<s>
The	O
Media	B-Device
Delivery	I-Device
Index	I-Device
(	O
MDI	O
)	O
is	O
a	O
set	O
of	O
measures	O
that	O
can	O
be	O
used	O
to	O
monitor	O
both	O
the	O
quality	O
of	O
a	O
delivered	O
video	O
stream	O
as	O
well	O
as	O
to	O
show	O
system	O
margin	O
for	O
IPTV	O
systems	O
by	O
providing	O
an	O
accurate	O
measurement	O
of	O
jitter	O
and	O
delay	B-Protocol
at	O
network	O
level	O
(	O
Internet	B-Protocol
Protocol	I-Protocol
,	I-Protocol
IP	I-Protocol
)	O
,	O
which	O
are	O
the	O
main	O
causes	O
for	O
quality	O
loss	O
.	O
</s>
<s>
The	O
Media	B-Device
Delivery	I-Device
Index	I-Device
is	O
typically	O
displayed	O
as	O
two	O
numbers	O
separated	O
by	O
a	O
colon	O
:	O
the	O
Delay	B-Protocol
Factor	O
(	O
DF	O
)	O
and	O
the	O
Media	O
Loss	O
Rate	O
(	O
MLR	O
)	O
.	O
</s>
<s>
The	O
Media	B-Device
Delivery	I-Device
Index	I-Device
(	O
MDI	O
)	O
may	O
be	O
able	O
to	O
identify	O
problems	O
caused	O
by	O
:	O
</s>
<s>
If	O
packets	B-Protocol
are	O
delayed	O
by	O
the	O
network	O
,	O
some	O
packets	B-Protocol
arrive	O
in	O
bursts	O
with	O
interpacket	O
delays	O
shorter	O
than	O
when	O
they	O
were	O
transmitted	O
,	O
while	O
others	O
are	O
delayed	O
such	O
that	O
they	O
arrive	O
with	O
greater	O
delay	B-Protocol
between	O
packets	B-Protocol
than	O
when	O
they	O
were	O
transmitted	O
from	O
the	O
source	O
(	O
see	O
figure	O
below	O
)	O
.	O
</s>
<s>
This	O
time	O
difference	O
between	O
when	O
a	O
packet	B-Protocol
actually	O
arrives	O
and	O
the	O
expected	O
arrival	O
time	O
is	O
defined	O
as	O
packet	B-Protocol
jitter	O
or	O
time	O
distortion	O
.	O
</s>
<s>
A	O
receiver	B-Application
displaying	B-Device
the	O
video	O
at	O
its	O
nominal	O
rate	O
must	O
accommodate	O
the	O
varying	O
input	O
stream	O
arrival	O
times	O
by	O
buffering	O
the	O
data	O
arriving	O
early	O
and	O
assuring	O
that	O
there	O
is	O
enough	O
already	O
stored	O
data	O
to	O
face	O
the	O
possible	O
delays	O
in	O
the	O
received	O
data	O
(	O
because	O
of	O
this	O
the	O
buffer	O
is	O
filled	O
before	O
displaying	B-Device
)	O
.	O
</s>
<s>
Similarly	O
,	O
the	O
network	O
infrastructure	O
(	O
switches	O
,	O
routers	B-Protocol
,…	O
)	O
uses	O
buffers	O
at	O
each	O
node	O
to	O
avoid	O
packet	B-Protocol
loss	O
.	O
</s>
<s>
These	O
buffers	O
must	O
be	O
sized	O
appropriately	O
to	O
handle	O
network	B-Protocol
congestion	I-Protocol
.	O
</s>
<s>
Packet	B-Protocol
delays	O
can	O
be	O
caused	O
by	O
multiple	O
facts	O
,	O
among	O
which	O
there	O
are	O
the	O
way	O
traffic	B-Protocol
is	O
routed	O
through	O
the	O
infrastructure	O
and	O
possible	O
differences	O
between	O
link	O
speeds	O
in	O
the	O
infrastructure	O
.	O
</s>
<s>
Moreover	O
,	O
some	O
methods	O
for	O
delivering	O
Quality	O
of	O
Service	O
(	O
QOS	O
)	O
using	O
packet	B-Protocol
metering	O
algorithms	O
may	O
intentionally	O
hold	O
back	O
packets	B-Protocol
to	O
meet	O
the	O
quality	O
specifications	B-Application
in	O
the	O
transmission	O
.	O
</s>
<s>
The	O
effects	O
of	O
all	O
these	O
facts	O
on	O
the	O
amount	O
of	O
packets	B-Protocol
received	O
by	O
a	O
specific	O
point	O
in	O
the	O
network	O
can	O
be	O
seen	O
in	O
the	O
next	O
graphics	O
:	O
</s>
<s>
Packets	B-Protocol
may	O
be	O
lost	O
due	O
to	O
buffer	B-General_Concept
overflows	I-General_Concept
or	O
environmental	O
electrical	O
noise	O
that	O
creates	O
corrupted	O
packets	B-Protocol
.	O
</s>
<s>
Even	O
small	O
packet	B-Protocol
loss	O
rates	O
result	O
in	O
a	O
poor	O
video	O
display	O
.	O
</s>
<s>
Packet	B-Protocol
delay	B-Protocol
variation	O
and	O
packet	B-Protocol
loss	O
have	O
been	O
shown	O
to	O
be	O
the	O
key	O
characteristics	O
in	O
determining	O
whether	O
a	O
network	O
can	O
transport	O
good	O
quality	O
video	O
.	O
</s>
<s>
These	O
features	O
are	O
represented	O
as	O
the	O
Delay	B-Protocol
Factor	O
(	O
DF	O
)	O
and	O
the	O
Media	O
Loss	O
Rate	O
(	O
MLR	O
)	O
,	O
and	O
they	O
are	O
combined	O
to	O
produce	O
the	O
Media	B-Device
Delivery	I-Device
Index	I-Device
(	O
MDI	O
)	O
,	O
which	O
is	O
displayed	O
as	O
:	O
</s>
<s>
The	O
different	O
components	O
of	O
the	O
Media	B-Device
Delivery	I-Device
Index	I-Device
(	O
MDI	O
)	O
are	O
explained	O
in	O
this	O
section	O
.	O
</s>
<s>
The	O
Delay	B-Protocol
Factor	O
is	O
a	O
temporal	O
value	O
given	O
in	O
milliseconds	O
that	O
indicates	O
how	O
much	O
time	O
is	O
required	O
to	O
drain	O
the	O
virtual	O
buffer	O
at	O
the	O
concrete	O
network	B-Protocol
node	I-Protocol
and	O
at	O
a	O
specific	O
time	O
.	O
</s>
<s>
It	O
is	O
computed	O
as	O
packets	B-Protocol
arrive	O
at	O
the	O
node	O
and	O
is	O
displayed/recorded	O
at	O
regular	O
intervals	O
(	O
typically	O
one	O
second	O
)	O
.	O
</s>
<s>
At	O
every	O
packet	B-Protocol
arrival	O
,	O
the	O
difference	O
between	O
the	O
bytes	O
received	O
and	O
the	O
bytes	O
drained	O
is	O
calculated	O
.	O
</s>
<s>
The	O
Media	O
Loss	O
Rate	O
is	O
the	O
number	O
of	O
media	O
packets	B-Protocol
lost	O
over	O
a	O
certain	O
time	O
interval	O
(	O
typically	O
one	O
second	O
)	O
.	O
</s>
<s>
It	O
is	O
computed	O
by	O
subtracting	O
the	O
number	O
of	O
media	O
packets	B-Protocol
received	O
during	O
an	O
interval	O
from	O
the	O
number	O
of	O
media	O
packets	B-Protocol
expected	O
during	O
that	O
interval	O
and	O
scaling	O
the	O
value	O
to	O
the	O
chosen	O
time	O
period	O
(	O
typically	O
one	O
second	O
)	O
:	O
</s>
<s>
For	O
channel	O
zapping	O
,	O
a	O
channel	O
is	O
generally	O
viewed	O
for	O
a	O
brief	O
period	O
,	O
so	O
one	O
would	O
be	O
bothered	O
if	O
any	O
packet	B-Protocol
loss	O
occurred	O
.	O
</s>
<s>
For	O
this	O
case	O
the	O
maximum	O
acceptable	O
MLR	O
is	O
0	O
,	O
as	O
stated	O
before	O
,	O
because	O
any	O
greater	O
a	O
value	O
would	O
mean	O
a	O
loss	O
of	O
one	O
or	O
more	O
packets	B-Protocol
in	O
a	O
small	O
viewing	O
timeframe	O
(	O
after	O
the	O
zap	B-Device
time	I-Device
)	O
.	O
</s>
<s>
Generally	O
,	O
the	O
Media	B-Device
Delivery	I-Device
Index	I-Device
(	O
MDI	O
)	O
can	O
be	O
used	O
to	O
install	O
,	O
modify	O
or	O
evaluate	O
a	O
video	O
network	O
following	O
the	O
next	O
steps	O
:	O
</s>
<s>
Identify	O
,	O
locate	O
,	O
and	O
address	O
any	O
packet	B-Protocol
loss	O
issues	O
using	O
the	O
Media	O
Loss	O
Rate	O
.	O
</s>
<s>
Identify	O
and	O
measure	O
jitter	O
margins	O
using	O
the	O
Delay	B-Protocol
Factor	O
.	O
</s>
<s>
Some	O
of	O
them	O
are	O
:	O
redefining	O
system	O
specifications	B-Application
,	O
modifying	O
the	O
network	O
components	O
in	O
order	O
to	O
meet	O
the	O
expected	O
quality	O
requirements	O
(	O
or	O
number	O
of	O
users	O
)	O
,	O
etc	O
.	O
</s>
<s>
High	O
utilization	O
level	O
is	O
also	O
an	O
indicator	O
that	O
localized	O
congestion	B-Protocol
is	O
likely	O
due	O
to	O
queue	O
behavior	O
in	O
network	O
components	O
.	O
</s>
<s>
The	O
DF	O
provides	O
a	O
measure	O
of	O
the	O
results	O
of	O
congestion	B-Protocol
on	O
a	O
given	O
stream	O
.	O
</s>
