<s>
End-to-end	B-Protocol
delay	I-Protocol
or	O
one-way	B-Protocol
delay	I-Protocol
(	O
OWD	B-Protocol
)	O
refers	O
to	O
the	O
time	O
taken	O
for	O
a	O
packet	B-Protocol
to	O
be	O
transmitted	O
across	O
a	O
network	B-Architecture
from	O
source	O
to	O
destination	O
.	O
</s>
<s>
It	O
is	O
a	O
common	O
term	O
in	O
IP	B-Protocol
network	I-Protocol
monitoring	O
,	O
and	O
differs	O
from	O
round-trip	O
time	O
(	O
RTT	O
)	O
in	O
that	O
only	O
path	O
in	O
the	O
one	O
direction	O
from	O
source	O
to	O
destination	O
is	O
measured	O
.	O
</s>
<s>
The	O
ping	B-Protocol
utility	I-Protocol
measures	O
the	O
RTT	O
,	O
that	O
is	O
,	O
the	O
time	O
to	O
go	O
and	O
come	O
back	O
to	O
a	O
host	O
.	O
</s>
<s>
Half	O
the	O
RTT	O
is	O
often	O
used	O
as	O
an	O
approximation	O
of	O
OWD	B-Protocol
but	O
this	O
assumes	O
that	O
the	O
forward	O
and	O
back	O
paths	O
are	O
the	O
same	O
in	O
terms	O
of	O
congestion	O
,	O
number	O
of	O
hops	O
,	O
or	O
quality	O
of	O
service	O
(	O
QoS	O
)	O
.	O
</s>
<s>
To	O
avoid	O
such	O
problems	O
,	O
the	O
OWD	B-Protocol
may	O
be	O
measured	O
directly	O
.	O
</s>
<s>
OWDs	B-Protocol
may	O
be	O
measured	O
between	O
two	O
points	O
A	O
and	O
B	O
of	O
an	O
IP	B-Protocol
network	I-Protocol
through	O
the	O
use	O
of	O
synchronized	O
clocks	O
;	O
A	O
records	O
a	O
timestamp	O
on	O
the	O
packet	B-Protocol
and	O
sends	O
it	O
to	O
B	O
,	O
which	O
notes	O
the	O
receiving	O
time	O
and	O
calculates	O
the	O
OWD	B-Protocol
as	O
their	O
difference	O
.	O
</s>
<s>
The	O
transmitted	O
packets	B-Protocol
need	O
to	O
be	O
identified	O
at	O
source	O
and	O
destination	O
in	O
order	O
to	O
avoid	O
packet	B-Protocol
loss	I-Protocol
or	O
packet	B-Protocol
reordering	O
.	O
</s>
<s>
The	O
Minimum-Pairs	O
Protocol	O
is	O
an	O
example	O
by	O
which	O
several	O
cooperating	O
entities	O
,	O
A	O
,	O
B	O
,	O
and	O
C	O
,	O
could	O
measure	O
OWDs	B-Protocol
between	O
one	O
of	O
them	O
and	O
a	O
fourth	O
less	O
cooperative	O
one	O
(	O
e.g.	O
,	O
between	O
B	O
and	O
X	O
)	O
.	O
</s>
<s>
Transmission	O
between	O
two	O
network	B-Architecture
nodes	O
may	O
be	O
asymmetric	O
,	O
and	O
the	O
forward	O
and	O
reverse	O
delays	O
are	O
not	O
equal	O
.	O
</s>
<s>
Half	O
the	O
RTT	O
value	O
is	O
the	O
average	O
of	O
the	O
forward	O
and	O
reverse	O
delays	O
and	O
so	O
may	O
be	O
sometimes	O
used	O
as	O
an	O
approximation	O
to	O
the	O
end-to-end	B-Protocol
delay	I-Protocol
.	O
</s>
<s>
The	O
probability	O
mass	O
function	O
(	O
PMF	O
)	O
of	O
absolute	O
error	O
,	O
E	O
,	O
between	O
the	O
smaller	O
of	O
the	O
forward	O
and	O
reverse	O
OWDs	B-Protocol
and	O
their	O
average	O
(	O
i.e.	O
,	O
RTT/2	O
)	O
can	O
be	O
expressed	O
as	O
a	O
function	O
of	O
the	O
network	B-Protocol
delay	I-Protocol
distribution	O
as	O
follows	O
:	O
</s>
<s>
End-to-end	B-Protocol
delay	I-Protocol
in	O
networks	O
comes	O
from	O
several	O
sources	O
including	O
transmission	B-General_Concept
delay	I-General_Concept
,	O
propagation	O
delay	O
,	O
processing	B-Protocol
delay	I-Protocol
and	O
queuing	B-Protocol
delay	I-Protocol
.	O
</s>
