How Many VC4s Are Required for a 3000M Ethernet Service on OSN1800V?

1. Bandwidth Requirement for a 3000M Ethernet Service

When configuring a 3000M Ethernet service on the OSN1800V, at least 22 VC4s are required to provide sufficient bandwidth for testing and ensure that the Ethernet service can reach approximately 3G throughput.

The reason is that the actual bandwidth required by an Ethernet service is not simply equal to the nominal Ethernet rate. Ethernet overhead must also be taken into consideration.

Therefore, when a 3000M Ethernet service needs to be mapped and tested on an OSN1800V, 22 VC4s should be reserved at minimum.

2. Why Are More VC4s Required Than the Theoretical Bandwidth?

Ethernet traffic contains not only user data but also various frame and transmission overheads.

The overhead ratio is related to the size of the Ethernet frames being transmitted.

Generally:

Smaller Ethernet frames → Higher overhead ratio → Lower effective throughput

Larger Ethernet frames → Lower overhead ratio → Higher effective throughput

When the Ethernet frames are relatively small, more transmission resources are consumed by overhead. Therefore, additional VC4 bandwidth is required to achieve the expected 3G throughput.

3. Relationship Between Ethernet Frame Size and Throughput

For example, if the test traffic contains a large number of small Ethernet packets, the overhead becomes more significant. Even if the configured VC4 bandwidth appears to be close to 3G, the actual measured throughput may be lower than 3000M.

Therefore, 22 VC4s provide the necessary bandwidth margin for a 3G-class Ethernet service.

4. What Are VC4-4C, VC4-16C and VC4-64C?

VC4-C signals use virtual concatenation to combine multiple VC4 channels into one larger logical transmission channel.

For a 3000M Ethernet service, VC4-16C alone provides approximately 2.5G, which is not sufficient for a full 3G service. Therefore, additional VC4 resources are required depending on the specific mapping and configuration.

5. VC4-C Signals Are Different from STM-4/STM-16/STM-64

Although their nominal bandwidths are similar to STM-4, STM-16 and STM-64, VC4-C signals should not simply be regarded as ordinary STM signals.

The main difference is that VC4-C uses multiple VC4s as a concatenated logical channel, while the corresponding service board must support the required concatenation channels.

6. Overhead of VC4-C Signals

Another important characteristic is that a VC4-C signal does not use independent channel overhead for every VC4.

The concatenated signal uses the channel overhead of the first VC4 as the unified channel overhead.

This reduces the overhead compared with treating every VC4 as an independent service channel and is one of the characteristics of concatenated transmission.

7. Recommended Configuration Considerations

For a 3000M Ethernet service on OSN1800V, the following points should be checked before testing:

• Ensure that at least 22 VC4 bandwidths are available
• Confirm that the Ethernet service board supports the required VC4/concatenation mapping.
• Check whether VC4-C is supported by the relevant boards and software version.
• Consider the actual Ethernet frame size used during the throughput test.
• Do not judge the available Ethernet throughput only by the nominal VC4 bandwidth; Ethernet overhead must also be considered.

8. Summary

For an OSN1800V 3000M Ethernet service, at least 22 VC4s should be considered when preparing the transmission bandwidth for testing.

The actual Ethernet throughput is affected by frame size and transmission overhead. Smaller Ethernet frames introduce a higher overhead ratio and therefore result in lower effective throughput.

Meanwhile, VC4-4C, VC4-16C and VC4-64C combine multiple VC4s into larger logical channels, providing approximately 622M, 2.5G and 10G capacity respectively. However, the relevant equipment and service boards must support VC4 concatenation channels before these signals can be used.