<s>
Spatial	B-Protocol
Reuse	I-Protocol
Protocol	I-Protocol
is	O
a	O
networking	O
protocol	O
developed	O
by	O
Cisco	O
.	O
</s>
<s>
SRP	O
was	O
first	O
developed	O
as	O
a	O
data-link	O
layer	O
protocol	O
to	O
link	O
Cisco	O
's	O
Dynamic	B-Protocol
Packet	I-Protocol
Transport	I-Protocol
(	O
DPT	O
)	O
protocol	O
(	O
a	O
method	O
of	O
delivering	O
packet-based	O
traffic	O
over	O
a	O
SONET/SDH	B-Protocol
infrastructure	O
)	O
to	O
the	O
physical	O
SONET/SDH	B-Protocol
layer	O
.	O
</s>
<s>
DPT	O
cannot	O
communicate	O
directly	O
with	O
the	O
physical	O
layer	O
,	O
therefore	O
it	O
was	O
necessary	O
to	O
develop	O
an	O
intermediate	O
layer	O
between	O
DPT	O
and	O
SONET/SDH	B-Protocol
,	O
SRP	O
filled	O
this	O
role	O
.	O
</s>
<s>
SRP	O
behaves	O
quite	O
like	O
the	O
Point-to-Point	B-Protocol
Protocol	I-Protocol
(	O
PPP	O
)	O
does	O
in	O
a	O
Packet	B-Protocol
Over	I-Protocol
SONET	I-Protocol
(	O
POS	O
)	O
environment	O
.	O
</s>
<s>
PPP	O
acts	O
as	O
an	O
abstraction	O
layer	O
between	O
a	O
higher	O
level	O
layer	O
2	O
technology	O
such	O
as	O
POS	O
and	O
a	O
layer	O
1	O
technology	O
such	O
as	O
SONET/SDH	B-Protocol
.	O
</s>
<s>
DPT	O
environments	O
contain	O
dual	O
,	O
counter-rotating	O
rings	O
,	O
somewhat	O
like	O
FDDI	B-Protocol
.	O
</s>
<s>
Consider	O
the	O
following	O
environment	O
:	O
a	O
ring	O
with	O
6	O
routers	O
(	O
A	O
through	O
F	O
sequentially	O
)	O
operating	O
at	O
OC-48c	B-Protocol
speed	O
(	O
2.5	O
Gbit/s	O
)	O
.	O
</s>
<s>
FDDI	B-Protocol
and	O
Token	B-Device
Ring	I-Device
networks	I-Device
use	O
source	O
stripping	O
,	O
whereas	O
DPT	O
and	O
SRP	O
use	O
destination	O
stripping	O
.	O
</s>
<s>
Again	O
,	O
consider	O
the	O
previous	O
example	O
of	O
the	O
OC-48c	B-Protocol
ring	O
.	O
</s>
<s>
In	O
a	O
source	O
stripping	O
(	O
FDDI	B-Protocol
or	O
Token	B-Device
Ring	I-Device
)	O
environment	O
,	O
in	O
the	O
event	O
that	O
router	O
A	O
wanted	O
to	O
communicate	O
with	O
router	O
D	O
,	O
the	O
entire	O
network	O
would	O
be	O
taken	O
up	O
while	O
the	O
data	O
was	O
being	O
transmitted	O
because	O
it	O
would	O
have	O
to	O
wait	O
until	O
it	O
completed	O
the	O
loop	O
and	O
got	O
back	O
to	O
router	O
A	O
before	O
it	O
was	O
eliminated	O
.	O
</s>
<s>
The	O
SRP	O
header	B-General_Concept
is	O
16	O
bits	O
(	O
2	O
bytes	O
)	O
total	O
.	O
</s>
<s>
These	O
fields	O
are	O
as	O
follows	O
:	O
Time	B-Protocol
to	I-Protocol
Live	I-Protocol
(	O
TTL	O
)	O
,	O
Ring	O
Identifier	O
(	O
R	O
)	O
,	O
Priority	O
(	O
PRI	O
)	O
,	O
Mode	O
,	O
and	O
Parity	O
(	O
P	O
)	O
.	O
</s>
