How get the raw binary stream from a fiber ? Assuming we have a SFP (ethernet, FC, GPON, other), this transceiver is not protocol independant, and will treat and interpret the binary stream received following the protocol design it implement, then transmit the binary flow corrected and treated to the upper layers. Do a classical transceiver could get and display the raw binary stream received ? (I doubt about this) In this case, how can we get the binary stream of an optical fiber ?

1 Answer 1


The optical signal is a binary stream. I assume you mean to diagnose the equivalent electrical signal.

SFP transceivers are ignorant to the actual L1 protocol in use. Their main job is to convert an electrical signal (e.g. 1000BASE-X) to an optical signal (1000BASE-SX) and vice versa. You could use the TD+/- and RD+/- pins to extract the raw, differential signals (see INF-8074i at snia.org for details). Those signals are still PCS and PMA encoded.

If you're trying to run a transceiver in stand-alone mode, without a suitable device slot, you'll need to make sure that the protocol is initialized correctly which may not be trivial (in addition to the xcvr initialization, obviously). In a PON environment you must make sure that the transmitter side is only active in its allocated time slot.

  • Thanks for the reply. You say "SFP transceivers are ignorant to the actual L1 protocol in use", why we could find Ethernet SFP, GPON SFP, FC SFP, or others SFP, if SFP transceiver are ignorant to layer 1 protocol ? Good idea for the TD+/- and RD+/- pins for the extraction. PCS and PMA are Ethernet standard, so it's not "totally" ignorant to layer 1 protocol ? Finally, my use case: using a 1:2 optical splitter to split GPON upstream signal to two fibers, 1 fiber to the OLT, and second fiber for the binary stream extraction we are discussing.
    – bdes31
    Commented Oct 22, 2019 at 11:09
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    @bdes31 The difference is the device with the SFP slot. The xcvr has a bit of memory (I2C EEPROM) where its compatibility etc is recorded (see section B4 in INF-8074i). Using that, a device can accept or reject a module in a certain port for a certain protocol. The module itself doesn't care.
    – Zac67
    Commented Oct 22, 2019 at 11:20
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    @bdes31 I was referring to PCS and PMA as these are the prevalent sublayers in on-topic devices here. Note that an SFP module is not much more than the PMD - all encoding is done in the switch/router/NIC. The splitter should work, provided you find a suitable SFP module (wavelength/speed) for reception.
    – Zac67
    Commented Oct 22, 2019 at 11:31
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    datasheets.maximintegrated.com/en/ds/MAX3748.pdf (3795 driver) There are slight enough differences that manufacturers only mark them for how they were tested. An ethernet SFP might work for FC or SONET, but also might not. (plus the greedier scum like to brand their optics, even when they are purely outsourced commodity parts)
    – Ricky
    Commented Oct 22, 2019 at 18:29

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