EXFO FTB-8100 Series Transport Blazer for FTB-500 - Manual (Page 687)

Glossary
SONET/SDH Application 673
Next-Gen - Link-Capacity Adjustment Scheme (LCAS)
Next-Gen - Link-Capacity Adjustment Scheme
(LCAS)
LCAS, as defined per ITU-T recommendation G.7042, is a complementary
technology to virtual concatenation. LCAS allows for the dynamic changing
of the size of a VCAT group. To do so, signaling messages are exchanged
within the same SONET/SDH overhead bytes used for VCAT (H4 for HO
VCAT and Z7/K4 for LO VCAT) between the source PTE to the end-point
PTE in order to change the number of tributaries being used by a virtually
concatenated group (VCG). For example, the number of tributaries can be
increased or decreased in response to an identified change in
service-bandwidth requirement, or in response to a fault condition of an
existing VCG member.
Increasing VCG Size Using LCAS
LCAS works by ensuring synchronization between the sender (PTE),
referred to as the source node, and receiver (PTE), referred to as the sink
node, during the increase/decrease of the size of a virtually concatenated
circuit, in such a way that it doesn’t interfere with the underlying client data
service. Should failures occur on an individual member of a group, the size
of the group can be reduced temporarily, instead of taking the entire group
out of service (which would be the case if LCAS were not enabled – the
entire VCG would be declared as “failed” in the event of a failure of one
VCG members). With LCAS, once the defect is repaired, the group size can
be restored to full bandwidth without affecting the underlying service.