<s>
The	O
Data	B-Protocol
Stream	I-Protocol
Interface	I-Protocol
(	O
DSI	O
)	O
is	O
a	O
session	O
layer	O
used	O
to	O
carry	O
Apple	B-Protocol
Filing	I-Protocol
Protocol	I-Protocol
traffic	O
over	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
.	O
</s>
<s>
When	O
Apple	O
introduced	O
TCP	O
with	O
MacTCP	B-Operating_System
and	O
Open	B-Protocol
Transport	I-Protocol
in	O
System	B-Operating_System
7	I-Operating_System
in	O
the	O
1990s	O
,	O
they	O
needed	O
their	O
file	O
sharing	O
protocol	O
(	O
AFP	O
)	O
to	O
run	O
on	O
both	O
TCP	O
and	O
AppleTalk	B-Application
.	O
</s>
<s>
They	O
introduced	O
AppleTalk	B-Application
Session	I-Application
Protocol	I-Application
(	O
ASP	O
)	O
and	O
DSI	O
for	O
TCP	O
coincidentally	O
with	O
AFP	O
2.x	O
.	O
</s>
<s>
The	O
concepts	O
of	O
DSI	O
are	O
identical	O
to	O
AppleTalk	B-Application
Session	I-Application
Protocol	I-Application
(	O
ASP	O
)	O
,	O
and	O
the	O
overview	O
in	O
Inside	O
AppleTalk	B-Application
,	O
Second	O
Edition	O
can	O
be	O
helpful	O
.	O
</s>
