How Data Flows through the OSI Layers

To get a better understanding of how the OSI layers function, it is important to know how data flows between the layers. In this section, we'll trace the data as it flows through the layers of the OSI model. As you will see in this section, each layer adds (or encapsulates) some form of header or trailer. (Layer 2, the Data Link layer, is responsible for adding a trailer.) Figure 2.2 shows the data flow from Device A to Device B.

Note: The example in Figure 2.2 demonstrates how end user packets (header and data) flow through the OSI model. The figure assumes there are no intermediate devices.

When the end system receives the unstructured bit stream from the physical wire, each layer removes the header information applicable to it until the application receives the data. The following depicts what occurs in the OSI model's layers when an email is sent from Device A to Device B:

1. An application, such as an email program, creates data that will be sent by an end user, such as an email message. The Application layer (layer 7) places a header (encapsulation) field that contains information such as screen size and fonts, and passes the data to the Presentation layer (layer 6).

2. The Presentation layer places layer 6 header information. For example, the text in the message might be converted to ASCII. The Presentation layer will then pass the new data to the Session layer (layer 5).

3. The Session layer follows the same process by adding layer 5 header information, such as information that the Session layer will manage the data flow, and passes this data to the Transport layer (layer 4).

4. The Transport layer places layer 4 information, such as an acknowledgment that the segment was received in the header, and passes it to the Network layer (layer 3).

5. The Network layer places layer 3 header information, such as the source and destination address so the Network layer can determine the best

Data Flow Osi Model

delivery path for the packets, and passes this data to the Data Link layer (layer 2).

6. The Data Link layer places layer 2 header and trailer information, such as a Frame Check Sequence (FCS) to ensure that the information is not corrupt, and passes this new data to the Physical layer (layer 1) for transmission across the media.

7. The bit stream is then transmitted as ones and zeros on the Physical layer. It is at this point that the Physical layer ensures bit synchronization. Bit synchronization will ensure the end user data is assembled in the correct order it was sent.

8. Steps 1 through 7 occur in reverse order on the destination device. Device B collects the raw bits from the physical wire and passes them up the

Data Link layer. The Data Link layer removes the headers and trailers and passes the remaining information to the Network layer and so forth until data is received by the Application layer. Eventually, Device B will receive an email notification displaying a message to indicate that a new email message has been received.

Familiarize yourself with the OSI model and each layer's responsibility. You should be able to recognize a function of each layer of the OSI model. The seven layers of the OSI reference model are typically divided into two categories: upper layers (layers 4 through 7) and lower layers (layers 1 through 3).

As you can determine from the example of encapsulation, the OSI model provides a service that allows information to flow smoothly from one layer to another. Eventually, the information will be presented to the end device in a readable format. Now that we've reviewed the OSI model, the next section takes a look at how packets are sent across a network using a routing algorithm.

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Responses

  • jere
    How data pass through osi layer?
    2 years ago
  • edda cremonesi
    How data moves through the osi model?
    2 years ago
  • andi
    How message is transformed when it passes through physical layer?
    2 years ago
  • alessandra
    How data get passed througg osi model?
    2 years ago
  • peter
    How a data flow through an internetwork?
    2 years ago
  • Graziella
    How information is sent through the OSI MODEL?
    2 years ago
  • pupa
    How packet flow through osi model?
    2 years ago
  • aatifa
    How does data travel through the osi model?
    2 years ago
  • JANA
    How data flows through osi model?
    2 years ago
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    What happens when data segment pass through osi model?
    2 years ago
  • Kibra
    How data is transferred through layers of osi model?
    2 years ago
  • Anne
    How data flow in osi layers?
    2 years ago
  • juliette
    How message travel to osi layer?
    2 years ago
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    How does data move through the osi model?
    2 years ago
  • JUDITH CHAN
    How information passes through one layer to another in osi model?
    2 years ago
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    2 years ago
  • LYLA BELL
    How data is transmitted and received in osi model?
    2 years ago
  • daniel
    How data flow through in 7 layer osi model?
    2 years ago
  • ramiro
    How does info pass in OSI?
    1 year ago
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    How to data passes through layers?
    1 year ago
  • Tewolde
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    1 year ago
  • jon
    How data move between OSI layer?
    1 year ago
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    How data flows through osi layers during transmission?
    1 year ago
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    How email is sent through 7 layers?
    1 year ago
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    How data travel in layers?
    1 year ago
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    1 year ago
  • JULIA
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    12 months ago
  • celio
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    11 months ago
  • ADONAY
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    11 months ago
  • pasi
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    11 months ago
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    How data flows through OSI layer?
    11 months ago
  • MUHAMMED
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    11 months ago
  • samira
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    11 months ago
  • delinda
    How data transmission take place in osi?
    10 months ago
  • sam
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    10 months ago
  • Birgit
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    10 months ago
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    10 months ago
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    10 months ago
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    How data flow occurs based upon isi model?
    9 months ago
  • Ambretta
    Do layer in osi layer need to pass to lower layer?
    9 months ago
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    9 months ago
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    When data moves from lower layer to upper layer in osi then what happens to headed?
    9 months ago
  • Kaiju
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    9 months ago
  • karin
    What happens with data packets in OSI model?
    8 months ago
  • Seppo Isokoski
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    8 months ago
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    8 months ago
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    8 months ago
  • george harris
    How does mail go in osi layer?
    6 months ago
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    6 months ago
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    6 months ago
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    How data flows through the infrastructure.?
    5 months ago
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    5 months ago
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    How packets are transfered from source to destonation in osi model?
    4 months ago
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    4 months ago
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    4 months ago
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    How data passes from one computer to an other?
    4 months ago
  • stephan
    How data transformed in osi layer?
    4 months ago
  • mebrahtu
    How data flows through network osi?
    4 months ago
  • cedivar
    How data flows from one layer to another layer in switch?
    3 months ago
  • Roberto
    How do data travel through internet with OSI layers?
    3 months ago
  • retu
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    3 months ago
  • kerttu
    How do data get transfered through the osi model?
    3 months ago
  • james
    How packets move from one layer to another in the osi mod?
    3 months ago
  • nadia piccio
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    3 months ago
  • giancarlo greece
    What is the directional flow of data through the five layer network?
    3 months ago
  • justin
    What form does data take at each layer of the osi model?
    3 months ago
  • riley clark
    What data passes through the pysical layer on the osi model?
    2 months ago
  • olga
    How does data move through the several layers of the osi?
    2 months ago
  • tanja
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    2 months ago
  • Melanie
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    2 months ago
  • geraldo
    How data flows in application layer of OSI model?
    1 month ago
  • tewolde
    How data packet is received OSI?
    1 month ago
  • William Campbell
    How data moves through a network?
    15 days ago

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