virtual concatenation group (VCG)
In Next Generation SDH( NG-SDH), the payloads of many small, virtual SDH containers are combined into one large group, the Virtual Concatenation Group (VCG), via Virtual Concatenation ( VCAT).
This procedure was specified by the International Telecommunication Union( ITU) in Recommendation G.707. According to this recommendation, the virtual small containers( VC) may have three different sizes: VC-12, the smallest data stream, is 2 Mbit/s; VC-3 is 50 Mbit/s; and VC-4 is 150 Mbit/s. After that, a 10 Mbit/s data stream would be split into four VC-12 containers.
The Virtual Concatenation Group is treated as a group of independent Virtual Concatenation, so each virtual concatenation occupies its own time slot across the end-to-end link.