<s>
In	O
computer	B-Architecture
networking	I-Architecture
,	O
an	O
Ethernet	B-Protocol
frame	I-Protocol
is	O
a	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
protocol	B-Protocol
data	I-Protocol
unit	I-Protocol
and	O
uses	O
the	O
underlying	O
Ethernet	B-Protocol
physical	I-Protocol
layer	I-Protocol
transport	O
mechanisms	O
.	O
</s>
<s>
In	O
other	O
words	O
,	O
a	O
data	B-Protocol
unit	I-Protocol
on	O
an	O
Ethernet	O
link	O
transports	O
an	O
Ethernet	B-Protocol
frame	I-Protocol
as	O
its	O
payload	O
.	O
</s>
<s>
An	O
Ethernet	B-Protocol
frame	I-Protocol
is	O
preceded	O
by	O
a	O
preamble	O
and	O
start	B-Protocol
frame	I-Protocol
delimiter	I-Protocol
(	O
SFD	O
)	O
,	O
which	O
are	O
both	O
part	O
of	O
the	O
Ethernet	O
packet	B-Protocol
at	O
the	O
physical	B-Application
layer	I-Application
.	O
</s>
<s>
Each	O
Ethernet	B-Protocol
frame	I-Protocol
starts	O
with	O
an	O
Ethernet	O
header	O
,	O
which	O
contains	O
destination	O
and	O
source	O
MAC	O
addresses	O
as	O
its	O
first	O
two	O
fields	O
.	O
</s>
<s>
The	O
middle	O
section	O
of	O
the	O
frame	B-Protocol
is	O
payload	O
data	O
including	O
any	O
headers	O
for	O
other	O
protocols	O
(	O
for	O
example	O
,	O
Internet	B-Protocol
Protocol	I-Protocol
)	O
carried	O
in	O
the	O
frame	B-Protocol
.	O
</s>
<s>
The	O
frame	B-Protocol
ends	O
with	O
a	O
frame	B-Protocol
check	I-Protocol
sequence	I-Protocol
(	O
FCS	O
)	O
,	O
which	O
is	O
a	O
32-bit	O
cyclic	O
redundancy	O
check	O
used	O
to	O
detect	O
any	O
in-transit	O
corruption	O
of	O
data	O
.	O
</s>
<s>
A	O
data	B-Protocol
packet	I-Protocol
on	O
the	O
wire	O
and	O
the	O
frame	B-Protocol
as	O
its	O
payload	O
consist	O
of	O
binary	O
data	O
.	O
</s>
<s>
The	O
internal	O
structure	O
of	O
an	O
Ethernet	B-Protocol
frame	I-Protocol
is	O
specified	O
in	O
IEEE	O
802.3	O
.	O
</s>
<s>
The	O
table	O
below	O
shows	O
the	O
complete	O
Ethernet	O
packet	B-Protocol
and	O
the	O
frame	B-Protocol
inside	O
,	O
as	O
transmitted	O
,	O
for	O
the	O
payload	O
size	O
up	O
to	O
the	O
MTU	B-Protocol
of	O
1500	O
octets	O
.	O
</s>
<s>
Some	O
implementations	O
of	O
Gigabit	O
Ethernet	O
and	O
other	O
higher-speed	O
variants	O
of	O
Ethernet	O
support	O
larger	O
frames	O
,	O
known	O
as	O
jumbo	B-Protocol
frames	I-Protocol
.	O
</s>
<s>
The	O
optional	O
802.1Q	O
tag	O
consumes	O
additional	O
space	O
in	O
the	O
frame	B-Protocol
.	O
</s>
<s>
IEEE	O
802.1ad	O
(	O
Q-in-Q	O
)	O
allows	O
for	O
multiple	O
tags	O
in	O
each	O
frame	B-Protocol
.	O
</s>
<s>
An	O
Ethernet	O
packet	B-Protocol
starts	O
with	O
a	O
seven-octet	O
preamble	O
and	O
one-octet	O
start	B-Protocol
frame	I-Protocol
delimiter	I-Protocol
(	O
SFD	O
)	O
.	O
</s>
<s>
It	O
is	O
followed	O
by	O
the	O
SFD	O
to	O
provide	O
byte-level	O
synchronization	O
and	O
to	O
mark	O
a	O
new	O
incoming	O
frame	B-Protocol
.	O
</s>
<s>
For	O
Ethernet	O
variants	O
transmitting	O
serial	O
bits	O
instead	O
of	O
larger	O
symbols	O
,	O
the	O
(	O
uncoded	O
)	O
on-the-wire	O
bit	O
pattern	O
for	O
the	O
preamble	O
together	O
with	O
the	O
SFD	O
portion	O
of	O
the	O
frame	B-Protocol
is	O
10101010	O
10101010	O
10101010	O
10101010	O
10101010	O
10101010	O
10101010	O
10101011	O
;	O
The	O
bits	O
are	O
transmitted	O
in	O
order	O
,	O
from	O
left	O
to	O
right	O
.	O
</s>
<s>
The	O
SFD	O
is	O
the	O
eight-bit	O
(	O
one-byte	O
)	O
value	O
that	O
marks	O
the	O
end	O
of	O
the	O
preamble	O
,	O
which	O
is	O
the	O
first	O
field	O
of	O
an	O
Ethernet	O
packet	B-Protocol
,	O
and	O
indicates	O
the	O
beginning	O
of	O
the	O
Ethernet	B-Protocol
frame	I-Protocol
.	O
</s>
<s>
The	O
SFD	O
is	O
designed	O
to	O
break	O
the	O
bit	O
pattern	O
of	O
the	O
preamble	O
and	O
signal	O
the	O
start	O
of	O
the	O
actual	O
frame	B-Protocol
.	O
</s>
<s>
The	O
SFD	O
is	O
immediately	O
followed	O
by	O
the	O
destination	O
MAC	O
address	O
,	O
which	O
is	O
the	O
first	O
field	O
in	O
an	O
Ethernet	B-Protocol
frame	I-Protocol
.	O
</s>
<s>
Physical	B-Application
layer	I-Application
transceiver	O
circuitry	O
(	O
PHY	O
for	O
short	O
)	O
is	O
required	O
to	O
connect	O
the	O
Ethernet	O
MAC	O
to	O
the	O
physical	O
medium	O
.	O
</s>
<s>
The	O
connection	O
between	O
a	O
PHY	O
and	O
MAC	O
is	O
independent	O
of	O
the	O
physical	O
medium	O
and	O
uses	O
a	O
bus	O
from	O
the	O
media	B-Protocol
independent	I-Protocol
interface	I-Protocol
family	O
(	O
MII	B-Protocol
,	O
GMII	O
,	O
RGMII	O
,	O
SGMII	B-Protocol
,	O
XGMII	O
)	O
.	O
</s>
<s>
Fast	B-Protocol
Ethernet	I-Protocol
transceiver	O
chips	O
utilize	O
the	O
MII	B-Protocol
bus	O
,	O
which	O
is	O
a	O
four-bit	O
(	O
one	O
nibble	O
)	O
wide	O
bus	O
,	O
therefore	O
the	O
preamble	O
is	O
represented	O
as	O
14	O
instances	O
of	O
0x5	O
,	O
and	O
the	O
SFD	O
is	O
0x5	O
0xD	O
(	O
as	O
nibbles	O
)	O
.	O
</s>
<s>
The	O
header	O
features	O
destination	O
and	O
source	O
MAC	O
addresses	O
(	O
each	O
six	O
octets	O
in	O
length	O
)	O
,	O
the	O
EtherType	B-Protocol
field	O
and	O
,	O
optionally	O
,	O
an	O
IEEE	O
802.1Q	O
tag	O
or	O
IEEE	O
802.1ad	O
tag	O
.	O
</s>
<s>
The	O
EtherType	B-Protocol
field	O
is	O
two	O
octets	O
long	O
and	O
it	O
can	O
be	O
used	O
for	O
two	O
different	O
purposes	O
.	O
</s>
<s>
Values	O
of	O
1500	O
and	O
below	O
mean	O
that	O
it	O
is	O
used	O
to	O
indicate	O
the	O
size	O
of	O
the	O
payload	O
in	O
octets	O
,	O
while	O
values	O
of	O
1536	O
and	O
above	O
indicate	O
that	O
it	O
is	O
used	O
as	O
an	O
EtherType	B-Protocol
,	O
to	O
indicate	O
which	O
protocol	O
is	O
encapsulated	B-Protocol
in	O
the	O
payload	O
of	O
the	O
frame	B-Protocol
.	O
</s>
<s>
When	O
used	O
as	O
EtherType	B-Protocol
,	O
the	O
length	O
of	O
the	O
frame	B-Protocol
is	O
determined	O
by	O
the	O
location	O
of	O
the	O
interpacket	B-Protocol
gap	I-Protocol
and	O
valid	O
frame	B-Protocol
check	I-Protocol
sequence	I-Protocol
(	O
FCS	O
)	O
.	O
</s>
<s>
The	O
IEEE	O
802.1Q	O
tag	O
or	O
IEEE	O
802.1ad	O
tag	O
,	O
if	O
present	O
,	O
is	O
a	O
four-octet	O
field	O
that	O
indicates	O
virtual	B-General_Concept
LAN	I-General_Concept
(	O
VLAN	B-General_Concept
)	O
membership	O
and	O
IEEE	O
802.1p	O
priority	O
.	O
</s>
<s>
The	O
first	O
two	O
octets	O
of	O
the	O
tag	O
are	O
called	O
the	O
Tag	O
Protocol	O
IDentifier	O
(	O
TPID	O
)	O
and	O
double	O
as	O
the	O
EtherType	B-Protocol
field	O
indicating	O
that	O
the	O
frame	B-Protocol
is	O
either	O
802.1Q	O
or	O
802.1ad	O
tagged	O
.	O
</s>
<s>
Its	O
minimum	O
size	O
is	O
governed	O
by	O
a	O
requirement	O
for	O
a	O
minimum	O
frame	B-Protocol
transmission	O
of	O
64	O
octets	O
(	O
bytes	O
)	O
.	O
</s>
<s>
Non-standard	O
jumbo	B-Protocol
frames	I-Protocol
allow	O
for	O
larger	O
payloads	O
on	O
networks	O
built	O
to	O
support	O
them	O
.	O
</s>
<s>
The	O
frame	B-Protocol
check	I-Protocol
sequence	I-Protocol
(	O
FCS	O
)	O
is	O
a	O
four-octet	O
cyclic	O
redundancy	O
check	O
(	O
CRC	O
)	O
that	O
allows	O
detection	O
of	O
corrupted	O
data	O
within	O
the	O
entire	O
frame	B-Protocol
as	O
received	O
on	O
the	O
receiver	O
side	O
.	O
</s>
<s>
According	O
to	O
the	O
standard	O
,	O
the	O
FCS	O
value	O
is	O
computed	O
as	O
a	O
function	O
of	O
the	O
protected	O
MAC	O
frame	B-Protocol
fields	O
:	O
source	O
and	O
destination	O
address	O
,	O
length/type	O
field	O
,	O
MAC	O
client	O
data	O
and	O
padding	O
(	O
that	O
is	O
,	O
all	O
fields	O
except	O
the	O
FCS	O
)	O
.	O
</s>
<s>
The	O
end	O
of	O
a	O
frame	B-Protocol
is	O
usually	O
indicated	O
by	O
the	O
end-of-data-stream	O
symbol	O
at	O
the	O
physical	B-Application
layer	I-Application
or	O
by	O
loss	O
of	O
the	O
carrier	O
signal	O
;	O
an	O
example	O
is	O
10BASE-T	B-Protocol
,	O
where	O
the	O
receiving	O
station	O
detects	O
the	O
end	O
of	O
a	O
transmitted	O
frame	B-Protocol
by	O
loss	O
of	O
the	O
carrier	O
.	O
</s>
<s>
Later	O
physical	B-Application
layers	I-Application
use	O
an	O
explicit	O
end	O
of	O
data	O
or	O
end	O
of	O
stream	O
symbol	O
or	O
sequence	O
to	O
avoid	O
ambiguity	O
,	O
especially	O
where	O
the	O
carrier	O
is	O
continually	O
sent	O
between	O
frames	O
;	O
an	O
example	O
is	O
Gigabit	O
Ethernet	O
with	O
its	O
8b/10b	B-Protocol
encoding	I-Protocol
scheme	O
that	O
uses	O
special	O
symbols	O
which	O
are	O
transmitted	O
before	O
and	O
after	O
a	O
frame	B-Protocol
is	O
transmitted	O
.	O
</s>
<s>
Interpacket	B-Protocol
gap	I-Protocol
(	O
IPG	O
)	O
is	O
idle	O
time	O
between	O
packets	B-Protocol
.	O
</s>
<s>
After	O
a	O
packet	B-Protocol
has	O
been	O
sent	O
,	O
transmitters	O
are	O
required	O
to	O
transmit	O
a	O
minimum	O
of	O
96	O
bits	O
(	O
12	O
octets	O
)	O
of	O
idle	O
line	O
state	O
before	O
transmitting	O
the	O
next	O
packet	B-Protocol
.	O
</s>
<s>
There	O
are	O
several	O
types	O
of	O
Ethernet	B-Protocol
frames	I-Protocol
:	O
</s>
<s>
Ethernet	O
II	O
frame	B-Protocol
,	O
or	O
Ethernet	O
Version	O
2	O
,	O
or	O
DIX	O
frame	B-Protocol
is	O
the	O
most	O
common	O
type	O
in	O
use	O
today	O
,	O
as	O
it	O
is	O
often	O
used	O
directly	O
by	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
.	O
</s>
<s>
The	O
different	O
frame	B-Protocol
types	O
have	O
different	O
formats	O
and	O
MTU	B-Protocol
values	O
,	O
but	O
can	O
coexist	O
on	O
the	O
same	O
physical	O
medium	O
.	O
</s>
<s>
Differentiation	O
between	O
frame	B-Protocol
types	O
is	O
possible	O
based	O
on	O
the	O
table	O
on	O
the	O
right	O
.	O
</s>
<s>
In	O
addition	O
,	O
all	O
four	O
Ethernet	B-Protocol
frame	I-Protocol
types	O
may	O
optionally	O
contain	O
an	O
IEEE	O
802.1Q	O
tag	O
to	O
identify	O
what	O
VLAN	B-General_Concept
it	O
belongs	O
to	O
and	O
its	O
priority	O
(	O
quality	O
of	O
service	O
)	O
.	O
</s>
<s>
This	O
encapsulation	B-Protocol
is	O
defined	O
in	O
the	O
IEEE	O
802.3ac	O
specification	O
and	O
increases	O
the	O
maximum	O
frame	B-Protocol
by	O
4	O
octets	O
.	O
</s>
<s>
The	O
IEEE	O
802.1Q	O
tag	O
,	O
if	O
present	O
,	O
is	O
placed	O
between	O
the	O
Source	O
Address	O
and	O
the	O
EtherType	B-Protocol
or	O
Length	O
fields	O
.	O
</s>
<s>
This	O
is	O
located	O
in	O
the	O
same	O
place	O
as	O
the	O
EtherType/Length	O
field	O
in	O
untagged	O
frames	O
,	O
so	O
an	O
EtherType	B-Protocol
value	O
of	O
0x8100	O
means	O
the	O
frame	B-Protocol
is	O
tagged	O
,	O
and	O
the	O
true	O
EtherType/Length	O
is	O
located	O
after	O
the	O
Q-tag	O
.	O
</s>
<s>
The	O
TPID	O
is	O
followed	O
by	O
two	O
octets	O
containing	O
the	O
Tag	O
Control	O
Information	O
(	O
TCI	O
)	O
(	O
the	O
IEEE	O
802.1p	O
priority	O
(	O
quality	O
of	O
service	O
)	O
and	O
VLAN	B-General_Concept
id	O
)	O
.	O
</s>
<s>
The	O
Q-tag	O
is	O
followed	O
by	O
the	O
rest	O
of	O
the	O
frame	B-Protocol
,	O
using	O
one	O
of	O
the	O
types	O
described	O
above	O
.	O
</s>
<s>
Ethernet	B-Protocol
II	I-Protocol
framing	I-Protocol
(	O
also	O
known	O
as	O
DIX	O
Ethernet	O
,	O
named	O
after	O
DEC	O
,	O
Intel	O
and	O
Xerox	O
,	O
the	O
major	O
participants	O
in	O
its	O
design	O
)	O
,	O
defines	O
the	O
two-octet	O
EtherType	B-Protocol
field	O
in	O
an	O
Ethernet	B-Protocol
frame	I-Protocol
,	O
preceded	O
by	O
destination	O
and	O
source	O
MAC	O
addresses	O
,	O
that	O
identifies	O
an	O
upper	B-Protocol
layer	I-Protocol
protocol	I-Protocol
encapsulated	B-Protocol
by	O
the	O
frame	B-Protocol
data	O
.	O
</s>
<s>
Most	O
notably	O
,	O
an	O
EtherType	B-Protocol
value	O
of	O
0x0800	O
indicates	O
that	O
the	O
frame	B-Protocol
contains	O
an	O
IPv4	B-Protocol
datagram	O
,	O
0x0806	O
indicates	O
an	O
ARP	O
datagram	O
,	O
and	O
0x86DD	O
indicates	O
an	O
IPv6	B-Protocol
datagram	O
.	O
</s>
<s>
As	O
this	O
industry-developed	O
standard	O
went	O
through	O
a	O
formal	O
IEEE	O
standardization	O
process	O
,	O
the	O
EtherType	B-Protocol
field	O
was	O
changed	O
to	O
a	O
(	O
data	O
)	O
length	O
field	O
in	O
the	O
new	O
802.3	O
standard	O
.	O
</s>
<s>
Since	O
the	O
recipient	O
still	O
needs	O
to	O
know	O
how	O
to	O
interpret	O
the	O
frame	B-Protocol
,	O
the	O
standard	O
required	O
an	O
IEEE	O
802.2	O
header	O
to	O
follow	O
the	O
length	O
and	O
specify	O
the	O
type	O
.	O
</s>
<s>
Ethernet	B-Protocol
II	I-Protocol
framing	I-Protocol
is	O
the	O
most	O
common	O
in	O
Ethernet	O
local	O
area	O
networks	O
,	O
due	O
to	O
its	O
simplicity	O
and	O
lower	O
overhead	O
.	O
</s>
<s>
In	O
order	O
to	O
allow	O
some	O
frames	O
using	O
Ethernet	O
II	O
framing	O
and	O
some	O
using	O
the	O
original	O
version	O
of	O
802.3	O
framing	O
to	O
be	O
used	O
on	O
the	O
same	O
Ethernet	O
segment	O
,	O
EtherType	B-Protocol
values	O
must	O
be	O
greater	O
than	O
or	O
equal	O
to	O
1536	O
(	O
0x0600	O
)	O
.	O
</s>
<s>
That	O
value	O
was	O
chosen	O
because	O
the	O
maximum	O
length	O
of	O
the	O
payload	O
field	O
of	O
an	O
Ethernet	O
802.3	O
frame	B-Protocol
is	O
1500	O
octets	O
(	O
0x05DC	O
)	O
.	O
</s>
<s>
Thus	O
if	O
the	O
field	O
's	O
value	O
is	O
greater	O
than	O
or	O
equal	O
to	O
1536	O
,	O
the	O
frame	B-Protocol
must	O
be	O
an	O
Ethernet	O
II	O
frame	B-Protocol
,	O
with	O
that	O
field	O
being	O
a	O
type	O
field	O
.	O
</s>
<s>
If	O
it	O
's	O
less	O
than	O
or	O
equal	O
to	O
1500	O
,	O
it	O
must	O
be	O
an	O
IEEE	O
802.3	O
frame	B-Protocol
,	O
with	O
that	O
field	O
being	O
a	O
length	O
field	O
.	O
</s>
<s>
This	O
convention	O
allows	O
software	O
to	O
determine	O
whether	O
a	O
frame	B-Protocol
is	O
an	O
Ethernet	O
II	O
frame	B-Protocol
or	O
an	O
IEEE	O
802.3	O
frame	B-Protocol
,	O
allowing	O
the	O
coexistence	O
of	O
both	O
standards	O
on	O
the	O
same	O
physical	O
medium	O
.	O
</s>
<s>
Novell	O
's	O
"	O
raw	O
"	O
802.3	O
frame	B-Protocol
format	O
was	O
based	O
on	O
early	O
IEEE	O
802.3	O
work	O
.	O
</s>
<s>
Novell	O
used	O
this	O
as	O
a	O
starting	O
point	O
to	O
create	O
the	O
first	O
implementation	O
of	O
its	O
own	O
IPX	B-Protocol
Network	O
Protocol	O
over	O
Ethernet	O
.	O
</s>
<s>
They	O
did	O
not	O
use	O
any	O
LLC	O
header	O
but	O
started	O
the	O
IPX	B-Protocol
packet	B-Protocol
directly	O
after	O
the	O
length	O
field	O
.	O
</s>
<s>
This	O
does	O
not	O
conform	O
to	O
the	O
IEEE	O
802.3	O
standard	O
,	O
but	O
since	O
IPX	B-Protocol
always	O
has	O
FF	O
as	O
the	O
first	O
two	O
octets	O
(	O
while	O
in	O
IEEE	O
802.2	O
LLC	O
that	O
pattern	O
is	O
theoretically	O
possible	O
but	O
extremely	O
unlikely	O
)	O
,	O
in	O
practice	O
this	O
usually	O
coexists	O
on	O
the	O
wire	O
with	O
other	O
Ethernet	O
implementations	O
,	O
with	O
the	O
notable	O
exception	O
of	O
some	O
early	O
forms	O
of	O
DECnet	B-Protocol
which	O
got	O
confused	O
by	O
this	O
.	O
</s>
<s>
Novell	B-Operating_System
NetWare	I-Operating_System
used	O
this	O
frame	B-Protocol
type	O
by	O
default	O
until	O
the	O
mid-nineties	O
,	O
and	O
since	O
NetWare	B-Operating_System
was	O
then	O
very	O
widespread	O
,	O
while	O
IP	B-Protocol
was	O
not	O
,	O
at	O
some	O
point	O
in	O
time	O
most	O
of	O
the	O
world	O
's	O
Ethernet	O
traffic	O
ran	O
over	O
"	O
raw	O
"	O
802.3	O
carrying	O
IPX	B-Protocol
.	O
</s>
<s>
Since	O
NetWare	B-Operating_System
4.10	O
,	O
NetWare	B-Operating_System
defaults	O
to	O
IEEE	O
802.2	O
with	O
LLC	O
(	O
NetWare	B-Operating_System
Frame	B-Protocol
Type	O
Ethernet_802.2	O
)	O
when	O
using	O
IPX	B-Protocol
.	O
</s>
<s>
Some	O
protocols	O
,	O
such	O
as	O
those	O
designed	O
for	O
the	O
OSI	O
stack	O
,	O
operate	O
directly	O
on	O
top	O
of	O
IEEE	O
802.2	O
LLC	O
encapsulation	B-Protocol
,	O
which	O
provides	O
both	O
connection-oriented	O
and	O
connectionless	O
network	O
services	O
.	O
</s>
<s>
IEEE	O
802.2	O
LLC	O
encapsulation	B-Protocol
is	O
not	O
in	O
widespread	O
use	O
on	O
common	O
networks	O
currently	O
,	O
with	O
the	O
exception	O
of	O
large	O
corporate	O
NetWare	B-Operating_System
installations	O
that	O
have	O
not	O
yet	O
migrated	O
to	O
NetWare	B-Operating_System
over	O
IP	B-Protocol
.	O
</s>
<s>
In	O
the	O
past	O
,	O
many	O
corporate	O
networks	O
used	O
IEEE	O
802.2	O
to	O
support	O
transparent	O
translating	O
bridges	O
between	O
Ethernet	O
and	O
Token	B-Device
Ring	I-Device
or	O
FDDI	B-Protocol
networks	O
.	O
</s>
<s>
There	O
exists	O
an	O
Internet	O
standard	O
for	O
encapsulating	O
IPv4	B-Protocol
traffic	O
in	O
IEEE	O
802.2	O
LLC	O
SAP/SNAP	O
frames	O
.	O
</s>
<s>
It	O
is	O
almost	O
never	O
implemented	O
on	O
Ethernet	O
,	O
although	O
it	O
is	O
used	O
on	O
FDDI	B-Protocol
,	O
Token	B-Device
Ring	I-Device
,	O
IEEE	O
802.11	O
(	O
with	O
the	O
exception	O
of	O
the	O
5.9	O
GHz	O
band	O
,	O
where	O
it	O
uses	O
EtherType	B-Protocol
)	O
and	O
other	O
IEEE	O
802	O
LANs	O
.	O
</s>
<s>
IPv6	B-Protocol
can	O
also	O
be	O
transmitted	O
over	O
Ethernet	O
using	O
IEEE	O
802.2	O
LLC	O
SAP/SNAP	O
,	O
but	O
,	O
again	O
,	O
that	O
's	O
almost	O
never	O
used	O
.	O
</s>
<s>
By	O
examining	O
the	O
802.2	O
LLC	O
header	O
,	O
it	O
is	O
possible	O
to	O
determine	O
whether	O
it	O
is	O
followed	O
by	O
a	O
SNAP	B-Protocol
header	I-Protocol
.	O
</s>
<s>
The	O
LLC	O
header	O
includes	O
two	O
eight-bit	O
address	O
fields	O
,	O
called	O
service	O
access	O
points	O
(	O
SAPs	O
)	O
in	O
OSI	O
terminology	O
;	O
when	O
both	O
source	O
and	O
destination	O
SAP	O
are	O
set	O
to	O
the	O
value	O
0xAA	O
,	O
the	O
LLC	O
header	O
is	O
followed	O
by	O
a	O
SNAP	B-Protocol
header	I-Protocol
.	O
</s>
<s>
The	O
SNAP	B-Protocol
header	I-Protocol
allows	O
EtherType	B-Protocol
values	O
to	O
be	O
used	O
with	O
all	O
IEEE	O
802	O
protocols	O
,	O
as	O
well	O
as	O
supporting	O
private	O
protocol	O
ID	O
spaces	O
.	O
</s>
<s>
The	O
AppleTalk	B-Application
v2	O
protocol	O
suite	O
on	O
Ethernet	O
(	O
"	O
EtherTalk	B-Application
"	O
)	O
uses	O
IEEE	O
802.2	O
LLC	O
+	O
SNAP	O
encapsulation	B-Protocol
.	O
</s>
<s>
for	O
untagged	O
frames	O
,	O
since	O
the	O
packet	B-Protocol
size	O
is	O
maximum	O
1500	O
octet	O
payload	O
+	O
8	O
octet	O
preamble	O
+	O
14	O
octet	O
header	O
+	O
4	O
octet	O
trailer	O
+	O
minimum	O
interpacket	B-Protocol
gap	I-Protocol
corresponding	O
to	O
12	O
octets	O
=	O
1538	O
octets	O
.	O
</s>
<s>
when	O
802.1Q	O
VLAN	B-General_Concept
tagging	O
is	O
used	O
.	O
</s>
<s>
where	O
the	O
physical	B-Application
layer	I-Application
net	O
bit	O
rate	O
(	O
the	O
wire	O
bit	O
rate	O
)	O
depends	O
on	O
the	O
Ethernet	B-Protocol
physical	I-Protocol
layer	I-Protocol
standard	O
,	O
and	O
may	O
be	O
10	O
Mbit/s	O
,	O
100	O
Mbit/s	O
,	O
1	O
Gbit/s	O
or	O
10	O
Gbit/s	O
.	O
</s>
<s>
Maximum	O
throughput	O
for	O
100BASE-TX	B-Protocol
Ethernet	O
is	O
consequently	O
97.53	O
Mbit/s	O
without	O
802.1Q	O
,	O
and	O
97.28	O
Mbit/s	O
with	O
802.1Q	O
.	O
</s>
<s>
At	O
the	O
physical	B-Application
layer	I-Application
,	O
the	O
link	O
channel	O
and	O
equipment	O
do	O
not	O
know	O
the	O
difference	O
between	O
data	O
and	O
control	O
frames	O
.	O
</s>
<s>
A	O
runt	O
frame	B-Protocol
is	O
an	O
Ethernet	B-Protocol
frame	I-Protocol
that	O
is	O
less	O
than	O
the	O
IEEE	O
802.3	O
'	O
s	O
minimum	O
length	O
of	O
64	O
octets	O
.	O
</s>
<s>
Runt	O
frames	O
are	O
most	O
commonly	O
caused	O
by	O
collisions	O
;	O
other	O
possible	O
causes	O
are	O
a	O
malfunctioning	O
network	B-Protocol
card	I-Protocol
,	O
buffer	O
underrun	O
,	O
duplex	B-Protocol
mismatch	I-Protocol
or	O
software	O
issues	O
.	O
</s>
