In the OTN architecture, the ESC mode is adopted. Sometimes, the GCC byte mode needs to be set by using the :cm-set-fiberport command. The last parameter of this command indicates the channel rate. 13 denotes three-byte GCC0; 14 denotes the GCC12_9 byte; and, 15 denotes the GCC12_18 byte. How are GCC0, GCC12_9, and GCC_18 calculated?
1. The channel rate is an equivalent rate. GCC0 indicates that the bandwidth provided by GCC0 is 3*64K; GCC12_9 indicates that the bandwidth provided by GCC1 and GCC2 together is 9*64K. In the OTN architecture, GCC0 is of two bytes, and the frame structure is always 4*4080 bytes.
2. At the 2.5G rate, the bandwidth of GCC0 is calculated by using the following formula:
Frame frequency = 2.5G/(4*4080*8)
Bandwidth of GCC0 = 2*frame frequency*8
Hence, the approximate bandwidth is: 320K = 5*64K
Likewise, at the 5G and 10G rates, the approximate bandwidth is 10*64K and 20*64K respectively. (The length of an OTN frame is fixed, whereas the frame frequency varies. ) Due to the limit on CPU channels, the bandwidth provided by GCC0 must be reduced so that the equipment can be used like the previous equipment. That is, GCC0 is used as three bytes only. Hence, the supervisory bandwidth provided by GCC0 is 3*64K.
3. According to the preceding calculation method, at the 2.5G rate, the combination of GCC1 and GCC2 provides 10*64K bandwidth. That is, GCC1 and GCC2 are used as nine bytes. At the 5G and 10G rates, the combination of GCC1 and GCC2 (GCC1 and GCC2 are always bound together when used) provides 20*64K and 40*64K bandwidth.
3. The OTN framed OTU board supports DCC types GCC0, GCC12_9, and GCC12_18. Where, the OTN2.5G board supports GCC0 and GCC12_9, and the OTN5G and OTN10G boards support GCC0 and GCC12_18.