Data Encapsulation Process on the OSI Model

• Whenever any data is sent from one node to another node in a computer network, this data is encapsulated at the sender's side, while it is de-encapsulated at the receiver's side.
• This data encapsulation occurs at various layers of the networking model like OSI or TCP/IP.
• This process adds various functionalities and features to the data transmission process.
• The most important feature that it adds is the security and reliability of data transmission between two nodes in a network.
• So, in simple words, data encapsulation can be defined as follows:

Data Encapsulation -

It is the process in which some extra information is added to the data to provide some extra beneficial features to it.

• When data encapsulation is carried out with the networking models like OSI or the TCP/IP the data transmission takes place through various layers in these models.
• Data encapsulation adds the protocol information to the data so that data transmission can properly take place.
• This information can either be added to the header or the footer of the data.
• The data encapsulation process is done at the sender’s side and it starts from the application layer to the physical layer.
• Each layer takes the encapsulated data from the previous layer and adds some more information to encapsulate it and some more functionalities with the data.
• These functionalities may include proper data sequencing, error detection, and control, flow control, congestion control, routing information, etc.

Data Encapsulation Process at each level of the OSI Model -

• Step 1 -

  • The Application, Presentation, and Session Layers in the OSI model take the user data in the form of data streams, encapsulate it, and forward the data to the Transport layer.
  • It does not necessarily add any header or footer to the data. But it is application-specific and can add the header if needed.
  • Protocols associated with these layers are NetBIOS, SAP, PPTP, and L2TP for the Session layer, XDR, MPEG, ASCH, SSL, TLS, and MIME for the Presentation layer, and SMTP, DHCP, HTTP, FTP, POP3, SNMP, and Telnet for the Application layer.

• Step 2 -

  • The Transport Layer in the OSI model takes the data stream from the upper layers and divides it into multiple parts.
  • The Transport layer encapsulates the data by adding the appropriate header to each part.
  • The header contains the sequencing information so that the data parts can be reassembled at the receiver’s end.
  • Here, the encapsulated data part is called a Segment.
  • Protocols associated with this layer are TCP, UDP, SPX, DCCP, and SCTP.

• Step 3 -

  • The Network Layer in the OSI model takes the data segments from the Transport layer and encapsulates them by adding a header to the data segment.
  • This data header contains all the routing information for the proper delivery of the data.
  • Here, the encapsulated data is called a Data Packet or Datagram.
  • Protocols associated with this layer are IPV4, IPV6, ICMP, IPsec, MPLS, IPX, AppleTalk, and IGMP.

• Step 4 -

  • The Data-Link Layer in the OSI model takes the data packet or datagram from the Network layer and encapsulates it by adding a header and footer to the data packet or datagram.
  • The header contains all the switching information for the proper delivery of the data to the appropriate hardware components, and the trailer contains all the information related to error detection and control.
  • Here, the encapsulated data is called a Data Frame.
  • Protocols associated with this layer are RAPA, CSLIP, HDLC, SDLC, PLIP, X-25, PPP, Frame Relay, ATM, Fiber Cable, etc.

• Step 5 -

  • The Physical Layer in the OSI model takes the data frames from the Data-Link layer and encapsulates them by converting them to appropriate data signals or corresponding to the physical medium.
  • Protocols associated with thIs layer are PON, OTN, DSL, TIA 449, RS232, 100BaseTX, ISDN, 11, IEEE.802.11, IEEE.802.3.