The following is an explanation of the OSI Model. “Short for Open System Interconnection, an ISO standard for world
wide communications that defines a networking framework for implementing protocols in seven layers.?
Let’s breakdown this definition piece by piece and then we’ll move onto a thorough explanation of each layer. Standards
are rules of communication between two or more machines. Protocols are instances of standards that apply to communication
between equal processes on different machines but on the same layer. This same layer communication is known as horizontal
communication. In an attempt to create an analogy imagine standards as Federal Laws, protocols would be like State Laws.
A framework is like a blueprint, a basic design. Lastly, a network is a system of computer components that connects two
or more computers.
Application Layer
Starting at the top, the Application Layer allows communication to take place between two different applications on two
different machines. Different applications have different protocols, just as different file systems have different naming
conventions and other such incompatibilities are all dealt with on the application layer. Examples of different applications
are file transfers and e-mail.
Presentation Layer
Just below the Application Layer is the Presentation Layer. The basic design of the Presentation Layer is to format the
information to be delivered or information received to the preferences of the two computers involved in the transaction.
These computers agree on a transfer syntax. “It is as if English and German speakers, who both also speak French and
Italian, agree to communicate in French,?(Panko). This layer is also were processes such as data compression and data
encryption also occur. This layer also causes many problems for any computer trying to communicate with it using TCP/IP
because TCP/IP does not have a specific layer to serve these purposes.
Session Layer
The Session Layer establishes a session between two computers. This session may be remotely timed, may allow file transfer,
it may manage dialogue. This dialogue can allow traffic to go in both directions at the same time or may limit transfer
so only one party may transmit at a time. The session can also be set up for token transfers. This token is like a talking
stick in the kindergarten. The person with the talking stick is the only one allowed to talk at a time. When it is passed,
then that person becomes the only one allowed to talk. Another service of the Session Layer is to enable synchronization.
This option prevents all possibility of collision during transmission. Examples of Session Layer Protocols include NetBIOS,
Name Pipes, Mail Slots, and RPC (OSI Model Layers).
Transport Layer
The main function of the Transport Layer is to receive data from the Session Layer, break it up into smaller units if
needed, pass them all to the network layer, and ensure that all of the pieces arrive at the destination correctly. The
Transport Layer establishes the correct network connection specified by the Session Layer. The Transport Layer may create
multiple network connections, to increase throughput. Depending on the options set due to expensive transmission costs,
the Transport Layer may also multiplex many connections onto the same network connection. Multiplexing is the act of
breaking up the connection into sections to send more information at once. The type of service is also determined on this
layer, such as Point-to-Point. The Transport Layer uses the transport header to tell the receiver what message belongs to
what connection. The final responsibility of the Transport Layer is to establish network connections and delete them.
Examples of protocols used on the Transport Layer are NetBIOS, TCP, and ATM (OSI Model Layers).
Network Layer
I know this is boring, but there’s only three more layers to go. The Network Layer is next. “The network and transport
layers of the OSI correspond closely to the internet and transport layers of TCP/IP (Panko). The Network layer controls
the operation of the subnet. The Network Layer decides the route for the packets to take. This route may be “wired into?
such as in a terminal session, or may be dynamic which allows for decision making according to the current network workload.
The Network Layer also keeps track of the amount of data sent for billing purposes.
Data Link Layer
The Data Link Layer is what you could consider the organizer of the system. The Physical Layer accepts data with no
regard for organization. The DLL (Data Link Layer) organizes the received data into a single stream in order as
described by the frame. The DLL provides error control, by announcing any missing frames or damaged ones. The DLL can
also regulate the speed of transmission. This is necessary when the sender is capable of sending information much faster
than the receiver can take it. This is critical in preventing loss of data and congestion. If the Session Layer has
allowed for transmission in both directions, the DLL must compensate for lack of transmission capabilities by using
techniques such as piggybacking. The protocol for this layer is the 802.1 OSI Model (OSI Model Layers).
Physical Layer
Finally, the Physical Layer is the most basic of all the layers in concept. All it does is transmit and receive data in
the form of electrical pulses. It uses binary language to transmit. The electrical signal is in pulses, so a 0 represents
off and 1 represents on. Problems on this layer come from use of physical transmission medium like a phone line or a cable
line or even a fiber optic line. The transmission protocols for the Physical Layer include IEEE 802, IEEE 802.2, ISO 2110,
and ISDN (OSI Model Layers).
wide communications that defines a networking framework for implementing protocols in seven layers.?
Let’s breakdown this definition piece by piece and then we’ll move onto a thorough explanation of each layer. Standards
are rules of communication between two or more machines. Protocols are instances of standards that apply to communication
between equal processes on different machines but on the same layer. This same layer communication is known as horizontal
communication. In an attempt to create an analogy imagine standards as Federal Laws, protocols would be like State Laws.
A framework is like a blueprint, a basic design. Lastly, a network is a system of computer components that connects two
or more computers.
Application Layer
Starting at the top, the Application Layer allows communication to take place between two different applications on two
different machines. Different applications have different protocols, just as different file systems have different naming
conventions and other such incompatibilities are all dealt with on the application layer. Examples of different applications
are file transfers and e-mail.
Presentation Layer
Just below the Application Layer is the Presentation Layer. The basic design of the Presentation Layer is to format the
information to be delivered or information received to the preferences of the two computers involved in the transaction.
These computers agree on a transfer syntax. “It is as if English and German speakers, who both also speak French and
Italian, agree to communicate in French,?(Panko). This layer is also were processes such as data compression and data
encryption also occur. This layer also causes many problems for any computer trying to communicate with it using TCP/IP
because TCP/IP does not have a specific layer to serve these purposes.
Session Layer
The Session Layer establishes a session between two computers. This session may be remotely timed, may allow file transfer,
it may manage dialogue. This dialogue can allow traffic to go in both directions at the same time or may limit transfer
so only one party may transmit at a time. The session can also be set up for token transfers. This token is like a talking
stick in the kindergarten. The person with the talking stick is the only one allowed to talk at a time. When it is passed,
then that person becomes the only one allowed to talk. Another service of the Session Layer is to enable synchronization.
This option prevents all possibility of collision during transmission. Examples of Session Layer Protocols include NetBIOS,
Name Pipes, Mail Slots, and RPC (OSI Model Layers).
Transport Layer
The main function of the Transport Layer is to receive data from the Session Layer, break it up into smaller units if
needed, pass them all to the network layer, and ensure that all of the pieces arrive at the destination correctly. The
Transport Layer establishes the correct network connection specified by the Session Layer. The Transport Layer may create
multiple network connections, to increase throughput. Depending on the options set due to expensive transmission costs,
the Transport Layer may also multiplex many connections onto the same network connection. Multiplexing is the act of
breaking up the connection into sections to send more information at once. The type of service is also determined on this
layer, such as Point-to-Point. The Transport Layer uses the transport header to tell the receiver what message belongs to
what connection. The final responsibility of the Transport Layer is to establish network connections and delete them.
Examples of protocols used on the Transport Layer are NetBIOS, TCP, and ATM (OSI Model Layers).
Network Layer
I know this is boring, but there’s only three more layers to go. The Network Layer is next. “The network and transport
layers of the OSI correspond closely to the internet and transport layers of TCP/IP (Panko). The Network layer controls
the operation of the subnet. The Network Layer decides the route for the packets to take. This route may be “wired into?
such as in a terminal session, or may be dynamic which allows for decision making according to the current network workload.
The Network Layer also keeps track of the amount of data sent for billing purposes.
Data Link Layer
The Data Link Layer is what you could consider the organizer of the system. The Physical Layer accepts data with no
regard for organization. The DLL (Data Link Layer) organizes the received data into a single stream in order as
described by the frame. The DLL provides error control, by announcing any missing frames or damaged ones. The DLL can
also regulate the speed of transmission. This is necessary when the sender is capable of sending information much faster
than the receiver can take it. This is critical in preventing loss of data and congestion. If the Session Layer has
allowed for transmission in both directions, the DLL must compensate for lack of transmission capabilities by using
techniques such as piggybacking. The protocol for this layer is the 802.1 OSI Model (OSI Model Layers).
Physical Layer
Finally, the Physical Layer is the most basic of all the layers in concept. All it does is transmit and receive data in
the form of electrical pulses. It uses binary language to transmit. The electrical signal is in pulses, so a 0 represents
off and 1 represents on. Problems on this layer come from use of physical transmission medium like a phone line or a cable
line or even a fiber optic line. The transmission protocols for the Physical Layer include IEEE 802, IEEE 802.2, ISO 2110,
and ISDN (OSI Model Layers).
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