2. Open Systems Interconnection (OSI) is a set of
internationally recognized standards for networking
and for operating system involved in networking
functions.
7. Application layer
6. Presentation layer
5. Session layer
4. Transport layer
3. Network layer
2. Data link layer
1. Physical layer
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5. The OSI Reference Model (Encapsulation)
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H: header
T: trail
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7. LAYER 7 – The APPLICATION Layer
• The top layer of the OSI model
• Provides a set of interfaces for sending and
receiving applications to gain access and to
use network services, such as: network file
transfer, message handling and database query
processing.
The Application Layer Is Responsible For
Providing Services To The User.
9. LAYER 6 – The PRESENTATION Layer
• For outgoing messages, it converts data into a generic format for
network transmission; for incoming messages, it converts data
from the generic network format to a format that the receiving
application can understand
• This layer is also responsible for certain protocol conversions,
data encryption/decryption, or data compression/decompression
• A special software facility called a “redirector” operates at this
layer to determine if a request is network related on not and
forward network-related requests to an appropriate network
resource
The presentation layer is responsible for
translation, compression, and encryption.
11. LAYER 5 – The SESSION Layer
• Enables two networked resources to hold ongoing
communications (called a session) across a network.
• Applications on either end of the session are able to ex-
change data for the duration of the session.
• This layer is:
• Responsible for initiating, maintaining and terminating sessions
• Responsible for security and access control to session information (via
session participant identification)
• Responsible for synchronization services, and for checkpoint services
The session layer is responsible for dialog
control and synchronization.
13. LAYER 4 – The TRANSPORT Layer
• Manages the transmission of data across a network
• Manages the flow of data between parties by
segmenting long data streams into smaller data
chunks (based on allowed “packet” size for a
given transmission medium)
• Reassembles chunks into their original sequence at
the receiving end
• Provides acknowledgements of successful
transmissions and requests resends for packets
which arrive with errors
The transport layer is responsible for the delivery
of a message from one process to another.
15. Transport Layer
The transport layer include the following:
• Service-point addressing.
• Segmentation and reassembly.
• Connection control
• Flow control
18. LAYER 3 – The NETWORK Layer
• Handles addressing messages for delivery, as well as
translating logical network addresses and names into their
physical counterparts
• Responsible for deciding how to route transmissions
between computers
• This layer also handles the decisions needed to get data
from one point to the next point along a network path
• This layer also handles packet switching and network
congestion control.
The network layer is responsible for the delivery of
individual packets from the source host to the
destination host & Logical Addressing and Routing
22. LAYER 2 – The DATA LINK Layer
• Handles special data frames (packets) between the
Network layer and the Physical layer
• At the receiving end, this layer packages raw data
from the physical layer into data frames for
delivery to the Network layer
• At the sending end this layer handles conversion of
data into raw formats that can be handled by the
Physical Layer
The data link layer is responsible for moving
frames from one hop (node) to the next
26. LAYER 1 – The PHYSICAL Layer
• Converts bits into electronic signals for outgoing
messages
• Converts electronic signals into bits for incoming
messages
• This layer manages the interface between the computer
and the network medium (coax, twisted pair, etc.)
• The bottom layer of the OSI model
The physical layer is responsible for movements of
individual bits from one hop (node) to the next.
28. Physical Layer
The physical layer is concerned with the following:
• Physical characteristics of interfaces and medium
• Representation of bits.
• Data rate.
• Synchronization of bits.
• Line configuration.
• Physical topology.
• Transmission mode.
32. A Comparison of the OSI and TCP/IP Reference
Model
SIMILARITIES
The main similarities between the two models include the following:
• They share similar architecture :- Both of the models share a similar
architecture. This can be illustrated by the fact that both of them are
constructed with layers.
• They share a common application layer:- Both of the models share a
common "application layer". However in practice this layer includes
different services depending upon each model.
• Both models have comparable transport and network layers:- This
can be illustrated by the fact that whatever functions are performed
between the presentation and network layer of the OSI model similar
functions are performed at the Transport layer of the TCP/IP model.
33. •Knowledge of both models is required by networking professionals.-
According to article obtained from the internet networking
professionals "need to know both models".
•Both models assume that packets are switched.- Basically this
means that individual packets may take differing paths in order to
reach the same destination.
DIFFERENCES
•The main differences between the two models are as follows:
•TCP/IP Protocols are considered to be standards around which
the internet has developed. The OSI model however is a
"generic, protocol- independent standard.”
•TCP/IP combines the presentation and session layer issues into
its application layer.
•TCP/IP combines the OSI data link and physical layers into the
network access layer.
34. •TCP/IP appears to be a more simpler model and this is
mainly due to the fact that it has fewer layers.
•TCP/IP is considered to be a more credible model- This
is mainly due to the fact because TCP/IP protocols are the
standards around which the internet was developed
therefore it mainly gains creditability due to this
reason. Where as in contrast networks are not usually built
around the OSI model as it is merely used as a guidance tool.
•The OSI model consists of 7 architectural layers whereas the
TCP/IP only has 4 layers
