Introduction to Data

inexpensivedetailedNetworking and Communications

Oct 23, 2013 (4 years and 21 days ago)

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© 2001 by Prentice Hall

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Local Area Networks
,
3rd Edition

David A. Stamper

Part 1:
Introduction to Data
Communications and Local Area
Networks

Chapter 1

Introduction to Data
communications

© 2001 by Prentice Hall

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Chapter Preview

In this chapter you will study:


The requirements for communication


What constitutes a network


The various types of networks in
common use today


The OSI Reference Model


Some of the basic terminology of
data communications and networks

© 2001 by Prentice Hall

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Essential Elements of
Communication


A message


A sender


A receiver


A medium

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Understanding the Message


In computer systems, data can be
represented by any of several
different codes, the two most
common being:


the American Standard Code for Information
Interchange (ASCII)


the Extended Binary Coded Decimal Interchange
Code (EBCDIC)

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Security


Sensitive data like your credit card
number or other secret data should be
safeguarded during transmission. The
most common mechanism for protecting
data during transmission is encryption.


Encryption transforms plain text into an (presumably)
undecipherable form called
cipher
-
text
.

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Two Types of Networks


Terminal Network


consists of a single host computer with attached
terminals


the host computer does all or most of the processing,
and the terminals imply act as input/output (I/O) devices
through which a person gains access to the host’s
applications.


Network of Computers


two or more nodes connected by a data communications
medium.


individual nodes may have terminals attached to them


a single node on this network can look just like the
terminal network

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Three Network Subtypes


Local Area Network (LAN)


Metropolitan Area Network (MAN)


Wide Area Network (WAN)

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LAN
/
MAN
/
WAN Comparison

Limited

typically up
to 2,500 meters or 2
miles

High

typically in
excess of 10 Mbps

10,100 and 1,000 are
standard

Locally owned


twisted
-
pair wires, fiber
optic cable, wireless
(not satellite)





Can be any, but most
are desktop computers

Limited

typically up
to 200 kilometers or
100 miles

High

typically

100 Mbps






Locally owned and
common carrier


twisted
-
pair wires, fiber
optic cable





Can be any, but most
are desktop computers
and minicomputers

Unlimited






Slower

usually 1.5
Mbps






Locally owned and
common carrier


twisted
-
pair wires,
coaxial cable, fiber
optic cable, wireless to
include satellite

Can be any, but most
are desktop computers

Distance



Speed


Media


Nodes


LAN


MAN


WAN


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The OSI Reference Model


The problem of network interconnection is
so important that the ISO created the OSI
Reference Model that describes the
functions a generic network needs to
provide.


The OSI Reference Model has become the
basis for many data communications
standards.


Because these standards are placed in the public domain, they are
called
open standards

and lead to open systems.

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OSI Peer Layer Communication

Application

Presentation

Session

Transport

Network

Data Link

Physical

Application

Presentation

Session

Transport

Network

Data Link

Physical

Processor 1

Processor 2

Logical Path

Physical Path

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OSI Reference Model Formatting

Trans
-
Id Data Date=dd/mm/yy

Trans
-
Id Data Date=mm
-
dd
-
yyyy

ID Length


Trans
-
Id Data Date=mm
-
dd
-
yyyy

TSAP ChkSum ID Length Trans
-
Id Data Date=mm
-
dd
-
yyyy

Address Seq Nbr TSAP ChkSum ID Length Trans
-
Id Data Date=mm
-
dd
-
yyyy

Header Address Seq Nbr TSAP ChkSum ID Length Trans
-
Id Data Date=mm
-
dd
-
yyyy Chksum

(a) Application Layer

(b) Presentation Layer

(c) Session Layer

(d) Transport Layer

(e) Network Layer

(f) Data Link Layer

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The OSI Model at Work


Application Layer


The application on Node A builds a record with a transaction
identifier, the number of the account to be updated, the date and
time of the transaction, and the amount to be deducted.


Presentation Layer


The presentation layer is responsible for translating from one format
to another.


Session Layer


The session layer’s major functions are to set up and perhaps
monitor a set of dialogue rules by which the two applications can
communicate and to bring a session to an orderly conclusion.


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The OSI Model at Work (cont.)


Transport Layer


The transport layer is the first of the OSI layers responsible for
actually transmitting the data.


Network Layer


The network layer provides accounting and routing functions.


Data Link Layer


The data link layer is responsible for data delineation, error
detection,and logical control of the link.


Physical Layer


The physical layer does not append anything to the message. It
simply accepts the message from the data link layer and translates
the bits into signals on the medium.

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Receiving the Message

1. The message is passed over the link connecting Nodes A
and X.

2. The message is passed to the data link layer in Node X. The
message is checked for transmission errors, the PDU
information applied by A’s data link layer is removed, and
the message is sent to X’s network layer.

3. X’s network layer records the accounting information for
the message and then strips off the network layer protocol
data and examines the destination address. The destination
is not Node X in this case, so the network layer consults its
network routing table and determines the next link on the
path to Node M. X’s network layer affixes the proper
network layer protocol data and sends the message to
Node X’s data link layer.


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Receiving the Message (cont.)

4. Node X’s data link layer creates its PDU and sends the
message to Node M.

5. Node M’s data link layer receives the message, strips off
Node X’s data link layer protocol data, checks for
transmission errors, and passes the data up to Node M’s
network layer.

6. Node M’s network layer gathers accounting data, strips off
the network layer protocol data, and fins that the message
is destined for an application in this node.

7. The message is passed up to M’s transport layer, where the
sequence number is checked to ensure that no messages
have been lost. The transport layer protocol data is
removed.

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Receiving the Message (cont.)

8. The message arrives at the session layer, where
relevant protocol data is examined and remove.

9. The message arrives at Node M’s presentation
layer, where appropriate action is taken.

10.The message arrives at the application, where


it is acted on.

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General Network Implementations:
LANs


A LAN services a limited geographic area at high speeds

usually 10 million bits per second or higher. All
components of the LAN are commonly owned by the
organization that uses it.


The nodes in many of today’s LANs are desktop systems
like personal computers. Henceforth, we will also use the
terms
workstations
,
clients
, and
servers

in referring to LAN
nodes.


A
workstation

is used here to represent a LAN user’s
computer; other terms used in referring to a workstation are
client

and
node
.


A
server

is a network node that is dedicated to providing
services to client nodes.

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General Network Implementations:
MANs


A MAN (metropolitan area network) is a high
-
speed network covering wider distances than
LAN.


A MAN spans distances of approximately 100
miles; therefore, it is suitable for connecting
devices and LANs in a metropolitan area.


MAN speeds are typically 100 Mbps or higher.


The most commonly implemented MAN is the
fiber distributed data interface (FDDI). It operates
at 100 Mbps over fiber optic cable for distances
up to 200 kilometers.

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General Network Implementations:
WANs


A WAN is the oldest type of network.


WANs generally span a wide geographic area like
a state, province, country, or multiple countries.
However, some WANs are confined to a limited
geographic area, like a LAN.


A WAN in a limited geographic area could be
easily extended over a wide area using the same
technologies. The same is not true of a LAN.


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General Network Implementations:
VANs


A VAN is a network owned by a communications
utility that sells the services of the network to
other companies.


A communications utility that owns a VAN
provides connectivity to multiple locations.


The value added by the communications utility is
the maintenance and management of the
communications circuits.

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General Network Implementations:
Enterprise Networks


An enterprise network is an organization’s
complete network.


With the advent of LANs, many companies
installed departmental LANs to improve the
productivity of work groups.


Soon, these companies realized that there was a
benefit to having users on one LAN communicate
with users or applications on other LANs or on
the WAN, and the various networks were
connected together to form one corporate
-
wide
network, the enterprise network.

© 2001 by Prentice Hall

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General Network Implementations:
The Internet


An internet (with a lowercase ‘i’) is the
interconnection of two or more networks. An
enterprise networks just described is an example
of an internet.


The Internet (with an uppercase ‘I’) is a specific
instance of an internet.


The Internet is a global network of networks. The
Internet is made up of hundreds of networks,
thousands of nodes, and millions of users
throughout most countries of the world.

© 2001 by Prentice Hall

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General Network Implementations:
Intranets


An intranet is an organization’s private Web.


Companies have found that WWW capabilities
can improve the information flow and availability
in a company.


Companies may use an intranet rather than
publishing on the Internet because the
information being provided is intended for
corporate use only and not for the public at large.