<s>
TRAME	B-General_Concept
(	O
TRAnsmission	O
of	O
MEssages	O
)	O
was	O
the	O
name	O
of	O
the	O
second	O
computer	O
network	O
in	O
the	O
world	O
similar	O
to	O
the	O
internet	O
to	O
be	O
used	O
in	O
an	O
electric	O
utility	O
.	O
</s>
<s>
Like	O
the	O
internet	O
,	O
the	O
base	O
technology	O
was	O
packet	B-Protocol
switching	I-Protocol
;	O
it	O
was	O
developed	O
by	O
the	O
electric	O
utility	O
ENHER	O
in	O
Barcelona	O
.	O
</s>
<s>
Its	O
development	O
started	O
in	O
1974	O
and	O
the	O
first	O
routers	B-Protocol
,	O
called	O
nodes	O
at	O
that	O
time	O
,	O
were	O
deployed	O
by	O
1978	O
.	O
</s>
<s>
In	O
1974	O
,	O
packet	B-Protocol
switching	I-Protocol
was	O
a	O
technology	O
known	O
only	O
in	O
research	O
circles	O
.	O
</s>
<s>
The	O
idea	O
of	O
applying	O
the	O
packet	B-Protocol
switching	I-Protocol
concept	O
to	O
electric	O
utilities	O
control	O
communication	O
networks	O
first	O
appeared	O
in	O
1974	O
when	O
the	O
Swedish	O
power	O
utility	O
Vattenfall	O
started	O
to	O
create	O
its	O
TIDAS	O
packet-switching	B-Protocol
network	O
and	O
was	O
followed	O
by	O
the	O
Spanish	O
electric	O
utility	O
ENHER	O
,	O
which	O
aimed	O
to	O
telecontrol	O
and	O
automate	O
its	O
high-voltage	O
power	O
grid	O
.	O
</s>
<s>
For	O
this	O
purpose	O
,	O
ENHER	O
created	O
a	O
specific	O
team	O
of	O
people	O
to	O
develop	O
both	O
the	O
packet-switching	B-Protocol
network	O
and	O
the	O
supervisory	O
control	O
and	O
data	O
acquisition	O
(	O
SCADA	O
)	O
system	O
,	O
also	O
called	O
the	O
telecontrol	O
system	O
.	O
</s>
<s>
By	O
1978	O
the	O
first	O
four	O
TRAME	B-General_Concept
routers	B-Protocol
were	O
available	O
and	O
by	O
1980	O
,	O
eight	O
of	O
them	O
were	O
deployed	O
and	O
operating	O
.	O
</s>
<s>
The	O
printed	O
circuit	O
boards	O
(	O
PCBs	O
)	O
controlling	O
the	O
communication	O
lines	O
were	O
connected	O
to	O
a	O
shared	B-Operating_System
memory	I-Operating_System
PCB	O
allowing	O
them	O
to	O
exchange	O
data	O
and	O
messages	O
.	O
</s>
<s>
The	O
basic	O
service	O
provided	O
by	O
the	O
TRAME	B-General_Concept
network	O
was	O
SCADA	O
or	O
Telecontrol	O
to	O
automate	O
the	O
high-voltage	O
power	O
grid	O
,	O
thus	O
improving	O
operational	O
efficiency	O
,	O
which	O
was	O
until	O
then	O
operated	O
manually	O
with	O
telephone	O
communication	O
between	O
human	O
operators	O
.	O
</s>
<s>
Each	O
TRAME	B-General_Concept
router	B-Protocol
was	O
associated	O
with	O
one	O
or	O
more	O
remote	B-Device
terminal	I-Device
units	I-Device
(	O
RTUs	O
)	O
of	O
the	O
SICL	O
telecontrol	O
system	O
.	O
</s>
<s>
Later	O
,	O
in	O
the	O
1990s	O
,	O
other	O
protocols	O
(	O
X.25	B-Protocol
,	O
IP	B-Protocol
)	O
were	O
developed	O
to	O
include	O
corporate	O
information	O
technology	O
(	O
IT	O
)	O
terminals	O
,	O
company	O
physical	O
surveillance	O
systems	O
and	O
other	O
services	O
.	O
</s>
<s>
Additionally	O
,	O
applications	O
and	O
terminals	O
were	O
developed	O
for	O
the	O
transmission	O
of	O
voice	O
and	O
video	O
over	O
the	O
TRAME	B-General_Concept
network	O
.	O
</s>
<s>
The	O
TRAME	B-General_Concept
routing	B-Protocol
system	O
,	O
like	O
that	O
of	O
the	O
original	O
ARPANET	O
,	O
was	O
based	O
on	O
the	O
Bellman-Ford	B-Algorithm
algorithm	I-Algorithm
but	O
with	O
"	O
split-horizon	O
"	O
as	O
in	O
the	O
Swedish	O
TIDAS	O
network	O
,	O
but	O
with	O
an	O
original	O
improvement	O
.	O
</s>
<s>
In	O
contrast	O
,	O
traditional	O
circuit-switched	B-Protocol
technology	O
used	O
to	O
establish	O
dedicated	O
circuits	O
for	O
each	O
service	O
or	O
communication	O
.	O
</s>
<s>
The	O
addressing	O
of	O
routers	B-Protocol
and	O
terminals	O
used	O
a	O
proprietary	O
system	O
with	O
a	O
16-bit	O
address	O
;	O
it	O
would	O
be	O
the	O
equivalent	O
of	O
the	O
well-known	O
IP	B-Protocol
(	O
Internet	B-Protocol
Protocol	I-Protocol
)	O
version	O
4	O
(	O
IPv4	B-Protocol
)	O
,	O
still	O
in	O
use	O
on	O
the	O
internet	O
today	O
,	O
which	O
uses	O
32-bit	O
addresses	O
.	O
</s>
<s>
It	O
is	O
necessary	O
to	O
take	O
into	O
account	O
that	O
in	O
1978	O
,	O
the	O
IPv4	B-Protocol
protocol	O
did	O
not	O
yet	O
exist	O
since	O
the	O
IPv4	B-Protocol
version	O
used	O
on	O
the	O
internet	O
did	O
not	O
appear	O
until	O
1981	O
,	O
and	O
in	O
fact	O
,	O
did	O
not	O
reach	O
the	O
general	O
public	O
until	O
much	O
later	O
.	O
</s>
<s>
The	O
line	O
protocols	O
were	O
also	O
proprietary	O
and	O
were	O
called	O
UCL	O
(	O
,	O
'	O
line	O
control	O
unit	O
 '	O
)	O
,	O
which	O
linked	O
the	O
routers	B-Protocol
together	O
,	O
and	O
UTR	O
(	O
)	O
,	O
the	O
access	O
protocol	O
.	O
</s>
<s>
They	O
were	O
designed	O
to	O
offer	O
the	O
highest	O
quality	O
of	O
service	O
required	O
by	O
the	O
telecontrol/SCADA	O
function	O
in	O
terms	O
of	O
data	O
integrity	O
and	O
availability	B-Operating_System
set	O
by	O
the	O
International	O
Electrotechnical	O
Commission	O
(	O
IEC	O
)	O
IEC-870-5-1	O
and	O
ANSI	O
C37.1	O
.	O
</s>
<s>
Later	O
on	O
,	O
other	O
protocols	O
like	O
X.25	B-Protocol
and	O
IP	B-Protocol
were	O
also	O
made	O
compatible	O
with	O
the	O
aforementioned	O
TRAME	B-General_Concept
protocols	O
.	O
</s>
<s>
An	O
end-to-end	B-Application
protocol	O
was	O
also	O
added	O
for	O
some	O
flows	O
requiring	O
order	O
preservation	O
like	O
X.25	B-Protocol
.	O
</s>
<s>
There	O
were	O
essentially	O
four	O
TRAME	B-General_Concept
generations	O
which	O
are	O
summarized	O
in	O
the	O
table	O
.	O
</s>
<s>
A	O
description	O
of	O
the	O
four	O
generations	O
of	O
TRAME	B-General_Concept
is	O
provided	O
below	O
.	O
</s>
<s>
The	O
project	O
began	O
in	O
1974	O
and	O
in	O
1978	O
a	O
first	O
network	O
with	O
four	O
routers	B-Protocol
was	O
already	O
installed	O
and	O
in	O
operation	O
at	O
the	O
electric	O
utility	O
ENHER	O
.	O
</s>
<s>
The	O
hardware	O
was	O
based	O
on	O
the	O
Zilog	B-General_Concept
Z80	I-General_Concept
processor	O
and	O
had	O
a	O
multiprocessor	B-Operating_System
structure	O
with	O
16	O
processors	O
sharing	O
a	O
common	O
memory	O
.	O
</s>
<s>
The	O
software	O
was	O
developed	O
at	O
ENHER	O
's	O
headquarters	O
located	O
in	O
the	O
well-known	O
Casa	O
Fuster	O
,	O
,	O
132	O
,	O
Barcelona	O
,	O
using	O
the	O
Z80	B-General_Concept
assembly	O
language	O
.	O
</s>
<s>
Beyond	O
1980	O
the	O
software	O
began	O
to	O
be	O
written	O
in	O
C	B-Language
programming	I-Language
language	I-Language
and	O
an	O
HP64000	B-Device
Logic	O
Development	O
System	O
emulator	B-Application
was	O
used	O
for	O
the	O
purpose	O
.	O
</s>
<s>
The	O
routing	B-Protocol
system	O
was	O
a	O
variant	O
of	O
Bellman-Ford	B-Algorithm
with	O
split-horizon	O
.	O
</s>
<s>
It	O
was	O
an	O
improvement	O
of	O
the	O
original	O
ARPA	O
network	B-Protocol
routing	I-Protocol
system	O
consisting	O
of	O
an	O
original	O
update	O
procedure	O
which	O
allowed	O
for	O
a	O
faster	O
reaction	O
to	O
changes	O
.	O
</s>
<s>
The	O
line	O
protocols	O
(	O
UCL	O
for	O
internal	O
lines	O
linking	O
routers	B-Protocol
and	O
UTR	O
for	O
accessing	O
the	O
network	O
)	O
were	O
designed	O
to	O
meet	O
the	O
stringent	O
requirements	O
set	O
for	O
telecontrol	O
(	O
SCADA	O
)	O
of	O
high-voltage	O
power	O
networks	O
(	O
IEC-870-5-1	O
and	O
ANSI	O
C37.1	O
standards	O
)	O
.	O
</s>
<s>
Initially	O
,	O
addresses	O
were	O
only	O
14	O
bits	O
long	O
to	O
address	O
both	O
the	O
routers	B-Protocol
(	O
called	O
nodes	O
by	O
then	O
)	O
and	O
the	O
devices	O
connected	O
to	O
them	O
.	O
</s>
<s>
They	O
were	O
made	O
up	O
of	O
two	O
fields	O
,	O
an	O
8-bit	O
field	O
to	O
address	O
the	O
router	B-Protocol
and	O
a	O
6-bit	O
sub-address	O
to	O
address	O
the	O
terminals	O
connected	O
to	O
it	O
.	O
</s>
<s>
The	O
basic	O
advantages	O
of	O
TRAME	B-General_Concept
over	O
other	O
technologies	O
used	O
in	O
electric	O
utilities	O
at	O
the	O
time	O
were	O
in	O
part	O
due	O
to	O
the	O
packet	O
technology	O
itself	O
:	O
ability	O
to	O
manage	O
any	O
network	O
topology	O
,	O
automatic	O
adaptability	O
to	O
topological	O
and	O
traffic	O
changes	O
,	O
integration	O
of	O
different	O
link	O
technologies	O
(	O
digital	O
or	O
analog	O
)	O
and	O
capacities	O
in	O
a	O
single	O
network	O
,	O
open	O
and	O
decentralized	O
intercommunicability	O
between	O
users	O
and	O
devices	O
,	O
simultaneous	O
communication	O
with	O
several	O
users	O
and	O
locations	O
from	O
a	O
single	O
physical	O
connection	O
,	O
and	O
integrated	O
network	O
supervision	O
.	O
</s>
<s>
But	O
other	O
advantages	O
were	O
due	O
to	O
the	O
specific	O
design	O
of	O
TRAME	B-General_Concept
:	O
high	O
data	O
integrity	O
,	O
priority	O
support	O
for	O
packets	O
,	O
and	O
ease	O
of	O
including	O
special	O
protocols	O
such	O
as	O
the	O
many	O
SCADA	O
protocols	O
in	O
use	O
at	O
that	O
time	O
.	O
</s>
<s>
All	O
of	O
the	O
above	O
resulted	O
in	O
improved	O
quality	O
of	O
service	O
,	O
especially	O
with	O
respect	O
to	O
data	B-Operating_System
availability	I-Operating_System
and	O
data	O
integrity	O
,	O
and	O
in	O
the	O
integration	O
of	O
services	O
in	O
a	O
single	O
network	O
.	O
</s>
<s>
In	O
1990	O
,	O
TRAME	B-General_Concept
2	O
was	O
fully	O
deployed	O
and	O
TRAME	B-General_Concept
1	O
was	O
replaced	O
.	O
</s>
<s>
The	O
processor	O
of	O
the	O
new	O
hardware	O
was	O
Intel	B-General_Concept
80286	I-General_Concept
and	O
the	O
hardware	O
structure	O
and	O
external	O
appearance	O
of	O
the	O
routers	B-Protocol
was	O
very	O
similar	O
to	O
that	O
of	O
TRAME	B-General_Concept
1	O
.	O
</s>
<s>
The	O
software	O
was	O
written	O
in	O
C	B-Language
and	O
the	O
above-mentioned	O
emulator	B-Application
continued	O
to	O
be	O
used	O
.	O
</s>
<s>
Improvements	O
over	O
TRAME	B-General_Concept
1	O
were	O
the	O
introduction	O
of	O
the	O
standardized	O
X.25	B-Protocol
access	O
protocol	O
to	O
enable	O
the	O
connection	O
of	O
corporate	O
terminals	O
to	O
the	O
network	O
,	O
the	O
ability	O
to	O
handle	O
the	O
64kbit/s	O
of	O
the	O
new	O
digital	O
lines	O
,	O
increased	O
switching	O
capacity	O
,	O
and	O
the	O
introduction	O
of	O
an	O
end-to-end	B-Application
protocol	O
to	O
avoid	O
packet	B-Protocol
loss	I-Protocol
and	O
clutter	O
as	O
required	O
by	O
X.25	B-Protocol
.	O
</s>
<s>
An	O
important	O
improvement	O
was	O
the	O
possibility	O
of	O
using	O
dual	B-Protocol
homing	I-Protocol
to	O
increase	O
terminal	O
availability	B-Operating_System
;	O
they	O
could	O
be	O
connected	O
to	O
the	O
network	O
by	O
two	O
access	O
points	O
.	O
</s>
<s>
This	O
addressing	O
scheme	O
was	O
maintained	O
in	O
subsequent	O
versions	O
of	O
TRAME	B-General_Concept
.	O
</s>
<s>
The	O
hardware	O
was	O
again	O
a	O
multiprocessor	B-Operating_System
structure	O
with	O
16	O
processors	O
sharing	O
a	O
common	O
memory	O
but	O
the	O
latter	O
was	O
not	O
a	O
separate	O
PCB	O
but	O
instead	O
was	O
distributed	O
among	O
the	O
16	O
PCBs	O
to	O
avoid	O
single	O
points	O
of	O
failure	O
.	O
</s>
<s>
The	O
routing	B-Protocol
algorithm	I-Protocol
remained	O
the	O
same	O
,	O
but	O
the	O
distance	O
function	O
was	O
changed	O
to	O
a	O
less	O
dynamic	O
one	O
.	O
</s>
<s>
Improvements	O
over	O
TRAME2	O
were	O
IPv4	B-Protocol
support	O
,	O
the	O
introduction	O
of	O
an	O
SNMP	O
monitoring	O
agent	O
,	O
a	O
new	O
flow	O
control	O
system	O
,	O
an	O
improved	O
distance	O
metric	O
that	O
made	O
the	O
system	O
less	O
dynamic	O
,	O
and	O
an	O
autoexec	O
task	O
to	O
periodically	O
check	O
hardware	O
and	O
software	O
.	O
</s>
<s>
The	O
hardware	O
design	O
was	O
radically	O
modified	O
by	O
moving	O
to	O
a	O
single	O
processor	O
per	O
node	O
architecture	O
as	O
opposed	O
to	O
the	O
traditional	O
TRAME	B-General_Concept
hardware	O
.	O
</s>
<s>
It	O
had	O
two	O
alternative	O
base	O
modules	O
of	O
different	O
capacity	O
based	O
on	O
Intel	O
i960CA	O
and	O
i960RM	O
processors	O
with	O
a	O
1Gbit/s	O
bus	O
to	O
communicate	O
the	O
different	O
router	B-Protocol
boards	O
.	O
</s>
<s>
The	O
number	O
of	O
physical	O
interfaces	O
was	O
only	O
ten	O
(	O
eight	O
serial	O
+	O
two	O
Ethernet	O
(	O
10BASE2	O
or	O
10BASE-T	B-Protocol
)	O
)	O
since	O
Ethernet	O
allowed	O
for	O
the	O
connection	O
of	O
several	O
devices	O
on	O
a	O
single	O
LAN	B-General_Concept
.	O
</s>
<s>
By	O
losing	O
redundancy	O
(	O
a	O
single	O
processor	O
per	O
router	B-Protocol
)	O
the	O
node	O
lost	O
some	O
availability	B-Operating_System
over	O
previous	O
versions	O
of	O
TRAME	B-General_Concept
.	O
</s>
<s>
Dual	B-Protocol
homing	I-Protocol
could	O
help	O
in	O
places	O
with	O
more	O
stringent	O
availability	B-Operating_System
requirements	O
.	O
</s>
<s>
Improvements	O
over	O
TRAME	B-General_Concept
3	O
were	O
the	O
ability	O
to	O
handle	O
2Mbit/s	O
capacity	O
links	O
,	O
smaller	O
and	O
less	O
expensive	O
routers	B-Protocol
,	O
access	O
by	O
Ethernet	O
and	O
standard	O
protocols	O
,	O
and	O
the	O
change	O
from	O
the	O
proprietary	O
UTR	O
protocol	O
to	O
the	O
internationally	O
standardized	O
ones	O
for	O
SCADA	O
systems	O
(	O
IEC	O
60870-5-101	O
and	O
IEC	O
60870-5-104	O
)	O
with	O
an	O
original	O
adaptation	O
to	O
packet-switched	B-Protocol
networks	I-Protocol
.	O
</s>
