The document describes the Open Systems Interconnection (OSI) reference model, which is an abstract description for layered communications and computer network protocol design. It divides network architecture into seven layers from the physical layer dealing with transmission of raw bits up to the application layer dealing with services for users. Each layer has specific responsibilities and concerns such as framing data, addressing, error control, and providing services like file transfer. The model is important for standardizing how network communication should work across different hardware and software platforms.

1. OSI REFERENCE
MODEL
1
ISHAN UDYOGA

2. Introduction
2
 Open Systems Interconnection Basic Reference Model (OSI
Reference Model or OSI Model) is an abstract description for
layered communications and computer network protocol
design. It was developed as part of the Open Systems
Interconnection (OSI) initiative. In its most basic form, it
divides network architecture into seven layers which, from
top to bottom, are the Application, Presentation, Session,
Transport, Network, Data-Link, and Physical Layers. It is
therefore often referred to as the OSI Seven Layer Model.

3. OSI Model's 7 Layers
Application
3
Presentation
Session
Transport
Network
Data Link
Physical
TCP/IP
Application
Host to Host
Internet
Internet
Access
Data
Segments
Packets
Frames
Bits

4. OSI Model's 7 Layers 4
User 1 User 2
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Presentation
Session
Transport
Network
Data Link
Physical
Higher
Layer
Middle
Layer
Lower
Layer
Physical Medium
Data

5. 5
Application Layer
User 1
FTAM X.500 X.400
Data
Application Layer
 The application layer is responsible for providing services to the user.
 Concerned:
 Network virtual terminal (Software)
 File transfer, access and management
 Mail services
 Directory services (access to distributed database sources for global information
about various objects and services)
FTAM X.500 X.400
Data
User 2
To Presentation Layer From Presentation Layer

6. 6
Presentation Layer
User 1 User 2
From Application Layer
ASCII Binary JPEG
Data
To Session Layer
 The presentation layer is responsible for translation, compression and encryption
 Concerned:
 Translation (interoperability between different encoding system)
 Encryption (Privacy schemes)
 Compression (data compression)
To Application Layer
ASCII Binary JPEG
Data
From Session Layer
presentation Layer

7. 7
Session Layer
User 1 User 2
From Presentation Layer
Session Layer
Communicate with user 2 Communicate with user 1
Data
To Transport Layer
To Presentation Layer
Data
From Transport Layer
 The session layer is responsible for dialog control and synchronization
 Concerned:
 Dialog Control (Half Duplex/Full duplex)
 Synchronization (Synchronization points, process inline within same page)

8. 8
Transport Layer
User 1 User 2
From Session Layer
Data
To Network Layer
To Session Layer
Data
From Network Layer
TCP/UDP
Transport Layer
 The transport layer is responsible for the delivery of a message from one process to
another
 Concerned:
 Service-point addressing (Port address)
 Segmentation and reassembly (Sequence number)
 Connection control (Connectionless or connection oriented)
 Flow control (end to end)
TCP/UDP

9. 9
Network Layer
User 1 User 2
From Transport Layer
Data
To Data Link Layer
To Transport Layer
Data
From Data Link Layer
IP/IPX
Network Layer
IP/IPX
 The network layer is responsible for the delivery of individual packets from the
source host to the destination host.
 Concerned:
 Logical addressing (IP Address)
 Routing (Source to destination transmission between networks)

10. 10
Data Link Layer
User 1 User 2
From Network Layer
Data
To Physical Layer
To Network Layer
Data
From Physical Layer
STP/VTP/CDP
Data Link Layer
STP/VTP/CDP
 Data link layer is responsible for moving frames from one hop (Node) to the next.
 Concerned:
 Framing (stream of bits into manageable data units)
 Physical addressing (MAC Address)
 Flow Control (mechanism for overwhelming the receiver)
 Error Control (trailer, retransmission)
 Access Control (defining master device in the same link)

11. 11
Physical Layer
User 1 User 2
From Data Link Layer
10110110011101011
To Data Link Layer
10110110011101011
Bits/Bytes
Physical Layer
Bits/Bytes
 One of the major function of the physical layer is to move data using electromagnetic signals
across a transmission medium.
 Its responsible for movements of individual bits from one hop (Node) to next.
 Concerned:
 Physical characteristics of interface and medium (Transmission medium)
 Data rate (duration of a bit, which is how long it last)
Transmission Medium

12. Data, Protocol & Activities
12
OSI Layers TCP/IP Suit Activities
Application
Telnet, FTP, SMTP, HTTP, DNS, SNMP, Specific address etc…
Presentation
Session
Transport
SCTP, TCP, UDP, Sockets and Ports address
Network
IP, ARP/RARP, ICMP, IGMP, Logical address
Data Link
IEEE 802 Standards, TR, FDDI, PPP, Physical address
Application
Presentation
Session
Transport
Network
Data Link
To allow access to network resources
To Translate, encrypt, and compress
data
To establish, manage, and terminate
session
To Provide reliable process-to-process
Message delivery and error recovery
To move packets from source to
destination; to provide internetworking
To organize bits into frames; to provide
Hop-to-hop delivery
Physical
Medium, Coax, Fiber, 10base, Wireless
Physical
To Transmit bits over a medium; to provide
Mechanical and electrical specifications

13. 13
Thanks !