Information Technology Reference
In-Depth Information
Data Link Layer:
The second layer provides error detection and con-
trol. It adds reliability to the physical layer by grouping bits into frames
and providing synchronization, error control, and flow control over the
frames. Basically, it controls the transfer of data across a network media.
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Network Layer:
The third layer is responsible for determining a path
through the network between systems that want to communicate. It
understands the data communication and switching technologies used to
interconnect systems.
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Transport Layer:
The fourth layer provides end-to-end error recovery
and flow control. These services ensure that the data is delivered with-
out errors and in sequence without duplication.
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Session:
The fifth layer provides a control structure for communication
between applications. It is responsible for establishing, maintaining, and
terminating connections.
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Presentation:
The sixth layer is responsible for handling the differences
in data representation or syntax. This layer maps data between formats
so that the application can understand the data.
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Application:
The seventh layer provides utilities used by humans
including functionality such as remote logins, file transfers, and so on.
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The Transmission Control Protocol/Internet
Protocol (TCP/IP) Model
Like the OSI network model, the TCP/IP network model consists of a stack
of service layers. Unlike the OSI model, it provides the same functionality
using five layers instead of seven. For the most part, the four lowest layers
between the OSI and TCP/IP network provide similar functionality, where-
as the top three OSI layers (Session, Presentation, and Application) are
grouped into the TCP/IP Application layer.
The five TCP/IP layers (from lowest to the highest) are
Physical Layer:
The first layer is concerned with the physical interface
between devices. It controls the transmission of a bit stream over the
physical medium and deals with the mechanical and electrical character-
istics of the physical medium.
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Data Link Layer:
The second layer provides error detection and con-
trol. It adds reliability to the physical layer by grouping bits into
frames
and providing synchronization, error control, and flow control over the
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