<s>
iWARP	B-General_Concept
is	O
a	O
computer	O
networking	O
protocol	O
that	O
implements	O
remote	B-General_Concept
direct	I-General_Concept
memory	I-General_Concept
access	I-General_Concept
(	O
RDMA	B-General_Concept
)	O
for	O
efficient	O
data	O
transfer	O
over	O
Internet	O
Protocol	O
networks	O
.	O
</s>
<s>
Contrary	O
to	O
some	O
accounts	O
,	O
iWARP	B-General_Concept
is	O
not	O
an	O
acronym	O
.	O
</s>
<s>
Because	O
iWARP	B-General_Concept
is	O
layered	O
on	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
-standard	O
congestion-aware	O
protocols	O
such	O
as	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
TCP	O
)	O
and	O
Stream	B-Protocol
Control	I-Protocol
Transmission	I-Protocol
Protocol	I-Protocol
(	O
SCTP	B-Protocol
)	O
,	O
it	O
makes	O
few	O
requirements	O
on	O
the	O
network	O
,	O
and	O
can	O
be	O
successfully	O
deployed	O
in	O
a	O
broad	O
range	O
of	O
environments	O
.	O
</s>
<s>
In	O
2007	O
,	O
the	O
IETF	O
published	O
five	O
Request	O
for	O
Comments	O
(	O
RFCs	O
)	O
that	O
define	O
iWARP	B-General_Concept
:	O
</s>
<s>
RFC	O
5040	O
A	O
Remote	B-General_Concept
Direct	I-General_Concept
Memory	I-General_Concept
Access	I-General_Concept
Protocol	O
Specification	O
is	O
layered	O
over	O
Direct	O
Data	O
Placement	O
Protocol	O
(	O
DDP	O
)	O
.	O
</s>
<s>
It	O
defines	O
how	O
RDMA	B-General_Concept
Send	O
,	O
Read	O
,	O
and	O
Write	O
operations	O
are	O
encoded	O
using	O
DDP	O
into	O
headers	O
on	O
the	O
network	O
.	O
</s>
<s>
RFC	O
5041	O
Direct	O
Data	O
Placement	O
over	O
Reliable	O
Transports	O
is	O
layered	O
over	O
MPA/TCP	O
or	O
SCTP	B-Protocol
.	O
</s>
<s>
RFC	O
5042	O
Direct	O
Data	O
Placement	O
Protocol	O
(	O
DDP	O
)	O
/	O
Remote	B-General_Concept
Direct	I-General_Concept
Memory	I-General_Concept
Access	I-General_Concept
Protocol	O
(	O
RDMAP	O
)	O
Security	O
analyzes	O
security	O
issues	O
related	O
to	O
iWARP	B-General_Concept
DDP	O
and	O
RDMAP	O
protocol	O
layers	O
.	O
</s>
<s>
RFC	O
5043	O
Stream	B-Protocol
Control	I-Protocol
Transmission	I-Protocol
Protocol	I-Protocol
(	O
SCTP	B-Protocol
)	O
Direct	O
Data	O
Placement	O
(	O
DDP	O
)	O
Adaptation	O
defines	O
an	O
adaptation	O
layer	O
that	O
enables	O
DDP	O
over	O
SCTP	B-Protocol
.	O
</s>
<s>
These	O
RFCs	O
are	O
based	O
on	O
the	O
RDMA	B-General_Concept
Consortium	O
's	O
specifications	O
for	O
RDMA	B-General_Concept
over	O
TCP	O
.	O
</s>
<s>
The	O
RDMA	B-General_Concept
Consortium	O
's	O
specifications	O
are	O
influenced	O
by	O
earlier	O
RDMA	B-General_Concept
standards	O
,	O
including	O
Virtual	B-General_Concept
Interface	I-General_Concept
Architecture	I-General_Concept
(	O
VIA	O
)	O
and	O
InfiniBand	B-Architecture
(	O
IB	O
)	O
.	O
</s>
<s>
Since	O
2007	O
,	O
the	O
IETF	O
has	O
published	O
three	O
additional	O
RFCs	O
that	O
maintain	O
and	O
extend	O
iWARP	B-General_Concept
:	O
</s>
<s>
RFC	O
6581	O
Enhanced	O
Remote	B-General_Concept
Direct	I-General_Concept
Memory	I-General_Concept
Access	I-General_Concept
(	O
RDMA	B-General_Concept
)	O
Connection	O
Establishment	O
published	O
in	O
2011	O
fixes	O
shortcomings	O
with	O
iWARP	B-General_Concept
connection	O
setup	O
.	O
</s>
<s>
RFC	O
7306	O
Remote	B-General_Concept
Direct	I-General_Concept
Memory	I-General_Concept
Access	I-General_Concept
(	O
RDMA	B-General_Concept
)	O
Protocol	O
Extensions	O
published	O
in	O
2014	O
extends	O
RFC	O
5040	O
with	O
atomic	B-General_Concept
operations	I-General_Concept
and	O
RDMA	B-General_Concept
Write	O
with	O
Immediate	O
Data	O
.	O
</s>
<s>
The	O
main	O
component	O
in	O
the	O
iWARP	B-General_Concept
protocol	O
is	O
the	O
Direct	O
Data	O
Placement	O
Protocol	O
(	O
DDP	O
)	O
,	O
which	O
permits	O
the	O
actual	O
zero-copy	O
transmission	O
.	O
</s>
<s>
DDP	O
itself	O
does	O
not	O
perform	O
the	O
transmission	O
;	O
the	O
underlying	O
protocol	O
(	O
TCP	O
or	O
SCTP	B-Protocol
)	O
does	O
.	O
</s>
<s>
In	O
this	O
regard	O
,	O
DDP	O
itself	O
may	O
be	O
better	O
suited	O
for	O
SCTP	B-Protocol
,	O
and	O
indeed	O
the	O
IETF	O
proposed	O
a	O
standard	O
RDMA	B-General_Concept
over	O
SCTP	B-Protocol
.	O
</s>
<s>
Instead	O
,	O
a	O
separate	O
RDMA	B-General_Concept
protocol	O
(	O
RDMAP	O
)	O
provides	O
the	O
services	O
to	O
read	O
and	O
write	O
data	O
.	O
</s>
<s>
Therefore	O
,	O
the	O
entire	O
RDMA	B-General_Concept
over	O
TCP	O
specification	O
is	O
really	O
RDMAP	O
over	O
DDP	O
over	O
either	O
MPA/TCP	O
or	O
SCTP	B-Protocol
.	O
</s>
<s>
Unlike	O
IB	O
,	O
iWARP	B-General_Concept
only	O
has	O
reliable	O
connected	O
communication	O
,	O
as	O
this	O
is	O
the	O
only	O
service	O
that	O
TCP	O
and	O
SCTP	B-Protocol
provide	O
.	O
</s>
<s>
The	O
iWARP	B-General_Concept
specification	O
omits	O
other	O
features	O
of	O
IB	O
,	O
such	O
as	O
Send	O
with	O
Immediate	O
Data	O
operations	O
.	O
</s>
<s>
Because	O
a	O
kernel	B-Operating_System
implementation	O
of	O
the	O
TCP	O
stack	O
can	O
be	O
seen	O
as	O
a	O
bottleneck	O
,	O
the	O
protocol	O
is	O
typically	O
implemented	O
in	O
hardware	O
RDMA	B-General_Concept
network	B-Protocol
interface	I-Protocol
controllers	I-Protocol
(	O
rNICs	O
)	O
.	O
</s>
<s>
Furthermore	O
,	O
the	O
handling	O
of	O
iWARP	B-General_Concept
specific	O
protocol	O
details	O
is	O
typically	O
isolated	O
from	O
the	O
TCP	O
implementation	O
,	O
allowing	O
rNICs	O
to	O
be	O
used	O
for	O
both	O
as	O
RDMA	B-General_Concept
offload	O
and	O
TCP	B-Protocol
offload	I-Protocol
(	O
in	O
support	O
of	O
traditional	O
sockets	O
based	O
TCP/IP	O
applications	O
)	O
.	O
</s>
<s>
The	O
portion	O
of	O
the	O
hardware	O
implementation	O
used	O
for	O
implementing	O
the	O
TCP	B-Protocol
protocol	I-Protocol
is	O
known	O
as	O
the	O
TCP	B-Protocol
Offload	I-Protocol
Engine	I-Protocol
(	O
TOE	O
)	O
.	O
</s>
<s>
TOE	O
itself	O
does	O
not	O
prevent	O
copying	O
on	O
the	O
reception	O
side	O
,	O
and	O
must	O
be	O
combined	O
with	O
RDMA	B-General_Concept
hardware	O
for	O
zero-copy	O
results	O
.	O
</s>
<s>
The	O
RDMA	B-General_Concept
/	O
TCP	O
specification	O
is	O
a	O
set	O
of	O
different	O
wire	O
protocols	O
intended	O
to	O
be	O
implemented	O
in	O
hardware	O
(	O
though	O
it	O
seems	O
feasible	O
to	O
emulate	O
it	O
in	O
software	O
for	O
compatibility	O
but	O
without	O
the	O
performance	O
benefits	O
)	O
.	O
</s>
<s>
iWARP	B-General_Concept
is	O
a	O
protocol	O
,	O
not	O
an	O
implementation	O
,	O
but	O
defines	O
protocol	O
behavior	O
in	O
terms	O
of	O
the	O
operations	O
that	O
are	O
legal	O
for	O
the	O
protocol	O
,	O
known	O
as	O
Verbs	O
.	O
</s>
<s>
As	O
such	O
,	O
iWARP	B-General_Concept
does	O
not	O
have	O
any	O
single	O
standard	O
programming	O
interface	O
.	O
</s>
<s>
Several	O
programmatic	O
interfaces	O
have	O
been	O
proposed	O
,	O
including	O
OpenFabrics	B-General_Concept
Verbs	O
,	O
Network	O
Direct	O
,	O
uDAPL	O
,	O
kDAPL	O
,	O
IT-API	O
,	O
and	O
RNICPI	O
.	O
</s>
<s>
Implementations	O
of	O
some	O
of	O
these	O
interfaces	O
are	O
available	O
for	O
different	O
platforms	O
,	O
including	O
Windows	O
and	O
Linux	B-Application
.	O
</s>
<s>
Networking	O
services	O
implemented	O
over	O
iWARP	B-General_Concept
include	O
those	O
offered	O
in	O
the	O
OpenFabrics	B-General_Concept
Enterprise	I-General_Concept
Distribution	I-General_Concept
(	O
OFED	O
)	O
by	O
the	O
OpenFabrics	B-General_Concept
Alliance	I-General_Concept
for	O
Linux	B-Application
operating	I-Application
systems	I-Application
,	O
and	O
by	O
Microsoft	B-Application
Windows	I-Application
via	O
Network	O
Direct	O
.	O
</s>
<s>
Popular	O
vendors	O
of	O
iWarp	B-General_Concept
enabled	O
equipment	O
include	O
:	O
</s>
