).  And it starts at the OSI layer 3, since it was written independant of actual hardware requirements (datalink/physical media).

    LOL...okay, so I admit to being cranky and nitpicking this am :)
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    Expert Comment

    by:JonSh
    let's also add RFC 1122 :)
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    Expert Comment

    by:stevemjp
    OK. LOL

    8}
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    Expert Comment

    by:stevemjp
    pdoriley,

    Any help here?
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    Author Comment

    by:pdoriley
    Yes helpful 4sure
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    Author Comment

    by:pdoriley
    Stevemjp, I want to know because I am trying to learning about TCP/IP  and it started teaching me about the OSI 7 model and I was thinking, what does this have to do with TCP/IP?  
    Then I was thinking, what does any of this have to do with my home computer?  

    I just want to know how all this relates to my own PC on the internet, thats all.
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    Expert Comment

    by:JonSh
    pdoriley,

    On your Home PC:

    Layer 1 = Physical = Phone Wiring
    Layer 2 = Datalink/Signalling = ADSL
    Layer 2 = Datalink/Addressing = PPPoE Driver for your Modem (Windows)
    Layer 3 = Network = TCP Protocol Driver (Windows)
    Layer 4 = Transport = TCP Protocol Driver (Windows)
    Layer 5-7 = Local Formatting = Windows OS

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    Expert Comment

    by:stevemjp
    OSI 7 layer is the grandad of network models.

    Most others spawned from that.

    As such, to understand the terminology and functions of each layer of the stack, it is compared to the OSI model.

    This is why understanding the OSI comes first.

    Good luck.
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    Author Comment

    by:pdoriley
    Reg Comment from JonSh  Shouldn't Layer 3 read:

    Layer 3 = Network = IP Protocol Driver (Windows)  instead of Layer 3 = Network = TCP Protocol Driver (Windows)


    ?
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    Expert Comment

    by:JonSh
    Yeah, my apologies.  Well, sorta, anyway :)  I was referring to the Microsoft TCP stack (Protocol Driver) which starts at layer 3, as opposed to the actual TCP protocol (alongside UDP) which resides at layer 4 of this model.  In other words, Microsoft stuffs all these *protocols* into a software stack which starts at layer 3.

    LOL...or if we really want to be cranky, I could lie and say I meant ICMP :)
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