<s>
RDMA	B-Operating_System
over	I-Operating_System
Converged	I-Operating_System
Ethernet	I-Operating_System
(	O
RoCE	O
)	O
or	O
InfiniBand	B-Operating_System
over	I-Operating_System
Ethernet	I-Operating_System
(	O
IBoE	B-Operating_System
)	O
is	O
a	O
network	O
protocol	O
that	O
allows	O
remote	B-General_Concept
direct	I-General_Concept
memory	I-General_Concept
access	I-General_Concept
(	O
RDMA	B-General_Concept
)	O
over	O
an	O
Ethernet	O
network	O
.	O
</s>
<s>
It	O
does	O
this	O
by	O
encapsulating	O
an	O
InfiniBand	B-Architecture
(	O
IB	O
)	O
transport	O
packet	O
over	O
Ethernet	O
.	O
</s>
<s>
RoCE	O
v1	O
is	O
an	O
Ethernet	O
link	B-Protocol
layer	I-Protocol
protocol	O
and	O
hence	O
allows	O
communication	O
between	O
any	O
two	O
hosts	O
in	O
the	O
same	O
Ethernet	O
broadcast	B-Architecture
domain	I-Architecture
.	O
</s>
<s>
RoCE	O
v2	O
is	O
an	O
internet	B-Protocol
layer	I-Protocol
protocol	O
which	O
means	O
that	O
RoCE	O
v2	O
packets	O
can	O
be	O
routed	O
.	O
</s>
<s>
Although	O
the	O
RoCE	O
protocol	O
benefits	O
from	O
the	O
characteristics	O
of	O
a	O
converged	B-Protocol
Ethernet	I-Protocol
network	I-Protocol
,	O
the	O
protocol	O
can	O
also	O
be	O
used	O
on	O
a	O
traditional	O
or	O
non-converged	O
Ethernet	O
network	O
.	O
</s>
<s>
The	O
advantages	O
of	O
RDMA	B-General_Concept
over	O
other	O
network	O
application	B-Application
programming	I-Application
interfaces	I-Application
such	O
as	O
Berkeley	B-Protocol
sockets	I-Protocol
are	O
lower	O
latency	O
,	O
lower	O
CPU	O
load	O
and	O
higher	O
bandwidth	O
.	O
</s>
<s>
The	O
RoCE	O
protocol	O
allows	O
lower	O
latencies	O
than	O
its	O
predecessor	O
,	O
the	O
iWARP	B-Device
protocol	O
.	O
</s>
<s>
There	O
are	O
RoCE	O
HCAs	O
(	O
Host	B-Architecture
Channel	I-Architecture
Adapter	I-Architecture
)	O
with	O
a	O
latency	O
as	O
low	O
as	O
1.3	O
microseconds	O
while	O
the	O
lowest	O
known	O
iWARP	B-Device
HCA	O
latency	O
in	O
2011	O
was	O
3	O
microseconds	O
.	O
</s>
<s>
The	O
RoCE	O
v1	O
protocol	O
is	O
an	O
Ethernet	O
link	B-Protocol
layer	I-Protocol
protocol	O
with	O
Ethertype	O
0x8915	O
.	O
</s>
<s>
This	O
means	O
that	O
the	O
frame	O
length	O
limits	O
of	O
the	O
Ethernet	O
protocol	O
apply	O
:	O
1500	O
bytes	O
for	O
a	O
regular	O
Ethernet	B-Protocol
frame	I-Protocol
and	O
9000	O
bytes	O
for	O
a	O
jumbo	B-Protocol
frame	I-Protocol
.	O
</s>
<s>
RoCE	O
v1.5	O
uses	O
the	O
IP	O
protocol	O
field	O
to	O
differentiate	O
its	O
traffic	O
from	O
other	O
IP	O
protocols	O
such	O
as	O
TCP	B-Protocol
and	O
UDP	B-Protocol
.	O
</s>
<s>
The	O
RoCE	O
v2	O
protocol	O
exists	O
on	O
top	O
of	O
either	O
the	O
UDP/IPv4	O
or	O
the	O
UDP/IPv6	O
protocol	O
.	O
</s>
<s>
The	O
UDP	B-Protocol
destination	O
port	O
number	O
4791	O
has	O
been	O
reserved	O
for	O
RoCE	O
v2	O
.	O
</s>
<s>
Although	O
in	O
general	O
the	O
delivery	O
order	O
of	O
UDP	B-Protocol
packets	I-Protocol
is	O
not	O
guaranteed	O
,	O
the	O
RoCEv2	O
specification	O
requires	O
that	O
packets	O
with	O
the	O
same	O
UDP	B-Protocol
source	O
port	O
and	O
the	O
same	O
destination	O
address	O
must	O
not	O
be	O
reordered	O
.	O
</s>
<s>
RoCE	O
defines	O
how	O
to	O
perform	O
RDMA	B-General_Concept
over	O
Ethernet	O
while	O
the	O
InfiniBand	B-Architecture
architecture	I-Architecture
specification	O
defines	O
how	O
to	O
perform	O
RDMA	B-General_Concept
over	O
an	O
InfiniBand	B-Architecture
network	O
.	O
</s>
<s>
RoCE	O
was	O
expected	O
to	O
bring	O
InfiniBand	B-Architecture
applications	O
,	O
which	O
are	O
predominantly	O
based	O
on	O
clusters	O
,	O
onto	O
a	O
common	O
Ethernet	O
converged	O
fabric	O
.	O
</s>
<s>
Others	O
expected	O
that	O
InfiniBand	B-Architecture
will	O
keep	O
offering	O
a	O
higher	O
bandwidth	O
and	O
lower	O
latency	O
than	O
what	O
is	O
possible	O
over	O
Ethernet	O
.	O
</s>
<s>
The	O
technical	O
differences	O
between	O
the	O
RoCE	O
and	O
InfiniBand	B-Architecture
protocols	O
are	O
:	O
</s>
<s>
Link	O
Level	O
Flow	O
Control	O
:	O
InfiniBand	B-Architecture
uses	O
a	O
credit-based	O
algorithm	O
to	O
guarantee	O
lossless	O
HCA-to-HCA	O
communication	O
.	O
</s>
<s>
Implementations	O
may	O
require	O
lossless	B-Protocol
Ethernet	I-Protocol
network	O
for	O
reaching	O
to	O
performance	O
characteristics	O
similar	O
to	O
InfiniBand	B-Architecture
.	O
</s>
<s>
Lossless	B-Protocol
Ethernet	I-Protocol
is	O
typically	O
configured	O
via	O
Ethernet	O
flow	O
control	O
or	O
priority	O
flow	O
control	O
(	O
PFC	O
)	O
.	O
</s>
<s>
Configuring	O
a	O
Data	B-Protocol
center	I-Protocol
bridging	I-Protocol
(	O
DCB	O
)	O
Ethernet	O
network	O
can	O
be	O
more	O
complex	O
than	O
configuring	O
an	O
InfiniBand	B-Architecture
network	O
.	O
</s>
<s>
Congestion	O
Control	O
:	O
Infiniband	B-Architecture
defines	O
congestion	O
control	O
based	O
on	O
FECN/BECN	O
marking	O
,	O
RoCEv2	O
defines	O
a	O
congestion	O
control	O
protocol	O
that	O
uses	O
ECN	O
for	O
marking	O
as	O
implemented	O
in	O
standard	O
switches	O
and	O
CNP	O
frames	O
for	O
acknowledgments	O
.	O
</s>
<s>
InfiniBand	B-Architecture
switches	O
typically	O
have	O
lower	O
latency	O
than	O
Ethernet	O
switches	O
.	O
</s>
<s>
Port-to-port	O
latency	O
for	O
one	O
particular	O
type	O
of	O
Ethernet	O
switch	O
is	O
230ns	O
versus	O
100ns	O
for	O
an	O
InfiniBand	B-Architecture
switch	O
with	O
the	O
same	O
number	O
of	O
ports	O
.	O
</s>
<s>
While	O
the	O
RoCE	O
protocols	O
define	O
how	O
to	O
perform	O
RDMA	B-General_Concept
using	O
Ethernet	O
and	O
UDP/IP	B-Protocol
frames	O
,	O
the	O
iWARP	B-Device
protocol	O
defines	O
how	O
to	O
perform	O
RDMA	B-General_Concept
over	O
a	O
connection-oriented	O
transport	O
like	O
the	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
TCP	B-Protocol
)	O
.	O
</s>
<s>
RoCE	O
v1	O
is	O
limited	O
to	O
a	O
single	O
Ethernet	O
broadcast	B-Architecture
domain	I-Architecture
.	O
</s>
<s>
RoCE	O
v2	O
and	O
iWARP	B-Device
packets	O
are	O
routable	O
.	O
</s>
<s>
The	O
memory	O
requirements	O
of	O
a	O
large	O
number	O
of	O
connections	O
along	O
with	O
TCP	B-Protocol
's	O
flow	O
and	O
reliability	O
controls	O
lead	O
to	O
scalability	O
and	O
performance	O
issues	O
when	O
using	O
iWARP	B-Device
in	O
large-scale	O
datacenters	O
and	O
for	O
large-scale	O
applications	O
(	O
i.e.	O
,	O
large-scale	O
enterprises	O
,	O
cloud	O
computing	O
,	O
web	O
2.0	O
applications	O
etc	O
.	O
)	O
.	O
</s>
<s>
Also	O
,	O
multicast	O
is	O
defined	O
in	O
the	O
RoCE	O
specification	O
while	O
the	O
current	O
iWARP	B-Device
specification	O
does	O
not	O
define	O
how	O
to	O
perform	O
multicast	O
RDMA	B-General_Concept
.	O
</s>
<s>
Reliability	O
in	O
iWARP	B-Device
is	O
given	O
by	O
the	O
protocol	O
itself	O
,	O
as	O
TCP	B-Protocol
is	O
reliable	O
.	O
</s>
<s>
RoCEv2	O
on	O
the	O
other	O
hand	O
utilizes	O
UDP	B-Protocol
which	O
has	O
a	O
far	O
smaller	O
overhead	O
and	O
better	O
performance	O
but	O
does	O
not	O
provide	O
inherent	O
reliability	O
,	O
and	O
therefore	O
reliability	O
must	O
be	O
implemented	O
alongside	O
RoCEv2	O
.	O
</s>
<s>
One	O
solution	O
is	O
to	O
use	O
converged	B-Protocol
Ethernet	I-Protocol
switches	O
to	O
make	O
the	O
local	O
area	O
network	O
reliable	O
.	O
</s>
<s>
This	O
require	O
converged	B-Protocol
Ethernet	I-Protocol
support	O
on	O
all	O
the	O
switches	O
in	O
the	O
local	O
area	O
network	O
and	O
prevents	O
RoCEv2	O
packets	O
from	O
traveling	O
through	O
a	O
wide	O
area	O
network	O
such	O
as	O
the	O
internet	O
which	O
is	O
not	O
reliable	O
.	O
</s>
<s>
Chelsio	O
recommends	O
and	O
exclusively	O
support	O
iWARP	B-Device
.	O
</s>
<s>
Intel	O
initially	O
supported	O
iWARP	B-Device
but	O
now	O
supports	O
both	O
iWARP	B-Device
and	O
RoCEv2	O
.	O
</s>
<s>
Cisco	O
supports	O
both	O
RoCE	O
and	O
their	O
own	O
VIC	O
RDMA	B-General_Concept
protocol	O
.	O
</s>
<s>
Both	O
Protocols	O
are	O
standardized	O
with	O
iWARP	B-Device
being	O
the	O
standard	O
for	O
RDMA	B-General_Concept
over	O
TCP	B-Protocol
defined	O
by	O
the	O
IETF	O
and	O
RoCE	O
being	O
the	O
standard	O
for	O
RDMA	B-General_Concept
over	O
Ethernet	O
defined	O
by	O
the	O
IBTA	B-Architecture
.	O
</s>
<s>
As	O
of	O
September	O
2013	O
,	O
an	O
equivalent	O
of	O
the	O
Multicast	B-Protocol
Listener	I-Protocol
Discovery	I-Protocol
protocol	O
has	O
not	O
yet	O
been	O
defined	O
for	O
RoCE	O
v1	O
.	O
</s>
