<s>
In	O
interactive	O
multicast	O
at	O
the	O
data	O
link	O
or	O
network	O
layer	O
,	O
such	O
as	O
IP	B-Protocol
multicast	I-Protocol
,	O
Ethernet	O
multicast	O
or	O
MBMS	O
service	O
over	O
cellular	O
network	O
,	O
receivers	O
may	O
join	O
and	O
leave	O
the	O
group	O
using	O
an	O
interaction	O
channel	O
.	O
</s>
<s>
In	O
for	O
example	O
IP	B-Protocol
multicast	I-Protocol
,	O
a	O
multicast	O
group	O
is	O
identified	O
by	O
a	O
class	O
D	O
IP	B-Protocol
address	I-Protocol
.	O
</s>
<s>
A	O
host	B-Device
enters	O
or	O
exits	O
a	O
group	O
using	O
IGMP	B-Protocol
(	O
Internet	B-Protocol
Group	I-Protocol
Management	I-Protocol
Protocol	I-Protocol
)	O
.	O
</s>
<s>
Multicast	O
was	O
used	O
originally	O
in	O
LANs	B-General_Concept
,	O
with	O
Ethernet	O
being	O
the	O
best	O
example	O
.	O
</s>
<s>
A	O
solution	O
to	O
the	O
problem	O
of	O
ensuring	O
that	O
only	O
the	O
chosen	O
recipient	O
obtains	O
the	O
data	O
is	O
known	O
as	O
multicast	B-Protocol
encryption	I-Protocol
.	O
</s>
<s>
One	O
protocol	O
called	O
UFTP	B-Protocol
(	O
encrypted	O
UDP	O
based	O
FTP	O
over	O
multicast	O
)	O
was	O
created	O
in	O
an	O
attempt	O
to	O
solve	O
this	O
problem	O
.	O
</s>
<s>
Today	O
,	O
one	O
alternative	O
in	O
multicast	B-Protocol
encryption	I-Protocol
involves	O
the	O
use	O
of	O
symmetric	O
key	O
encryption	O
where	O
data	O
is	O
decoded	O
by	O
intended	O
receivers	O
using	O
a	O
traffic	O
encryption	O
key	O
(	O
TEK	O
)	O
.	O
</s>
