CompTIA exam study guide presentations by instructor Brian Ferrill, PACE-IT (Progressive, Accelerated Certifications for Employment in Information Technology) "Funded by the Department of Labor, Employment and Training Administration, Grant #TC-23745-12-60-A-53" Learn more about the PACE-IT Online program: www.edcc.edu/pace-it

1. The OSI
networking
reference model.

2. Page 2
Instructor, PACE-IT Program – Edmonds Community College
Areas of Expertise Industry Certifications
 PC Hardware
 Network Administration
 IT Project Management
 Network Design
 User Training
 IT Troubleshooting
Qualifications Summary
Education
 M.B.A., IT Management, Western Governor’s University
 B.S., IT Security, Western Governor’s University
Entrepreneur, executive leader, and proven manger
with 10+ years of experience turning complex issues
into efficient and effective solutions.
Strengths include developing and mentoring diverse
workforces, improving processes, analyzing
business needs and creating the solutions
required— with a focus on technology.

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PACE IT.
– A brief history.
– Networking reference models.
– OSI and TCP/IP comparison.

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The OSI networking reference model.

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The OSI (Open Systems
Interconnection) reference
model is a conceptual model
with two major components.
The first main component of the OSI networking
reference model is an abstract model of
networking—a seven layer model. The second is a
set of specific protocols, which allow differing
computing systems to communicate with one
another despite their different architectures.
The OSI networking reference model.

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The OSI networking reference model.
– Why a networking model was required.
» Early networks communicated using proprietary languages.
» Early networks could only communicate with like systems (e.g.,
IBM to IBM and DEC to DEC).
» The U.S. government desired a robust computer
communications system that could survive disasters.
– TCP/IP reference model.
» The Transmission Control Protocol/Internet Protocol (TCP/IP)
was published as the U.S. DoD standard in 1982.
» Adopted by the big players beginning in 1984.
• AT&T moved the UNIX implementation to open source in
1989.
– OSI reference model.
» Published in 1983.
» Defines the relationships between differing protocols.
» Defines the relationships between differing protocols and
hardware.

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The OSI networking reference model.

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The OSI networking reference model.
– The OSI reference model.
» Layer 1, the physical layer: standardizes the electrical signal
that networks use; also defines cable standards and how bits
are placed on the physical media.
• Network cables and hubs are part of Layer 1.
» Layer 2, the data link layer: responsible for identifying the
individual nodes (both sending and receiving); it also introduces
an error correction method known as frame check sequence
(FCS). It is composed of two sub-layers:
• The logical link control (LLC) layer is mainly responsible for
flow control and error correction.
• The media access control (MAC) layer is mainly responsible
for node addressing.
• Switches and bridges are Layer 2 devices.
» Layer 3, the network layer: responsible for routing functions
between networks. It identifies nodes and networks.
• Routers are Layer 3 devices.

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The OSI networking reference model.
– OSI reference model continued.
» Layer 4, the transport layer: responsible for breaking the data
into smaller pieces for the lower layers and for the actual data
transport protocols—TCP and UDP (Transmission Control
Protocol and User Datagram Protocol); the transport layer may
be required to confirm the actual delivery of the data stream
and error correction.
» Layer 5, the session layer: responsible for establishing the
initial parameters between two systems. Sets up and tears
down the communication channels.
» Layer 6, the presentation layer: responsible for taking data
and converting it from a machine dependent language to a
machine independent language. This is also the layer that
has the main responsibility for encryption between networks.
» Layer 7, the application layer: responsible for the protocols
that request services or functions from other systems. They
may not be the actual application; for instance, IE is an
application that uses HTTP (Hypertext Transfer Protocol) at
Layer 7 to request Web pages.

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The OSI networking reference model.
– TCP/IP reference model.
» Network interface layer (a.k.a. Link layer): handles electrical
signaling, flow control, error detection, and node addressing.
» Internet layer: handles routing functions and identifies network
systems and nodes.
» Transport layer: handles breaking the data into more
manageable chunks for lower layers; it is the layer responsible
for the delivery method, either reliable or unreliable, and error
correction for reliable delivery.
» Application layer: handles requests for services from
applications, translation to machine independent languages
and encryption. It also sets up and tears down sessions.

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The OSI networking reference model.

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While TCP/IP is the dominant
model, most technicians
communicate issues using the
OSI model because it is more
specific.
When problems occur—and they will—it is easier to
resolve them with a more highly defined set of
specifications (e.g., Layer 5 of the OSI model vs. the
Application layer of the TCP/IP model).
The OSI networking reference model.

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Both the OSI and TCP/IP
models are references only.
It is not mandatory that
they be followed.
Each developer and manufacturer determines its
own method of implementing the reference model.
While, in theory, there will never be a problem in
communication between devices and systems, it is
only a theory.
The OSI networking reference model.

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The OSI and TCP/IP networking models were created to allow disparate
systems and networks to communicate easily between each other.
Topic
A brief history.
Summary
The OSI reference model has seven layers: physical, data link, network,
transport, session, presentation, and application. The TCP/IP reference
model has four layers: Network interface, Internet, Transport, and
Application.
Networking reference models.
TCP/IP is the dominant model in use; however, the OSI model is more
commonly used when discussing problems. Both models are references
only; developers and manufacturers determine their own methods of
implementing network models.
OSI and TCP/IP comparison.
The OSI networking reference model.

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THANK YOU!

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