<s>
The	O
Precision	B-Protocol
Time	I-Protocol
Protocol	I-Protocol
(	O
PTP	O
)	O
is	O
a	O
protocol	O
used	O
to	O
synchronize	O
clocks	O
throughout	O
a	O
computer	B-Architecture
network	I-Architecture
.	O
</s>
<s>
On	O
a	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
,	O
it	O
achieves	O
clock	O
accuracy	O
in	O
the	O
sub-microsecond	O
range	O
,	O
making	O
it	O
suitable	O
for	O
measurement	O
and	O
control	O
systems	O
.	O
</s>
<s>
The	O
first	O
version	O
of	O
PTP	O
,	O
IEEE	B-Protocol
1588-2002	I-Protocol
,	O
was	O
published	O
in	O
2002	O
.	O
</s>
<s>
IEEE	B-Protocol
1588-2008	I-Protocol
,	O
also	O
known	O
as	O
PTP	O
Version	O
2	O
is	O
not	O
backward	B-General_Concept
compatible	I-General_Concept
with	O
the	O
2002	O
version	O
.	O
</s>
<s>
IEEE	B-Protocol
1588-2019	I-Protocol
was	O
published	O
in	O
November	O
2019	O
and	O
includes	O
backward-compatible	B-General_Concept
improvements	O
to	O
the	O
2008	O
publication	O
.	O
</s>
<s>
IEEE	B-Protocol
1588-2008	I-Protocol
includes	O
a	O
profile	O
concept	O
defining	O
PTP	O
operating	O
parameters	O
and	O
options	O
.	O
</s>
<s>
is	O
an	O
adaptation	O
of	O
PTP	O
for	O
use	O
with	O
Audio	B-Protocol
Video	I-Protocol
Bridging	I-Protocol
and	O
Time-Sensitive	B-Protocol
Networking	I-Protocol
.	O
</s>
<s>
According	O
to	O
John	O
Eidson	O
,	O
who	O
led	O
the	O
IEEE	B-Protocol
1588-2002	I-Protocol
standardization	O
effort	O
,	O
"	O
IEEE	B-Protocol
1588	I-Protocol
is	O
designed	O
to	O
fill	O
a	O
niche	O
not	O
well	O
served	O
by	O
either	O
of	O
the	O
two	O
dominant	O
protocols	O
,	O
NTP	B-Protocol
and	O
GPS	O
.	O
</s>
<s>
IEEE	B-Protocol
1588	I-Protocol
is	O
designed	O
for	O
local	O
systems	O
requiring	O
accuracies	O
beyond	O
those	O
attainable	O
using	O
NTP	B-Protocol
.	O
</s>
<s>
PTP	O
was	O
originally	O
defined	O
in	O
the	O
IEEE	B-Protocol
1588-2002	I-Protocol
standard	O
,	O
officially	O
entitled	O
"	O
Standard	O
for	O
a	O
Precision	O
Clock	O
Synchronization	O
Protocol	O
for	O
Networked	O
Measurement	O
and	O
Control	O
Systems	O
"	O
and	O
published	O
in	O
2002	O
.	O
</s>
<s>
In	O
2008	O
,	O
IEEE	B-Protocol
1588-2008	I-Protocol
was	O
released	O
as	O
a	O
revised	O
standard	O
;	O
also	O
known	O
as	O
PTP	O
version	O
2	O
(	O
PTPv2	O
)	O
,	O
it	O
improves	O
accuracy	O
,	O
precision	O
and	O
robustness	O
but	O
is	O
not	O
backward	B-General_Concept
compatible	I-General_Concept
with	O
the	O
original	O
2002	O
version	O
.	O
</s>
<s>
IEEE	B-Protocol
1588-2019	I-Protocol
was	O
published	O
in	O
November	O
2019	O
,	O
is	O
informally	O
known	O
as	O
PTPv2.1	O
and	O
includes	O
backwards-compatible	B-General_Concept
improvements	O
to	O
the	O
2008	O
publication	O
.	O
</s>
<s>
The	O
IEEE	B-Protocol
1588	I-Protocol
standards	O
describe	O
a	O
hierarchical	O
master	B-Operating_System
–	I-Operating_System
slave	I-Operating_System
architecture	I-Operating_System
for	O
clock	O
distribution	O
.	O
</s>
<s>
Under	O
this	O
architecture	O
,	O
a	O
time	O
distribution	O
system	O
consists	O
of	O
one	O
or	O
more	O
communication	O
media	O
(	O
network	B-Protocol
segments	I-Protocol
)	O
,	O
and	O
one	O
or	O
more	O
clocks	O
.	O
</s>
<s>
A	O
boundary	O
clock	O
has	O
multiple	O
network	O
connections	O
and	O
can	O
accurately	O
synchronize	O
one	O
network	B-Protocol
segment	I-Protocol
to	O
another	O
.	O
</s>
<s>
A	O
synchronization	O
master	O
is	O
selected	O
for	O
each	O
of	O
the	O
network	B-Protocol
segments	I-Protocol
in	O
the	O
system	O
.	O
</s>
<s>
The	O
grandmaster	O
transmits	O
synchronization	O
information	O
to	O
the	O
clocks	O
residing	O
on	O
its	O
network	B-Protocol
segment	I-Protocol
.	O
</s>
<s>
IEEE	B-Protocol
1588-2008	I-Protocol
introduces	O
a	O
clock	O
associated	O
with	O
network	O
equipment	O
used	O
to	O
convey	O
PTP	O
messages	O
.	O
</s>
<s>
This	O
scheme	O
improves	O
distribution	O
accuracy	O
by	O
compensating	O
for	O
delivery	B-Architecture
variability	I-Architecture
across	O
the	O
network	O
.	O
</s>
<s>
PTP	O
typically	O
uses	O
the	O
same	O
epoch	O
as	O
Unix	B-Operating_System
time	I-Operating_System
(	O
start	O
of	O
1	B-Operating_System
January	I-Operating_System
1970	I-Operating_System
)	O
.	O
</s>
<s>
While	O
the	O
Unix	B-Operating_System
time	I-Operating_System
is	O
based	O
on	O
Coordinated	O
Universal	O
Time	O
(	O
UTC	O
)	O
and	O
is	O
subject	O
to	O
leap	O
seconds	O
,	O
PTP	O
is	O
based	O
on	O
International	O
Atomic	O
Time	O
(	O
TAI	O
)	O
.	O
</s>
<s>
Transparent	O
clocks	O
and	O
these	O
messages	O
associated	O
with	O
them	O
are	O
not	O
available	O
in	O
original	O
IEEE	B-Protocol
1588-2002	I-Protocol
PTPv1	O
standard	O
,	O
and	O
were	O
added	O
in	O
PTPv2	O
.	O
</s>
<s>
Announce	O
messages	O
are	O
used	O
by	O
the	O
best	O
master	O
clock	O
algorithm	O
in	O
IEEE	B-Protocol
1588-2008	I-Protocol
to	O
build	O
a	O
clock	O
hierarchy	O
and	O
select	O
the	O
grandmaster	O
.	O
</s>
<s>
Signaling	O
messages	O
were	O
introduced	O
in	O
IEEE	B-Protocol
1588-2008	I-Protocol
.	O
</s>
<s>
General	O
messages	O
are	O
more	O
conventional	O
protocol	B-Protocol
data	I-Protocol
units	I-Protocol
in	O
that	O
the	O
data	O
in	O
these	O
messages	O
is	O
of	O
importance	O
to	O
PTP	O
,	O
but	O
their	O
transmission	O
and	O
receipt	O
timestamps	O
are	O
not	O
.	O
</s>
<s>
PTP	O
messages	O
may	O
use	O
the	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
over	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
UDP/IP	B-Protocol
)	O
for	O
transport	O
.	O
</s>
<s>
IEEE	B-Protocol
1588-2002	I-Protocol
uses	O
only	O
IPv4	B-Protocol
transports	O
,	O
but	O
this	O
has	O
been	O
extended	O
to	O
include	O
IPv6	B-Protocol
in	O
IEEE	B-Protocol
1588-2008	I-Protocol
.	O
</s>
<s>
In	O
IEEE	B-Protocol
1588-2002	I-Protocol
,	O
all	O
PTP	O
messages	O
are	O
sent	O
using	O
multicast	O
messaging	O
,	O
while	O
IEEE	B-Protocol
1588-2008	I-Protocol
introduced	O
an	O
option	O
for	O
devices	O
to	O
negotiate	O
unicast	B-Protocol
transmission	O
on	O
a	O
port-by-port	O
basis	O
.	O
</s>
<s>
Multicast	O
transmissions	O
use	O
IP	B-Protocol
multicast	I-Protocol
addressing	O
,	O
for	O
which	O
multicast	O
group	O
addresses	O
are	O
defined	O
for	O
IPv4	B-Protocol
and	O
IPv6	B-Protocol
(	O
see	O
table	O
)	O
.	O
</s>
<s>
Time-critical	O
event	O
messages	O
(	O
Sync	O
,	O
Delay_req	O
,	O
Pdelay_Req	O
and	O
Pdelay_Resp	O
)	O
are	O
sent	O
to	O
port	B-Protocol
number	I-Protocol
319	O
.	O
</s>
<s>
General	O
messages	O
(	O
Announce	O
,	O
Follow_Up	O
,	O
Delay_Resp	O
,	O
Pdelay_Resp_Follow_Up	O
,	O
management	O
and	O
signaling	O
)	O
use	O
port	B-Protocol
number	I-Protocol
320	O
.	O
</s>
<s>
In	O
IEEE	B-Protocol
1588-2008	I-Protocol
,	O
encapsulation	O
is	O
also	O
defined	O
for	O
DeviceNet	O
,	O
ControlNet	O
and	O
PROFINET	B-Protocol
.	O
</s>
<s>
Clocks	O
are	O
assigned	O
to	O
a	O
domain	O
by	O
virtue	O
of	O
the	O
contents	O
of	O
the	O
Subdomain	O
name	O
(	O
IEEE	B-Protocol
1588-2002	I-Protocol
)	O
or	O
the	O
domainNumber	O
(	O
IEEE	B-Protocol
1588-2008	I-Protocol
)	O
fields	O
in	O
PTP	O
messages	O
they	O
receive	O
or	O
generate	O
.	O
</s>
<s>
QualityBoth	O
versions	O
of	O
IEEE	B-Protocol
1588	I-Protocol
attempt	O
to	O
quantify	O
clock	O
quality	O
based	O
on	O
expected	O
timing	O
deviation	O
,	O
technology	O
used	O
to	O
implement	O
the	O
clock	O
or	O
location	O
in	O
a	O
clock	O
stratum	O
schema	O
,	O
although	O
only	O
V1	O
(	O
IEEE	B-Protocol
1588-2002	I-Protocol
)	O
knows	O
a	O
data	O
field	O
stratum	O
.	O
</s>
<s>
PTP	O
V2	O
(	O
IEEE	B-Protocol
1588-2008	I-Protocol
)	O
defines	O
the	O
overall	O
quality	O
of	O
a	O
clock	O
by	O
using	O
the	O
data	O
fields	O
clockAccuracy	O
and	O
clockClass	O
.	O
</s>
<s>
IEEE	B-Protocol
1588-2002	I-Protocol
used	O
a	O
single	O
boolean	O
variable	O
to	O
indicate	O
precedence	O
.	O
</s>
<s>
IEEE	B-Protocol
1588-2008	I-Protocol
features	O
two	O
8-bit	O
priority	O
fields	O
.	O
</s>
<s>
IEEE	B-Protocol
1588-2008	I-Protocol
uses	O
a	O
hierarchical	O
selection	O
algorithm	O
based	O
on	O
the	O
following	O
properties	O
,	O
in	O
the	O
indicated	O
order	O
:	O
</s>
<s>
IEEE	B-Protocol
1588-2002	I-Protocol
uses	O
a	O
selection	O
algorithm	O
based	O
on	O
similar	O
properties	O
.	O
</s>
<s>
Clock	O
properties	O
are	O
advertised	O
in	O
IEEE	B-Protocol
1588-2002	I-Protocol
Sync	O
messages	O
and	O
in	O
IEEE	B-Protocol
1588-2008	I-Protocol
Announce	O
messages	O
.	O
</s>
<s>
Once	O
the	O
current	O
master	O
recognises	O
the	O
better	O
clock	O
,	O
the	O
current	O
master	O
stops	O
transmitting	O
Sync	O
messages	O
and	O
associated	O
clock	O
properties	O
(	O
Announce	O
messages	O
in	O
the	O
case	O
of	O
IEEE	B-Protocol
1588-2008	I-Protocol
)	O
and	O
the	O
better	O
clock	O
takes	O
over	O
as	O
master	O
.	O
</s>
<s>
Through	O
use	O
of	O
the	O
BMC	O
algorithm	O
,	O
PTP	O
selects	O
a	O
master	O
source	O
of	O
time	O
for	O
an	O
IEEE	B-Protocol
1588	I-Protocol
domain	O
and	O
for	O
each	O
network	B-Protocol
segment	I-Protocol
in	O
the	O
domain	O
.	O
</s>
<s>
Under	O
IEEE	B-Protocol
1588-2002	I-Protocol
broadcasts	O
are	O
up	O
to	O
once	O
per	O
second	O
.	O
</s>
<s>
Under	O
IEEE	B-Protocol
1588-2008	I-Protocol
,	O
up	O
to	O
10	O
per	O
second	O
are	O
permitted	O
.	O
</s>
<s>
IEEE	B-Protocol
1588-2008	I-Protocol
standard	O
lists	O
the	O
following	O
set	O
of	O
features	O
that	O
implementations	O
may	O
choose	O
to	O
support	O
:	O
</s>
<s>
IEEE	B-Protocol
1588-2019	I-Protocol
adds	O
additional	O
optional	O
and	O
backward-compatible	B-General_Concept
features	O
:	O
</s>
<s>
IEEE	O
802.1AS-2011	O
is	O
part	O
of	O
the	O
IEEE	O
Audio	B-Protocol
Video	I-Protocol
Bridging	I-Protocol
(	O
AVB	O
)	O
group	O
of	O
standards	O
,	O
further	O
extended	O
by	O
the	O
IEEE	O
802.1	O
Time-Sensitive	B-Protocol
Networking	I-Protocol
(	O
TSN	O
)	O
Task	O
Group	O
.	O
</s>
<s>
It	O
specifies	O
a	O
profile	O
for	O
use	O
of	O
IEEE	B-Protocol
1588-2008	I-Protocol
for	O
time	O
synchronization	O
over	O
a	O
virtual	O
bridged	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
(	O
as	O
defined	O
by	O
IEEE	O
802.1Q	O
)	O
.	O
</s>
<s>
Dante	B-Protocol
uses	O
PTPv1	O
for	O
synchronization	O
.	O
</s>
<s>
Q-LAN	B-Protocol
and	O
RAVENNA	B-Protocol
uses	O
PTPv2	O
for	O
time	O
synchronization	O
.	O
</s>
