<s>
TCP	B-Protocol
offload	I-Protocol
engine	I-Protocol
(	O
TOE	O
)	O
is	O
a	O
technology	O
used	O
in	O
some	O
network	B-Protocol
interface	I-Protocol
cards	I-Protocol
(	O
NIC	O
)	O
to	O
offload	O
processing	O
of	O
the	O
entire	O
TCP/IP	B-Protocol
stack	I-Protocol
to	O
the	O
network	B-Protocol
controller	I-Protocol
.	O
</s>
<s>
TOEs	O
are	O
often	O
used	O
as	O
a	O
way	O
to	O
reduce	O
the	O
overhead	O
associated	O
with	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
IP	B-Protocol
)	O
storage	O
protocols	O
such	O
as	O
iSCSI	B-Protocol
and	O
Network	B-Protocol
File	I-Protocol
System	I-Protocol
(	O
NFS	O
)	O
.	O
</s>
<s>
Originally	O
TCP	B-Protocol
was	O
designed	O
for	O
unreliable	O
low	O
speed	O
networks	O
(	O
such	O
as	O
early	O
dial-up	B-Application
modems	I-Application
)	O
but	O
with	O
the	O
growth	O
of	O
the	O
Internet	O
in	O
terms	O
of	O
backbone	B-General_Concept
transmission	O
speeds	O
(	O
using	O
Optical	B-Protocol
Carrier	I-Protocol
,	O
Gigabit	O
Ethernet	O
and	O
10	O
Gigabit	O
Ethernet	O
links	O
)	O
and	O
faster	O
and	O
more	O
reliable	O
access	O
mechanisms	O
(	O
such	O
as	O
DSL	O
and	O
cable	B-Device
modems	I-Device
)	O
it	O
is	O
frequently	O
used	O
in	O
data	B-Operating_System
centers	I-Operating_System
and	O
desktop	O
PC	B-Device
environments	O
at	O
speeds	O
of	O
over	O
1	O
Gigabit	O
per	O
second	O
.	O
</s>
<s>
At	O
these	O
speeds	O
the	O
TCP	B-Protocol
software	O
implementations	O
on	O
host	O
systems	O
require	O
significant	O
computing	O
power	O
.	O
</s>
<s>
In	O
the	O
early	O
2000s	O
,	O
full-duplex	O
gigabit	O
TCP	B-Protocol
communication	O
could	O
consume	O
more	O
than	O
80%	O
of	O
a	O
2.4GHz	O
Pentium	B-General_Concept
4	I-General_Concept
processor	O
,	O
resulting	O
in	O
small	O
or	O
no	O
processing	O
resources	O
left	O
for	O
the	O
applications	O
to	O
run	O
on	O
the	O
system	O
.	O
</s>
<s>
TCP	B-Protocol
is	O
a	O
connection-oriented	B-Protocol
protocol	I-Protocol
which	O
adds	O
complexity	O
and	O
processing	O
overhead	O
.	O
</s>
<s>
Acknowledgment	O
of	O
packets	B-Protocol
as	O
they	O
are	O
received	O
by	O
the	O
far	O
end	O
,	O
adding	O
to	O
the	O
message	O
flow	O
between	O
the	O
endpoints	O
and	O
thus	O
the	O
protocol	O
load	O
.	O
</s>
<s>
Checksum	B-Algorithm
and	O
sequence	B-Protocol
number	I-Protocol
calculations	O
-	O
again	O
a	O
burden	O
on	O
a	O
general	O
purpose	O
CPU	B-General_Concept
to	O
perform	O
.	O
</s>
<s>
Sliding	O
window	O
calculations	O
for	O
packet	B-Protocol
acknowledgement	O
and	O
congestion	O
control	O
.	O
</s>
<s>
Connection	B-Protocol
termination	I-Protocol
.	O
</s>
<s>
Moving	O
some	O
or	O
all	O
of	O
these	O
functions	O
to	O
dedicated	O
hardware	O
,	O
a	O
TCP	B-Protocol
offload	I-Protocol
engine	I-Protocol
,	O
frees	O
the	O
system	O
's	O
main	O
CPU	B-General_Concept
for	O
other	O
tasks	O
.	O
</s>
<s>
As	O
of	O
2012	O
,	O
very	O
few	O
consumer	O
network	B-Protocol
interface	I-Protocol
cards	I-Protocol
support	O
TOE	O
.	O
</s>
<s>
A	O
generally	O
accepted	O
rule	O
of	O
thumb	O
is	O
that	O
1	O
Hertz	O
of	O
CPU	B-General_Concept
processing	O
is	O
required	O
to	O
send	O
or	O
receive	O
of	O
TCP/IP	B-Protocol
.	O
</s>
<s>
For	O
example	O
,	O
5Gbit/s	O
(	O
625MB/s	O
)	O
of	O
network	O
traffic	O
requires	O
5GHz	O
of	O
CPU	B-General_Concept
processing	O
.	O
</s>
<s>
This	O
implies	O
that	O
2	O
entire	O
cores	O
of	O
a	O
2.5GHz	O
multi-core	B-Architecture
processor	I-Architecture
will	O
be	O
required	O
to	O
handle	O
the	O
TCP/IP	B-Protocol
processing	O
associated	O
with	O
5Gbit/s	O
of	O
TCP/IP	B-Protocol
traffic	O
.	O
</s>
<s>
Many	O
of	O
the	O
CPU	B-General_Concept
cycles	O
used	O
for	O
TCP/IP	B-Protocol
processing	O
are	O
freed-up	O
by	O
TCP/IP	B-Protocol
offload	O
and	O
may	O
be	O
used	O
by	O
the	O
CPU	B-General_Concept
(	O
usually	O
a	O
server	B-Application
CPU	B-General_Concept
)	O
to	O
perform	O
other	O
tasks	O
such	O
as	O
file	O
system	O
processing	O
(	O
in	O
a	O
file	O
server	B-Application
)	O
or	O
indexing	O
(	O
in	O
a	O
backup	O
media	O
server	B-Application
)	O
.	O
</s>
<s>
In	O
other	O
words	O
,	O
a	O
server	B-Application
with	O
TCP/IP	B-Protocol
offload	O
can	O
do	O
more	O
server	B-Application
work	O
than	O
a	O
server	B-Application
without	O
TCP/IP	B-Protocol
offload	O
NICs	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
protocol	O
overhead	O
that	O
TOE	O
can	O
address	O
,	O
it	O
can	O
also	O
address	O
some	O
architectural	O
issues	O
that	O
affect	O
a	O
large	O
percentage	O
of	O
host	O
based	O
(	O
server	B-Application
and	O
PC	B-Device
)	O
endpoints	O
.	O
</s>
<s>
Many	O
older	O
end	O
point	O
hosts	O
are	O
PCI	B-Protocol
bus	I-Protocol
based	O
,	O
which	O
provides	O
a	O
standard	O
interface	O
for	O
the	O
addition	O
of	O
certain	O
peripherals	B-Device
such	O
as	O
Network	O
Interfaces	O
to	O
Servers	B-Application
and	O
PCs	B-Device
.	O
</s>
<s>
PCI	B-Protocol
is	O
inefficient	O
for	O
transferring	O
small	O
bursts	O
of	O
data	O
from	O
main	O
memory	O
,	O
across	O
the	O
PCI	B-Protocol
bus	I-Protocol
to	O
the	O
network	O
interface	O
ICs	O
,	O
but	O
its	O
efficiency	O
improves	O
as	O
the	O
data	O
burst	O
size	O
increases	O
.	O
</s>
<s>
Within	O
the	O
TCP	B-Protocol
protocol	I-Protocol
,	O
a	O
large	O
number	O
of	O
small	O
packets	B-Protocol
are	O
created	O
(	O
e.g.	O
</s>
<s>
acknowledgements	O
)	O
and	O
as	O
these	O
are	O
typically	O
generated	O
on	O
the	O
host	O
CPU	B-General_Concept
and	O
transmitted	O
across	O
the	O
PCI	B-Protocol
bus	I-Protocol
and	O
out	O
the	O
network	O
physical	O
interface	O
,	O
this	O
impacts	O
the	O
host	O
computer	O
IO	O
throughput	O
.	O
</s>
<s>
A	O
TOE	O
solution	O
,	O
located	O
on	O
the	O
network	O
interface	O
,	O
is	O
located	O
on	O
the	O
other	O
side	O
of	O
the	O
PCI	B-Protocol
bus	I-Protocol
from	O
the	O
CPU	B-General_Concept
host	O
so	O
it	O
can	O
address	O
this	O
I/O	O
efficiency	O
issue	O
,	O
as	O
the	O
data	O
to	O
be	O
sent	O
across	O
the	O
TCP	B-Protocol
connection	O
can	O
be	O
sent	O
to	O
the	O
TOE	O
from	O
the	O
CPU	B-General_Concept
across	O
the	O
PCI	B-Protocol
bus	I-Protocol
using	O
large	O
data	O
burst	O
sizes	O
with	O
none	O
of	O
the	O
smaller	O
TCP	B-Protocol
packets	B-Protocol
having	O
to	O
traverse	O
the	O
PCI	B-Protocol
bus	I-Protocol
.	O
</s>
<s>
One	O
of	O
the	O
first	O
patents	O
in	O
this	O
technology	O
,	O
for	O
UDP	B-Protocol
offload	O
,	O
was	O
issued	O
to	O
Auspex	O
Systems	O
in	O
early	O
1990	O
.	O
</s>
<s>
Auspex	O
founder	O
Larry	O
Boucher	O
and	O
a	O
number	O
of	O
Auspex	O
engineers	O
went	O
on	O
to	O
found	O
Alacritech	O
in	O
1997	O
with	O
the	O
idea	O
of	O
extending	O
the	O
concept	O
of	O
network	O
stack	O
offload	O
to	O
TCP	B-Protocol
and	O
implementing	O
it	O
in	O
custom	O
silicon	O
.	O
</s>
<s>
They	O
introduced	O
the	O
first	O
parallel-stack	O
full	O
offload	O
network	B-Protocol
card	I-Protocol
in	O
early	O
1999	O
;	O
the	O
company	O
's	O
SLIC	O
(	O
Session	O
Layer	O
Interface	O
Card	O
)	O
was	O
the	O
predecessor	O
to	O
its	O
current	O
TOE	O
offerings	O
.	O
</s>
<s>
Alacritech	O
holds	O
a	O
number	O
of	O
patents	O
in	O
the	O
area	O
of	O
TCP/IP	B-Protocol
offload	O
.	O
</s>
<s>
By	O
2002	O
,	O
as	O
the	O
emergence	O
of	O
TCP-based	O
storage	O
such	O
as	O
iSCSI	B-Protocol
spurred	O
interest	O
,	O
it	O
was	O
said	O
that	O
"	O
At	O
least	O
a	O
dozen	O
newcomers	O
,	O
most	O
founded	O
toward	O
the	O
end	O
of	O
the	O
dot-com	O
bubble	O
,	O
are	O
chasing	O
the	O
opportunity	O
for	O
merchant	O
semiconductor	O
accelerators	O
for	O
storage	O
protocols	O
and	O
applications	O
,	O
vying	O
with	O
half	O
a	O
dozen	O
entrenched	O
vendors	O
and	O
in-house	O
ASIC	O
designs.	O
"	O
</s>
<s>
In	O
2005	O
Microsoft	O
licensed	O
Alacritech	O
's	O
patent	O
base	O
and	O
along	O
with	O
Alacritech	O
created	O
the	O
partial	O
TCP	B-Protocol
offload	I-Protocol
architecture	O
that	O
has	O
become	O
known	O
as	O
TCP	B-Protocol
chimney	O
offload	O
.	O
</s>
<s>
TCP	B-Protocol
chimney	O
offload	O
centers	O
on	O
the	O
Alacritech	O
"	O
Communication	O
Block	O
Passing	O
Patent	O
"	O
.	O
</s>
<s>
At	O
the	O
same	O
time	O
,	O
Broadcom	O
also	O
obtained	O
a	O
license	O
to	O
build	O
TCP	B-Protocol
chimney	O
offload	O
chips	O
.	O
</s>
<s>
Instead	O
of	O
replacing	O
the	O
TCP	B-Protocol
stack	I-Protocol
with	O
a	O
TOE	O
entirely	O
,	O
there	O
are	O
alternative	O
techniques	O
to	O
offload	O
some	O
operations	O
in	O
co-operation	O
with	O
the	O
operating	O
system	O
's	O
TCP	B-Protocol
stack	I-Protocol
.	O
</s>
<s>
TCP	B-Protocol
checksum	B-Algorithm
offload	O
and	O
large	O
segment	O
offload	O
are	O
supported	O
by	O
the	O
majority	O
of	O
today	O
's	O
Ethernet	B-Protocol
NICs	I-Protocol
.	O
</s>
<s>
Newer	O
techniques	O
like	O
large	B-Device
receive	I-Device
offload	I-Device
and	O
TCP	B-Protocol
acknowledgment	O
offload	O
are	O
already	O
implemented	O
in	O
some	O
high-end	O
Ethernet	O
hardware	O
,	O
but	O
are	O
effective	O
even	O
when	O
implemented	O
purely	O
in	O
software	O
.	O
</s>
<s>
Parallel-stack	O
full	O
offload	O
gets	O
its	O
name	O
from	O
the	O
concept	O
of	O
two	O
parallel	O
TCP/IP	B-Protocol
Stacks	I-Protocol
.	O
</s>
<s>
The	O
second	O
or	O
"	O
parallel	O
stack	O
"	O
is	O
connected	O
between	O
the	O
Application	O
Layer	O
and	O
the	O
Transport	B-Architecture
Layer	I-Architecture
(	O
TCP	B-Protocol
)	O
using	O
a	O
"	O
vampire	O
tap	O
"	O
.	O
</s>
<s>
The	O
vampire	O
tap	O
intercepts	O
TCP	B-Protocol
connection	O
requests	O
by	O
applications	O
and	O
is	O
responsible	O
for	O
TCP	B-Protocol
connection	O
management	O
as	O
well	O
as	O
TCP	B-Protocol
data	O
transfer	O
.	O
</s>
<s>
Many	O
of	O
the	O
criticisms	O
in	O
the	O
following	O
section	O
relate	O
to	O
this	O
type	O
of	O
TCP	B-Protocol
offload	I-Protocol
.	O
</s>
<s>
HBA	O
(	O
Host	B-Architecture
Bus	I-Architecture
Adapter	I-Architecture
)	O
full	O
offload	O
is	O
found	O
in	O
iSCSI	B-Protocol
host	B-Architecture
adapters	I-Architecture
which	O
present	O
themselves	O
as	O
disk	O
controllers	O
to	O
the	O
host	O
system	O
while	O
connecting	O
(	O
via	O
TCP/IP	B-Protocol
)	O
to	O
an	O
iSCSI	B-Protocol
storage	O
device	O
.	O
</s>
<s>
This	O
type	O
of	O
TCP	B-Protocol
offload	I-Protocol
not	O
only	O
offloads	O
TCP/IP	B-Protocol
processing	O
but	O
it	O
also	O
offloads	O
the	O
iSCSI	B-Protocol
initiator	O
function	O
.	O
</s>
<s>
Because	O
the	O
HBA	O
appears	O
to	O
the	O
host	O
as	O
a	O
disk	O
controller	O
,	O
it	O
can	O
only	O
be	O
used	O
with	O
iSCSI	B-Protocol
devices	O
and	O
is	O
not	O
appropriate	O
for	O
general	O
TCP/IP	B-Protocol
offload	O
.	O
</s>
<s>
TCP	B-Protocol
chimney	O
offload	O
addresses	O
the	O
major	O
security	O
criticism	O
of	O
parallel-stack	O
full	O
offload	O
.	O
</s>
<s>
After	O
a	O
connection	O
has	O
been	O
established	O
between	O
the	O
local	O
host	O
(	O
usually	O
a	O
server	B-Application
)	O
and	O
a	O
foreign	O
host	O
(	O
usually	O
a	O
client	O
)	O
the	O
connection	O
and	O
its	O
state	O
are	O
passed	O
to	O
the	O
TCP	B-Protocol
offload	I-Protocol
engine	I-Protocol
.	O
</s>
<s>
Almost	O
all	O
TCP	B-Protocol
offload	I-Protocol
engines	I-Protocol
use	O
some	O
type	O
of	O
TCP/IP	B-Protocol
hardware	O
implementation	O
to	O
perform	O
the	O
data	O
transfer	O
without	O
host	O
CPU	B-General_Concept
intervention	O
.	O
</s>
<s>
Maintaining	O
control	O
of	O
TCP	B-Protocol
connections	O
allows	O
the	O
main	O
system	O
stack	O
to	O
implement	O
and	O
control	O
connection	O
security	O
.	O
</s>
<s>
Large	B-Device
receive	I-Device
offload	I-Device
(	O
LRO	O
)	O
is	O
a	O
technique	O
for	O
increasing	O
inbound	O
throughput	O
of	O
high-bandwidth	O
network	O
connections	O
by	O
reducing	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
(	O
CPU	B-General_Concept
)	O
overhead	O
.	O
</s>
<s>
It	O
works	O
by	O
aggregating	O
multiple	O
incoming	O
packets	B-Protocol
from	O
a	O
single	O
stream	B-Architecture
into	O
a	O
larger	O
buffer	O
before	O
they	O
are	O
passed	O
higher	O
up	O
the	O
networking	O
stack	O
,	O
thus	O
reducing	O
the	O
number	O
of	O
packets	B-Protocol
that	O
have	O
to	O
be	O
processed	O
.	O
</s>
<s>
Linux	B-Operating_System
implementations	O
generally	O
use	O
LRO	O
in	O
conjunction	O
with	O
the	O
New	B-Architecture
API	I-Architecture
(	O
NAPI	B-Architecture
)	O
to	O
also	O
reduce	O
the	O
number	O
of	O
interrupts	B-Application
.	O
</s>
<s>
,	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
supports	O
LRO	O
for	O
TCP	B-Protocol
in	O
software	O
only	O
.	O
</s>
<s>
FreeBSD	B-Operating_System
8	O
supports	O
LRO	O
in	O
hardware	O
on	O
adapters	O
that	O
support	O
it	O
.	O
</s>
<s>
LRO	O
should	O
not	O
operate	O
on	O
machines	O
acting	O
as	O
routers	O
,	O
as	O
it	O
breaks	O
the	O
end-to-end	B-Application
principle	I-Application
and	O
can	O
significantly	O
impact	O
performance	O
.	O
</s>
<s>
Generic	O
receive	O
offload	O
(	O
GRO	O
)	O
implements	O
a	O
generalised	O
LRO	O
in	O
software	O
that	O
is	O
n't	O
restricted	O
to	O
TCP/IPv4	O
or	O
have	O
the	O
issues	O
created	O
by	O
LRO	O
.	O
</s>
<s>
In	O
computer	B-Architecture
networking	I-Architecture
,	O
large	O
send	O
offload	O
(	O
LSO	O
)	O
is	O
a	O
technique	O
for	O
increasing	O
egress	O
throughput	O
of	O
high-bandwidth	O
network	O
connections	O
by	O
reducing	O
CPU	B-General_Concept
overhead	O
.	O
</s>
<s>
It	O
works	O
by	O
passing	O
a	O
multipacket	O
buffer	O
to	O
the	O
network	B-Protocol
interface	I-Protocol
card	I-Protocol
(	O
NIC	O
)	O
.	O
</s>
<s>
The	O
NIC	O
then	O
splits	O
this	O
buffer	O
into	O
separate	O
packets	B-Protocol
.	O
</s>
<s>
The	O
technique	O
is	O
also	O
called	O
TCP	B-Protocol
segmentation	B-Protocol
offload	O
(	O
TSO	O
)	O
or	O
generic	O
segmentation	B-Protocol
offload	O
(	O
GSO	O
)	O
when	O
applied	O
to	O
TCP	B-Protocol
.	O
</s>
<s>
When	O
a	O
system	O
needs	O
to	O
send	O
large	O
chunks	O
of	O
data	O
out	O
over	O
a	O
computer	B-Architecture
network	I-Architecture
,	O
the	O
chunks	O
first	O
need	O
breaking	O
down	O
into	O
smaller	O
segments	O
that	O
can	O
pass	O
through	O
all	O
the	O
network	O
elements	O
like	O
routers	O
and	O
switches	O
between	O
the	O
source	O
and	O
destination	O
computers	O
.	O
</s>
<s>
This	O
process	O
is	O
referred	O
to	O
as	O
segmentation	B-Protocol
.	O
</s>
<s>
Often	O
the	O
TCP	B-Protocol
protocol	I-Protocol
in	O
the	O
host	O
computer	O
performs	O
this	O
segmentation	B-Protocol
.	O
</s>
<s>
Offloading	O
this	O
work	O
to	O
the	O
NIC	O
is	O
called	O
TCP	B-Protocol
segmentation	B-Protocol
offload	O
(	O
TSO	O
)	O
.	O
</s>
<s>
With	O
some	O
intelligence	O
in	O
the	O
NIC	O
,	O
the	O
host	O
CPU	B-General_Concept
can	O
hand	O
over	O
the	O
64	O
KB	O
of	O
data	O
to	O
the	O
NIC	O
in	O
a	O
single	O
transmit-request	O
,	O
the	O
NIC	O
can	O
break	O
that	O
data	O
down	O
into	O
smaller	O
segments	O
of	O
1460	O
bytes	O
,	O
add	O
the	O
TCP	B-Protocol
,	O
IP	B-Protocol
,	O
and	O
data	O
link	O
layer	O
protocol	O
headers	O
—	O
according	O
to	O
a	O
template	O
provided	O
by	O
the	O
host	O
's	O
TCP/IP	B-Protocol
stack	I-Protocol
—	O
to	O
each	O
segment	O
,	O
and	O
send	O
the	O
resulting	O
frames	O
over	O
the	O
network	O
.	O
</s>
<s>
This	O
significantly	O
reduces	O
the	O
work	O
done	O
by	O
the	O
CPU	B-General_Concept
.	O
</s>
<s>
Some	O
network	B-Protocol
cards	I-Protocol
implement	O
TSO	O
generically	O
enough	O
that	O
it	O
can	O
be	O
used	O
for	O
offloading	O
fragmentation	O
of	O
other	O
transport	B-Architecture
layer	I-Architecture
protocols	O
,	O
or	O
for	O
doing	O
IP	B-Protocol
fragmentation	I-Protocol
for	O
protocols	O
that	O
do	O
n't	O
support	O
fragmentation	O
by	O
themselves	O
,	O
such	O
as	O
UDP	B-Protocol
.	O
</s>
<s>
Unlike	O
other	O
operating	O
systems	O
,	O
such	O
as	O
FreeBSD	B-Operating_System
,	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
does	O
not	O
include	O
support	O
for	O
TOE	O
(	O
not	O
to	O
be	O
confused	O
with	O
other	O
types	O
of	O
network	O
offload	O
)	O
.	O
</s>
<s>
While	O
there	O
are	O
patches	O
from	O
the	O
hardware	O
manufacturers	O
such	O
as	O
Chelsio	O
or	O
Qlogic	O
that	O
add	O
TOE	O
support	O
,	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
developers	O
are	O
opposed	O
to	O
this	O
technology	O
for	O
several	O
reasons	O
:	O
</s>
<s>
Security	O
–	O
because	O
TOE	O
is	O
implemented	O
in	O
hardware	O
,	O
patches	O
must	O
be	O
applied	O
to	O
the	O
TOE	O
firmware	B-Application
,	O
instead	O
of	O
just	O
software	O
,	O
to	O
address	O
any	O
security	O
vulnerabilities	O
found	O
in	O
a	O
particular	O
TOE	O
implementation	O
.	O
</s>
<s>
This	O
is	O
further	O
compounded	O
by	O
the	O
newness	O
and	O
vendor-specificity	O
of	O
this	O
hardware	O
,	O
as	O
compared	O
to	O
a	O
well	O
tested	O
TCP/IP	B-Protocol
stack	I-Protocol
as	O
is	O
found	O
in	O
an	O
operating	O
system	O
that	O
does	O
not	O
use	O
TOE	O
.	O
</s>
<s>
Limitations	O
of	O
hardware	O
–	O
because	O
connections	O
are	O
buffered	O
and	O
processed	O
on	O
the	O
TOE	O
chip	O
,	O
resource	O
starvation	O
can	O
more	O
easily	O
occur	O
as	O
compared	O
to	O
the	O
generous	O
CPU	B-General_Concept
and	O
memory	O
available	O
to	O
the	O
operating	O
system	O
.	O
</s>
<s>
Complexity	O
–	O
TOE	O
breaks	O
the	O
assumption	O
that	O
kernels	B-Operating_System
make	O
about	O
having	O
access	O
to	O
all	O
resources	O
at	O
all	O
times	O
–	O
details	O
such	O
as	O
memory	O
used	O
by	O
open	O
connections	O
are	O
not	O
available	O
with	O
TOE	O
.	O
</s>
<s>
TOE	O
also	O
requires	O
very	O
large	O
changes	O
to	O
a	O
networking	O
stack	O
in	O
order	O
to	O
be	O
supported	O
properly	O
,	O
and	O
even	O
when	O
that	O
is	O
done	O
,	O
features	O
like	O
quality	O
of	O
service	O
and	O
packet	B-Application
filtering	I-Application
might	O
not	O
work	O
.	O
</s>
<s>
Furthermore	O
,	O
TOE	O
firmware	B-Application
cannot	O
be	O
easily	O
modified	O
since	O
it	O
is	O
closed-source	O
.	O
</s>
