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How capture GPON upstream traffic ?

Some professional tools exist: GPON doctor, GPON Xpert, displaying the GPON frames, etc, but is it possible to perform this task without using these tools ?

My understanding: Since GPON is not Ethernet, we could not interpret easily the frame with classical Ethernet Adapter . We need to convert the GPON to Ethernet with optical terminal (typical: ONT) . But the ONT respect a process to initialize it (state Init O1 to O5 Operational, G.984.3 10.3.1 section) and to start the communication and extract Ethernet frames from GEM frames .

I would have the following scheme: using a 1:2 splitter: ONT -> 1:2 . 1 fiber to the OLT to continue the ONU OLT communication, and get the splitted signal to the second fiber, but how interpret it and convert it to Ethernet (Ethernet extraction from GPON GEM frame), to allow the analyze for example with wireshark .

If it's not possible, we should go at the bottom layer: pure raw binary stream extraction, and in this perspective, any device could get and display the raw binary stream of the splitted fiber in this example ?

Or any others suggestions about this work ?

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GPON is a a collective term for various technology including 1G Ethernet variants (1000BASE-PX10, 1000BASE-PX20) or 10G-EPON 10GBASE-P(X). However, most Ethernet equipment isn't compatible with -P. First you need to find out what exactly it is you want to capture, then select/build the required device.

We need to convert the GPON to Ethernet with optical terminal (typical: ONT)

Standard ONTs are not likely to be able to capture a single-direction data stream. You might need specialized hardware. Product recommendations are off-topic here, however.

With a good knowledge of hardware you might be able to build that capturing device yourself (using a generic SFP as in your previous question), but those details would only be suited at Electrical Engineering or so.

is it possible to perform this task without using these tools?

Possible? Absolutely. Practical? Possibly.

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