The OTUk frame rate can be concluded based on OTU1, OTU2, and OTU3 frame rates. Which of the following is the correct formula for calculating the OTUk frame rate?

This formula correctly defines the relationship for the OTN bit rates, not frame rates. The question contains a common terminological error. The factor 255 / (239 - k) represents the ratio of the OTUk line bit rate to the corresponding OPUk payload bit rate for k=1, 2, and 3. This ratio accounts for all overhead (ODU, OTU, and FEC) added to the client payload. For OTU1 (k=1), the factor is 255/238. For OTU2 (k=2), the factor is 255/237. For OTU3 (k=3), the factor is 255/236. This structure is explicitly defined by the ITU-T G.709 standard, which governs OTN interfaces.

A. The denominator (235 - k) results in incorrect ratios (255/234, 255/233, etc.) that do not align with the standard OTN overhead structure.
C. The denominator (237 - k) results in incorrect ratios (255/236, 255/235, etc.) that do not match the specified overhead for OTUk levels.
D. The denominator (236 - k) results in incorrect ratios (255/235, 255/234, etc.) and is inconsistent with the G.709 standard.

1. International Telecommunication Union (ITU-T). (2021). Recommendation G.709/Y.1331: Interfaces for the Optical Transport Network. Clause 7.1

"Bit rates". This section specifies the bit rate relationships: "The OTUk (k=1

2

3) bit rate is (255/238)

(255/237) and (255/236) times the OPUk payload bit rate

respectively." This directly corresponds to the formula 255 / (239 - k).

2. Huawei Technologies Co.

Ltd. Huawei OTN Basic Principles Training Material. In sections covering OTN frame structure and rates

the derivation of OTUk line rates from OPUk payload rates is shown. For example

"OTU2 bit rate = OPU2 bit rate × 255/237

" which aligns with the formula in option B for k=2. (Note: Specific internal training document numbers are not public

but this information is standard in vendor OTN documentation based on G.709).

3. Ramaswami

R.

Sivarajan

K. N.

& Sasaki

G. H. (2010). Optical Networks: A Practical Perspective (3rd ed.). Morgan Kaufmann. In Chapter 4

"SONET/SDH and OTN

" the text describes the OTN hierarchy and rate calculations as specified by ITU-T G.709

including the overhead ratios that lead to the multipliers 255/238

255/237

and 255/236.