<s>
The	O
Session	B-Language
Description	I-Language
Protocol	I-Language
(	O
SDP	O
)	O
is	O
a	O
format	O
for	O
describing	O
multimedia	O
communication	B-Protocol
sessions	I-Protocol
for	O
the	O
purposes	O
of	O
announcement	O
and	O
invitation	O
.	O
</s>
<s>
Its	O
predominant	O
use	O
is	O
in	O
support	O
of	O
streaming	O
media	O
applications	O
,	O
such	O
as	O
voice	B-Application
over	I-Application
IP	I-Application
(	O
VoIP	B-Application
)	O
and	O
video	B-Application
conferencing	I-Application
.	O
</s>
<s>
SDP	O
was	O
originally	O
a	O
component	O
of	O
the	O
Session	B-Protocol
Announcement	I-Protocol
Protocol	I-Protocol
(	O
SAP	B-Protocol
)	O
,	O
but	O
found	O
other	O
uses	O
in	O
conjunction	O
with	O
the	O
Real-time	B-Protocol
Transport	I-Protocol
Protocol	I-Protocol
(	O
RTP	O
)	O
,	O
the	O
Real-time	B-Protocol
Streaming	I-Protocol
Protocol	I-Protocol
(	O
RTSP	B-Protocol
)	O
,	O
Session	B-Application
Initiation	I-Application
Protocol	I-Application
(	O
SIP	B-Application
)	O
,	O
and	O
as	O
a	O
standalone	O
protocol	O
for	O
describing	O
multicast	O
sessions	B-Protocol
.	O
</s>
<s>
The	O
Session	B-Language
Description	I-Language
Protocol	I-Language
describes	O
a	O
session	O
as	O
a	O
group	O
of	O
fields	O
in	O
a	O
text-based	O
format	O
,	O
one	O
field	O
per	O
line	O
.	O
</s>
<s>
Its	O
name	O
is	O
"	O
SDP	O
Seminar	O
"	O
and	O
extended	O
session	O
information	O
(	O
"	O
A	O
Seminar	O
on	O
the	O
session	B-Language
description	I-Language
protocol	I-Language
"	O
)	O
is	O
included	O
along	O
with	O
a	O
link	O
for	O
additional	O
information	O
and	O
an	O
email	O
address	O
to	O
contact	O
the	O
responsible	O
party	O
,	O
Jane	O
Doe	O
.	O
</s>
<s>
This	O
session	O
is	O
specified	O
to	O
last	O
for	O
two	O
hours	O
using	O
NTP	O
timestamps	O
,	O
with	O
a	O
connection	O
address	O
(	O
which	O
indicates	O
the	O
address	O
clients	O
must	O
connect	O
to	O
or	O
—	O
when	O
a	O
multicast	O
address	O
is	O
provided	O
,	O
as	O
it	O
is	O
here	O
—	O
subscribe	O
to	O
)	O
specified	O
as	O
IPv4	O
224.2.17.12	O
with	O
a	O
TTL	B-Protocol
of	O
127	O
.	O
</s>
<s>
The	O
first	O
is	O
an	O
audio	O
stream	O
on	O
port	O
49170	O
using	O
RTP/AVP	O
payload	O
type	O
0	O
(	O
defined	O
by	O
RFC	O
3551	O
as	O
PCMU	B-Algorithm
)	O
,	O
and	O
the	O
second	O
is	O
a	O
video	O
stream	O
on	O
port	O
51372	O
using	O
RTP/AVP	O
payload	O
type	O
99	O
(	O
defined	O
as	O
"	O
dynamic	O
"	O
)	O
.	O
</s>
<s>
RTCP	B-Protocol
ports	O
for	O
the	O
audio	O
and	O
video	O
streams	O
of	O
49171	O
and	O
51373	O
,	O
respectively	O
,	O
are	O
implied	O
.	O
</s>
<s>
It	O
is	O
intended	O
to	O
be	O
distributed	O
over	O
different	O
transport	O
protocols	O
as	O
necessary	O
,	O
including	O
SAP	B-Protocol
,	O
SIP	B-Application
,	O
and	O
RTSP	B-Protocol
.	O
</s>
<s>
Absolute	O
times	O
are	O
represented	O
in	O
Network	B-Protocol
Time	I-Protocol
Protocol	I-Protocol
(	O
NTP	O
)	O
format	O
(	O
the	O
number	O
of	O
seconds	O
since	O
1900	O
)	O
.	O
</s>
<s>
Unbounded	O
and	O
permanent	O
sessions	B-Protocol
are	O
discouraged	O
but	O
not	O
prohibited	O
.	O
</s>
<s>
As	O
SDP	O
announcements	O
for	O
repeated	O
sessions	B-Protocol
should	O
not	O
be	O
made	O
to	O
cover	O
very	O
long	O
periods	O
exceeding	O
a	O
few	O
years	O
,	O
the	O
number	O
of	O
daylight	O
adjustments	O
to	O
include	O
in	O
the	O
z	O
=	O
parameter	O
should	O
remain	O
small	O
.	O
</s>
<s>
Sessions	B-Protocol
may	O
be	O
repeated	O
irregularly	O
over	O
a	O
week	O
but	O
scheduled	O
the	O
same	O
way	O
for	O
all	O
weeks	O
in	O
the	O
period	O
,	O
by	O
adding	O
more	O
tuples	O
in	O
the	O
r	O
parameter	O
.	O
</s>
<s>
The	O
SDP	O
protocol	O
does	O
not	O
support	O
repeating	O
sessions	B-Protocol
monthly	O
and	O
yearly	O
schedules	O
with	O
such	O
simple	O
repeat	O
times	O
,	O
because	O
they	O
are	O
irregularly	O
spaced	O
in	O
time	O
;	O
instead	O
,	O
additional	O
t/r	O
tuples	O
may	O
be	O
supplied	O
for	O
each	O
month	O
or	O
year	O
.	O
</s>
