The general communication channel (GCC) was defined by G.709 is an in-band side channel used to carry transmission management and signaling information within optical transport network elements. Two types of GCC are available: * GCC0 – two bytes within OTUk overhead. GCC0 is terminated at every 3R (re-shaping, re-timing, re-amplification) point and used to carry GMPLS signaling protocol and/or management information. * GCC1/2 – four bytes (each of two bytes) within ODUk overhead. These bytes are used for client end-to-end information and shouldn't be touched by the OTN equipment.