<s>
Ethernet	B-Protocol
Over	I-Protocol
SDH	I-Protocol
(	O
EoS	O
or	O
EoSDH	B-Protocol
)	O
or	O
Ethernet	B-Protocol
over	I-Protocol
SONET	I-Protocol
refers	O
to	O
a	O
set	O
of	O
protocols	O
which	O
allow	O
Ethernet	O
traffic	O
to	O
be	O
carried	O
over	O
synchronous	B-Protocol
digital	I-Protocol
hierarchy	I-Protocol
networks	O
in	O
an	O
efficient	O
and	O
flexible	O
way	O
.	O
</s>
<s>
The	O
same	O
functions	O
are	O
available	O
using	O
SONET	B-Protocol
.	O
</s>
<s>
Ethernet	O
frames	O
which	O
are	O
to	O
be	O
sent	O
on	O
the	O
SDH	O
link	O
are	O
sent	O
through	O
an	O
"	O
encapsulation	O
"	O
block	O
(	O
typically	O
Generic	B-Protocol
Framing	I-Protocol
Procedure	I-Protocol
or	O
GFP	O
)	O
to	O
create	O
a	O
synchronous	O
stream	O
of	O
data	O
from	O
the	O
asynchronous	O
Ethernet	O
packets	O
.	O
</s>
<s>
The	O
synchronous	O
stream	O
of	O
encapsulated	O
data	O
is	O
then	O
passed	O
through	O
a	O
mapping	O
block	O
which	O
typically	O
uses	O
virtual	B-Protocol
concatenation	I-Protocol
(	O
VCAT	O
)	O
to	O
route	O
the	O
stream	O
of	O
bits	O
over	O
one	O
or	O
more	O
SDH	O
paths	O
.	O
</s>
<s>
After	O
traversing	O
SDH	O
paths	O
,	O
the	O
traffic	O
is	O
processed	O
in	O
the	O
reverse	O
fashion	O
:	O
virtual	B-Protocol
concatenation	I-Protocol
path	O
processing	O
to	O
recreate	O
the	O
original	O
synchronous	O
byte	O
stream	O
,	O
followed	O
by	O
decapsulation	O
to	O
converting	O
the	O
synchronous	O
data	O
stream	O
to	O
an	O
asynchronous	O
stream	O
of	O
Ethernet	O
frames	O
.	O
</s>
<s>
An	O
additional	O
protocol	O
,	O
called	O
link	B-Protocol
capacity	I-Protocol
adjustment	I-Protocol
scheme	I-Protocol
(	O
LCAS	B-Protocol
)	O
,	O
allows	O
the	O
two	O
endpoints	O
of	O
the	O
SDH	O
paths	O
to	O
negotiate	O
which	O
paths	O
are	O
working	O
and	O
can	O
carry	O
traffic	O
versus	O
which	O
paths	O
should	O
not	O
be	O
used	O
to	O
carry	O
traffic	O
.	O
</s>
