Answer Posted / jitendra

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.


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.

.

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.

.

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.



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.

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.


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.

If all of the other layers are working and have been
tested, then this is usually just a matter of applying
patches to software or reinstalling. Everyone probably has
experience troubleshooting problems in windows. Telnet is
an excellent tool for connecting to virtually any port to
check to see if the above layers are functioning properly.

.

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