<s>
A	O
reliable	B-Operating_System
multicast	I-Operating_System
is	O
any	O
computer	B-Architecture
networking	I-Architecture
protocol	O
that	O
provides	O
a	O
reliable	B-Protocol
sequence	O
of	O
packets	O
to	O
multiple	O
recipients	O
simultaneously	O
,	O
making	O
it	O
suitable	O
for	O
applications	O
such	O
as	O
multi-receiver	O
file	B-Protocol
transfer	I-Protocol
.	O
</s>
<s>
Multicast	O
is	O
a	O
network	O
addressing	O
method	O
for	O
the	O
delivery	O
of	O
information	O
to	O
a	O
group	O
of	O
destinations	O
simultaneously	O
using	O
the	O
most	O
efficient	O
strategy	O
to	O
deliver	O
the	O
messages	O
over	O
each	O
link	O
of	O
the	O
network	O
only	O
once	O
,	O
creating	O
copies	O
only	O
when	O
the	O
links	O
to	O
the	O
multiple	O
destinations	O
split	O
(	O
typically	O
network	B-Protocol
switches	I-Protocol
and	O
routers	B-Protocol
)	O
.	O
</s>
<s>
However	O
,	O
like	O
the	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
,	O
multicast	O
does	O
not	O
guarantee	O
the	O
delivery	O
of	O
a	O
message	O
stream	O
.	O
</s>
<s>
A	O
reliable	B-Operating_System
multicast	I-Operating_System
protocol	O
adds	O
the	O
ability	O
for	O
receivers	O
to	O
detect	O
lost	O
and/or	O
out-of-order	O
messages	O
and	O
take	O
corrective	O
action	O
(	O
similar	O
in	O
principle	O
to	O
TCP	B-Protocol
)	O
,	O
resulting	O
in	O
a	O
gap-free	O
,	O
in-order	O
message	O
stream	O
.	O
</s>
<s>
A	O
minimal	O
definition	O
of	O
reliable	B-Operating_System
multicast	I-Operating_System
is	O
eventual	O
delivery	O
of	O
all	O
the	O
data	O
to	O
all	O
the	O
group	O
members	O
,	O
without	O
enforcing	O
any	O
particular	O
delivery	O
order	O
.	O
</s>
<s>
However	O
,	O
not	O
all	O
reliable	B-Operating_System
multicast	I-Operating_System
protocols	O
ensure	O
this	O
level	O
of	O
reliability	O
;	O
many	O
of	O
them	O
trade	O
efficiency	O
for	O
reliability	O
,	O
in	O
different	O
ways	O
.	O
</s>
<s>
For	O
example	O
,	O
while	O
TCP	B-Protocol
makes	O
the	O
sender	O
responsible	O
for	O
transmission	O
reliability	O
,	O
multicast	O
NAK-based	O
protocols	O
shift	O
the	O
responsibility	O
to	O
receivers	O
:	O
the	O
sender	O
never	O
knows	O
for	O
sure	O
that	O
all	O
the	O
receivers	O
have	O
in	O
fact	O
received	O
all	O
the	O
data	O
.	O
</s>
<s>
RFC	O
-	O
2887	O
explores	O
the	O
design	O
space	O
for	O
bulk	O
data	O
transfer	O
,	O
with	O
a	O
brief	O
discussion	O
on	O
the	O
various	O
issues	O
and	O
some	O
hints	O
at	O
the	O
possible	O
different	O
meanings	O
of	O
reliable	B-Protocol
.	O
</s>
<s>
Reliable	B-Protocol
Group	O
Data	O
Delivery	O
(	O
RGDD	O
)	O
is	O
a	O
form	O
of	O
multicasting	O
where	O
an	O
object	O
is	O
to	O
be	O
moved	O
from	O
a	O
single	O
source	O
to	O
a	O
fixed	O
set	O
of	O
receivers	O
known	O
before	O
transmission	O
begins	O
.	O
</s>
<s>
Such	O
delivery	O
is	O
frequent	O
within	O
datacenters	O
due	O
to	O
plethora	O
of	O
servers	O
communicating	O
while	O
running	O
highly	O
distributed	B-Architecture
applications	I-Architecture
.	O
</s>
<s>
Modern	O
systems	O
like	O
the	B-General_Concept
Spread	I-General_Concept
Toolkit	I-General_Concept
,	O
Quicksilver	B-General_Concept
,	O
and	O
Corosync	B-Operating_System
can	O
achieve	O
data	O
rates	O
of	O
10,000	O
multicasts	O
per	O
second	O
or	O
more	O
,	O
and	O
can	O
scale	O
to	O
large	O
networks	O
with	O
huge	O
numbers	O
of	O
groups	O
or	O
processes	O
.	O
</s>
<s>
Most	O
distributed	B-Architecture
computing	I-Architecture
platforms	O
support	O
one	O
or	O
more	O
of	O
these	O
models	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
widely	O
supported	O
object-oriented	O
CORBA	B-Architecture
platforms	O
all	O
support	O
transactions	O
and	O
some	O
CORBA	B-Architecture
products	O
support	O
transactional	O
replication	O
in	O
the	O
one-copy-serializability	O
model	O
.	O
</s>
<s>
Virtual	O
synchrony	O
was	O
also	O
used	O
in	O
developing	O
the	O
New	O
York	O
Stock	O
Exchange	O
fault-tolerance	O
architecture	O
,	O
the	O
French	O
Air	O
Traffic	O
Control	O
System	O
,	O
the	O
US	O
Navy	O
AEGIS	O
system	O
,	O
IBM	O
's	O
Business	O
Process	O
replication	O
architecture	O
for	O
WebSphere	B-Language
and	O
Microsoft	O
's	O
Windows	O
Clustering	O
architecture	O
for	O
Windows	O
Longhorn	O
enterprise	O
servers	O
.	O
</s>
<s>
Cornell	O
's	O
most	O
current	O
version	O
,	O
Vsync	O
was	O
released	O
in	O
2013	O
under	O
the	O
name	O
Isis2	B-Operating_System
(	O
the	O
name	O
was	O
changed	O
from	O
Isis2	B-Operating_System
to	O
Vsync	O
in	O
2015	O
in	O
the	O
wake	O
of	O
a	O
terrorist	O
attack	O
in	O
Paris	O
by	O
an	O
extremist	O
organization	O
called	O
ISIS	O
)	O
,	O
with	O
periodic	O
updates	O
and	O
revisions	O
since	O
that	O
time	O
.	O
</s>
<s>
Vsync	O
aims	O
at	O
the	O
massive	O
data	O
centers	O
that	O
support	O
cloud	B-Architecture
computing	I-Architecture
.	O
</s>
<s>
Other	O
such	O
systems	O
include	O
the	O
Horus	O
system	O
the	O
Transis	O
system	O
,	O
the	O
Totem	O
system	O
,	O
an	O
IBM	O
system	O
called	O
Phoenix	O
,	O
a	O
distributed	O
security	O
key	O
management	O
system	O
called	O
Rampart	O
,	O
the	O
"	O
Ensemble	O
system	O
"	O
,	O
the	O
Quicksilver	B-General_Concept
system	O
,	O
"	O
The	O
OpenAIS	O
project	O
"	O
,	O
its	O
derivative	O
the	B-Operating_System
Corosync	I-Operating_System
Cluster	I-Operating_System
Engine	I-Operating_System
and	O
a	O
number	O
of	O
products	O
(	O
including	O
the	O
IBM	O
and	O
Microsoft	O
ones	O
mentioned	O
earlier	O
)	O
.	O
</s>
<s>
Tibco	O
Software	O
's	O
TRDP	O
(	O
part	O
of	O
RV	B-Application
)	O
.	O
</s>
