Data Encapsulation

Explain how data encapsulation allows data to be transported across the network.

Segmenting Messages

Segmenting is the process of breaking up messages into smaller units. Multiplexing is the processes of taking multiple streams of segmented data and interleaving them together. Segmenting messages has two primary benefits:

• Increases speed – Large amounts of data can be sent over the network without tying up a communications link.
• Increases efficiency – Only segments which fail to reach the destination need to be retransmitted, not the entire data stream.

Sequencing

Sequencing messages is the process of numbering the segments so that the message may be reassembled at the destination. TCP is responsible for sequencing the individual segments.

Protocol Data Units

Encapsulation is the process where protocols add their information to the data. At each stage of the process, a PDU has a different name to reflect its new functions. There is no universal naming convention for PDUs, in this course, the PDUs are named according to the protocols of the TCP/IP suite. PDUs passing down the stack are as follows:

1. Data (Data Stream)
2. Segment
3. Packet
4. Frame
5. Bits (Bit Stream)

Encapsulation Example

Encapsulation is a top down process. The level above does its process and then passes it down to the next level of the model. This process is repeated by each layer until it is sent out as a bit stream.

De-encapsulation Example

Data is de-encapsulated as it moves up the stack. When a layer completes its process, that layer strips off its header and passes it up to the next level to be processed. This is repeated at each layer until it is a data stream that the application can process.

• Received as Bits (Bit Stream)
• Frame
• Packet
• Segment
• Data (Data Stream)

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