<s>
Protocol	B-General_Concept
engineering	I-General_Concept
is	O
the	O
application	O
of	O
systematic	O
methods	O
to	O
the	O
development	O
of	O
communication	O
protocols	O
.	O
</s>
<s>
It	O
uses	O
many	O
of	O
the	O
principles	O
of	O
software	B-General_Concept
engineering	I-General_Concept
,	O
but	O
it	O
is	O
specific	O
to	O
the	O
development	O
of	O
distributed	B-Architecture
systems	I-Architecture
.	O
</s>
<s>
When	O
the	O
first	O
experimental	O
and	O
commercial	O
computer	B-Architecture
networks	I-Architecture
were	O
developed	O
in	O
the	O
1970s	O
,	O
the	O
concept	O
of	O
protocols	O
was	O
not	O
yet	O
well	O
developed	O
.	O
</s>
<s>
These	O
were	O
the	O
first	O
distributed	B-Architecture
systems	I-Architecture
.	O
</s>
<s>
In	O
the	O
context	O
of	O
the	O
newly	O
adopted	O
layered	O
protocol	O
architecture	O
(	O
see	O
OSI	O
model	O
)	O
,	O
the	O
definition	O
of	O
the	O
protocol	O
of	O
a	O
specific	O
layer	O
should	O
be	O
such	O
that	O
any	O
entity	O
implementing	O
that	O
specification	B-Application
in	O
one	O
computer	O
would	O
be	O
compatible	O
with	O
any	O
other	O
computer	O
containing	O
an	O
entity	O
implementing	O
the	O
same	O
specification	B-Application
,	O
and	O
their	O
interactions	O
should	O
be	O
such	O
that	O
the	O
desired	O
communication	O
service	O
would	O
be	O
obtained	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
the	O
protocol	O
specification	B-Application
should	O
be	O
abstract	O
enough	O
to	O
allow	O
different	O
choices	O
for	O
the	O
implementation	O
on	O
different	O
computers	O
.	O
</s>
<s>
It	O
was	O
recognized	O
that	O
a	O
precise	O
specification	B-Application
of	O
the	O
expected	O
service	O
provided	O
by	O
the	O
given	O
layer	O
was	O
important	O
.	O
</s>
<s>
It	O
is	O
important	O
for	O
the	O
verification	O
of	O
the	O
protocol	O
,	O
which	O
should	O
demonstrate	O
that	O
the	O
communication	O
service	O
is	O
provided	O
if	O
both	O
protocol	O
entities	O
implement	O
the	O
protocol	O
specification	B-Application
correctly	O
.	O
</s>
<s>
This	O
principle	O
was	O
later	O
followed	O
during	O
the	O
standardization	O
of	O
the	O
OSI	O
protocol	O
stack	O
,	O
in	O
particular	O
for	O
the	O
transport	B-Architecture
layer	I-Architecture
.	O
</s>
<s>
It	O
was	O
also	O
recognized	O
that	O
some	O
kind	O
of	O
formalized	O
protocol	O
specification	B-Application
would	O
be	O
useful	O
for	O
the	O
verification	O
of	O
the	O
protocol	O
and	O
for	O
developing	O
implementations	O
,	O
as	O
well	O
as	O
test	O
cases	O
for	O
checking	O
the	O
conformance	O
of	O
an	O
implementation	O
against	O
the	O
specification	B-Application
.	O
</s>
<s>
While	O
initially	O
mainly	O
finite-state	O
machine	O
were	O
used	O
as	O
(	O
simplified	O
)	O
models	O
of	O
a	O
protocol	O
entity	O
,	O
in	O
the	O
1980s	O
three	O
formal	B-Application
specification	I-Application
languages	O
were	O
standardized	O
,	O
two	O
by	O
ISO	O
and	O
one	O
by	O
ITU	O
.	O
</s>
<s>
The	O
latter	O
,	O
called	O
SDL	B-Application
,	O
was	O
later	O
used	O
in	O
industry	O
and	O
has	O
been	O
merged	O
with	O
UML	B-Application
state	I-Application
machines	I-Application
.	O
</s>
<s>
The	O
service	O
specification	B-Application
of	O
a	O
layer	O
describes	O
,	O
in	O
an	O
abstract	O
and	O
global	O
view	O
,	O
the	O
behavior	O
of	O
the	O
layer	O
as	O
visible	O
at	O
the	O
service	O
interfaces	O
of	O
the	O
layer	O
.	O
</s>
<s>
The	O
protocol	O
specification	B-Application
defines	O
the	O
requirements	O
that	O
should	O
be	O
satisfied	O
by	O
each	O
entity	O
implementation	O
.	O
</s>
<s>
Protocol	O
verification	O
consists	O
of	O
showing	O
that	O
two	O
(	O
or	O
more	O
)	O
entities	O
satisfying	O
the	O
protocol	O
specification	B-Application
will	O
provide	O
at	O
their	O
service	O
interfaces	O
the	O
specified	O
service	O
of	O
that	O
layer	O
.	O
</s>
<s>
The	O
(	O
verified	O
)	O
protocol	O
specification	B-Application
is	O
used	O
mainly	O
for	O
the	O
following	O
two	O
activities	O
:	O
</s>
<s>
Note	O
that	O
the	O
abstract	O
properties	O
of	O
the	O
service	O
interface	O
are	O
defined	O
by	O
the	O
service	O
specification	B-Application
(	O
and	O
also	O
used	O
by	O
the	O
protocol	O
specification	B-Application
)	O
,	O
but	O
the	O
detailed	O
nature	O
of	O
the	O
interface	O
can	O
be	O
chosen	O
during	O
the	O
implementation	O
process	O
,	O
separately	O
for	O
each	O
entity	O
.	O
</s>
<s>
Protocol	O
conformance	O
testing	O
checks	O
that	O
a	O
given	O
entity	O
implementation	O
conforms	O
to	O
the	O
protocol	O
specification	B-Application
.	O
</s>
<s>
The	O
conformance	O
test	O
cases	O
are	O
developed	O
based	O
on	O
the	O
protocol	O
specification	B-Application
and	O
are	O
applicable	O
to	O
all	O
entity	O
implementations	O
.	O
</s>
<s>
Tools	O
for	O
the	O
activities	O
of	O
protocol	O
verification	O
,	O
entity	O
implementation	O
and	O
test	O
suite	O
development	O
can	O
be	O
developed	O
when	O
the	O
protocol	O
specification	B-Application
is	O
written	O
in	O
a	O
formalized	O
language	O
which	O
can	O
be	O
understood	O
by	O
the	O
tool	O
.	O
</s>
<s>
As	O
mentioned	O
,	O
formal	B-Application
specification	I-Application
languages	O
have	O
been	O
proposed	O
for	O
protocol	O
specification	B-Application
,	O
and	O
the	O
first	O
methods	O
and	O
tools	O
where	O
based	O
on	O
finite-state	O
machine	O
models	O
.	O
</s>
<s>
Reachability	O
analysis	O
was	O
proposed	O
to	O
understand	O
all	O
possible	O
behaviors	O
of	O
a	O
distributed	B-Architecture
system	I-Architecture
,	O
which	O
is	O
essential	O
for	O
protocol	O
verification	O
.	O
</s>
<s>
This	O
was	O
later	O
complemented	O
with	O
model	B-Application
checking	I-Application
.	O
</s>
<s>
Such	O
constraints	O
can	O
be	O
described	O
by	O
the	O
standardized	O
formal	B-Application
specification	I-Application
languages	O
mentioned	O
above	O
,	O
for	O
which	O
powerful	O
tools	O
have	O
been	O
developed	O
.	O
</s>
<s>
It	O
is	O
in	O
the	O
field	O
of	O
protocol	B-General_Concept
engineering	I-General_Concept
that	O
model-based	B-Language
development	I-Language
was	O
used	O
very	O
early	O
.	O
</s>
<s>
These	O
methods	O
and	O
tools	O
have	O
later	O
been	O
used	O
for	O
software	B-General_Concept
engineering	I-General_Concept
as	O
well	O
as	O
hardware	O
design	O
,	O
especially	O
for	O
distributed	O
and	O
real-time	O
systems	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
many	O
methods	O
and	O
tools	O
developed	O
in	O
the	O
more	O
general	O
context	O
of	O
software	B-General_Concept
engineering	I-General_Concept
can	O
also	O
be	O
used	O
of	O
the	O
development	O
of	O
protocols	O
,	O
for	O
instance	O
model	B-Application
checking	I-Application
for	O
protocol	O
verification	O
,	O
and	O
agile	O
methods	O
for	O
entity	O
implementations	O
.	O
</s>
<s>
Protocol	O
derived	O
from	O
service	O
specification	B-Application
:	O
The	O
service	O
specification	B-Application
is	O
given	O
by	O
the	O
user	O
and	O
the	O
method	O
derives	O
a	O
suitable	O
protocol	O
for	O
all	O
entities	O
.	O
</s>
<s>
Protocol	O
for	O
control	O
applications	O
:	O
The	O
specification	B-Application
of	O
one	O
entity	O
(	O
called	O
the	O
plant	O
-	O
which	O
must	O
be	O
controlled	O
)	O
is	O
given	O
,	O
and	O
the	O
method	O
derives	O
a	O
specification	B-Application
of	O
the	O
other	O
entity	O
such	O
that	O
certain	O
fail	O
states	O
of	O
the	O
plant	O
are	O
never	O
reached	O
and	O
certain	O
given	O
properties	O
of	O
the	O
plant	O
's	O
service	O
interactions	O
are	O
satisfied	O
.	O
</s>
<s>
Ming	O
T	O
.	O
Liu	O
,	O
Protocol	B-General_Concept
Engineering	I-General_Concept
,	O
Advances	O
in	O
Computers	O
,	O
Volume	O
29	O
,	O
1989	O
,	O
Pages	O
79-195	O
.	O
</s>
<s>
H	O
.	O
König	O
,	O
Protocol	B-General_Concept
Engineering	I-General_Concept
,	O
Springer	O
,	O
2012	O
.	O
</s>
<s>
M	O
.	O
Popovic	O
,	O
Communication	O
Protocol	B-General_Concept
Engineering	I-General_Concept
,	O
CRC	O
Press	O
,	O
2nd	O
Ed	O
.	O
</s>
<s>
Babu	O
,	O
Communication	O
Protocol	B-General_Concept
Engineering	I-General_Concept
,	O
2014	O
.	O
</s>
