<s>
The	O
Real-time	B-Protocol
Transport	I-Protocol
Protocol	I-Protocol
(	O
RTP	O
)	O
is	O
a	O
network	O
protocol	O
for	O
delivering	O
audio	O
and	O
video	O
over	O
IP	B-Protocol
networks	I-Protocol
.	O
</s>
<s>
RTP	O
is	O
used	O
in	O
communication	O
and	O
entertainment	O
systems	O
that	O
involve	O
streaming	O
media	O
,	O
such	O
as	O
telephony	O
,	O
video	B-Application
teleconference	I-Application
applications	O
including	O
WebRTC	B-Protocol
,	O
television	O
services	O
and	O
web-based	O
push-to-talk	O
features	O
.	O
</s>
<s>
RTP	O
typically	O
runs	O
over	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	O
)	O
.	O
</s>
<s>
RTP	O
is	O
used	O
in	O
conjunction	O
with	O
the	O
RTP	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
RTCP	B-Protocol
)	O
.	O
</s>
<s>
While	O
RTP	O
carries	O
the	O
media	O
streams	O
(	O
e.g.	O
,	O
audio	O
and	O
video	O
)	O
,	O
RTCP	B-Protocol
is	O
used	O
to	O
monitor	O
transmission	O
statistics	O
and	O
quality	O
of	O
service	O
(	O
QoS	O
)	O
and	O
aids	O
synchronization	O
of	O
multiple	O
streams	O
.	O
</s>
<s>
RTP	O
is	O
one	O
of	O
the	O
technical	O
foundations	O
of	O
Voice	B-Application
over	I-Application
IP	I-Application
and	O
in	O
this	O
context	O
is	O
often	O
used	O
in	O
conjunction	O
with	O
a	O
signaling	O
protocol	O
such	O
as	O
the	O
Session	B-Application
Initiation	I-Application
Protocol	I-Application
(	O
SIP	O
)	O
which	O
establishes	O
connections	O
across	O
the	O
network	O
.	O
</s>
<s>
The	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
began	O
developing	O
RTP	O
starting	O
in	O
1992	O
,	O
along	O
with	O
the	O
Session	B-Protocol
Announcement	I-Protocol
Protocol	I-Protocol
(	O
SAP	O
)	O
,	O
the	O
Session	B-Language
Description	I-Language
Protocol	I-Language
(	O
SDP	O
)	O
,	O
and	O
the	O
Session	B-Application
Initiation	I-Application
Protocol	I-Application
(	O
SIP	O
)	O
.	O
</s>
<s>
RTP	O
is	O
designed	O
for	O
end-to-end	B-Application
,	O
real-time	B-General_Concept
transfer	O
of	O
streaming	O
media	O
.	O
</s>
<s>
The	O
protocol	O
provides	O
facilities	O
for	O
jitter	O
compensation	O
and	O
detection	O
of	O
packet	B-Protocol
loss	I-Protocol
and	O
out-of-order	B-Protocol
delivery	I-Protocol
,	O
which	O
are	O
common	O
especially	O
during	O
UDP	O
transmissions	O
on	O
an	O
IP	B-Protocol
network	I-Protocol
.	O
</s>
<s>
RTP	O
allows	O
data	O
transfer	O
to	O
multiple	O
destinations	O
through	O
IP	B-Protocol
multicast	I-Protocol
.	O
</s>
<s>
RTP	O
is	O
regarded	O
as	O
the	O
primary	O
standard	O
for	O
audio/video	O
transport	O
in	O
IP	B-Protocol
networks	I-Protocol
and	O
is	O
used	O
with	O
an	O
associated	O
profile	O
and	O
payload	O
format	O
.	O
</s>
<s>
The	O
design	O
of	O
RTP	O
is	O
based	O
on	O
the	O
architectural	O
principle	O
known	O
as	O
application-layer	B-Protocol
framing	I-Protocol
where	O
protocol	O
functions	O
are	O
implemented	O
in	O
the	O
application	O
as	O
opposed	O
to	O
the	O
operating	O
system	O
's	O
protocol	B-Protocol
stack	I-Protocol
.	O
</s>
<s>
Real-time	B-General_Concept
multimedia	O
streaming	O
applications	O
require	O
timely	O
delivery	O
of	O
information	O
and	O
often	O
can	O
tolerate	O
some	O
packet	B-Protocol
loss	I-Protocol
to	O
achieve	O
this	O
goal	O
.	O
</s>
<s>
For	O
example	O
,	O
loss	O
of	O
a	O
packet	O
in	O
audio	O
application	O
may	O
result	O
in	O
loss	O
of	O
a	O
fraction	O
of	O
a	O
second	O
of	O
audio	O
data	O
,	O
which	O
can	O
be	O
made	O
unnoticeable	O
with	O
suitable	O
error	B-Error_Name
concealment	I-Error_Name
algorithms	O
.	O
</s>
<s>
The	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
TCP	O
)	O
,	O
although	O
standardized	O
for	O
RTP	O
use	O
,	O
is	O
not	O
normally	O
used	O
in	O
RTP	O
applications	O
because	O
TCP	O
favors	O
reliability	O
over	O
timeliness	O
.	O
</s>
<s>
Instead	O
the	O
majority	O
of	O
the	O
RTP	O
implementations	O
are	O
built	O
on	O
the	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	O
)	O
.	O
</s>
<s>
Other	O
transport	O
protocols	O
specifically	O
designed	O
for	O
multimedia	O
sessions	O
are	O
SCTP	B-Protocol
and	O
DCCP	B-Protocol
,	O
although	O
,	O
,	O
they	O
were	O
not	O
in	O
widespread	O
use	O
.	O
</s>
<s>
RTP	O
is	O
used	O
in	O
conjunction	O
with	O
other	O
protocols	O
such	O
as	O
H.323	B-Protocol
and	O
RTSP	B-Protocol
.	O
</s>
<s>
The	O
RTP	O
specification	O
describes	O
two	O
protocols	O
:	O
RTP	O
and	O
RTCP	B-Protocol
.	O
</s>
<s>
RTP	O
is	O
used	O
for	O
the	O
transfer	O
of	O
multimedia	O
data	O
,	O
and	O
the	O
RTCP	B-Protocol
is	O
used	O
to	O
periodically	O
send	O
control	O
information	O
and	O
QoS	O
parameters	O
.	O
</s>
<s>
The	O
data	O
transfer	O
protocol	O
,	O
RTP	O
,	O
carries	O
real-time	B-General_Concept
data	O
.	O
</s>
<s>
Information	O
provided	O
by	O
this	O
protocol	O
includes	O
timestamps	O
(	O
for	O
synchronization	O
)	O
,	O
sequence	B-Protocol
numbers	I-Protocol
(	O
for	O
packet	B-Protocol
loss	I-Protocol
and	O
reordering	O
detection	O
)	O
and	O
the	O
payload	O
format	O
which	O
indicates	O
the	O
encoded	O
format	O
of	O
the	O
data	O
.	O
</s>
<s>
The	O
control	O
protocol	O
,	O
RTCP	B-Protocol
,	O
is	O
used	O
for	O
quality	O
of	O
service	O
(	O
QoS	O
)	O
feedback	O
and	O
synchronization	O
between	O
the	O
media	O
streams	O
.	O
</s>
<s>
The	O
bandwidth	O
of	O
RTCP	B-Protocol
traffic	O
compared	O
to	O
RTP	O
is	O
small	O
,	O
typically	O
around	O
5%	O
.	O
</s>
<s>
RTP	O
sessions	O
are	O
typically	O
initiated	O
between	O
communicating	O
peers	O
using	O
a	O
signaling	O
protocol	O
,	O
such	O
as	O
H.323	B-Protocol
,	O
the	O
Session	B-Application
Initiation	I-Application
Protocol	I-Application
(	O
SIP	O
)	O
,	O
RTSP	B-Protocol
,	O
or	O
Jingle	B-Protocol
(	O
XMPP	B-Protocol
)	O
.	O
</s>
<s>
These	O
protocols	O
may	O
use	O
the	O
Session	B-Language
Description	I-Language
Protocol	I-Language
to	O
specify	O
the	O
parameters	O
for	O
the	O
sessions	O
.	O
</s>
<s>
The	O
RTP	O
and	O
RTCP	B-Protocol
design	O
is	O
independent	O
of	O
the	O
transport	O
protocol	O
.	O
</s>
<s>
The	O
Stream	B-Protocol
Control	I-Protocol
Transmission	I-Protocol
Protocol	I-Protocol
(	O
SCTP	B-Protocol
)	O
and	O
the	O
Datagram	B-Protocol
Congestion	I-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
DCCP	B-Protocol
)	O
may	O
be	O
used	O
when	O
a	O
reliable	O
transport	O
protocol	O
is	O
desired	O
.	O
</s>
<s>
The	O
RTP	O
specification	O
recommends	O
even	O
port	O
numbers	O
for	O
RTP	O
,	O
and	O
the	O
use	O
of	O
the	O
next	O
odd	O
port	O
number	O
for	O
the	O
associated	O
RTCP	B-Protocol
session	O
.	O
</s>
<s>
A	O
single	O
port	O
can	O
be	O
used	O
for	O
RTP	O
and	O
RTCP	B-Protocol
in	O
applications	O
that	O
multiplex	O
the	O
protocols	O
.	O
</s>
<s>
RTP	O
is	O
used	O
by	O
real-time	B-General_Concept
multimedia	O
applications	O
such	O
as	O
voice	B-Application
over	I-Application
IP	I-Application
,	O
audio	O
over	O
IP	O
,	O
WebRTC	B-Protocol
and	O
Internet	O
Protocol	O
television	O
.	O
</s>
<s>
Examples	O
of	O
audio	O
payload	O
formats	O
are	O
G.711	B-Algorithm
,	O
G.723	B-Algorithm
,	O
G.726	B-Algorithm
,	O
G.729	B-Algorithm
,	O
GSM	O
,	O
QCELP	B-Algorithm
,	O
MP3	B-Application
,	O
and	O
DTMF	O
,	O
and	O
examples	O
of	O
video	O
payloads	O
are	O
H.261	B-Algorithm
,	O
H.263	B-Algorithm
,	O
H.264	B-Application
,	O
H.265	B-Algorithm
and	O
MPEG-1/MPEG	O
-2	O
.	O
</s>
<s>
The	O
mapping	O
of	O
MPEG-4	B-Algorithm
audio/video	O
streams	O
to	O
RTP	O
packets	O
is	O
specified	O
in	O
,	O
and	O
H.263	B-Algorithm
video	O
payloads	O
are	O
described	O
in	O
.	O
</s>
<s>
The	O
RTP	O
profile	O
for	O
Audio	O
and	O
video	B-Application
conferences	I-Application
with	O
minimal	O
control	O
(	O
)	O
defines	O
a	O
set	O
of	O
static	O
payload	O
type	O
assignments	O
,	O
and	O
a	O
dynamic	O
mechanism	O
for	O
mapping	O
between	O
a	O
payload	O
format	O
,	O
and	O
a	O
PT	O
value	O
using	O
Session	B-Language
Description	I-Language
Protocol	I-Language
(	O
SDP	O
)	O
.	O
</s>
<s>
The	O
Secure	B-Protocol
Real-time	I-Protocol
Transport	I-Protocol
Protocol	I-Protocol
(	O
SRTP	O
)	O
(	O
)	O
defines	O
an	O
RTP	O
profile	O
that	O
provides	O
cryptographic	O
services	O
for	O
the	O
transfer	O
of	O
payload	O
data	O
.	O
</s>
<s>
Sequence	B-Protocol
number	I-Protocol
:	O
(	O
16	O
bits	O
)	O
The	O
sequence	B-Protocol
number	I-Protocol
is	O
incremented	O
for	O
each	O
RTP	O
data	O
packet	O
sent	O
and	O
is	O
to	O
be	O
used	O
by	O
the	O
receiver	O
to	O
detect	O
packet	B-Protocol
loss	I-Protocol
and	O
to	O
accommodate	O
out-of-order	B-Protocol
delivery	I-Protocol
.	O
</s>
<s>
The	O
initial	O
value	O
of	O
the	O
sequence	B-Protocol
number	I-Protocol
should	O
be	O
randomized	O
to	O
make	O
known-plaintext	O
attacks	O
on	O
Secure	B-Protocol
Real-time	I-Protocol
Transport	I-Protocol
Protocol	I-Protocol
more	O
difficult	O
.	O
</s>
<s>
Protocols	O
such	O
as	O
SIP	O
,	O
Jingle	B-Protocol
,	O
RTSP	B-Protocol
,	O
H.225	B-Protocol
and	O
H.245	B-Application
are	O
used	O
for	O
session	O
initiation	O
,	O
control	O
and	O
termination	O
.	O
</s>
<s>
Other	O
standards	O
,	O
such	O
as	O
H.264	B-Application
,	O
MPEG	O
and	O
H.263	B-Algorithm
,	O
are	O
used	O
for	O
encoding	O
the	O
payload	O
data	O
as	O
specified	O
by	O
the	O
applicable	O
RTP	O
profile	O
.	O
</s>
<s>
An	O
RTP	O
sender	O
captures	O
the	O
multimedia	O
data	O
,	O
then	O
encodes	O
,	O
frames	O
and	O
transmits	O
it	O
as	O
RTP	O
packets	O
with	O
appropriate	O
timestamps	O
and	O
increasing	O
timestamps	O
and	O
sequence	B-Protocol
numbers	I-Protocol
.	O
</s>
