Sending Computer

The flow of data on the sending computer is in the downwards direction of the OSI model. At each layer in the OSI model protocols can be found adding headers and trailers or footers which contain important information such as addressing and error control information.

Upon receiving information from an upper layer, the lower layer would consider the entire package as data and add its own head and then if needed a footer or trailer data. This additive process of adding headers and footers to data at each layer (layer by layer) is called encapsulation.

Receiving Computer

The flow of data on the Receiving Computer is in the upwards direction of the OSI model. At each of the layers the addressing or protocol information is examined and then removed layer by layer until the computer finally gets to the actual data. This subtractive process of removing headers at each layer of the OSI model is called de-encapsulation.

Learn more fundamental networking from these resources:

• Getting Started with Networking (eLearning) (juniper.net)
• CCNA 200-301 Exam Cram, 6th Edition (oreilly.com)

Glossary

OSI Model: A conceptual model divided into seven layers, created by the International Organization for Standardization which enables systems to communicate using protocols over a network. OSI Model Reference Chart