Transcript CCNA1_Chapter_2 - UWC Computer Science

University of the Western Cape
Chapter 2: The OSI Model
Aleksandar Radovanovic
Network Communication



University of the Western Cape

The most basic level of computer information consists of binary digits, or bits (0s
(zeros) and 1s).
In order for computers to send information through a network, all communications
on a network originate at a source and then travel to a destination.
Computers that send one or two bits of information, however, would not be very
useful. Other groupings, bytes, kilobytes, megabytes, and gigabytes are therefore
necessary.
In order for data packets to travel from a source to a destination on a network, it is
important that all the devices on the network speak the same language or protocol.
OSI Reference Model
University of the Western Cape
The OSI reference model, released in 1984 by International
Organization for Standardization (ISO) is the primary
model for network communications.
• It breaks network communication into smaller parts to
make it easier to understand.
• It standardizes network components to allow multiplevendor development and support.
• It allows different types of network hardware and
software to communicate with each other.
• It prevents changes in one layer from affecting the other
layers, so that they can develop more quickly.
University of the Western Cape
The 7 Layers of the OSI Model
University of the Western Cape
Encapsulation
Peer-to-Peer Communications

University of the Western Cape

Communication between the same OSI reference model layer in two
different network devices
During this process, the protocol of each layer exchanges information,
called protocol data units (PDUs), between peer layers.
The TCP/IP Reference Model
Application layer handles high level protocols,
issues of representation, encoding, and dialog
control.
University of the Western Cape
The transport layer deals with the quality of
service issues of reliability, flow control, and
error correction.
The purpose of the internet layer is to
send packets and have them arrive at the
destination.
Network Access Layer includes the LAN
and WAN technology details.
University of the Western Cape
Comparison of the OSI and the TCP/IP model
Differences
Similarities
•TCP/IP
the presentation and session layer issues into its application layer
•Bothcombines
have layers
•TCP/IP
the OSI layers,
data link
and physical
layersvery
intodifferent
one layerservices
•Bothcombines
have application
though
they include
•TCP/IP
simpler because
it has
layers,
however this is a misconception.
•Bothappears
have comparable
transport
andfewer
network
layers
The
OSI reference model,
with its less complex
and multiple
layers, is simpler to develop
•Packet-switched
(not circuit-switched)
technology
is assumed
•TCP/IP protocols are the standards around which the Internet developed –
typically networks are not built on the OSI protocol.
Labs

University of the Western Cape



2.3.4 (homework) In this lab, you will learn to relate the seven layers
of the OSI model to the four layers of the TCP/IP model as well as name
the primary TCP/IP protocols and utilities that operate at each layer.
2.3.5 (homework) In this lab, you will identify the characteristics of
each layer as well as the terminology and physical devices that operate at
each layer.
Interactive Labs:
2.3.5 (homework) Test your knowledge of the functions of the OSI
Model layers.