<s>
The	O
GTD-5	B-Device
EAX	I-Device
(	O
General	B-Device
Telephone	I-Device
Digital	I-Device
Number	I-Device
5	I-Device
Electronic	I-Device
Automatic	I-Device
Exchange	I-Device
)	O
is	O
the	O
Class	B-Device
5	I-Device
telephone	I-Device
switch	I-Device
developed	O
by	O
GTE	O
Automatic	O
Electric	O
Laboratories	O
.	O
</s>
<s>
This	O
digital	B-General_Concept
central	O
office	O
telephone	O
circuit	B-Protocol
switching	I-Protocol
system	O
is	O
used	O
in	O
the	O
former	O
GTE	O
service	O
areas	O
and	O
by	O
many	O
smaller	O
telecommunications	O
service	O
providers	O
.	O
</s>
<s>
The	O
GTD-5	B-Device
EAX	I-Device
first	O
appeared	O
in	O
Banning	O
,	O
California	O
on	O
June	O
26	O
,	O
1982	O
,	O
slowly	O
replacing	O
the	O
electromechanical	O
systems	O
still	O
in	O
use	O
in	O
the	O
independent	O
switch	O
market	O
at	O
that	O
time	O
.	O
</s>
<s>
The	O
GTD-5	B-Device
EAX	I-Device
was	O
also	O
used	O
as	O
a	O
Class	B-Device
4	I-Device
telephone	I-Device
switch	I-Device
or	O
as	O
a	O
mixed	O
Class	O
4/5	O
in	O
markets	O
too	O
small	O
for	O
a	O
GTD-3	O
EAX	O
or	O
4ESS	B-Device
switch	I-Device
.	O
</s>
<s>
The	O
GTD-5	B-Device
EAX	I-Device
was	O
also	O
exported	O
internationally	O
,	O
and	O
manufactured	O
outside	O
of	O
the	O
U.S.	O
under	O
license	O
,	O
primarily	O
in	O
Canada	O
,	O
Belgium	O
and	O
Italy	O
.	O
</s>
<s>
The	O
processing	O
building	O
block	O
of	O
the	O
GTD-5	B-Device
EAX	I-Device
was	O
the	O
"	O
processor	O
complex	O
"	O
.	O
</s>
<s>
These	O
were	O
replaced	O
by	O
NEC	B-Device
V30s	I-Device
(	O
an	O
80186	O
instruction	O
set	O
compatible	O
processor	O
with	O
8086	O
pinout	O
implemented	O
in	O
CMOS	O
and	O
somewhat	O
faster	O
than	O
the	O
8086	O
due	O
to	O
internal	O
improvements	O
)	O
in	O
the	O
second	O
generation	O
,	O
and	O
ultimately	O
by	O
80386	O
processors	O
.	O
</s>
<s>
Each	O
FIU	O
was	O
responsible	O
for	O
connecting	O
the	O
system	O
to	O
a	O
particular	O
class	O
of	O
physical	O
connection	O
:	O
analog	O
lines	O
in	O
the	O
Analog	O
Line	O
FIU	O
(	O
and	O
its	O
successor	O
,	O
the	O
Extended	O
Line	O
FIU	O
)	O
;	O
analog	O
trunks	O
in	O
the	O
Analog	O
Trunk	O
FIU	O
;	O
and	O
digital	B-General_Concept
carrier	O
in	O
the	O
Digital	B-General_Concept
Trunk	O
FIU	O
and	O
its	O
successor	O
,	O
the	O
EDT	O
FIU	O
.	O
</s>
<s>
Unlike	O
the	O
SM	O
in	O
the	O
competitive	O
5ESS	B-Device
Switch	I-Device
,	O
the	O
TCUs	O
did	O
not	O
perform	O
all	O
call	O
processing	O
functions	O
,	O
but	O
limited	O
themselves	O
to	O
digit	O
collection	O
and	O
signalling	O
interpretation	O
.	O
</s>
<s>
The	O
MXU	O
was	O
actually	O
a	O
Lenkurt	O
914E	O
Subscriber	B-Application
Loop	I-Application
Carrier	I-Application
.	O
</s>
<s>
When	O
integrated	O
with	O
the	O
GTD-5	B-Device
EAX	I-Device
,	O
it	O
used	O
a	O
custom	O
software	O
load	O
that	O
permitted	O
message	O
communication	O
with	O
the	O
remainder	O
of	O
the	O
system	O
.	O
</s>
<s>
The	O
GTD-5	B-Device
EAX	I-Device
ran	O
on	O
a	O
Time-Space-Time	O
(	O
TST	O
)	O
topology	O
.	O
</s>
<s>
The	O
digital	B-General_Concept
output	O
of	O
the	O
768	O
codecs	O
was	O
concentrated	O
to	O
192	O
timeslots	O
before	O
presentation	O
to	O
the	O
timeswitch	O
,	O
a	O
4:1	O
concentration	O
.	O
</s>
<s>
T-carrier	O
spans	O
were	O
terminated	O
,	O
four	O
per	O
card	O
,	O
on	O
the	O
Quad	O
Span	O
Interface	O
Circuit	O
(	O
QSIC	O
)	O
in	O
Digital	B-General_Concept
Trunk	O
Facility	O
Interface	O
Units	O
(	O
DTUs	O
)	O
.	O
</s>
<s>
The	O
span	O
interface	O
circuits	O
were	O
completely	O
redundant	O
,	O
and	O
all	O
control	O
circuitry	O
operated	O
in	O
lockstep	B-General_Concept
between	O
the	O
two	O
copies	O
.	O
</s>
<s>
The	O
later	O
generation	O
Extended	O
Digital	B-General_Concept
Trunk	O
Unit	O
(	O
EDT	O
)	O
included	O
8	O
T-carriers	O
per	O
card	O
,	O
and	O
incorporated	O
ESF	O
and	O
PRI	O
interfaces	O
.	O
</s>
<s>
This	O
FIU	O
operated	O
also	O
operated	O
in	O
lockstep	B-General_Concept
between	O
the	O
two	O
copies	O
,	O
but	O
incorporated	O
a	O
small	O
backplane	O
mounted	O
"	O
fingerboard	O
"	O
to	O
house	O
the	O
transformer	O
circuit	O
.	O
</s>
<s>
Throughout	O
its	O
lifecycle	O
,	O
the	O
GTD-5	B-Device
EAX	I-Device
incorporated	O
a	O
quad-redundant	O
processor	O
architecture	O
.	O
</s>
<s>
The	O
GTD-5	B-Device
EAX	I-Device
was	O
programmed	O
in	O
a	O
custom	O
version	O
of	O
Pascal	B-Application
.	O
</s>
<s>
This	O
Pascal	B-Application
was	O
extended	O
to	O
include	O
a	O
separate	O
data	O
and	O
type	O
compilation	O
phase	O
,	O
known	O
as	O
the	O
COMPOOL	O
(	O
Communications	O
Pool	O
)	O
.	O
</s>
<s>
The	O
assembler	O
used	O
had	O
a	O
preprocessor	O
that	O
imported	O
identifiers	O
from	O
the	O
COMPOOL	O
,	O
allowing	O
type	O
compatibility	O
checking	O
between	O
Pascal	B-Application
and	O
assembly	O
.	O
</s>
<s>
The	O
system	O
is	O
administered	O
through	O
an	O
assortment	O
of	O
teletypewriter	O
"	O
Channels	O
"	O
(	O
also	O
called	O
the	O
system	B-Device
console	I-Device
)	O
.	O
</s>
