<s>
In	O
computer	O
networking	O
,	O
the	O
Message	B-Protocol
Session	I-Protocol
Relay	I-Protocol
Protocol	I-Protocol
(	O
MSRP	B-Protocol
)	O
is	O
a	O
protocol	O
for	O
transmitting	O
a	O
series	O
of	O
related	O
instant	B-Application
messages	I-Application
in	O
the	O
context	O
of	O
a	O
communications	O
session	O
.	O
</s>
<s>
An	O
application	O
instantiates	O
the	O
session	O
with	O
the	O
Session	B-Language
Description	I-Language
Protocol	I-Language
(	O
SDP	O
)	O
over	O
Session	B-Application
Initiation	I-Application
Protocol	I-Application
(	O
SIP	B-Application
)	O
or	O
other	O
rendezvous	O
methods	O
.	O
</s>
<s>
The	O
MSRP	B-Protocol
protocol	O
is	O
defined	O
in	O
.	O
</s>
<s>
MSRP	B-Protocol
messages	O
can	O
also	O
be	O
transmitted	O
by	O
using	O
intermediaries	O
peers	O
,	O
by	O
using	O
the	O
relay	O
extensions	O
defined	O
in	O
.	O
</s>
<s>
MSRP	B-Protocol
is	O
used	O
in	O
the	O
RCS	O
context	O
,	O
especially	O
for	O
the	O
instant	B-Application
messaging	I-Application
,	O
file	B-Protocol
transfer	I-Protocol
and	O
photo	B-Algorithm
sharing	I-Algorithm
features	O
.	O
</s>
<s>
MSRP	B-Protocol
syntax	O
is	O
similar	O
to	O
other	O
IETF	O
text	O
based	O
protocols	O
such	O
as	O
SIP	B-Application
,	O
HTTP	B-Protocol
and	O
RTSP	B-Protocol
.	O
</s>
<s>
MSRP	B-Protocol
requires	O
a	O
reliable	O
transport	O
layer	O
,	O
like	O
TCP	B-Protocol
.	O
</s>
<s>
Each	O
message	O
is	O
either	O
a	O
request	O
or	O
a	O
response	O
and	O
uses	O
URIs	B-Protocol
;	O
a	O
message	O
contains	O
headers	O
and	O
a	O
body	O
that	O
can	O
carry	O
any	O
type	O
of	O
data	O
,	O
including	O
binary	O
information	O
.	O
</s>
<s>
An	O
MSRP	B-Protocol
URI	B-Protocol
has	O
a	O
scheme	O
(	O
which	O
is	O
"	O
msrp	B-Protocol
"	O
or	O
"	O
msrps	B-Protocol
"	O
)	O
,	O
authority	O
,	O
as	O
defined	O
by	O
RFC	O
3986	O
,	O
which	O
holds	O
the	O
IP/domain	O
name	O
and	O
possibly	O
the	O
port	O
,	O
an	O
optional	O
session	O
identifier	O
,	O
the	O
transport	O
and	O
additional	O
optional	O
parameters	O
.	O
</s>
<s>
MSRP	B-Protocol
can	O
be	O
used	O
within	O
a	O
SIP	B-Application
session	O
:	O
</s>
<s>
MSRP	B-Protocol
session	O
is	O
set	O
up	O
through	O
SIP	B-Application
's	O
offer-answer	O
model	O
.	O
</s>
<s>
The	O
SDP	O
m-line	O
media	O
type	O
is	O
message	O
and	O
the	O
protocol	O
is	O
either	O
TCP/MSRP	O
for	O
MSRP	B-Protocol
over	O
TCP	B-Protocol
and	O
TCP/TLS/MSRP	O
for	O
MSRP	B-Protocol
over	O
secure	O
TLS	O
.	O
</s>
<s>
Furthermore	O
,	O
the	O
MSRP	B-Protocol
URI	B-Protocol
is	O
specified	O
in	O
a	O
path	O
attribute	O
.	O
</s>
<s>
Generally	O
,	O
other	O
media	O
types	O
use	O
the	O
c-line	O
and	O
m-line	O
to	O
describe	O
the	O
address	O
and	O
port	O
,	O
but	O
the	O
MSRP	B-Protocol
RFC	O
4975	O
section	O
8.1	O
says	O
the	O
path	O
attribute	O
is	O
the	O
authoritative	O
source	O
for	O
MSRP	B-Protocol
.	O
</s>
