CCNA 1 Class: How e-mail moves through the OSI model

Posted: November 17, 2011 in CISCO CCNA Discovery

Hello all,

You are required to explain in your own words how an e-mail message comes from your computer and gets delivered to another using the OSI model as your point of refrence.

You have a week from this date to submit the assignment

Michael E. Ochieng

  1. Philip Kolale says:

    How email moves through the OSI model
    When email is sent, the email moves down through the OSI stack and then is transmitted over the network media. When the email is received by the recipient such on the network, it moves up through the OSI stack until it is again in a form that can be accessed by a user on that computer.
    Each of the layers in the OSI model is responsible for certain aspects of getting user data into a format that can be transmitted on the network. Some layers are also for establishing and maintaining the connection between the communicating computers, and other layers are responsible for the addressing of the email so that it can be determined where the email originated and where the data’s destination is.
    The process of moving user data down the OSI stack on a sending node (again, such as a computer) is called encapsulation. The process of moving raw data received by a node up the OSI stack is referred to as de-encapsulation.
    To encapsulate means to enclose or surround, and this is what happens to the email that is created at the Application layer and then moves down through the other layers of the OSI model. A header, which is a segment of information affixed to the beginning of the data, is generated at each layer of the OSI model, except for the Physical layer. This means that the data is encapsulated in a succession of headers—first the Application layer header, then the Presentation layer header, and so on.
    When the data is transmitted to the recipient the data travels up the OSI stack and each header is stripped off of the data. First, the Data Link layer header is removed, then the Network layer header, and so on. Also, the headers are not just removed by the receiving computer; the header information is read and used to determine what the receiving computer should do with the received data at each layer of the OSI model.
    It is by using these headers that the sending computer is able to communicate with the receiving computer and provide the receiving computer with either information or actual instructions related to the disposition of the data at the various levels of the OSI model.

  2. For message to move from the host (sender) to the client (receiver) through networking media it must undergo through seven layers of OSI and each layer is very vital for the successful transmission of data. When message is to be transmitted from any host to another, the communication partners, quality of information, authentication, privacy, and any constraints on data syntax are identified before transmission of data in any OSI layer.

    Data is then converted from one presentation format to another by the operating system to a text stream into a pop up window with newly arrived text.

    The packed are checked if it has incomplete information or if it contain any error, because for data to be transmitted the packet must have complete information for it to be transmitted to the client. If the packet have no error and also have complete information then it’s directed to the right destination, therefore data is synchronize into bits. In process of data transmission from host to client, the data travels up the OSI stack and each header is stripped off the data. The header information is used to determine the right client and also enable communication between the host and the client. Lastly the data is delivered to the right client. e.g

  3. When a user sends an email message, message is converted to 0s and 1s (bits). Application, presentation and session layers ensure that the message is placed in a format (0s and 1s) that can be understood by the application running on the destination host. This process is called encoding. Application, presentation and session layer (upper Layer) then send the encoded messages to the lower layers for transport across the network.
    The email message is packaged then layer 4 breaks it down into smaller segment for network transport. A header is placed on each segment indicating the User Data gram Protocol port number that corresponds to the correct application layer application. Therefore packet delivery is acknowledged by the destination.
    The email data received from the transport layer is put into a packet that contains a header with the source and destination logical IP addresses. Routers use the destination address to direct the packets across the network along the appropriate path.
    Network device in the layer 7 encapsulates the packet into a frame which contains the physical address of the next directly-connected network device on the link. Switches and network interface cards use the information in the frame to deliver the message to the correct destination device and lastly the receiver will be in apposition to receive his/mail in alphanumeric form.

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