<s>
Binary	B-Protocol
Synchronous	I-Protocol
Communication	O
(	O
BSC	O
or	O
Bisync	B-Protocol
)	O
is	O
an	O
IBM	O
character-oriented	O
,	O
half-duplex	O
link	O
protocol	O
,	O
announced	O
in	O
1967	O
after	O
the	O
introduction	O
of	O
System/360	B-Application
.	O
</s>
<s>
It	O
replaced	O
the	O
synchronous	B-Protocol
transmit-receive	I-Protocol
(	O
STR	O
)	O
protocol	O
used	O
with	O
second	O
generation	O
computers	O
.	O
</s>
<s>
Six-bit	O
Transcode	B-Device
looked	O
backwards	O
to	O
older	O
systems	O
;	O
USASCII	B-Protocol
with	O
128	O
characters	O
and	O
EBCDIC	B-Language
with	O
256	O
characters	O
looked	O
forward	O
.	O
</s>
<s>
Transcode	B-Device
disappeared	O
very	O
quickly	O
but	O
the	O
EBCDIC	B-Language
and	O
USASCII	B-Protocol
dialects	O
of	O
Bisync	B-Protocol
continued	O
in	O
use	O
.	O
</s>
<s>
At	O
one	O
time	O
Bisync	B-Protocol
was	O
the	O
most	O
widely	O
used	O
communications	O
protocol	O
and	O
is	O
still	O
in	O
limited	O
use	O
in	O
2013	O
.	O
</s>
<s>
Bisync	B-Protocol
differs	O
from	O
protocols	O
that	O
succeeded	O
it	O
in	O
the	O
complexity	O
of	O
message	O
framing	O
.	O
</s>
<s>
HDLC	O
,	O
Digital	B-Protocol
Data	I-Protocol
Communications	I-Protocol
Message	I-Protocol
Protocol	I-Protocol
(	O
DDCMP	B-Protocol
)	O
,	O
Point-to-Point	B-Protocol
Protocol	I-Protocol
(	O
PPP	O
)	O
,	O
etc	O
.	O
</s>
<s>
Bisync	B-Protocol
has	O
five	O
different	O
framing	O
formats	O
.	O
</s>
<s>
ACK0	O
and	O
ACK1	O
(	O
even/odd	O
affirmative	O
acknowledgement	B-Protocol
)	O
are	O
encoded	O
as	O
two	O
charactersDLE	O
'	O
70'x	O
,	O
and	O
DLE	O
/	O
for	O
EBCDIC	B-Language
,	O
DLE	O
0	O
and	O
DLE	O
1	O
for	O
USASCII	B-Protocol
,	O
DLE	O
-	O
and	O
DLE	O
T	O
for	O
Transcode	B-Device
.	O
</s>
<s>
A	O
normal	O
block	O
ending	O
character	O
(	O
ETB	O
or	O
ETX	O
)	O
is	O
followed	O
by	O
a	O
check	B-Algorithm
sum	I-Algorithm
(	O
block	O
check	O
character	O
or	O
BCC	O
)	O
.	O
</s>
<s>
For	O
USASCII	B-Protocol
,	O
this	O
is	O
a	O
one	O
character	O
longitudinal	B-Error_Name
redundancy	I-Error_Name
check	I-Error_Name
(	O
LRC	O
)	O
;	O
for	O
Transcode	B-Device
and	O
EBCDIC	B-Language
,	O
the	O
check	B-Algorithm
sum	I-Algorithm
is	O
a	O
two	O
character	O
cyclic	O
redundancy	O
check(CRC )	O
.	O
</s>
<s>
A	O
data	O
frame	O
may	O
contain	O
an	O
intermediate	O
check	B-Algorithm
sum	I-Algorithm
preceded	O
by	O
an	O
ITB	O
character	O
.	O
</s>
<s>
This	O
ability	O
to	O
include	O
intermediate	O
check	B-Algorithm
sums	I-Algorithm
in	O
a	O
long	O
data	O
frame	O
allows	O
a	O
considerable	O
improvement	O
of	O
the	O
error	O
detection	O
probability	O
.	O
</s>
<s>
USASCII	B-Protocol
characters	O
are	O
also	O
transmitted	O
using	O
odd	B-Error_Name
parity	I-Error_Name
for	O
additional	O
checking	O
.	O
</s>
<s>
The	O
number	O
of	O
unique	O
characters	O
that	O
can	O
be	O
transmitted	O
is	O
therefore	O
limited	O
to	O
59	O
for	O
Transcode	B-Device
,	O
123	O
for	O
USASCII	B-Protocol
,	O
or	O
251	O
for	O
EBCDIC	B-Language
.	O
</s>
<s>
This	O
technique	O
became	O
known	O
as	O
character	O
stuffing	O
,	O
by	O
analogy	O
with	O
bit	B-Protocol
stuffing	I-Protocol
.	O
</s>
<s>
The	O
protocol	O
requires	O
that	O
every	O
message	O
be	O
acknowledged	O
(	O
ACK0/ACK1	O
)	O
or	O
negatively	B-Protocol
acknowledged	I-Protocol
(	O
NAK	B-Protocol
)	O
,	O
so	O
transmission	O
of	O
small	O
packets	O
has	O
high	O
transmission	O
overhead	O
.	O
</s>
<s>
The	O
protocol	O
can	O
recover	O
from	O
a	O
corrupted	O
data	O
frame	O
,	O
a	O
lost	O
data	O
frame	O
,	O
and	O
a	O
lost	O
acknowledgment	B-Protocol
.	O
</s>
<s>
Since	O
Bisync	B-Protocol
data	O
packets	O
are	O
not	O
serial-numbered	O
,	O
it	O
's	O
considered	O
possible	O
for	O
a	O
data	O
frame	O
to	O
go	O
missing	O
without	O
the	O
receiver	O
realizing	O
it	O
.	O
</s>
<s>
Therefore	O
,	O
alternating	O
ACK0s	O
and	O
ACK1s	O
are	O
deployed	O
;	O
if	O
the	O
transmitter	O
receives	O
the	O
wrong	O
ACK	B-Protocol
,	O
it	O
can	O
assume	O
a	O
data	O
packet	O
(	O
or	O
an	O
ACK	B-Protocol
)	O
went	O
missing	O
.	O
</s>
<s>
In	O
this	O
environment	O
,	O
packets	O
or	O
frames	O
of	O
transmission	O
are	O
strictly	O
unidirectional	O
,	O
necessitating	O
'	O
turn-around	O
'	O
for	O
even	O
the	O
simplest	O
purposes	O
,	O
such	O
as	O
acknowledgments	B-Protocol
.	O
</s>
<s>
In	O
typical	O
full-duplex	O
,	O
data	O
packets	O
are	O
transmitted	O
along	O
one	O
wire	O
pair	O
while	O
the	O
acknowledgements	B-Protocol
are	O
returned	O
along	O
the	O
other	O
.	O
</s>
<s>
Much	O
Bisync	B-Protocol
traffic	O
is	O
point-to-point	B-Architecture
.	O
</s>
<s>
Point-to-point	B-Architecture
lines	O
can	O
optionally	O
use	O
contention	O
to	O
determine	O
the	O
master	O
station	O
.	O
</s>
<s>
The	O
other	O
device	O
can	O
reply	O
ACK0	O
to	O
accept	O
the	O
bid	O
and	O
prepare	O
to	O
receive	O
,	O
or	O
NAK	B-Protocol
or	O
WABT	O
to	O
refuse	O
.	O
</s>
<s>
Multi-drop	O
is	O
part	O
of	O
the	O
initial	O
Bisync	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
The	O
original	O
purpose	O
of	O
Bisync	B-Protocol
was	O
for	O
batch	O
communications	O
between	O
a	O
System/360	B-Application
mainframe	B-Architecture
and	O
another	O
mainframe	B-Architecture
or	O
a	O
Remote	B-Protocol
Job	I-Protocol
Entry	I-Protocol
(	O
RJE	B-Protocol
)	O
terminal	O
such	O
as	O
the	O
IBM	B-Device
2780	I-Device
or	O
IBM	O
3780	B-Device
.	O
</s>
<s>
The	O
RJE	B-Protocol
terminals	O
support	O
a	O
limited	O
number	O
of	O
data	O
formats	O
:	O
punched	O
card	O
images	O
in	O
and	O
out	O
and	O
print	O
line	O
images	O
to	O
the	O
terminal	O
.	O
</s>
<s>
Some	O
non-IBM	O
hardware	O
vendors	O
such	O
as	O
Mohawk	O
Data	O
Sciences	O
used	O
Bisync	B-Protocol
for	O
other	O
purposes	O
such	O
as	O
tape-to-tape	O
transmission	O
.	O
</s>
<s>
A	O
programmer	O
can	O
easily	O
emulate	O
an	O
RJE	B-Protocol
terminal	O
or	O
other	O
device	O
.	O
</s>
<s>
During	O
the	O
System/360	B-Application
era	O
,	O
these	O
access	B-Application
methods	I-Application
were	O
BTAM	B-Application
(	O
Basic	B-Application
Telecommunications	I-Application
Access	I-Application
Method	I-Application
)	O
and	O
QTAM	B-Application
(	O
Queued	B-Application
Telecommunications	I-Application
Access	I-Application
Method	I-Application
)	O
–	O
which	O
was	O
later	O
replaced	O
by	O
Telecommunications	B-Application
Access	I-Application
Method	I-Application
(	O
TCAM	O
)	O
.	O
</s>
<s>
IBM	O
introduced	O
VTAM	B-Application
(	O
Virtual	B-Application
Telecommunications	I-Application
Access	I-Application
Method	I-Application
)	O
with	O
the	O
System/370	B-Device
.	O
</s>
<s>
Teleprocessing	B-General_Concept
monitors	I-General_Concept
such	O
as	O
IBM	O
's	O
CICS	B-Application
and	O
third-party	O
software	O
such	O
as	O
Remote	B-Application
DUCS	I-Application
(	O
display	O
unit	O
control	O
system	O
)	O
and	O
Westi	B-Application
platforms	O
used	O
Bisync	B-Protocol
line	O
control	O
to	O
communicate	O
with	O
remote	O
devices	O
.	O
</s>
<s>
The	O
academic	O
computing	O
network	O
Bitnet	B-General_Concept
,	O
together	O
with	O
connecting	O
networks	O
in	O
other	O
geographic	O
areas	O
,	O
used	O
Bisync	B-Protocol
to	O
connect	O
3000	O
computer	O
systems	O
at	O
its	O
peak	O
.	O
</s>
<s>
In	O
a	O
mid-1990	O
BSC	O
was	O
replaced	O
to	O
the	O
X.25	B-Protocol
infrastructure	O
.	O
</s>
<s>
Some	O
important	O
systems	O
use	O
Bisync	B-Protocol
data	O
framing	O
with	O
a	O
different	O
link	O
control	O
protocol	O
.	O
</s>
<s>
Houston	B-Application
Automatic	I-Application
Spooling	I-Application
Priority	I-Application
(	O
HASP	O
)	O
uses	O
Bisync	B-Protocol
half-duplex	O
hardware	O
in	O
conjunction	O
with	O
its	O
own	O
link	O
control	O
protocol	O
to	O
provide	O
full-duplex	O
multi-datastream	O
communication	O
between	O
a	O
small	O
computer	O
and	O
a	O
mainframe	B-Architecture
running	O
HASP	O
.	O
</s>
<s>
In	O
Bisync	B-Protocol
terms	O
,	O
this	O
is	O
conversational	O
mode	O
.	O
</s>
<s>
Some	O
early	O
X.25	B-Protocol
networks	O
tolerated	O
a	O
connection	O
scheme	O
where	O
transparent	O
Bisync	B-Protocol
data	O
frames	O
encapsulated	O
HDLC	O
LAPB	B-Protocol
data	O
and	O
control	O
packets	O
.	O
</s>
<s>
,	O
several	O
vendors	O
encapsulate	O
Bisync	B-Protocol
transmissions	O
within	O
TCP/IP	O
data	O
streams	O
.	O
</s>
<s>
Bisync	B-Protocol
began	O
to	O
be	O
displaced	O
in	O
the	O
1970s	O
by	O
Systems	B-Architecture
Network	I-Architecture
Architecture	I-Architecture
(	O
SNA	O
)	O
which	O
allows	O
construction	O
of	O
a	O
network	O
with	O
multiple	O
hosts	O
and	O
multiple	O
programs	O
using	O
telecommunications	O
.	O
</s>
<s>
X.25	B-Protocol
and	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
are	O
later	O
protocols	O
which	O
,	O
like	O
SNA	O
,	O
provide	O
more	O
than	O
mere	O
link	O
control	O
.	O
</s>
<s>
A	O
large	O
number	O
of	O
devices	O
use	O
the	O
Bisync	B-Protocol
protocol	I-Protocol
,	O
some	O
of	O
these	O
are	O
:	O
</s>
<s>
IBM	B-Operating_System
3270	I-Operating_System
Display	O
Terminal	O
Subsystem	O
control	O
units	O
.	O
</s>
<s>
IBM	B-Device
2780	I-Device
Data	O
Transmission	O
Terminal	O
.	O
</s>
<s>
IBM	B-Device
2703	I-Device
Transmission	O
Control	O
.	O
</s>
<s>
IBM	B-Application
HASP	I-Application
workstations	I-Application
.	O
</s>
<s>
IBM	B-Device
1130	I-Device
Computing	O
System	O
.	O
</s>
<s>
IBM	B-Device
2922	I-Device
Programmable	O
Terminal	O
.	O
</s>
