Application
(Layer 7) |
This layer supports application and end-user
processes. Communication partners are identified, quality of service is
identified, user authentication and privacy are considered, and any
constraints on data syntax are identified. Everything at this layer is
application-specific. This layer provides application services for file
transfers, e-mail, and other network software services. Telnet and FTP are
applications that exist entirely in the application level. Tiered
application architectures are part of this layer. |
Presentation
(Layer 6) |
This layer provides independence from
differences in data representation (e.g., encryption) by translating from
application to network format, and vice versa. The presentation layer works
to transform data into the form that the application layer can accept. This
layer formats and encrypts data to be sent across a network, providing
freedom from compatibility problems. It is sometimes called the syntax
layer. |
Session
(Layer 5) |
This layer establishes, manages and terminates
connections between applications. The session layer sets up, coordinates,
and terminates conversations, exchanges, and dialogues between the
applications at each end. It deals with session and connection coordination. |
Transport
(Layer 4) |
This layer provides transparent transfer of data
between end systems, or hosts, and is responsible for end-to-end error
recovery and flow control. It ensures complete data transfer. |
Network
(Layer 3) |
This layer provides switching and routing
technologies, creating logical paths, known as virtual circuits, for
transmitting data from node to node. Routing and forwarding are functions of
this layer, as well as addressing, internetworking, error handling,
congestion control and packet sequencing. |
Data Link
(Layer 2) |
At this layer, data packets are encoded and
decoded into bits. It furnishes transmission protocol knowledge and
management and handles errors in the physical layer, flow control and frame
synchronization. The data link layer is divided into two sublayers: The
Media Access Control (MAC) layer and the Logical Link Control (LLC) layer.
The MAC sublayer controls how a computer on the network gains access to the
data and permission to transmit it. The LLC layer controls frame
synchronization, flow control and error checking. |
Physical
(Layer 1) |
This layer conveys the bit stream - electrical
impulse, light or radio signal -- through the network at the electrical and
mechanical level. It provides the hardware means of sending and receiving
data on a carrier, including defining cables, cards and physical aspects.
Fast Ethernet, RS232, and ATM are protocols with physical layer components. |
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