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OSI Model

The document describes the seven layers of the OSI model from top to bottom. The application layer contains end-user software and protocols that allow for sending and receiving of information between devices. Examples include HTTP, FTP, POP, SMTP, and DNS. The presentation layer prepares data for the application layer by encoding, encrypting, and compressing data to ensure correct receipt. The session layer creates communication sessions between devices, opening and closing sessions and allowing for data transfer checkpoints if sessions are interrupted. The transport layer takes session data and breaks it into segments, reassembling them on the receiving end and handling flow control and error checking. The network layer routes packets through physical networks using addresses and

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87 views3 pages

OSI Model

The document describes the seven layers of the OSI model from top to bottom. The application layer contains end-user software and protocols that allow for sending and receiving of information between devices. Examples include HTTP, FTP, POP, SMTP, and DNS. The presentation layer prepares data for the application layer by encoding, encrypting, and compressing data to ensure correct receipt. The session layer creates communication sessions between devices, opening and closing sessions and allowing for data transfer checkpoints if sessions are interrupted. The transport layer takes session data and breaks it into segments, reassembling them on the receiving end and handling flow control and error checking. The network layer routes packets through physical networks using addresses and

Uploaded by

shotamt
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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7.

Application Layer

The application layer is used by end-user software such as web


browsers and email clients. It provides protocols that allow software
to send and receive information and present meaningful data to
users. A few examples of application layer protocols are
the Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP),
Post Office Protocol (POP), Simple Mail Transfer Protocol (SMTP),
and Domain Name System (DNS).

6. Presentation Layer
The presentation layer prepares data for the application layer. It
defines how two devices should encode, encrypt, and compress data
so it is received correctly on the other end. The presentation layer
takes any data transmitted by the application layer and prepares it
for transmission over the session layer.

5. Session Layer

The session layer creates communication channels, called sessions,


between devices. It is responsible for opening sessions, ensuring
they remain open and functional while data is being transferred, and
closing them when communication ends. The session layer can also
set checkpoints during a data transfer—if the session is interrupted,
devices can resume data transfer from the last checkpoint.

4. Transport Layer

The transport layer takes data transferred in the session layer and
breaks it into “segments” on the transmitting end. It is responsible
for reassembling the segments on the receiving end, turning it back
into data that can be used by the session layer. The transport layer
carries out flow control, sending data at a rate that matches the
connection speed of the receiving device, and error control,
checking if data was received incorrectly and if not, requesting it
again.

3. Network Layer

The network layer has two main functions. One is breaking up


segments into network packets, and reassembling the packets on
the receiving end. The other is routing packets by discovering the
best path across a physical network. The network layer uses
network addresses (typically Internet Protocol addresses) to route
packets to a destination node.

2. Data Link Layer


The data link layer establishes and terminates a connection between
two physically-connected nodes on a network. It breaks up packets
into frames and sends them from source to destination. This layer is
composed of two parts—Logical Link Control (LLC), which identifies
network protocols, performs error checking and synchronizes
frames, and Media Access Control (MAC) which uses MAC addresses
to connect devices and define permissions to transmit and receive
data.

1. Physical Layer

The physical layer is responsible for the physical cable or wireless


connection between network nodes. It defines the connector, the
electrical cable or wireless technology connecting the devices, and is
responsible for transmission of the raw data, which is simply a
series of 0s and 1s, while taking care of bit rate control.

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