EXFO IQS-8100 Series Transport Blazer for IQS-600 - Manual (Page 676)

Glossary
662 IQS-8100 Series Transport Blazer
Next-Gen - Virtual Concatenation (VCAT)
transport of the traffic to be unaware of concatenated nature of the signal.
As such, only the termination points in the transport path must support the
VCAT functionality.
In essence, virtual concatenation is an inverse multiplexing procedure
whereby the contiguous bandwidth is broken into individual SPEs at the
source transmitter and logically represents them in a virtual concatenation
group (VCG). Control packets, which contain the necessary information for
reassembling the original data stream at its destination PTE, are inserted in
some of the currently unused SONET/SDH overhead bytes (H4 byte for
high-order, and Z7 (SONET) and K4 (SDH) for low-order). This information
contains the sequence order of the channels and a frame number, which is
used as a time stamp. The VCG members are transported as individual
SPEs across the SONET/SDH network with all the intelligence required to
handle virtual concatenation located at the end points of the connections
(i.e., at the path termination equipment, or PTE). The receiving end-point
(PTE) is responsible for reassembling the original byte stream. This allows
SONET/SDH channels to be routed independently through the network
without requiring any acknowledgement of the virtual concatenation. In
this manner, virtually concatenated channels may be deployed on the
existing SONET/SDH network with a simple end-point node upgrade.
As presented in the table below, VCAT provides a much more efficient use
of the transport bandwidth for data user interfaces. With VCAT, an OC-48
link can carry two full Gigabit Ethernet signals with 95% of the link used
through seven virtual STS-3c/VC-4s each, instead of just one Gigabit
Ethernet signal with 42% of the link used through an STS-48c/AU-4-16c.