<s>
The	O
3GPP/NGN	O
IP	B-Protocol
Multimedia	I-Protocol
Subsystem	I-Protocol
(	O
IMS	O
)	O
multimedia	B-Protocol
telephony	I-Protocol
service	O
(	O
MMTel	B-Protocol
)	O
is	O
a	O
global	O
standard	O
based	O
on	O
the	O
IMS	O
,	O
offering	O
converged	O
,	O
fixed	O
and	O
mobile	O
real-time	O
multimedia	O
communication	O
using	O
the	O
media	O
capabilities	O
such	O
as	O
voice	O
,	O
real-time	O
video	O
,	O
text	O
,	O
file	O
transfer	O
and	O
sharing	O
of	O
pictures	O
,	O
audio	O
and	O
video	O
clips	O
.	O
</s>
<s>
With	O
MMTel	B-Protocol
,	O
users	O
have	O
the	O
capability	O
to	O
add	O
and	O
drop	O
media	O
during	O
a	O
session	O
.	O
</s>
<s>
You	O
can	O
start	O
with	O
chat	O
,	O
add	O
voice	O
(	O
for	O
instance	O
Mobile	O
VoIP	B-Application
)	O
,	O
add	O
another	O
caller	O
,	O
add	O
video	O
,	O
share	O
media	O
and	O
transfer	O
files	O
,	O
and	O
drop	O
any	O
of	O
these	O
without	O
losing	O
or	O
having	O
to	O
end	O
the	O
session	O
.	O
</s>
<s>
MMTel	B-Protocol
is	O
one	O
of	O
the	O
registered	O
ICSI	O
(	O
IMS	O
Communication	O
Service	O
Identifier	O
)	O
feature	O
tags	O
.	O
</s>
<s>
The	O
MMTel	B-Protocol
standard	O
is	O
a	O
joint	O
project	O
between	O
the	O
3GPP	O
and	O
ETSI/TISPAN	O
standardization	O
bodies	O
.	O
</s>
<s>
The	O
MMTel	B-Protocol
standard	O
is	O
today	O
the	O
only	O
global	O
standard	O
that	O
defines	O
an	O
evolved	O
telephony	O
service	O
that	O
enables	O
real-time	O
multimedia	O
communication	O
with	O
the	O
characteristics	O
of	O
a	O
telephony	O
service	O
over	O
both	O
fixed	O
broadband	O
,	O
fixed	O
narrowband	O
and	O
mobile	O
access	O
types	O
.	O
</s>
<s>
MMTel	B-Protocol
also	O
provides	O
a	O
standardized	O
network-to-network	B-Protocol
interface	I-Protocol
(	O
NNI	O
)	O
.	O
</s>
<s>
This	O
allow	O
operators	O
to	O
interconnect	O
their	O
networks	O
which	O
in	O
turn	O
enables	O
users	O
belonging	O
to	O
different	O
operators	O
to	O
communicate	O
with	O
each	O
other	O
,	O
using	O
the	O
full	O
set	O
of	O
media	O
capabilities	O
and	O
supplementary	O
services	O
defined	O
within	O
the	O
MMTel	B-Protocol
service	O
definition	O
.	O
</s>
<s>
One	O
of	O
the	O
main	O
differences	O
with	O
the	O
MMTel	B-Protocol
standard	O
is	O
that	O
,	O
in	O
contrast	O
to	O
legacy	O
circuit	B-Protocol
switched	I-Protocol
telephony	O
services	O
,	O
IP	O
transport	O
is	O
used	O
over	O
the	O
mobile	O
access	O
.	O
</s>
<s>
This	O
means	O
that	O
the	O
mobile	O
access	O
technologies	O
that	O
are	O
in	O
main	O
focus	O
for	O
MMTel	B-Protocol
are	O
access	O
types	O
such	O
as	O
high-speed	O
packet	O
access	O
(	O
HSPA	O
)	O
,	O
3GPP	O
long-term	O
evolution	O
(	O
LTE	O
)	O
and	O
EDGE	O
Evolution	O
that	O
all	O
are	O
developed	O
with	O
efficient	O
IP	O
transport	O
in	O
mind	O
.	O
</s>
<s>
MMTel	B-Protocol
allows	O
a	O
single	O
SIP	O
session	O
to	O
control	O
virtually	O
all	O
MMTel	B-Protocol
supplementary	O
services	O
and	O
MMTel	B-Protocol
media	O
.	O
</s>
<s>
Even	O
though	O
it	O
is	O
possible	O
to	O
manage	O
single-session	O
user	O
scenarios	O
with	O
several	O
sessions	O
–	O
for	O
instance	O
,	O
using	O
a	O
circuit-switched	B-Protocol
voice	O
service	O
that	O
is	O
complemented	O
with	O
a	O
packet-switched	B-Protocol
video	O
session	O
,	O
a	O
messaging	O
service	O
or	O
both	O
–	O
there	O
are	O
some	O
concrete	O
benefits	O
to	O
MMTel	B-Protocol
’s	O
single-session	O
approach	O
.	O
</s>
<s>
A	O
single	O
SIP	O
session	O
in	O
an	O
all-IP	B-Protocol
environment	O
benefits	O
conferencing	O
;	O
in	O
particular	O
,	O
lip	O
synchronization	O
,	O
which	O
is	O
quite	O
complex	O
when	O
the	O
voice	O
part	O
is	O
carried	O
over	O
a	O
circuit-switched	B-Protocol
service	O
and	O
the	O
video	O
part	O
is	O
carried	O
over	O
a	O
packet-switched	B-Protocol
service	O
.	O
</s>
