<s>
In	O
computing	O
,	O
a	O
handshake	B-Protocol
is	O
a	O
signal	O
between	O
two	O
devices	O
or	O
programs	O
,	O
used	O
to	O
,	O
e.g.	O
,	O
authenticate	O
,	O
coordinate	O
.	O
</s>
<s>
An	O
example	O
is	O
the	O
handshaking	O
between	O
a	O
hypervisor	B-Operating_System
and	O
an	O
application	O
in	O
a	O
guest	B-General_Concept
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
In	O
telecommunications	O
,	O
a	O
handshake	B-Protocol
is	O
an	O
automated	O
process	O
of	O
negotiation	O
between	O
two	O
participants	O
(	O
example	O
"	O
Alice	O
and	O
Bob	O
"	O
)	O
through	O
the	O
exchange	O
of	O
information	O
that	O
establishes	O
the	O
protocols	O
of	O
a	O
communication	O
link	O
at	O
the	O
start	O
of	O
the	O
communication	O
,	O
before	O
full	O
communication	O
begins	O
.	O
</s>
<s>
For	O
example	O
,	O
when	O
a	O
computer	O
communicates	O
with	O
another	O
device	O
such	O
as	O
a	O
modem	B-Application
,	O
the	O
two	O
devices	O
will	O
signal	O
each	O
other	O
that	O
they	O
are	O
switched	O
on	O
and	O
ready	O
to	O
work	O
,	O
as	O
well	O
as	O
to	O
agree	O
to	O
which	O
protocols	O
are	O
being	O
used	O
.	O
</s>
<s>
Handshaking	O
can	O
negotiate	O
parameters	O
that	O
are	O
acceptable	O
to	O
equipment	O
and	O
systems	O
at	O
both	O
ends	O
of	O
the	O
communication	O
channel	O
,	O
including	O
information	O
transfer	O
rate	O
,	O
coding	O
alphabet	B-Application
,	O
parity	B-Error_Name
,	O
interrupt	B-Application
procedure	O
,	O
and	O
other	O
protocol	O
or	O
hardware	O
features	O
.	O
</s>
<s>
However	O
,	O
within	O
TCP/IP	O
RFCs	O
,	O
the	O
term	O
"	O
handshake	B-Protocol
"	O
is	O
most	O
commonly	O
used	O
to	O
reference	O
the	O
TCP	O
three-way	O
handshake	B-Protocol
.	O
</s>
<s>
For	O
example	O
,	O
the	O
term	O
"	O
handshake	B-Protocol
"	O
is	O
not	O
present	O
in	O
RFCs	O
covering	O
FTP	O
or	O
SMTP	B-Protocol
.	O
</s>
<s>
One	O
exception	O
is	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
,	O
TLS	O
,	O
setup	O
,	O
FTP	O
RFC	O
4217	O
.	O
</s>
<s>
In	O
place	O
of	O
the	O
term	O
"	O
handshake	B-Protocol
"	O
,	O
FTP	O
RFC	O
3659	O
substitutes	O
the	O
term	O
"	O
conversation	O
"	O
for	O
the	O
passing	O
of	O
commands	O
.	O
</s>
<s>
The	O
Simple	B-Protocol
Mail	I-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
(	O
SMTP	B-Protocol
)	O
is	O
the	O
key	O
Internet	O
standard	O
for	O
email	O
transmission	O
.	O
</s>
<s>
When	O
a	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
SSL	O
or	O
TLS	O
)	O
connection	O
starts	O
,	O
the	O
record	O
encapsulates	O
a	O
"	O
control	O
"	O
protocol	O
—	O
the	O
handshake	B-Protocol
messaging	O
protocol	O
(	O
content	O
type	O
22	O
)	O
.	O
</s>
<s>
The	O
WPA2	O
standard	O
for	O
wireless	O
uses	O
a	O
four-way	O
handshake	B-Protocol
defined	O
in	O
IEEE	B-Protocol
802.11i-2004	I-Protocol
.	O
</s>
<s>
One	O
classic	O
example	O
of	O
handshaking	O
is	O
that	O
of	O
dial-up	B-Application
modems	I-Application
,	O
which	O
typically	O
negotiate	O
communication	O
parameters	O
for	O
a	O
brief	O
period	O
when	O
a	O
connection	O
is	O
first	O
established	O
,	O
and	O
there	O
after	O
use	O
those	O
parameters	O
to	O
provide	O
optimal	O
information	O
transfer	O
over	O
the	O
channel	O
as	O
a	O
function	O
of	O
its	O
quality	O
and	O
capacity	O
.	O
</s>
<s>
The	O
"	O
squealing	O
"	O
(	O
which	O
is	O
actually	O
a	O
sound	O
that	O
changes	O
in	O
pitch	O
100	O
times	O
every	O
second	O
)	O
noises	O
made	O
by	O
some	O
modems	B-Application
with	O
speaker	O
output	O
immediately	O
after	O
a	O
connection	O
is	O
established	O
are	O
in	O
fact	O
the	O
sounds	O
of	O
modems	B-Application
at	O
both	O
ends	O
engaging	O
in	O
a	O
handshaking	O
procedure	O
;	O
once	O
the	O
procedure	O
is	O
completed	O
,	O
the	O
speaker	O
might	O
be	O
silenced	O
,	O
depending	O
on	O
the	O
settings	O
of	O
operating	O
system	O
or	O
the	O
application	O
controlling	O
the	O
modem	B-Application
.	O
</s>
<s>
It	O
is	O
therefore	O
very	O
important	O
for	O
the	O
device	O
and	O
charger	O
to	O
first	O
perform	O
a	O
handshake	B-Protocol
to	O
"	O
agree	O
"	O
on	O
mutually	O
supported	O
charge	O
parameters	O
.	O
</s>
