<s>
Frame	O
Relay	O
is	O
a	O
standardized	O
wide	O
area	O
network	O
(	O
WAN	O
)	O
technology	O
that	O
specifies	O
the	O
physical	B-Application
and	O
data	B-Protocol
link	I-Protocol
layers	I-Protocol
of	O
digital	O
telecommunications	O
channels	O
using	O
a	O
packet	B-Protocol
switching	I-Protocol
methodology	O
.	O
</s>
<s>
Originally	O
designed	O
for	O
transport	O
across	O
Integrated	B-Protocol
Services	I-Protocol
Digital	I-Protocol
Network	I-Protocol
(	O
ISDN	B-Protocol
)	O
infrastructure	O
,	O
it	O
may	O
be	O
used	O
today	O
in	O
the	O
context	O
of	O
many	O
other	O
network	O
interfaces	B-Application
.	O
</s>
<s>
Network	O
providers	O
commonly	O
implement	O
Frame	O
Relay	O
for	O
voice	O
(	O
VoFR	B-Protocol
)	O
and	O
data	O
as	O
an	O
encapsulation	B-Protocol
technique	O
used	O
between	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
(	O
LANs	B-General_Concept
)	O
over	O
a	O
WAN	O
.	O
</s>
<s>
Each	O
end-user	O
gets	O
a	O
private	O
line	O
(	O
or	O
leased	B-Architecture
line	I-Architecture
)	O
to	O
a	O
Frame	O
Relay	O
node	B-Protocol
.	O
</s>
<s>
It	O
is	O
less	O
expensive	O
than	O
leased	B-Architecture
lines	I-Architecture
and	O
that	O
is	O
one	O
reason	O
for	O
its	O
popularity	O
.	O
</s>
<s>
With	O
the	O
advent	O
of	O
Ethernet	O
over	O
fiber	O
optics	O
,	O
MPLS	B-Protocol
,	O
VPN	B-Application
and	O
dedicated	O
broadband	B-General_Concept
services	O
such	O
as	O
cable	B-Device
modem	I-Device
and	O
DSL	O
,	O
Frame	O
Relay	O
has	O
become	O
less	O
popular	O
in	O
recent	O
years	O
.	O
</s>
<s>
The	O
designers	O
of	O
Frame	O
Relay	O
aimed	O
to	O
provide	O
a	O
telecommunication	O
service	O
for	O
cost-efficient	O
data	O
transmission	O
for	O
intermittent	O
traffic	O
between	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
(	O
LANs	B-General_Concept
)	O
and	O
between	O
end-points	O
in	O
a	O
wide	O
area	O
network	O
(	O
WAN	O
)	O
.	O
</s>
<s>
Frame	O
Relay	O
puts	O
data	O
in	O
variable-size	O
units	O
called	O
"	O
frames	O
"	O
and	O
leaves	O
any	O
necessary	O
error-correction	B-Error_Name
(	O
such	O
as	O
retransmission	O
of	O
data	O
)	O
up	O
to	O
the	O
end-points	O
.	O
</s>
<s>
For	O
most	O
services	O
,	O
the	O
network	O
provides	O
a	O
permanent	O
virtual	O
circuit	O
(	O
PVC	O
)	O
,	O
which	O
means	O
that	O
the	O
customer	O
sees	O
a	O
continuous	O
,	O
dedicated	O
connection	O
without	O
having	O
to	O
pay	O
for	O
a	O
full-time	O
leased	B-Architecture
line	I-Architecture
,	O
while	O
the	O
service-provider	O
figures	O
out	O
the	O
route	O
each	O
frame	O
travels	O
to	O
its	O
destination	O
and	O
can	O
charge	O
based	O
on	O
usage	O
.	O
</s>
<s>
Frame	O
Relay	O
can	O
run	O
on	O
fractional	O
T-1	B-Protocol
or	O
full	O
T-carrier	O
system	O
carriers	O
(	O
outside	O
the	O
Americas	O
,	O
E1	O
or	O
full	O
E-carrier	O
)	O
.	O
</s>
<s>
Frame	O
Relay	O
complements	O
and	O
provides	O
a	O
mid-range	O
service	O
between	O
basic	O
rate	O
ISDN	B-Protocol
,	O
which	O
offers	O
bandwidth	O
at	O
128	O
kbit/s	O
,	O
and	O
Asynchronous	O
Transfer	O
Mode	O
(	O
ATM	O
)	O
,	O
which	O
operates	O
in	O
somewhat	O
similar	O
fashion	O
to	O
Frame	O
Relay	O
but	O
at	O
speeds	O
from	O
155.520	O
Mbit/s	O
to	O
622.080	O
Mbit/s	O
.	O
</s>
<s>
Frame	O
Relay	O
has	O
its	O
technical	O
base	O
in	O
the	O
older	O
X.25	B-Protocol
packet-switching	I-Protocol
technology	O
,	O
designed	O
for	O
transmitting	O
data	O
on	O
analog	O
voice	O
lines	O
.	O
</s>
<s>
Unlike	O
X.25	B-Protocol
,	O
whose	O
designers	O
expected	O
analog	O
signals	O
with	O
a	O
relatively	O
high	O
chance	O
of	O
transmission	O
errors	O
,	O
Frame	O
Relay	O
is	O
a	O
fast	B-Protocol
packet	I-Protocol
switching	I-Protocol
technology	O
operating	O
over	O
links	O
with	O
a	O
low	O
chance	O
of	O
transmission	O
errors	O
(	O
usually	O
practically	O
lossless	O
like	O
PDH	B-Protocol
)	O
,	O
which	O
means	O
that	O
the	O
protocol	O
does	O
not	O
attempt	O
to	O
correct	O
errors	O
.	O
</s>
<s>
(	O
However	O
,	O
digital	B-Architecture
networks	I-Architecture
offer	O
an	O
incidence	O
of	O
error	O
extraordinarily	O
small	O
relative	O
to	O
that	O
of	O
analog	O
networks	O
.	O
)	O
</s>
<s>
Frame	O
Relay	O
often	O
serves	O
to	O
connect	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
(	O
LANs	B-General_Concept
)	O
with	O
major	O
backbones	B-General_Concept
,	O
as	O
well	O
as	O
on	O
public	O
wide-area	O
networks	O
(	O
WANs	O
)	O
and	O
also	O
in	O
private	O
network	O
environments	O
with	O
leased	B-Architecture
lines	I-Architecture
over	O
T-1	B-Protocol
lines	O
.	O
</s>
<s>
Frame	O
Relay	O
originated	O
as	O
an	O
extension	O
of	O
integrated	B-Protocol
services	I-Protocol
digital	I-Protocol
network	I-Protocol
(	O
ISDN	B-Protocol
)	O
.	O
</s>
<s>
Its	O
designers	O
aimed	O
to	O
enable	O
a	O
packet-switched	B-Protocol
network	I-Protocol
to	O
transport	O
over	O
circuit-switched	O
technology	O
.	O
</s>
<s>
Frame	O
Relay	O
switches	O
create	O
virtual	O
circuits	O
to	O
connect	O
remote	O
LANs	B-General_Concept
to	O
a	O
WAN	O
.	O
</s>
<s>
The	O
Frame	O
Relay	O
network	O
exists	O
between	O
a	O
LAN	B-General_Concept
border	O
device	O
,	O
usually	O
a	O
router	O
,	O
and	O
the	O
carrier	O
switch	O
.	O
</s>
<s>
Each	O
Frame	O
Relay	O
protocol	B-Protocol
data	I-Protocol
unit	I-Protocol
(	O
PDU	O
)	O
consists	O
of	O
the	O
following	O
fields	O
:	O
</s>
<s>
To	O
ensure	O
that	O
the	O
01111110	O
pattern	O
does	O
not	O
appear	O
somewhere	O
inside	O
the	O
frame	O
,	O
bit	B-Protocol
stuffing	I-Protocol
and	I-Protocol
destuffing	I-Protocol
procedures	O
are	O
used	O
.	O
</s>
<s>
DLCI-Data	O
Link	O
Connection	O
Identifier	O
Bits	O
.	O
</s>
<s>
The	O
DLCI	B-Protocol
serves	O
to	O
identify	O
the	O
virtual	O
connection	O
so	O
that	O
the	O
receiving	O
end	O
knows	O
which	O
information	O
connection	O
a	O
frame	O
belongs	O
to	O
.	O
</s>
<s>
Note	O
that	O
this	O
DLCI	B-Protocol
has	O
only	O
local	O
significance	O
.	O
</s>
<s>
A	O
single	O
physical	B-Application
channel	I-Application
can	O
multiplex	B-Architecture
several	O
different	O
virtual	O
connections	O
.	O
</s>
<s>
Since	O
one	O
cannot	O
completely	O
ignore	O
the	O
bit	O
error-rate	O
of	O
the	O
medium	O
,	O
each	O
switching	O
node	B-Protocol
needs	O
to	O
implement	O
error	B-Error_Name
detection	I-Error_Name
to	O
avoid	O
wasting	O
bandwidth	O
due	O
to	O
the	O
transmission	O
of	O
erred	O
frames	O
.	O
</s>
<s>
The	O
error	B-Error_Name
detection	I-Error_Name
mechanism	O
used	O
in	O
Frame	O
Relay	O
uses	O
the	O
cyclic	O
redundancy	O
check	O
(	O
CRC	O
)	O
as	O
its	O
basis	O
.	O
</s>
<s>
The	O
Frame	O
Relay	O
network	O
uses	O
a	O
simplified	O
protocol	O
at	O
each	O
switching	O
node	B-Protocol
.	O
</s>
<s>
Committed	B-Protocol
Information	I-Protocol
Rate	I-Protocol
(	O
CIR	O
)	O
.	O
</s>
<s>
Once	O
the	O
network	O
has	O
established	O
a	O
connection	O
,	O
the	O
edge	O
node	B-Protocol
of	O
the	O
Frame	O
Relay	O
network	O
must	O
monitor	O
the	O
connection	O
's	O
traffic	O
flow	O
to	O
ensure	O
that	O
the	O
actual	O
usage	O
of	O
network	O
resources	O
does	O
not	O
exceed	O
this	O
specification	O
.	O
</s>
<s>
Frame	O
Relay	O
began	O
as	O
a	O
stripped-down	O
version	O
of	O
the	O
X.25	B-Protocol
protocol	O
,	O
releasing	O
itself	O
from	O
the	O
error-correcting	B-Error_Name
burden	O
most	O
commonly	O
associated	O
with	O
X.25	B-Protocol
.	O
</s>
<s>
Frame	O
Relay	O
uses	O
the	O
concept	O
of	O
shared	O
access	O
and	O
relies	O
on	O
a	O
technique	O
referred	O
to	O
as	O
"	O
best-effort	O
"	O
,	O
whereby	O
error-correction	B-Error_Name
practically	O
does	O
not	O
exist	O
and	O
practically	O
no	O
guarantee	O
of	O
reliable	O
data	O
delivery	O
occurs	O
.	O
</s>
<s>
Frame	O
Relay	O
provides	O
an	O
industry-standard	O
encapsulation	B-Protocol
,	O
utilizing	O
the	O
strengths	O
of	O
high-speed	O
,	O
packet-switched	B-Protocol
technology	O
able	O
to	O
service	O
multiple	O
virtual	O
circuits	O
and	O
protocols	O
between	O
connected	O
devices	O
,	O
such	O
as	O
two	O
routers	O
.	O
</s>
<s>
X.25	B-Protocol
remained	O
the	O
primary	O
standard	O
until	O
the	O
wide	O
availability	O
of	O
IP	O
made	O
packet	B-Protocol
switching	I-Protocol
almost	O
obsolete	O
.	O
</s>
<s>
It	O
was	O
used	O
sometimes	O
as	O
backbone	O
for	O
other	O
services	O
,	O
such	O
as	O
X.25	B-Protocol
or	O
IP	O
traffic	O
.	O
</s>
<s>
X.25	B-Protocol
was	O
an	O
important	O
early	O
WAN	O
protocol	O
,	O
and	O
is	O
often	O
considered	O
to	O
be	O
the	O
grandfather	O
of	O
Frame	O
Relay	O
as	O
many	O
of	O
the	O
underlying	O
protocols	O
and	O
functions	O
of	O
X.25	B-Protocol
are	O
still	O
in	O
use	O
today	O
(	O
with	O
upgrades	O
)	O
by	O
Frame	O
Relay	O
.	O
</s>
<s>
X.25	B-Protocol
provides	O
quality	O
of	O
service	O
and	O
error-free	O
delivery	O
,	O
whereas	O
Frame	O
Relay	O
was	O
designed	O
to	O
relay	O
data	O
as	O
quickly	O
as	O
possible	O
over	O
low	O
error	O
networks	O
.	O
</s>
<s>
Frame	O
Relay	O
eliminates	O
a	O
number	O
of	O
the	O
higher-level	O
procedures	O
and	O
fields	O
used	O
in	O
X.25	B-Protocol
.	O
</s>
<s>
Frame	O
Relay	O
was	O
designed	O
for	O
use	O
on	O
links	O
with	O
error-rates	O
far	O
lower	O
than	O
available	O
when	O
X.25	B-Protocol
was	O
designed	O
.	O
</s>
<s>
X.25	B-Protocol
prepares	O
and	O
sends	O
packets	O
,	O
while	O
Frame	O
Relay	O
prepares	O
and	O
sends	O
frames	O
.	O
</s>
<s>
X.25	B-Protocol
packets	O
contain	O
several	O
fields	O
used	O
for	O
error	B-Error_Name
checking	I-Error_Name
and	O
flow	O
control	O
,	O
most	O
of	O
which	O
are	O
not	O
used	O
by	O
Frame	O
Relay	O
.	O
</s>
<s>
The	O
frames	O
in	O
Frame	O
Relay	O
contain	O
an	O
expanded	O
link	B-Protocol
layer	I-Protocol
address	O
field	O
that	O
enables	O
Frame	O
Relay	O
nodes	O
to	O
direct	O
frames	O
to	O
their	O
destinations	O
with	O
minimal	O
processing	O
.	O
</s>
<s>
The	O
elimination	O
of	O
functions	O
and	O
fields	O
over	O
X.25	B-Protocol
allows	O
Frame	O
Relay	O
to	O
move	O
data	O
more	O
quickly	O
,	O
but	O
leaves	O
more	O
room	O
for	O
errors	O
and	O
larger	O
delays	O
should	O
data	O
need	O
to	O
be	O
retransmitted	O
.	O
</s>
<s>
X.25	B-Protocol
packet	B-Protocol
switched	I-Protocol
networks	I-Protocol
typically	O
allocated	O
a	O
fixed	O
bandwidth	O
through	O
the	O
network	O
for	O
each	O
X.25	B-Protocol
access	O
,	O
regardless	O
of	O
the	O
current	O
load	O
.	O
</s>
<s>
Frame	O
Relay	O
networks	O
can	O
dynamically	O
allocate	O
bandwidth	O
at	O
both	O
the	O
physical	B-Application
and	O
logical	O
channel	O
level	O
.	O
</s>
<s>
As	O
a	O
WAN	O
protocol	O
,	O
Frame	O
Relay	O
is	O
most	O
commonly	O
implemented	O
at	O
Layer	B-Protocol
2	I-Protocol
(	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
)	O
of	O
the	O
Open	O
Systems	O
Interconnection	O
(	O
OSI	O
)	O
seven	O
layer	O
model	O
.	O
</s>
<s>
Two	O
types	O
of	O
circuits	O
exist	O
:	O
permanent	O
virtual	O
circuits	O
(	O
PVCs	O
)	O
which	O
are	O
used	O
to	O
form	O
logical	O
end-to-end	O
links	O
mapped	O
over	O
a	O
physical	B-Application
network	O
,	O
and	O
switched	O
virtual	O
circuits	O
(	O
SVCs	O
)	O
.	O
</s>
<s>
These	O
Frame	O
Relay	O
extensions	O
are	O
referred	O
to	O
as	O
the	O
local	B-Protocol
management	I-Protocol
interface	I-Protocol
(	O
LMI	O
)	O
.	O
</s>
<s>
Datalink	O
connection	O
identifiers	O
(	O
DLCIs	B-Protocol
)	O
are	O
numbers	O
that	O
refer	O
to	O
paths	O
through	O
the	O
Frame	O
Relay	O
network	O
.	O
</s>
<s>
They	O
are	O
only	O
locally	O
significant	O
,	O
which	O
means	O
that	O
when	O
device-A	O
sends	O
data	O
to	O
device-B	O
it	O
will	O
most	O
likely	O
use	O
a	O
different	O
DLCI	B-Protocol
than	O
device-B	O
would	O
use	O
to	O
reply	O
.	O
</s>
<s>
Multiple	O
virtual	O
circuits	O
can	O
be	O
active	O
on	O
the	O
same	O
physical	B-Application
end-points	O
(	O
performed	O
by	O
using	O
subinterfaces	B-Application
)	O
.	O
</s>
<s>
The	O
LMI	O
global	O
addressing	O
extension	O
gives	O
Frame	O
Relay	O
data-link	O
connection	O
identifier	O
(	O
DLCI	B-Protocol
)	O
values	O
global	O
rather	O
than	O
local	O
significance	O
.	O
</s>
<s>
DLCI	B-Protocol
values	O
become	O
DTE	O
addresses	O
that	O
are	O
unique	O
in	O
the	O
Frame	O
Relay	O
WAN	O
.	O
</s>
<s>
Individual	O
network	O
interfaces	B-Application
and	O
the	O
end	O
nodes	O
attached	O
to	O
them	O
,	O
for	O
example	O
,	O
can	O
be	O
identified	O
by	O
using	O
standard	O
address-resolution	O
and	O
discovery	O
techniques	O
.	O
</s>
<s>
In	O
addition	O
,	O
the	O
entire	O
Frame	O
Relay	O
network	O
appears	O
to	O
be	O
a	O
typical	O
LAN	B-General_Concept
to	O
routers	O
on	O
its	O
periphery	O
.	O
</s>
<s>
Frame	O
Relay	O
connections	O
are	O
often	O
given	O
a	O
committed	B-Protocol
information	I-Protocol
rate	I-Protocol
(	O
CIR	O
)	O
and	O
an	O
allowance	O
of	O
burstable	O
bandwidth	O
known	O
as	O
the	O
extended	O
information	O
rate	O
(	O
EIR	O
)	O
.	O
</s>
<s>
Frame	O
Relay	O
aimed	O
to	O
make	O
more	O
efficient	O
use	O
of	O
existing	O
physical	B-Application
resources	O
,	O
permitting	O
the	O
over-provisioning	O
of	O
data	O
services	O
by	O
telecommunications	O
companies	O
to	O
their	O
customers	O
,	O
as	O
clients	O
were	O
unlikely	O
to	O
be	O
using	O
a	O
data	O
service	O
45	O
percent	O
of	O
the	O
time	O
.	O
</s>
<s>
Telecommunications	O
companies	O
often	O
sell	O
Frame	O
Relay	O
to	O
businesses	O
looking	O
for	O
a	O
cheaper	O
alternative	O
to	O
dedicated	B-Protocol
lines	I-Protocol
;	O
its	O
use	O
in	O
different	O
geographic	O
areas	O
depended	O
greatly	O
on	O
governmental	O
and	O
telecommunication	O
companies	O
 '	O
policies	O
.	O
</s>
<s>
As	O
of	O
June	O
2007	O
,	O
AT&T	O
was	O
the	O
largest	O
Frame	O
Relay	O
service	O
provider	O
in	O
the	O
US	O
,	O
with	O
local	B-General_Concept
networks	I-General_Concept
in	O
22	O
states	O
,	O
plus	O
national	O
and	O
international	O
networks	O
.	O
</s>
<s>
When	O
multiplexing	B-Architecture
packet	O
data	O
from	O
different	O
virtual	O
circuits	O
or	O
flows	O
,	O
quality	O
of	O
service	O
concerns	O
often	O
arise	O
.	O
</s>
<s>
IP	B-Protocol
fragmentation	I-Protocol
is	O
a	O
method	O
for	O
addressing	O
this	O
.	O
</s>
<s>
FRF.12	B-Protocol
is	O
a	O
specification	O
from	O
the	O
Frame	O
Relay	O
Forum	O
which	O
specifies	O
how	O
to	O
perform	O
fragmentation	O
on	O
frame	O
relay	O
traffic	O
primarily	O
for	O
voice	O
traffic	O
.	O
</s>
<s>
The	O
FRF.12	B-Protocol
specification	O
describes	O
the	O
method	O
of	O
fragmenting	O
Frame	O
Relay	O
frames	O
into	O
smaller	O
frames	O
.	O
</s>
