Overview: General Introduction Overview: General Introduction

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

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Overview:GeneralIntroduction
Overview:

General

Introduction

ComputationandCommunication
Computation

and

Communication
•Inter-networked Computers
•Communication Protocols
•OSI Model
•Protocol introduction:
•IP
•TCP and UDP
•FTP and HTTP
1
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t
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Abacus
Adding
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Computer
Mainframe
Timeline
Adding
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Citi
C
ommun
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ti
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ConversationTelephoneNetwork
Timeline
MailData Transfer
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t
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ommun
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ca
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Timeline
Mainframe
PC
s
N
e
t
wor
k
Resource Sharing (equipment, programs, data)

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Parallelism (distribution of tasks)

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ers
How do the
computers inter-
communicate?
Data exchange (main factor)

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Inter-personal communication (e-mail, messaging, etc.)

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Computer communications
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Network

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networks

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applications
when exchanging messages
Some incompatible with others
Communication Protocols
PROTOCOL
(agreement about the format and meaning of the messages exchanged)
Communication is performed
:
in diverse forms, and

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In order to reduce the complexity, a layered structure was proposed

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offers a set of services to the layer above, and
uses those services
p
rovided b
y
the la
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er underneath
pyy
Who does the standardisation?
•Legal Standards
ITUIilTliiUiflh

ITU
,
I
nternat
i
ona
l

T
e
l
ecommun
i
cat
i
ons
U
n
i
on
f
ormer
l
y t
h
e
(CCITT)
ISOInternationalStandardsOrganisation

ISO
,
International

Standards

Organisation
•FCC, Federal Communications Commission
LdllETSICEPTCCIR

L
oa
d
s more as we
ll
.
ETSI
,
CEPT
,
CCIR
...
•Informal Standards
•IEEE, LAN's WAN's
•ATM Forum, X Consortium
•Zerox, IBM, Digital, Telecom Eireann, BT, AT&T
Closed & Open Systems
•The original implementations were not based on any globally
acceptedstandardsandthemanufacturersproducedtheir
accepted

standards

and

the

manufacturers

produced

their

own standards.

Suchsystemsareknownas

ClosedSystems

sinceonly
Such

systems

are

known

as

Closed

Systems

since

only

computers from the same manufacturer can exchange
information.
•To overcome this a wide range of network and protocol
standards was produced where equipment complying to a
particularstandardcanbeusedinterchangeablyThisisan
particular

standard

can

be

used

interchangeably
.
This

is

an

Open System Interconnection Environment (OSIE).
What is the OSI Model?
•The International Standardisation Organisation (ISO)
describedalayeredmodelfornetworkprotocolarchitectures
described

a

layered

model

for

network

protocol

architectures

called the Reference Model for Open Systems
Interconnection (OSI model).
•It is notan implementation standard, but partitions the
communication functions into la
y
ers so the
y
can be
yy
individually standardised.

InternationalStandardsOrganizationhasproposedthe
International

Standards

Organization

has

proposed

the

Open Systems Interconnection (OSI) Reference Model
OSIMdl
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OSI

M
o
d
e
l
-
P
r
i
nc
i
p
l
e
Computer A
Computer B
AP
AP
Network
SessionLayer
Presentation Layer
Application Layer
SessionLayer
Presentation Layer
Application Layer
Network Layer
Transport Layer
Session

Layer
Network Layer
Transport Layer
Session

Layer
Physical Layer
Link Laye
r
Physical Layer
Link Laye
r
Subnet
Network
OSIMdl
Dtil
OSI

M
o
d
e
l
-
D
e
t
a
il
s
Physical Layer
–concerned with the
transmissionofdatabitsbetweentwo
transmission

of

data

bits

between

two

directly inter-connected devices

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Transport Layer
–provides end-to-end
sender-destination communication,
includin
g
correct
p
acketization
Presentation Layer –concerned with syntax
and coding when exchanging data
gp
Session Layer –supports sessions and
synchronization during data exchange
Application Layer
–provides access to
extensive network-related services (file
transfer
,
messa
g
e exchan
g
e
,
etc.
)
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D
a
t
a
E
xc
h
ange
Computer A
Computer B
AliiL
AP
AP
Data
Session Layer
Presentation Layer
A
pp
li
cat
i
on
L
aye
r
Session La
y
e
r
Presentation Layer
Application Laye
r
Data
AH
Data
AH
PH
Data
AH
PH
SH
Network Layer
Transport Layer
LikLe
Network Layer
Transport Layer
LikL
y
Data
AH
PH
SH
Data
AH
PH
SH
TH
TH
NH
Physical Layer
Li
n
k

L
ay
er
Physical Layer
Li
n
k

L
aye
r
Data
AH
PH
SH
Bits
TH
NH
DH
DT
Network
OSI Terminology
•Service Access Point (SAP) is the point between the layer
andthenexthigherlayer
and

the

next

higher

layer
•Service Data Unit (SDU) is the block of data coming down
fromthenexthigherlayer
from

the

next

higher

layer
•Protocol Control Information (PCI) is the header that is
added on to the SDU to make the relevant data block at this
layer
•Protocol Data Unit (PDU) is the block of data that is given to
the next layer underneath the current laye
r
OSI Terminology
La
y
er N+1
N+1
PDU
y
N
SDU
N
PCI
N+1
-
PDU
N -SAP
Layer N
N
-
SDU
N -PDU
N
-
PCI
Network Layer
IP

Internet Protocol
Provides support for computer communications in a world of heterogeneous networks
A
Computer A
Computer B
NetworkB
Router

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Sender & destination addresses

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Best effort delivery, so can have:

duplication

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IP header format

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data corruption
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IP routing

delay

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TCP and UDP
Transport Layer
Supports reliable data exchange
TCP (Transmission Control Protocol)
UDP (User Data Protocol)
Supports connectionless data exchange
Connection-based protocol
Exchange of TCP packets
Connectionless protocol
Exchange of UDP datagrams
Ensures delivery
correct
Ensures encapsulated data
delivery
no loss
in-order
Less complex, faster than TCP
Non-reliable
Other issues:
Data
TCP header
Other issues:
Data
UDP header

TCP header format
Connection management

UDP header format
Support for real-time
liti
Congestion control
app
li
ca
ti
ons
Optional: Compare TCP and UDP in details
FTP and HTTP
Application Layer
FTP (File Transfer Protocol)
HTTP (HyperText Transfer Protocol)
Supports remote file transfers
Supports web pages transfer and display
Relies on services offered by TCP
Provides a set of primitives that
lltltidtf
Built on top of TCP
Based on client (browser)
ttt
a
ll
ow remo
t
e se
l
ec
ti
on an
d

t
rans
f
er
of files
reques
t
s sen
t

t
o servers
Each request is followed by the
requestedpageand/orstatuscode
requested

page

and/or

status

code
The browser interprets the
document and dis
p
la
y
s its
py
content, waiting for further
interaction with the user
OSIdTCP/IPMdlCitiPtl
OSI
an
d

TCP/IP

M
o
d
e
l
s vs.
C
ommun
i
ca
ti
on
P
ro
t
oco
l
s
Major Protocols
OSI ModelTCP/IP Model
AP
APAPAP
AP
ApplicationLayer
HTTP
TFTP
FTP
i
Application Layer
Application

Layer
Transport Layer
TCP
UDP
Session Layer
Presentat
i
on La
y
er
Transport Layer
Internet Layer
Network Layer
Network Layer
Link Layer
Physical Layer
IP
Physical Layer
Optional: Why TCP/IP Model was more successful?
Summary
Summary
Need for inter-computer communication

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OSI Model: application, session, presentation, transport,
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networ
k
,
d
ata
li
n
k
an
d
p
h
ys
i
ca
l

l
ayers

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IP, TCP, UDP, FTP, HTTP