This document discusses the seven layers of the OSI network model: Physical, Data Link, Network, Transport, Session, Presentation, and Application. It describes the purpose and responsibilities of each layer, including how layers communicate with each other on the same or different machines through peer-to-peer protocols. Functions like framing, addressing, error control, routing, and establishing sessions are managed across the layers to enable end-to-end communication between applications.

1. THE LAYERS OF
OSI NETWORK MODEL
PRINCE KUMAR
BSC.IT
GAYA COLLEGE GAYA

2. Contents…
• Introduction to OSI network model.
• OSI Layers.
• Layer to layer communication.
• Study of Layers.

3. Introduction to OSI network model.
• In 1970,on a world wide agreement to make networking
more flexible, robust and interoperable a network model is
standardized by ISO (international organization of
standards),came as OSI (open system interconnection)
network model.
• This model is very helpful in study and designing of
networks.

4. OSI Layers.
• The OSI model is divided into seven separated but
interrelated layers, Actually these are set of protocols
required for establishment of a better network.
• These are as follows_

5. Layer to layer communication.
• Depending on the machine arrangement layers
communicates as follows_
• Case 1: Layers on the same machine communicates by accepting
data units from the backward layer and sent to the next layer. At
each layer some Headers are added to the data parts for the
control of flow and securities issues.
• While sending Application layer and Physical layer don’t accept
data from the backward layer and forward to the next layer
respectively and while receiving vice versa.
• Data link layer also add a trailer to detect error and handle it by
retransmitting. It is helpful in layer to layer communication in two
machines.

6. Layer to layer communication.
• Case 2: Layer to
layer communication
on two different
networks is
processed by set of
protocols and these
layer communicates
with the same layer
in the different
network and this
mechanism is
defined as PEER to
PEER
communication.

7. Study of Layers.
• Let us see about layers and their duties one by one_
• Application layer : This layer is the first OSI layer in the sending
condition and the last one while receiving. It provides interfaces to
the end users to compose messages and specifies its format and
then forward to the next layer presentation layer and while
receiving it collects contents form presentation layer.
• There are so many protocols like SMTP, HTTP, TELNET, FTP,
TFTP, DNS etc.
• Presentation layer : This layer accepts message from layer I and
sends to the session layer. This layer provides following facilities_
1. Translation of data in a common format for both of the users.
2. Encryption/Decryption for security of sensitive data.
3. Compression to reduce the data size. It is very useful in multimedia
transmission.

8. Study of Layers.
• Session layer: It is third layer while are sending some data. It
accepts data from the presentation layer. It establishes sessions for
communication. Major responsibilities of session layer are as
follows_
• Dialog control: After defining sessions it provides unique id for each
sessions.
• Synchronize: It means session layer is responsible to balance the
equation of sending and receiving rate during session.
• Transport layer: This is the next layer in the OSI model. That
accepts data from the session layer. It is responsible for_
• Process to process delivery: Complete message delivery by maintaining
the order of processes running on the both of the system.
• Segmentation/ Reassembling: Conversion of data into segments or user
datagrams and reassemble them again at receiving. It is managed by
TCP or UDP protocols.
• Flow and Error control: This layer also balance the equation of sending
and receiving of data segments or datagrams and correct erroneous
(damage, lost or duplicate) contents by retransmission.

9. Study of Layers.
• Network layer: This layer is below the transport layer and accepts
data segments or user datagrams from the upper layer. It convert
them into smaller data packets. Major responsibilities are_
• Logical Addressing: Association of the physical address (MAC address)
to the logical address at each of nodes in route. If it get matched, data
packets are delivered. Actually it is managed by IP, ARP & RARP
protocols.
• Routing: Select a route over data packets are transmitted from the
source to the destination. ICMP & IGMP protocols helps in routing.
• Data link layer: This is the second last layer of the OSI model,
responsible for_
• Framing: Conversions of data packets into smaller frames.
• Physical Addressing: Add a header to define the physical address of
the sender and receiver.
• Flow and Error control: Balance the rate of data transmission and add a
trailer to the frames to detect erroneous phenomenon (loss of frame
and its duplication)

10. Study of Layers.
• Physical layer: This the seventh layer for sender is responsible for_
• Bit stream conversion of frames in the form of 0s and 1s.
• Encoding and Decoding of bits in the signals (electrical, optical etc.) as
transmission media type.
• Bit rate synchronization at both, the sender and the receiver.
• Providing interfaces between devices and media.
• Control transmission mode during bit signaling either simplex or Half
and Full Duplex.

11. THE END
Send your
feedbacks:
824207prince@gma
il.com
In the next video _
TCP/IP
Protocol
Suite