Data Communication Introduction

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26 Οκτ 2013 (πριν από 3 χρόνια και 11 μήνες)

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Data Communication

Introduction

Behrouz

A.
Forouzan

1

Data Communication
-

Introduction

DATA
COMMUNICATIONS

Definition


Data
communications:


exchange
of data between two devices via
transmission
medium
(wired or wireless)


data communications Effectiveness:


Delivery.


Data
must
be received
by the intended device or user and only by that
device or user.


Accuracy
.


The
system must deliver the data
accurately (not altered)


Timeliness.


system
must deliver data in a timely
manner (
real
-
time transmission
like Audio or Video)


Jitter
.


variation
in the packet arrival
time (uneven
quality in
Video or Voice)



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Data Communication
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Introduction

DATA COMMUNICATIONS

Components


Message


Sender


Receiver


Transmition

Medium


Wired


twisted pair, coaxial , fiber optic


Wireless


Protocol


Without a protocol,
two devices
may be connected but not
communicating,


just
as a person speaking
French cannot
be understood by a
person who speaks only Japanese


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Data Communication
-

Introduction

DATA COMMUNICATIONS

Data Representation


Text


Unicode
: prevalent
coding
system, uses
32 bits to represent a
character in
any
language in the world.


ASCII
,
developed some decades
ago, constitutes
the first 127 characters in
Unicode


Numbers


Decimal, Binary, …


Images


JPEG, BPM, ..


Audio


It differs from others since it is analog


G.711, G.729, …


Video


Analog (TV) or Digital (combination of Images)


MPEG4 , …





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Data Communication
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Introduction

DATA COMMUNICATIONS

Data Flow


Simplex


Only
one of two
devices
can transmit. other
can
only
receive (Monitor, Keyboard)


Half
-
Duplex


each station can both transmit and receive, but
not at the same time


Full
-
Duplex


both stations
transmit
and receive
simultaneously


Example: telephone network





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Data Communication
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Introduction

NETWORKS


A network is a set of devices
(
nodes
) connected by
communication
links



Network Criteria:


Performance


throughput and
delay


Reliability


accuracy
of
delivery, frequency of failure
,
network's
robustness
in
a
catastrophe


Security


protecting data from unauthorized
access, from damage,


implementing policies and procedures
for recovery
from breaches
and data losses

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Data Communication
-

Introduction

NETWORKS Physical Structures

(
Type of Connection
)


Point
-
to
-
Point


provides
a dedicated link
(physically or logically)
between two devices
.


The
entire capacity of the link is reserved for transmission
between those
two devices


wire
or
wireless (microwave or satellite links)


Multipoint


More than
two specific devices share a single
link


capacity
of the channel is
shared


spatially shared
:
If
several devices
can use
the link
simultaneously


timeshared

:

If users must take
turns
.




7

Data Communication
-

Introduction

NETWORKS Physical Structures

(
Type of Connection
)

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Data Communication
-

Introduction

NETWORKS

Physical Topologies


geometric representation of the relationship
of all the links
and linking devices







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Data Communication
-

Introduction

NETWORKS

Physical Topologies


Mesh (like telephone regional offices)


every device has a dedicated point
-
to
-
point link to
every other device


number
of physical links in a fully connected
mesh
network
with
n
nodes


n* (n
-
1) / 2 full
-
duplex links


Advantages:


Reliable, Secure


Disadvantages:


the
number of
cabling and
the


number
of I/O ports




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Data Communication
-

Introduction

NETWORKS

Physical Topologies


Star (Ethernet)


each device has a dedicated point
-
to
-
point
link
only
to a central controller,
called
hub


Data are relayed through HUB between devices


Advantages:


Less cable and i/o ports (cheap)


If a link fails only a single device is disconnected


Disadvantages:


Single point of failure


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Data Communication
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Introduction

NETWORKS

Physical Topologies


BUS


Advantages:


ease of
installation


less cabling than mesh or star topologies


Disadvantages:


difficult reconnection and fault
isolation


a fault or break in the bus cable stops all transmission


Example: early
ethernets







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Data Communication
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Introduction

NETWORKS

Physical Topologies


Ring Topology (IBM LAN called Token Ring)


each device has a dedicated point
-
to
-
point
connection
with
only the two
devices


unidirectional
traffic can be a disadvantage.
a
break
in
the
ring

can disable the entire network. This
weakness
can be
solved by using a
dual


Advantages:


fault isolation is simplified


Disadvantages:


maximum ring length and number of
devices are
constraint




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Data Communication
-

Introduction

NETWORKS

Physical Topologies

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Data Communication
-

Introduction

NETWORKS

Physical Topologies


Hybrid
Topology


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Data Communication
-

Introduction

NETWORKS

Network Categories


Local Area
Network

(LAN)


Wide Area
Network (WAN)


Metropolitan Area
Networks (MAN)






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Data Communication
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Introduction

NETWORKS

Network Categories: LAN


Ethernet, Token Ring, FDDI


privately
owned and links the devices in a
single office
, building, or
campus


Today
speeds are normally 100 or 1000
Mbps



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Data Communication
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Introduction

NETWORKS

Network Categories: WAN


Like SONET, ATM,
FrameRelay


provides
long
-
distance transmission
over
large
geographic areas that may comprise a country,
a
continent, or
even the whole world.

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Data Communication
-

Introduction

NETWORKS

Network Categories: WAN

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Data Communication
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Introduction

NETWORKS

Network Categories: MAN


Like
high
-
speed DSL
line


network
with a size between a LAN and
a
WAN (
the area inside a town or a city
)







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Data Communication
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Introduction

NETWORKS

Internetwork

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Data Communication
-

Introduction

THE INTERNET


a collaboration of more than hundreds of
thousands of interconnected
networks


came into being in
1969





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Data Communication
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Introduction

THE INTERNET

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Data Communication
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Introduction

PROTOCOLS AND STANDARDS


Protocol
: set
of rules that govern
data
communications in any aspect


Mail communication: pop3,
smtp
,
imap


Web communication: http, https


File transfer: ftp,
tftp


Includes
syntax
,
semantics
, and
timing




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Data Communication
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Introduction

PROTOCOLS AND STANDARDS


Syntax
.


format
of the
data


first
8 bits of data to be the address of the sender, the
second 8 bits to be the
address of
the receiver, and
the rest of the stream to be the message itself


Semantics


meaning of each section of
bits


Timing


when data should be
sent and


how
fast they can be
sent (sender and receiver speed
match otherwise receiver congestion)




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Data Communication
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Introduction

PROTOCOLS AND STANDARDS


Standards
: guidelines
to manufacturers,
vendors, government agencies, and other
service providers to
ensure the
kind of
interconnectivity necessary in today's
marketplace and in
international
communications


Include:
de facto
(
meaning
"by
fact" or "by
convention") and
de jure
(meaning "by law" or
"by regulation")

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Data Communication
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Introduction

PROTOCOLS AND STANDARDS


Standards organizations:


International Organization for Standardization
(ISO
)


International Telecommunication Union
-
Telecommunication
Standards Sector
(ITU
-
T
)


American National Standards Institute (ANSI
)


Institute of Electrical and Electronics Engineers
(IEEE
)


Electronic Industries Association (EIA)

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Data Communication
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Introduction