Download Book cover slide

Section 3.1
• Describe data packets
• Explain the role of network interface cards
• Compare analog and digital signals
Section 3.2
• Explain the OSI reference model
• Identify the layers of the OSI reference model
Section 3.3
• Explain the role of protocols
• Identify industry standard protocol stacks
• Describe how protocols work within a reference model
3.1
How Network Traffic Gets from
Here to There
pp.
70-76
Guide to Reading
Main Ideas
Key Terms
Two important
components needed to
transfer data are data
packets and network
interface cards. Data can
be transmitted using a
digital or analog signal.
data packet
cyclical redundancy check
(CRC)
bus
parallel transmission
serial transmission
analog
broadband transmission
digital
baseband transmission
multiplexing
3.1
How Network Traffic Gets from
Here to There
pp.
70-76
Data Packets
Networks are very fast,
but there is a limit to the
amount of traffic networks
can transport at one time.
The solution to this
problem is to break this
traffic into small pieces
known as data packets.
A data packet, also called
a packet, is a very small
part of the entire piece of
data that needs to be
sent.
data packet Data that
consist of three parts—a
header, the data itself, and a
trailer. (p. 70)
3.1
How Network Traffic Gets from
Here to There
pp.
70-76
Data Packets
A cyclical redundancy
check (CRC) is
performed at the sending
and receiving computers
to make sure the data
packet arrived with no
errors.
cyclical redundancy check
(CRC) Error checking used
in networks. A sending node
performs a mathematical
calculation on the packet and
the result is attached to the
packet’s trailer. The receiving
node performs the same
calculation on the packet it
received. If the calculations
differ, the CRC signals the
source computer to
retransmit the packet. (p. 71)
3.1
How Network Traffic Gets from
Here to There
pp.
70-76
Data Packets
The job to neatly chunk, address, and deliver the
information in a network is handled by the network
interface card (NIC) in each computer.
The NIC does the following:
• Provides the source, or hardware, address of the computer.
• Prepares the data from the computer for the network cable.
• Sends data to another computer.
• Controls the flow of data between the computer and the
cabling.
• Receives incoming data from another computer.
• Translates electrical impulses from the cable into binary code
that the computer understands.
3.1
How Network Traffic Gets from
Here to There
pp.
70-76
Data Packets
Within the computer itself,
information travels along
pathways known as
buses. A bus consists of
multiple “lanes” (wires) set
side by side.
bus A data pathway that
connects components in a
computer using parallel
cabling or wire. (p. 72)
3.1
How Network Traffic Gets from
Here to There
pp.
70-76
Data Packets
Data packets travel in
parallel transmission
within the computer, but in
serial transmission on a
cable.
Data on a network move
from the “multilane”
computer cable to a
“single-lane” network
cable.
parallel transmission The
orderly procession of
transmitted data in
computers in which groups of
bits are transferred
simultaneously side by side
over two or more wires.
(p. 72)
serial transmission The
procession of transmitted
data in which bits are sent
over network cables and
travel bit by bit one at a time.
(p. 73)
3.1
How Network Traffic Gets from
Here to There
pp.
70-76
Transmitting Data Packets
Baseband and broadband are two techniques used to
transmit data packets over cable.
Bandwidth is the maximum speed at which a particular
communications medium, such as cables, can transfer
information. Bandwidth measurement depends on the type
of signal (analog or digital) and the media used to carry
the information.
Type of Signal (analog or digital) + Type of Media =
Bandwidth
3.1
How Network Traffic Gets from
Here to There
pp.
70-76
Transmitting Data Packets
In an analog signal,
information travels as a
continuously changing
wave. This signal cycles
up and down in a
wavelike pattern.
analog A signal that travels
as a continuously variable
wavelike pattern. (p. 74)
3.1
How Network Traffic Gets from
Here to There
pp.
70-76
Transmitting Data Packets
Broadband transmissions
can be divided into multiple
channels separated by small
bands of unused frequencies
to avoid one channel
interfering with the signal
being transmitted on its
neighbors.
Broadband is
unidirectional—it moves in
one direction only. To send
and receive, the
communications bandwidth
is divided into two channels,
one for each direction.
broadband transmission
Transmissions that rely on an
analog signal, a range of
frequencies, and a
communications medium.
Broadband signals can be
divided into multiple
channels separated by small
bands of unused frequencies
to avoid interference. (p. 74)
3.1
How Network Traffic Gets from
Here to There
pp.
70-76
Transmitting Data Packets
An example of broadband transmissions are digital
signals. Digital signals encode information numerically,
using 0s and 1s. These simple signals convey information
in separate on/off pulses over the communications
medium, such as cables.
3.1
How Network Traffic Gets from
Here to There
pp.
70-76
Transmitting Data Packets
Baseband
transmissions send
digital signals over a
single channel. Multiple
transmissions can be sent
through the channel
simultaneously through a
technique known as
multiplexing.
baseband transmission
Transmissions of digital
signals over a single
channel, typical of most
current LANs. One signal at
a time travels over the
network cable. (p. 75)
multiplexing Multiple
transmissions sent through a
channel simultaneously and
are interwoven into a single
signal. (p. 75)
3.1
How Network Traffic Gets from
Here to There
pp.
70-76
Transmitting Data Packets
This is an example of multiplexing, in which several
signals from different sources can be fed into one cable for
transmission.
pp.
3.2
78-85
Network Models
Guide to Reading
Main Ideas
Key Terms
Network models describe
how different network
devices communicate with
each other. The OSI model
consists of seven layers that
describe the tasks a network
component must handle.
protocol
Open Systems
Interconnection (OSI)
reference model
interface
session
data frame
Transmission Control
Protocol/Internet Protocol
(TCP/IP) reference model
Advanced Program to
Program Communications
(APPC)
Internetworking
pp.
3.2
78-85
Network Models
Models Versus Protocols
To ensure that products
from various
manufacturers can
communicate with each
other, network models
have been created.
A protocol, which is part
of software, is what
makes a network work.
The model describes what
needs to be done, and the
protocol performs the
work.
protocol Rules that define
how network devices
communicate with each other
and perform specific tasks.
(p. 78)
pp.
3.2
78-85
Network Models
The OSI Reference Model
The Open Systems
Interconnection (OSI)
reference model
consists of seven layers
that define how data are
sent from a computer,
through the network, and
into a receiving computer.
Understanding each layer
and how each one
interacts with other layers
helps you understand how
networks operate.
Open Systems
Interconnection (OSI)
reference model An
international standard that is
a guide for networking.
Defines how data are sent
from a computer, through the
network, and into a receiving
computer. Also called the
OSI model. (p. 79)
pp.
3.2
78-85
Network Models
The OSI Reference Model
The OSI model provides a description of how network
hardware and software work together in a layered fashion
to make communications between computers possible.
Each layer includes different network activities, equipment,
or protocols.
pp.
3.2
78-85
Network Models
The OSI Reference Model
Layers are separated from
each other by boundaries
called interfaces.
interface The connection
that provides communication
between layers. It also
shields neighboring layers
from the details of how
services are implemented.
(p. 80)
pp.
3.2
78-85
Network Models
OSI Layers
Beginning at the top of the OSI model (Layer 7), we work
down to the bottom (Layer 1). The lower layers in the OSI
model support the tasks that are performed at the upper
layers.
pp.
78-85
Network Models
3.2
OSI Layers
Layer
Number
Layer Name
Description
7
Application
Relates to services that directly support user applications
6
Presentation
Defines the format used to exchange data among networked
computers
5
Session
Allows two applications on different computers to open, use,
and close a connection between computers
4
Transport
Ensures that data packets are delivered error-free, in
sequence, and without data losses or duplications
3
Network
Responsible for addressing messages and finding the best
path to move data across the network
2
Data Link
Sends data frames from the Network Layer to the Physical
Layer
1
Physical
Carries the signals to transmit the data over the cable to the
network
pp.
3.2
78-85
Network Models
OSI Layers
Layer 5, the Session
Layer, allows two
applications on different
computers to open, use,
and close a connection
called a session.
The Session Layer is
responsible for managing
this dialogue.
session A highly structured
dialog between two
workstations. (p. 81)
pp.
3.2
78-85
Network Models
OSI Layers
Layer 2, the Data Link
Layer, sends data frames
from the Network Layer to
the Physical Layer. A data
frame is like a vehicle, in
which the data are the
people, or cargo, who ride
inside the vehicle across
the network.
data frame An organized,
logical structure in which
data can be placed. (p. 82)
pp.
3.2
78-85
Network Models
OSI Layers
A data frame is used to transport data across the network.
pp.
3.2
78-85
Network Models
Other Networking Models
Two other models, also
layered, tend to pop up in
descriptions of network
architectures.
• Systems Network
Architecture (SNA)
• Transmission Control
Protocol/Internet Protocol
(TCP/IP) reference model
Transmission Control
Protocol/Internet Protocol
(TCP/IP) reference model
An Internet-related network
architectural model. (p. 84)
pp.
3.2
78-85
Network Models
Other Networking Models
SNA was originally
designed around the
mainframe/terminal
relationship, but was later
modified, in a specification
known as Advanced
Program to Program
Communications
(APPC), to include
minicomputers and
personal computers.
Advanced Program to
Program Communications
(APPC) The SNA mainframe
communication model was
modified in a specification
known as APPC to include
minicomputers and personal
computers. (p. 84)
pp.
3.2
78-85
Network Models
Other Networking Models
The birth and evolution of
the Internet gave rise to
yet another model. This is
the TCP/IP reference
model, also referred to as
the Internet reference
model.
The TCP/IP reference
model reflects the world of
internetworking.
internetworking The
transfer and routing of
information between and
among varied workstations
and networks. (p. 84)
pp.
3.2
78-85
Network Models
Other Networking Models
This image below shows the difference between the TCP/IP and
OSI models, as well as rough—though not exact—equivalents
between the layers in the two models.
pp.
3.2
Network Models
You Try It
• Activity 3A – Learning the OSI Reference Model (p. 83)
78-85
pp.
3.3
Protocols
Guide to Reading
Main Ideas
Key Terms
Protocols are rules and
procedures used to make
network communications
possible. Multiple
protocols can be used by
a NIC. Many protocols
that operate in conjunction
perform the various tasks
needed to send and
receive data.
protocol stack
binding process
binding order
Media Access Control
(MAC)
87-92
pp.
3.3
87-92
Protocols
The Function of Protocols
When data are transmitted over a network, they are sent in
steps. A single step includes certain actions that cannot
take place at any other step. Each step has its own rules
and procedures, or protocols.
There are four points to keep in mind about protocols:
• There are many protocols.
• Some protocols work only at particular OSI layers.
• Some protocols work at multiple layers.
• Protocols are consistent.
pp.
3.3
87-92
Protocols
Protocols in a Layered Architecture
A protocol stack is a
combination of protocols.
Layers within the stack,
which generally
correspond to the OSI
model, specify various
protocols for handling a
function or subsystem of
the communication
process. Each layer in the
stack has its own set of
rules.
protocol stack Multiple
layers of protocols that work
together. (p. 88)
pp.
3.3
87-92
Protocols
Protocols in a Layered Architecture
The binding process is
used to connect protocols,
or protocol stacks, to the
NIC. Protocols and NICs
can be mixed and
matched on an as-needed
basis.
The binding order
determines the sequence
in which the operating
system runs the protocol.
binding process The
process of tying the protocols
together to provide data with
a route from the application
level to the NIC. (p. 88)
binding order The
sequence in which the
operating system runs the
protocol. (p. 88)
pp.
3.3
87-92
Protocols
Protocols in a Layered Architecture
The computer industry has designated several kinds of
protocol stacks as standard models. Hardware and
software manufacturers can develop their products to
meet any one or a combination of these protocol stacks.
The most important protocol stacks include:
• OSI protocol suite
• Digital DECnet
• Novell NetWare
• AppleTalk
• TCP/IP
• IBM SNA
pp.
3.3
87-92
Protocols
Protocols in a Layered Architecture
Protocols exist at each layer of these stacks, performing
the tasks specified by that layer. However, the
communication tasks that networks need to perform are
grouped into one of the three following types:
• application protocols
• transport protocols
• network protocols
pp.
3.3
87-92
Protocols
Protocols in a Layered Architecture
The Data Link Layer is
divided into two sublayers:
• Logical Link Control (LLC)
• Media Access Control
(MAC)
Media Access Control
(MAC) The lower of two
sublayers that make up the
Data Link Layer. The MAC
manages access to the
physical network, delimits
frames, and handles error
control. (p. 92)
pp.
3.3
Protocols
You Try It
• Activity 3B – Discovering What Protocols You Use (p. 89)
87-92
Chapter 3
Resources
For more resources on this chapter, go to the Introduction
to Networks and Networking Web site at
http://networking.glencoe.com.