Download OSI Model

OSI Model
Andres, Wen-Yuan Liao
Department of Computer Science and Engineering
De Lin Institute of Technology
[email protected]
http://www.cse.dlit.edu.tw/~andres
Overview
Explains how standards ensure greater
compatibility and interoperability
between various types of network
technologies
OSI reference model networking
scheme
The basic functions of the OSI model
General Model of
Communication
Using layers to analyze problems in a
flow of materials
Source, destination, and data
packets
Media
Protocol
The evolution of ISO networking
standards
The concept of layers will help
you understand the action that
occurs during communication
from one computer to another
Media
Telephone wires
Category 5 UTP (used for 10BASE-T
Ethernet)
Coaxial cables (used for cable TV)
Optical fibers (thin glass fibers that carry
light)
Protocol
A Protocol is a set of rules that
make communication on a network
more efficient.
A
set of rules, or an agreement, that
determines the format and
transmission of data
The OSI Reference Model
The purpose of the OSI reference
model
The seven layers of the OSI reference
model
The functions of each layer
Encapsulation
Names for data at each layer of the
OSI model
ISO OSI 7 Layers
In the OSI reference model, there
are seven numbered layers, each
of which illustrates a particular
network function. This separation of
networking functions is called
layering.
Application Layer
Is closest to the user
Provides network services to
applications
Does not provide services to any
other OSI layer
Think of browsers
Presentation Layer
The ensures that the information that
the application layer of one system
sends out is readable by the application
layer of another system
Think of a common data format
Session Layer
Synchronizes dialogue between the two
hosts' presentation layers and manages
their data exchange
Offers provisions for efficient data
transfer, class of service, and exception
reporting
Think of dialogues and conversations
Transport Layer
Provide a data transport service
that shields the upper layers from
transport implementation details
Think of quality of service, and
reliability
Network Layer
Think of path selection, routing, and
addressing.
Data Link Layer
Is concerned with physical (as opposed
to logical) addressing, network topology,
network access, error notification,
ordered delivery of frames, and flow
control
Think of frames and media access
control
Physical Layer
Defines the electrical, mechanical,
procedural, and functional specifications for
activating, maintaining, and deactivating the
physical link between end systems

Voltage levels, timing of voltage changes,
physical data rates, maximum transmission
distances, physical connectors, and other
Think of signals and media
Encapsulation
Encapsulation wraps data with the
necessary protocol information
before network transit
Peer-to-Peer Communications
Each layer of the OSI model at the
source must communicate with its
peer layer at the destination
Each layer's protocol exchanges
information, called protocol data
units (PDUs), between peer layers
Comparison of the OSI
Model and the TCP/IP Model
The TCP/IP reference model
The layers of the TCP/IP reference
model
TCP/IP protocol graph
Comparison of the OSI model and
the TCP/IP model
TCP/IP
TCP/IP reference model and the
TCP/IP protocol stack make data
communication possible between
any two computers, anywhere in
the world
U.S. Department of Defense (DoD)
Application Layer
Higher level protocols should
include the session and
presentation layer details
Handles high-level protocols,
issues of representation, encoding,
and dialog control
Transport Layer
Deals with the quality-of-service
issues of reliability, flow control,
and error correction
Transmission Control Protocol
(TCP)
 Connection-oriented
 Segment
 Packet
switching
Internet layer
Internet protocol (IP)
Best path determination and
packet switching
Postal system
Network Access Layer
Host-to-network layer
Includes the LAN and WAN
technology details, and all the
details in the OSI physical and
data link layers
Applications
FTP - File Transfer Protocol
HTTP - Hypertext Transfer Protocol
SMTP - Simple Mail Transfer
protocol
DNS - Domain Name System
TFTP - Trivial File Transfer Protocol
The transport layer involves two
protocols - transmission control
protocol (TCP) and user datagram
protocol (UDP)
There is only one network protocol internet protocol, or IP
The network access layer, refers to
the particular LAN or WAN technology
that is being used
Similarities
Both have layers
Both have application layers, though
they include very different services
Both have comparable transport and
network layers
Packet-switched (not circuit-switched)
technology is assumed
Networking professionals need to know
both
Differences
TCP/IP combines the presentation and session
layer issues into its application layer
TCP/IP combines the OSI data link and
physical layers into one layer
TCP/IP appears simpler because it has fewer
layers
TCP/IP protocols are the standards around
which the Internet developed, so the TCP/IP
model gains credibility just because of its
protocols. In contrast, typically networks aren't
built on the OSI protocol, even though the OSI
model is used as a guide
Summary
OSI reference model
Seven numbered layers
Encapsulation
Peer-to-Peer Communications