9-4-2 Communications protocols
A “protocol” is a set of rules for data communication between computers
over a network. In order to exchange data between computers, it is necessary to first decide on a mutual protocol.
Windows
Mac
Ability to build a network that is not
dependant on OS or type of computer
Protocol (Rules)
UNIX
Reference
OSI
Abbreviation for “Open Systems Interconnection.”
Reference
ITU
The ITU develops international standards in the field of telecommunications
for data and other communications.
Abbreviation for “International Telecommunication Union.”
267
1
Windows
Windows
OSI model
The “OSI (Open Systems Interconnection) model” is a protocol reference model and international standard. The OSI model was mainly developed by the ISO and ITU. It can be used as a starting point for developing
a protocol that enables communications between different systems and different types of computers.
The OSI model divides the many protocols necessary for communications
into functional layers.
The OSI model is comprised of the following seven layers.
Layer
Description
Layer 7
Application layer
Provides communication services such as file transfer
and e-mail.
Layer 6
Presentation
layer
Provides conversion into a form that is acceptable for
data communication, and conversion into a form that
the application layer can accept.
Layer 5
Session layer
Establishes and terminates communications.
Layer 4
Transport layer
Ensures reliable communications including retransmission in the event of communication errors.
Layer 3
Network layer
Transfers data between computers or relays data
across multiple networks.
Layer 2
Data link layer
Sends data between adjacent computers.
Layer 1
Physical layer
Provides conversion of data into electrical signals and
transmits the electrical signals.