is OSI software model?? - Network

This is a discussion on is OSI software model?? - Network ; Am I understanding OSI correctly OSI 7 layers are basically the software model of a software that is used to make 2 or more computers to communicate. so basically the 7 layers are the software design and it is up ...

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  1. is OSI software model??

    Am I understanding OSI correctly
    OSI 7 layers are basically the software model of a software that is
    used to make 2 or more computers to communicate. so basically the 7
    layers are the software design and it is up to the people who is going
    to implement the software how to implement each layer and which layer
    should be exist or which one should be not. Am I right???

    Also it is mention that each layer of OSI can communicate directly
    with a "peer" layer?? what does that mean?? I thought each layer in
    OSI uses the help from the layer below to do its task.. why they say
    for example Application layer of computer A can commuicate with
    Application Layer of computer B

    Host A Host B
    [Application Layer] <----------> [Application Layer]

    Now how Application Layer can communicate with Application Layer of
    computer B without needing the Physical Layer?? so what is the meaning
    of peer-to-peer communication??

    thanks a lot

  2. Re: is OSI software model??

    esara123@hotmail.com (esara) wrote in message news:...
    > Am I understanding OSI correctly
    > OSI 7 layers are basically the software model of a software that is
    > used to make 2 or more computers to communicate. so basically the 7
    > layers are the software design and it is up to the people who is going
    > to implement the software how to implement each layer and which layer
    > should be exist or which one should be not. Am I right???
    >
    > Also it is mention that each layer of OSI can communicate directly
    > with a "peer" layer?? what does that mean?? I thought each layer in
    > OSI uses the help from the layer below to do its task.. why they say
    > for example Application layer of computer A can commuicate with
    > Application Layer of computer B
    >
    > Host A Host B
    > [Application Layer] <----------> [Application Layer]
    >
    > Now how Application Layer can communicate with Application Layer of
    > computer B without needing the Physical Layer?? so what is the meaning
    > of peer-to-peer communication??
    >
    > thanks a lot


    This is kind of long, but hopefully it will help you understand what
    The OSI model is.

    The OSI model is something that has been made to help manufacturers
    and designers to design software and equipment so that everything can
    work together to allow internetworking (information being sent from
    one point to another). A long time ago, each company made it's own
    equipment (hardware) and it's own software and they would only be able
    to work with that particular company's things. For instance, IBM
    would make networking equipment like servers, routers, switches, etc.
    and it would make the software to run it. The equipment and software
    would only work with IBM stuff so it would make it difficult for
    companies and people to have equipment that was interchangeable and
    could work together. So they designed the OSI model to help everyone
    agree on some standards so that manufacturers could make stuff that
    would work with other companies products. It is broken down into
    layers that have specific functions and each of those layers have
    specific protocols and instructions so that manufacturers know what
    standards to design their products to.

    What happens is this: files go through a transformation so that they
    can be sent across the wires. As the data moves down through the
    layers on comp A, each layer adds its own instructions so that when
    the data arrives at comp B the computer will know what to do with it.
    Without the OSI model the computer would just detect a bunch of
    electrical signals but not know what to do with them. Let's try and
    get a mental picture.

    Let's imagine that we have two computers on opposite sides of the
    country. They want to share some pictures and some music. We've got
    to have a way to get that data from one side of the country to the
    other. The first thing that we need is a physical connection. Layer
    1 takes care of that. It contains standards that have to be met and
    agreed upon so that a physical connection can be made that will allow
    the two computers to just get an electric signal.

    Now let's go from one computer to the other. At the application
    level(Layer 7) you have the programs that run on the computer. They
    have files that are encoded a specific way so that the program can
    understand them. Microsoft Picture It! reads .jpg files. Windows
    Media player reads .mp3 files. The list goes on and on. Now we want
    to send our .jpg and .mp3 files to someone on the other side of the
    country. But how does the computer know how to do that? As you move
    down from Layer 7 to Layer 6, and Layer 5, there are specific
    instructions and protocols that the computer has for determining how
    the data should be broken down so that the other computer can display
    and present it correctly. At Layer 5 the computer has specific
    instructions that tell it how to break up the data into segments so
    that it can be transported across the network. Layer 5 (the session
    layer) and Layer 4 takes care of establishing the connection between
    the two computers. TCP (Transmission Control Protocol) works to help
    the computers agree when to send the data, how fast it should be sent,
    and how much should be sent at one time. It makes sure that your data
    gets from one side to the other. Now that the two computers have
    agreed on those things the data packets have to be able to get from
    comp A to comp B. Layer 3 takes care of the addressing. It routes it
    from one place to another. Layer 3 will slap an IP address on the
    packet and pass it down to Layer 2. Layer 2 gets the packet ready for
    transmission across the wire. It puts some information onto the front
    of the packet that helps the two computers to synchronize the
    communication. With that information on the front it is now called a
    frame and it is ready to be sent across the wire. As Layer 2 passes
    the frame down to Layer one it encodes it into bits and an electrical
    signal. This is then passed across the wire to the other computer.
    Remember, Layer 1 is the wire and we've already talked about that.
    Now we will see how the layers on either side communicate with each
    other. When comp B receives the electrical signals across the wire
    from comp A the instructions at Layer 2 tell it how to transform those
    signals into bytes and then how to transform those bytes into data.
    As it goes up the stack to Layer 3, Layer 3 makes sure that the packet
    got to the right place. If it did, it takes the ip address off of the
    front and passes the segment up to the Transport Layer (layer 4).
    Layer 4 reads the instructions that comp A's layer four put onto each
    segment and makes sure that all of the segments have arrived and makes
    sure that they are in the right order. If not, it requests that comp
    A send a certain segment again. As the data is passed up through the
    rest of the layers it reads the instructions that comp A's layers put
    on it so that it can reassemble things in the correct way. Layers 5,
    6, and 7 each put in their own instructions so that the data gets put
    together into either a .jpg or a .mp3 file so that your computer can
    read it.

    As you can see, each layer has a specific job to do. Some of the
    layers have devices that help them do their jobs. Layer 3 has routers
    that help it to route information across a network. Routers know the
    protocols that work at layer 3 and that is how they do their job. The
    NIC card on a computer works at layer two to turn data into a signal
    that can be sent across the ethernet cable. It knows the specific
    protocols that work at layer two so that it can do it's job.

    Here's a link that will explain it as well:
    http://searchnetworking.techtarget.c...212725,00.html

    Hopefully this was of some help to you. If not, keep asking questions
    until you understand it. That's the only way to learn!

  3. Re: is OSI software model??


    > Hopefully this was of some help to you. If not, keep asking questions
    > until you understand it. That's the only way to learn!


    A very helpful explanation !!! Great Job. Thank you

    Manos



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