Figure 10-25 Itu-T G.709 Frame Structure; Itu-T G.709 Optical Data Rates - Cisco ONS 15454 DWDM Reference Manual

Chapter 10 Network Reference
The rate is derived from the basic 9.95328 Gbps OC-192 rate. First, it has the 64-bit to 66-bit encoding
added, which brings it to the 10.3125 Gbps rate (10 Gbps x 66/64 = 10.3125 Gbps). Beyond that, the
WIS overhead is added, which is an additional two percent on top of the 10.3125 Gbps. This yields:

10.9.4 ITU-T G.709 Optical Data Rates

To understand optical networking data rates, an understanding of the ITU-T G.709 frame structure,
shown in
Figure 10-25 ITU-T G.709 Frame Structure
Columns: 1
Rows: 1
2
Info Bytes
3
4
Each of the sub-rows in
(16 x 255 = 4080). This is repeated four times to make up the complete ITU-T G.709 frame.
The Reed Solomon (RS) (255,239) designation indicates the forward error correction (FEC) bytes. There
are 16 FEC, or parity, bytes. The ITU-T G.709 protocol uses one overhead byte and 238 data bytes to
compute 16 parity bytes to form 255 byte blocks—the RS (255,239) algorithm. Interleaving the
information provides two key advantages. First, the encoding rate of each stream is reduced relative to
the line transmission rate and, second, it reduces the sensitivity to bursts of error. The interleaving
combined with the inherent correction strength of the RS (255,239) algorithm enables the correction of
transmission bursts of up to 128 consecutive errored bytes. As a result, the ITU-T G.709 contiguous burst
error correcting capability is enhanced 16 times above the capacity of the RS(255,239) algorithm by
itself.
ITU-T G.709 defines the Optical Transport Unit 2 (OTU2) rate as 10.70923 Gbps. ITU-T G.709 defines
three line rates:
1.
78-18343-02
10.3125 Gbps x .02 = 0.20625 Gbps
10.3125 Gbps + 0.20625 Gbps = 10.51875 Gbps
Figure 10-25, is needed.
Sub Row 3
Sub Row 2
Sub Row 1
17
Figure 10-25
2,666,057.143 kbps—Optical Transport Unit 1 (OTU1)
1 239 240
Info Bytes RS (255, 239)
Info Bytes RS (255, 239)
Info Bytes RS (255, 239)
Payload
contains 255 bytes. Sixteen are interleaved horizontally
Cisco ONS 15454 DWDM Reference Manual, R8.5
10.9.4 ITU-T G.709 Optical Data Rates
255
3825
FEC
4080
10-35