Editing OSI model (section)

==Definitions==
{{More citations needed section|date=November 2019}}
[[Communication protocol]]s enable an entity in one host to interact with a corresponding entity at the same layer in another host. Service definitions, like the OSI model, abstractly describe the functionality provided to a layer ''N'' by a layer ''N−1'', where ''N'' is one of the seven layers of protocols operating in the local host.

At each level ''N'', two entities at the communicating devices (layer N ''peers'') exchange [[protocol data unit]]s (PDUs) by means of a layer N ''protocol''. Each PDU contains a payload, called the [[service data unit]] (SDU), along with protocol-related headers or footers.

Data processing by two communicating OSI-compatible devices proceeds as follows:
# The data to be transmitted is composed at the topmost layer of the transmitting device (layer ''N'') into a ''[[protocol data unit]]'' (''PDU'').
# The ''PDU'' is passed to layer ''N−1'', where it is known as the ''[[service data unit]]'' (''SDU'').
# At layer ''N−1'' the ''SDU'' is [[concatenated]] with a header, a footer, or both, producing a ''layer N−1 PDU''. It is then passed to layer ''N−2''.
# The process continues until reaching the lowermost level, from which the data is transmitted to the receiving device.
# At the receiving device the data is passed from the lowest to the highest layer as a series of ''SDU''s while being successively stripped from each layer's header or footer until reaching the topmost layer, where the last of the data is consumed.

===Standards documents===
The OSI model was defined in ISO/IEC 7498 which consists of the following parts:
*ISO/IEC 7498-1 The Basic Model
*ISO/IEC 7498-2 Security Architecture
*ISO/IEC 7498-3 Naming and addressing
*ISO/IEC 7498-4 Management framework

ISO/IEC 7498-1 is also published as ITU-T Recommendation X.200.