Download local area network

CHAPTER
ONE
Introducing Networks
1
1
Objectives
Identify and describe the functions of each of the
seven layers of the OSI reference model
Identify the reasons why the networking industry
uses a layered model
Define and explain the conversion steps of data
encapsulation
Define and describe the function of a MAC
address
Describe connection-oriented network service
and connectionless network service, and identify
the key differences between them
Introduction to Networking
Network

Term that describes the connection of two
or more computers by some type of
medium, including:
 Wire cable
 Fiber-optic cable
 Infrared
 Radio equipment
Origin of Networking
Difficult to place actual origin as many
devices have been networked
throughout history
Today, networks include a wide variety
of computers and peripheral
components
Systems that are part of a network do
not have to be identical
Why Do We Use Networks?
Convenience
People expect interoperability from
electronic devices
Computer networks allow for the
transfer of files, data, and even shared
applications without copying anything
to floppy disk
Connection Media
Media

Cable, glass, or telephone lines that host the
signal from one computer to another on the
network
Electromagnetic interference (EMI)

Electric noise that disrupts signals on cables
Wireless

Communications that are not conducted over
physical wires or cables
Client/Server Networks
Networks that have computers that are
servers and computers that act as
clients to those servers
You may see a variety of servers on a
network:
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Print server
File server
Database server
Remote access server (RAS)
Web server
Peer-to-Peer
When every computer on a network acts
as both a client and a server, the network
is a peer-to-peer network
In a peer-to-peer network, all computers
can share resources with other computers
Peer-to-peer networks are also known as
“workgroups”
LAN, WAN, MAN, SAN
A local area network (LAN) is a group of
computers and other devices typically connected
by a cable
A wide area network (WAN) is a network
that spans two or more geographically diverse
locations
A metropolitan area network (MAN) is an
intermediate specification that defines networks
confined to a fairly restricted geographic area
A storage area network (SAN) is a
subsystem of networked storage devices
physically separated from servers
Network Operating System
Network operating system (NOS)

Allows communication over a network
End system

The location and/or set of controls that the
user can manipulate to interact with a
computer or a network
NIC, Networking Hardware,
and Networking Software
Network interface card (NIC)

Hardware device that transmits and receives
electronic signals on a network
Networking hardware is a generic term that
describes all the physical components of a
network
Networking software is a generic term that
describes the software programs used to run
a network
Understanding the OSI Model
International Organization for
Standardization (ISO)

Multi-industry association that attempts to
standardize and define items that increase
communication and compatibility in many
different countries
Open Systems Interconnection (OSI)


Seven layer reference model created by the
ISO
Defines and separates networking hardware
and software into distinct layers and functions
Reasons for Layering
Simplifies the network model
Enables programmers to specialize in a
particular level or layer of the
networking model
Provides design modularity
Encourages interoperability
Allows for standardized interfaces to be
produced by networking vendors
Seven Layers of the OSI
Model
Physical layer
Data Link layer
Network layer
Transport layer
Sessions layer
Presentation layer
Application layer
Reasons for Layering
As a group,
these
layers form
the OSI
protocol
stack
Figure 1-1:
OSI Reference
Model
Peer OSI Communication
The seven
layers of the
OSI reference
model
communicate
with each other
via peer
communicat
ion
Figure 1-2:
Peer
communication
Layer Functions:
Physical (Layer 1)
Layer 1 in the OSI model
Has the following responsibilities:



Definition of the physical characteristics of
the network hardware
Representation of binary digits as voltages
(encoding)
Transmission of signals on the wire
Layer Functions:
Physical (Layer 1)
Figure 1-3:
568B twisted pair
wiring scheme
Layer Functions:
Physical (Layer 1)
Connectors, cables, and devices like
repeaters and hubs can be associated with
the physical layer
When choosing cable, consider the following:

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Expense
Physical location
Distance
Security requirements
Transmission speed required
Layer Functions:
Data Link (Layer 2)
Has several responsibilities:

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NIC software functions, including identification
of source and destination nodes via physical
addresses
Definition of how data is packaged for
transport as frames
Error detection
Flow control of information sent across the link
Layer Functions:
Data Link (Layer 2)
Data Link layer has two sublayers that
further articulate its function:


Logical Link Control (LLC) layer
Media Access Control (MAC) layer
The Institute of Electrical and Electronics
Engineers (IEEE) created these sublayers
to identify and isolate the separate
responsibilities required at this level of the
protocol stack
Layer Functions:
Data Link (Layer 2)
Figure 1-4:
Data Link layer
subdivision
Layer Functions:
Data Link (Layer 2)
MAC layer defines the media access
method and provides a unique identifier
for the network card
The unique identifier is a 48-bit address
represented as 12-digit hexadecimal
number given to each network card during
production
Every network interface card must have a
unique physical address (also called the
MAC address)
Layer Functions:
Data Link (Layer 2)
Figure 1-5:
MAC address
Layer Functions:
Data Link (Layer 2)
Ethernet

A standard networking architecture that
defines the physical layout, lengths, and types
of media that can be used
Carrier Sense Multiple Access with Collision
Detection (CSMA/CD)

Network access method used by Ethernet
networks
Layer Functions:
Network (Layer 3)
Has the following function:



Error handling
Software addressing for data packets
Best path selection
The Network layer contains the logical
address for the computer
Layer Functions:
Transport (Layer 4)
Provides point-to-point data
transportation
Responsibilities include:


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End-to-end error-free transmission and
delivery
Data segmentation into maximum
transmission unit (MTU) size
Messaging service for the Session layer
Layer Functions:
Transport (Layer 4)
Protocols that reside at the Transport
layer can be:


Connection-oriented
Connectionless
 A packet sent by a connectionless protocol is
also called a datagram
Layer Functions:
Session (Layer 5)
Enables two applications on the
network to have an ongoing
conversation or dialog
Examples of Session layer protocols
include:

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SQL
RPC
X-Windows
Layer Functions:
Session (Layer 5)
Provides the following services:

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
Control for data exchange
Data synchronization definition
Failure recovery
Communication setup and teardown
Layer Functions:
Presentation (Layer 6)
Prepares the data from Application layer
for transmission over the network
Components include extensions and
coding schemes such as:

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BMP
WAV
EBCDIC
ASCII
Layer Functions:
Presentation (Layer 6)
Has these responsibilities:
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Data
Data
Data
Data
Data
translation
formatting
syntax restructuring
encryption
compression
Layer Functions:
Application (Layer 7)
Has the following responsibilities:


Initiating the request for network service
Providing services to applications
Data Encapsulation
Data is sent from one computer to another
in a data packet
The packet contains data from the sending
application and additional information
added by the protocol stack
Prior to transmission across the network,
the data is organized into a data frame at
layer 2
Data Encapsulation
Protocol data unit (PDU)

Information added to a data packet by the
layers of the protocol stack
Encapsulation

Process that occurs during transmission
through the protocol stack in which data
from the higher layers is wrapped in a
protocol header and/or trailer
Data Encapsulation
Figure 1-6: Encapsulation
Data Encapsulation
Table 1-1:
Five steps of
data
encapsulation
Chapter Summary
Two or more computers connected by
media form a network
The ISO developed the OSI model in
the mid-1980s to standardize
networking models
Data transmission can be connectionoriented or connectionless
Chapter Summary
The OSI model has seven layers:
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Physical layer
Data Link layer
Network layer
Transport layer
Session layer
Presentation layer
Application layer
Chapter Summary
When the network user sends data to
the network, it goes through a five-step
data encapsulation process
This process takes place as the data
packet travels down the OSI stack