Transcript KVIV course, part 2

Telecommunications
Concepts
Chapter 1.1
Evolution of
Telecommunications
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09-07-K.Steenhaut & J.Tiberghien - VUB
Contents
• The 19th century telecommunications
– Telegraph - Telephone
– Digital vs. analog communications
• The voice networks & the data networks
• The electronics revolution (1960-1980)
–
–
–
–
–
Digital sound
Mainframe computers with remote access
The first unification : ISDN
Local area networks
Wide area and local area networks integration
• The Internet
– The research project
– The universal computer communications medium
– The successful unification ?
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09-07-K.Steenhaut & J.Tiberghien - VUB
Contents
• The 19th century telecommunications
– Telegraph - Telephone
– Digital vs. analog communications
• The voice networks & the data networks
• The electronics revolution (1960-1980)
–
–
–
–
–
Digital sound
Mainframe computers with remote access
The first unification : ISDN
Local area networks
Wide area and local area networks integration
• The Internet
– The research project
– The universal computer communications medium
– The successful unification ?
3
09-07-K.Steenhaut & J.Tiberghien - VUB
The Chappe Telegraph
(Claude Chappe, 1763-1805)
92 out of
256 (= 4*8*8) positions
represented characters.
Integrity of message could
be restored at each relay
station
In 1844,
534 relays linked Paris
with 29 cities, covering in
total 5000 Km.
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The Morse Telegraph
Samuel Morse, 1791-1872
First electrical
telegraph
demonstrated
in 1837
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The Morse Telegraph
Signal strength can be restored by means of
electromechanical relays connecting separate
telegraphic circuits.
On land lines, unlimited distances can be covered,
without increasing significantly the error rate.
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The Telephone
Graham Bell, 1876.
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Analog vs. Digital Transmission
6:12
Analog
• Almost infinite number of
states
• External perturbations can
not be distinguished from
original signal (superposed
noise)
• Information degrades along
the lines
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Digital
• Finite, small, number of
states
• Most external perturbations
can be distinguished from
original signal
• Information can be restored
in relays
09-07-K.Steenhaut & J.Tiberghien - VUB
Digital Techniques
How are numbers represented in electronic devices ?
• Binary numbers (base 2) are used.
• A binary digit (bit) can be represented by a switch:
– Value 0 : switch open
– Value 1 : switch closed
• A number with n bits can take 2 n different values
– 2 bits :
4 combinations
00 01 10 11
– 3 bits :
8 combinations
000 001 010 011 100 101 110 111
– 8 bits (= 1 byte)
256 combinations
– 16 bits:
65 536 combinations
– 24 bits:
16 777 216 combinations
– 32 bits:
4 294 967 296 combinations
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09-07-K.Steenhaut & J.Tiberghien - VUB
Contents
• The 19th century telecommunications
– Telegraph - Telephone
– Digital vs. analog communications
• The voice networks & the data networks
• The electronics revolution (1960-1980)
–
–
–
–
–
Digital sound
Mainframe computers with remote access
The first unification : ISDN
Local area networks
Wide area and local area networks integration
• The Internet
– The research project
– The universal computer communications medium
– The successful unification ?
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The Telephone
Full mesh network
Links = n*(n-1)/2
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The Telephone
With central switchboard
Links = n
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Automatic Exchange
(1900)
Conversation with switch
operator replaced by
signaling protocol
- Voice
: analog
- Signaling : digital
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The Telephone Network
SW
SW
Trunk
lines
SW
SW
SW
SW
PABX
PABX
SW
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Telex Networks
(1930-1990)
Morse code
replaced by
Baudot or
ASCII code
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Alphabetical Codes
Morse
Baudot
ASCII
A
a
B
C
D
E
3
9
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Extended ASCII Character Set (8 bit)
032
17
048
0
064
@
080
P
096
`
112
p
128
Ç
144
É
160
á
033
!
049
1
065
A
081
Q
097
a
113
q
129
ü
145
æ
161
í
034
“
050
2
066
B
082
R
098
b
114
r
130
é
146
Æ 162
ó
035
#
051
3
067
C
083
S
099
c
115
s
131
â
147
ô
163
ú
036
$
052
4
068
D
084
T
100
d
116
t
132
ä
148
ö
164
ñ
037
% 053
5
069
E
085
U
101
e
117
u
133
à
149
ò
165
Ñ
038
&
054
6
070
F
086
V
102
f
118
v
134
å
150
û
166
ª
038
‘
055
7
071
G
087
W 103
g
119
w
135
ç
151
ù
167
º
040
(
056
8
072
H
088
X
104
h
120
x
136
ê
152
ÿ
168
¿
041
)
057
9
073
I
089
Y
105
i
121
y
137
ë
153
Ö
169
_
042
*
058
:
074
J
090
Z
106
j
122
z
138
è
154
Ü
170
¬
043
+
059
;
075
K
091
[
107
k
123
{
139
ï
155
¢
171
½
044
,
060
<
076
L
092
\
108
l
124
|
140
î
156
£
172
¼
045
-
061
=
077
M
093
]
109
m
125
}
141
ì
157
¥
173
¡
046
.
062
>
078
N
094
^
110
n
126
~
142
Ä
158
P
174
«
047
/
063
?
079
O
095
_
111
o
127
•
143
Å
159
ƒ
175
»
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Unicode (16 bit)
0000
ASCII
Latin,Greek,Cyrillic, and Armenian
Arabic and Hebrew
Indic
Punctuation, math, graphics
Chinese / Japanese / Korean symbols
Unified Chinese / Japanese / Korean ideographs
Private applications
FFFF
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The Dual Networks
Voice
Network
Analog+Digital
Data
Network
Digital
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Contents
• The 19th century telecommunications
– Telegraph - Telephone
– Digital vs. analog communications
• The voice networks & the data networks
• The electronics revolution (1960-1980)
–
–
–
–
–
Digital sound
Mainframe computers with remote access
The first unification : ISDN
Local area networks
Wide area and local area networks integration
• The Internet
– The research project
– The universal computer communications medium
– The successful unification ?
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09-07-K.Steenhaut & J.Tiberghien - VUB
The Electronics Revolution
(1970-1980)
• Integrated circuits (“chips”) make
electronics affordable.
• Mainframe computers become very powerful
• Mini & microcomputers become very popular
• Digital techniques offer better
price/performance for sound applications
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Music Records
-096
+057
+164
+210
+219
+216
+165
-003
-117
-183
-138
-067
Analog
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Digital (CD)
(44100 measurements/s)
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Records with a scratch
-096
+057
+164
+210
XXXX
XXXX
XXXX
XXXX
-117
-183
-138
-067
Analog
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+210
+145
+079
+014
-052
-117
Digital (CD)
09-07-K.Steenhaut & J.Tiberghien - VUB
Remote Access to Computers
(1970)
Mainframe Computer
Star Network
Dumb Terminals
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Integrated Services Digital Network
The first attempt to integrate voice and data
• Voice digitized at 64 Kb/s (8000 samples/s, 8 bit)
• Truly digital signaling
• A telephone connection = a 64 Kb/s digital link
+ A 64 Kb/s digital link is excellent for connecting a
terminal to a mainframe computer
- Connection time billing inadequate for data
ISDN widely used for telephony
ISDN marginal for data applications
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Local Area Networks
(1970)
LAN’s initially introduced for
• Printer sharing
• File sharing
• ...
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The Dual Screen Desk
(1980)
LAN
WAN
LAN
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LAN-WAN Integration
(1990)
LAN
WAN
LAN
LAN
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Client - Server Systems
Interconnection Network (LANs+WAN)
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Client - Server Systems
Benefits
• Sharing of storage
– Access to common data
– Professional back-up facilities
– Centralized software (& data) maintenance
• Sharing of processing power
– Unloading of central servers
– Supporting local clients for exceptional needs
• Sharing of expensive peripherals
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Terminal Emulation
= sub-minimal Client-server system
• The personal workstations are used
– as stand alone computers
– as terminals connected to other computers
• The user has to mentally switch between widely
different user interfaces and operating systems.
• Transferring data between local and remote
applications is far from trivial
• Terminal emulation is very user unfriendly !!!
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Virtual Mainframe
= true Client-Server system
• The users interface of all applications runs on the
personal workstations.
• For some applications, the workstation requests help
from specialized servers. The user remains unaware
of such requests.
• Servers can be optimized for specific tasks
• Virtual Mainframes can be
– Very user friendly
– cost effective
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09-07-K.Steenhaut & J.Tiberghien - VUB
Three Tier Virtual Mainframes
Back
Office
High-performance Local Area Network
Web servers
+
Access Control
Corporate intranet or Internet
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09-07-K.Steenhaut & J.Tiberghien - VUB
Contents
• The 19th century telecommunications
– Telegraph - Telephone
– Digital vs. analog communications
• The voice networks & the data networks
• The electronics revolution (1960-1980)
–
–
–
–
–
Digital sound
Mainframe computers with remote access
The first unification : ISDN
Local area networks
Wide area and local area networks integration
• The Internet
– The research project
– The universal computer communications medium
– The successful unification ?
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09-07-K.Steenhaut & J.Tiberghien - VUB
70’s: Need for Open Networks
CCITT/ISO start standardization work for
Open Systems Interconnection
ARPA finances Research on open Network
Technology:
• a Research WAN, ARPANET
• research on LAN interconnections
Combination of the two ARPA efforts resulted in the
INTERNET
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The Early ARPANET (1976)
London
Vince Cerf
Hawaii
56 Kbps terrestrial link
Satellite link
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The Results:
• TCP/IP + Set of Application Protocols
– Set of communication “standards” allowing
interoperability of almost all brands of computers.
– Applicable to
» Local Area Networks
» Wide Area Networks
» Interconnection of LAN’s through WAN’s
• The INTERNET
– Communication facility for the Research Community
– Financed by US government
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The success story of TCP/IP
• To connect a computer to the ARPANET,
TCP/IP is required !
• Many different computers in use in
Universities and research centers.
• TCP/IP becomes THE networking software
available on ALL machines.
• Many stand-alone networks using TCP/IP
appear due to the wide availability of
TCP/IP and the many applications
available for it.
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The success story of ARPANET
•
•
•
•
39
• Universities where TCP/IP was developed
start using the ARPANET backbone as a
general purpose communication network.
Other universities and research centers also want to
get connected: with the help of the NSF, ARPANET
becomes the North American Research Network.
FREE access but “Acceptable Use Policy” imposed
by ARPA on all users.
Exponential growth of number of users
Enormous help for US researchers.
09-07-K.Steenhaut & J.Tiberghien - VUB
Major Internet Changes
1989-1992
• DARPA is no longer the major funds provider.
• Apparition of the .COM domain
• Backbone operated by private companies and paid by
the US-NSF and the connected networks.
• “Acceptable Use Policy” no longer required on the
backbone, even if many of the connected networks
still have one.
• Commercial “Internet Service Providers” build private
networks to connect their subscribers to the Internet.
• The Internet has become a set of independently
financed, cooperating regional networks.
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Internet Cost Structure
GIANT
NL
USA
Surfnet
BE
Belnet
eunet
Planet
Planet
Uunet
Skynet
Uunet
- Backbone infrastructure and neutral interconnects
paid by interconnected networks, proportional to
their access bandwidth.
- Cost of direct interconnects shared by partners.
- Not ACTUAL but POTENTIAL traffic is charged.
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Firewalls
42
= Internet
= Firewall
= Intranet
= Secure Intranet
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The Internet
At last a successful integration of voice & data services ???
• Internet has become almost as ubiquitous as the
traditional telephone network.
• Internet cost structure based upon potential usage
capabilities rather than actual usage.
• Larger and larger parts of the Internet have multimedia capabilities.
• Talking over the Internet becomes a realistic lowcost alternative to the traditional telephone service.
• Can the present Internet survive a victory over the
traditional telephone operators ???
• Will telephone operators themselves move their
traffic to the Internet ???
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The Multi-media challenge
The notion of “Quality of Service”
Correctness:
Delay:
Data
Essential
Unimportant
Voice & Images
Non-essential
Small & Stable
Conclusion:
Data and multi-media traffic have
totally different requirements
Mixing them on a single network is
technically and economically challenging
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Introduced concepts
• Digital vs. Analog communications
– Analog signals degraded by noise
– Digital signals can be restored to their original shape
– Different requirements for data and multi-media
• Data transmission and Signaling
– Signaling = management of the data transmission
• Client-server systems
• The Internet
– A set of protocols
– A set of interconnected networks
• Intranet
– Part of the Internet behind a firewall.
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Bibliography
To know More about network modeling
Andrew Tanenbaum
Computer Networks
and Open Systems
Fourth Edition,
Prentice Hall, 2003.
ISBN 0-13-066102-3
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Bibliography
Om meer te leren of computer netwerken
(in dutch)
Andrew Tanenbaum
Computernetwerken
Vertaling Fourth Edition
Pearson Education Benelux 2003.
ISBN 90-430-0698-X
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Bibliography
Pour en apprendre d'avantage sur les réseaux
(in french)
Andrew Tanenbaum
Réseaux, 4e édition
Pearson, 2003
ISBN 2-7440-7001-7
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