<s>
In	O
the	O
United	O
Kingdom	O
,	O
Packet	B-Protocol
Switch	I-Protocol
Stream	I-Protocol
(	O
PSS	O
)	O
was	O
an	O
X.25-based	O
packet-switched	B-Protocol
network	I-Protocol
,	O
provided	O
by	O
the	O
British	O
Post	O
Office	O
Telecommunications	O
and	O
then	O
British	O
Telecommunications	O
starting	O
in	O
1980	O
.	O
</s>
<s>
Companies	O
and	O
individual	O
users	O
could	O
connect	O
into	O
the	O
PSS	O
network	O
using	O
the	O
full	O
X.25	B-Protocol
interface	O
,	O
via	O
a	O
dedicated	O
four-wire	O
telephone	O
circuit	O
using	O
a	O
PSS	O
analog	B-Application
modem	I-Application
and	O
later	O
on	O
,	O
when	O
problems	O
of	O
10-100	O
ms	O
transmission	O
failures	O
with	O
the	O
PCM	O
Voice	O
based	O
transmission	O
equipment	O
used	O
by	O
the	O
early	O
Kilostream	O
service	O
were	O
resolved	O
,	O
via	O
a	O
Kilostream	O
digital	O
access	O
circuit	O
(	O
actually	O
a	O
baseband	O
modem	B-Application
)	O
.	O
</s>
<s>
Companies	O
and	O
individual	O
users	O
could	O
also	O
connect	O
into	O
the	O
PSS	O
network	O
using	O
a	O
basic	O
non-error	O
correcting	O
RS232/V.24	O
asynchronous	O
character	O
based	O
interface	O
via	O
an	O
X.3/X.28/X.29	O
PAD	O
(	O
Packet	B-Protocol
Assembler/Disassembler	I-Protocol
)	O
service	O
oriented	O
to	O
the	O
then	O
prevalent	O
dumb	O
terminal	O
market	O
place	O
.	O
</s>
<s>
The	O
PAD	O
service	O
could	O
be	O
connected	O
to	O
via	O
a	O
dedicated	O
four-wire	O
telephone	O
circuit	O
using	O
a	O
PSS	O
analog	B-Application
modem	I-Application
and	O
later	O
on	O
via	O
a	O
Kilostream	O
digital	O
access	O
circuit	O
.	O
</s>
<s>
However	O
most	O
customers	O
,	O
for	O
cost	O
reasons	O
,	O
chose	O
to	O
dial	O
up	O
via	O
an	O
analog	B-Application
modem	I-Application
over	O
the	O
then	O
UK	O
analog	O
telephony	O
network	O
to	O
their	O
nearest	O
public	O
PAD	O
,	O
via	O
published	O
phone	O
numbers	O
,	O
using	O
an	O
ID/password	O
provided	O
as	O
a	O
subscription	O
service	O
.	O
</s>
<s>
Some	O
customers	O
connected	O
to	O
the	O
PSS	O
network	O
via	O
the	O
X.25	B-Protocol
service	O
and	O
bought	O
their	O
own	O
PADs	O
.	O
</s>
<s>
Logica	O
(	O
now	O
LogicaCMG	O
)	O
designed	O
the	O
CHAPS	O
system	O
and	O
incorporated	O
an	O
encryption	O
system	O
able	O
to	O
cope	O
with	O
HDLC	O
bit	O
stuffing	O
on	O
X.25	B-Protocol
links	O
.	O
</s>
<s>
Individual	O
users	O
could	O
link	O
into	O
PSS	O
,	O
on	O
a	O
pay	O
as	O
you	O
go	O
basis	O
,	O
by	O
using	O
a	O
110	O
,	O
300	O
,	O
1200/75	O
,	O
1,200	O
or	O
2,400	O
bit/s	O
PSTN	O
modem	B-Application
to	O
connect	O
a	O
Data	O
Terminal	O
Equipment	O
terminal	O
into	O
a	O
local	O
PSS	O
exchange	O
.	O
</s>
<s>
Note	O
:	O
in	O
those	O
days	O
2,400	O
bit/s	O
modems	B-Application
were	O
quite	O
rare	O
;	O
1,200	O
bit/s	O
was	O
the	O
usual	O
speed	O
in	O
the	O
1980s	O
,	O
although	O
110	O
and	O
300	O
bit/s	O
modems	B-Application
were	O
not	O
uncommon	O
.	O
</s>
<s>
The	O
International	B-Protocol
Packet	I-Protocol
Switch	I-Protocol
Stream	I-Protocol
(	O
IPSS	O
)	O
is	O
an	O
international	O
X.25	B-Protocol
network	O
service	O
launched	O
by	O
the	O
international	O
division	O
of	O
BT	O
to	O
which	O
PSS	O
was	O
linked	O
to	O
other	O
packet	B-Protocol
switched	I-Protocol
networks	I-Protocol
around	O
the	O
world	O
.	O
</s>
<s>
For	O
a	O
brief	O
time	O
the	O
EEC	O
operated	O
a	O
packet	B-Protocol
switched	I-Protocol
network	I-Protocol
,	O
Euronet	O
,	O
and	O
a	O
related	O
project	O
Diane	O
to	O
encourage	O
more	O
database	O
and	O
network	O
services	O
to	O
develop	O
in	O
Europe	O
.	O
</s>
<s>
These	O
connections	O
moved	O
over	O
to	O
PSS	O
and	O
other	O
European	O
networks	O
as	O
commercial	O
X.25	B-Protocol
services	O
launched	O
.	O
</s>
<s>
Later	O
on	O
the	O
InterStream	O
gateway	O
between	O
the	O
Telex	B-Application
network	O
and	O
PSS	O
was	O
introduced	O
based	O
on	O
a	O
low	O
speed	O
PAD	O
interface	O
.	O
</s>
<s>
The	O
network	O
was	O
initially	O
based	O
upon	O
a	O
dedicated	O
modular	O
packet	B-Protocol
switch	I-Protocol
using	O
DCC	O
's	O
TP	O
4000	O
communication	O
processor	O
hardware	O
.	O
</s>
<s>
The	O
operating	O
system	O
and	O
the	O
packet	B-Protocol
switching	I-Protocol
software	O
was	O
developed	O
by	O
Telenet	O
(	O
later	O
on	O
GTE	O
Telenet	O
)	O
.	O
</s>
<s>
At	O
the	O
time	O
of	O
PSS	O
's	O
launch	O
this	O
was	O
in	O
advance	O
of	O
both	O
Telenet	O
's	O
own	O
network	O
and	O
most	O
others	O
that	O
used	O
general	O
purpose	O
mini-computers	O
as	O
packet	B-Protocol
switches	I-Protocol
.	O
</s>
<s>
BT	O
bought	O
Telenet	O
's	O
system	O
via	O
Plessey	O
Controls	O
of	O
Poole	O
,	O
Dorset	O
who	O
also	O
sold	O
Telex	B-Application
and	O
Traffic	O
light	O
systems	O
.	O
</s>
<s>
Later	O
on	O
BT	O
used	O
Telematics	O
packet	B-Protocol
switches	I-Protocol
for	O
the	O
Vascom	O
network	O
to	O
support	O
the	O
Prestel	B-General_Concept
service	O
and	O
also	O
bought	O
the	O
Tymnet	B-Application
network	O
from	O
McDonneld	O
Douglas	O
.	O
</s>
<s>
British	O
Telecom	O
purchased	O
the	O
Tymnet	B-Application
network	O
systems	O
business	O
and	O
its	O
associated	O
applications	O
activities	O
from	O
the	O
McDonnell	O
Douglas	O
Corporation	O
on	O
19	O
November	O
(	O
1989	O
)	O
for	O
$355	O
million	O
.	O
</s>
<s>
Its	O
activities	O
included	O
TYMNET	B-Application
,	O
the	O
public	O
network	O
business	O
,	O
plus	O
its	O
associates	O
private	O
and	O
hybrid	O
(	O
mixed	O
public	O
and	O
private	O
)	O
network	O
activities	O
,	O
the	O
OnTyme	O
electronic	O
mail	O
service	O
,	O
the	O
Card	O
Service	O
processing	O
business	O
,	O
and	O
EDI*Net	O
,	O
the	O
US	O
market	O
leader	O
in	O
electronic	O
data	O
interchange	O
.	O
</s>
<s>
BT	O
Tymnet	B-Application
anticipated	O
developing	O
an	O
end	O
to	O
end	O
managed	O
network	O
service	O
for	O
multi-national	O
customers	O
,	O
and	O
developing	O
dedicated	O
or	O
hybrid	O
networks	O
that	O
embraced	O
major	O
trading	O
areas	O
.	O
</s>
<s>
It	O
is	O
believed	O
BT	O
subsequently	O
exchanged	O
major	O
US	O
elements	O
of	O
the	O
Tymnet	B-Application
business	O
with	O
MCI	B-Application
for	O
other	O
assets	O
when	O
the	O
proposed	O
merger	O
of	O
their	O
two	O
businesses	O
was	O
thwarted	O
by	O
MCI	B-Application
's	O
purchase	O
by	O
WorldCom	O
.	O
</s>
<s>
Network	O
management	O
had	O
been	O
run	O
on	O
a	O
system	O
of	O
24	O
Prime	O
63xx	O
and	O
48xx	O
computers	O
running	O
a	O
modified	O
versions	O
of	O
Revisions	O
20	O
and	O
22	O
of	O
the	O
Primos	B-General_Concept
operating	O
system	O
.	O
</s>
<s>
Packet	B-Protocol
switches	I-Protocol
were	O
installed	O
at	O
major	O
trunk	O
exchanges	O
in	O
most	O
major	O
conurbations	O
in	O
the	O
UK	O
.	O
</s>
<s>
BT	O
's	O
attitude	O
to	O
packet	B-Protocol
switching	I-Protocol
was	O
ambivalent	O
at	O
best	O
.	O
</s>
<s>
Compared	O
to	O
France	O
's	O
Transpac	O
that	O
had	O
a	O
separate	O
commercial	O
company	O
with	O
dedicated	O
management	O
and	O
saw	O
X.25	B-Protocol
packet	B-Protocol
switching	I-Protocol
as	O
a	O
core	O
offering	O
BT	O
's	O
then	O
senior	O
management	O
regarded	O
packet	B-Protocol
switching	I-Protocol
as	O
a	O
passing	O
phase	O
until	O
the	O
telecommunications	O
nirvana	O
of	O
ISDN	O
's	O
64	O
kbit/s	O
for	O
everyone	O
arrived	O
.	O
</s>
<s>
Investments	O
in	O
value	O
added	O
network	O
services	O
(	O
VANS	O
)	O
and	O
BT	O
's	O
own	O
access	O
level	O
packet	B-Protocol
switching	I-Protocol
hardware	O
delayed	O
operating	O
profit	O
.	O
</s>
<s>
Despite	O
healthy	O
demand	O
for	O
basic	O
X.25	B-Protocol
services	O
and	O
the	O
obvious	O
trend	O
for	O
more	O
demanding	O
bandwidth	O
intensive	O
applications	O
that	O
required	O
investment	O
in	O
more	O
powerful	O
switches	O
a	O
decision	O
to	O
develop	O
BT	O
's	O
own	O
hardware	O
and	O
network	O
applications	O
was	O
made	O
instead	O
.	O
</s>
<s>
It	O
was	O
believed	O
that	O
putting	O
a	O
packet	B-Protocol
switch	I-Protocol
in	O
every	O
local	O
telephone	O
exchange	O
would	O
allow	O
this	O
and	O
other	O
low	O
bandwidth	O
applications	O
to	O
drive	O
revenue	O
.	O
</s>
<s>
The	O
lesson	O
of	O
Tymnet	B-Application
's	O
similar	O
transaction	O
phone	O
that	O
just	O
used	O
a	O
dial	O
up	O
link	O
to	O
a	O
standard	O
PAD	O
based	O
service	O
was	O
not	O
followed	O
.	O
</s>
<s>
Each	O
low	O
end	O
packet	B-Protocol
switch	I-Protocol
installed	O
added	O
costs	O
for	O
floor	O
space	O
,	O
power	O
,	O
etc	O
.	O
</s>
<s>
Nor	O
were	O
they	O
adequate	O
for	O
X.25	B-Protocol
host	O
traffic	O
.	O
</s>
<s>
However	O
significant	O
on-going	O
expenditure	O
had	O
been	O
committed	O
already	O
to	O
manufacture	O
packet	B-Protocol
switch	I-Protocol
hardware	O
and	O
by	O
using	O
the	O
very	O
expensive	O
Tandem	O
computers	O
in	O
existing	O
VANS	O
.	O
</s>
<s>
PSS	O
was	O
then	O
merged	O
with	O
other	O
failing	O
business	O
like	O
Prestel	B-General_Concept
as	O
it	O
became	O
part	O
of	O
a	O
larger	O
Managed	O
Network	O
Services	O
division	O
that	O
was	O
used	O
to	O
fix	O
or	O
close	O
BT	O
's	O
problem	O
businesses	O
.	O
</s>
<s>
While	O
PSS	O
eventually	O
went	O
the	O
way	O
of	O
all	O
X.25	B-Protocol
networks	O
and	O
was	O
overwhelmed	O
by	O
the	O
internet	O
and	O
more	O
significantly	O
the	O
internet	O
's	O
superior	O
application	O
suite	O
and	O
cost	O
model	O
.	O
</s>
<s>
BT	O
did	O
not	O
capitalise	O
as	O
much	O
as	O
other	O
packet	B-Protocol
switch	I-Protocol
operators	O
by	O
subsequent	O
mistakes	O
concerning	O
the	O
internet	O
,	O
Tymnet	B-Application
,	O
BT	O
's	O
North	O
American	O
operations	O
and	O
the	O
Concert	O
Global	O
Services	O
with	O
ATT	O
.	O
</s>
<s>
Now	O
BT	O
appears	O
to	O
be	O
inheriting	O
a	O
dominating	O
position	O
in	O
the	O
Global	O
Network	O
Services	O
market	O
,	O
based	O
on	O
packet	B-Protocol
switching	I-Protocol
,	O
as	O
CSC	O
and	O
Reuters	O
sell	O
up	O
their	O
networks	O
to	O
BT	O
.	O
</s>
<s>
As	O
the	O
commodity	O
price	O
of	O
IP	O
services	O
based	O
in	O
their	O
core	O
21st	O
century	O
MPLS	O
network	O
to	O
carry	O
voice	O
and	O
data	O
finally	O
gives	O
them	O
the	O
real	O
cost	O
efficiencies	O
that	O
packet	B-Protocol
switching	I-Protocol
always	O
promised	O
.	O
</s>
