Comment on Google Fiber goes big with 20-gig plan

• Kazumara@feddit.de ⁨11⁩ ⁨months⁩ ago

  As opposed to a normal fiber link to the switch in the central office. No oversubscription or shared media.

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  • Squizzy@lemmy.world ⁨11⁩ ⁨months⁩ ago

    I don’t understand how it is shared media through a PON system? What is the name for this alternative I’d like to look into it.

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    • Kazumara@feddit.de ⁨11⁩ ⁨months⁩ ago

      In a typical PON (GPON, XG-PON, XGS-PON) you have a single fiber from the central office to the optical splitter in the street, from where up to 64 subscribers are connected one fiber each. The OLT in the central office sends on one wavelength (e.g. 1577 nm) and all subscriber ONTs send on one other common wavelenth (e.g. 1270 nm).

      In both directions a time division technique is applied. I believe in the downstream the individual time frames are encrypted such that only the real destination ONT can read the bitstream. In the upstream the ONTs have to make sure only to send in their own slots, as otherwise the OLT would receive superimposed optical signals that couldn’t be read.

      The alternative doesn’t really have a set of standards like PON, as you can just use whatever optical transceivers you want for each customer individually. Though I guess that for operational reasons an ISP would still standardise the setup for all customers. For example the ISP whose services I subscribe to tells customers to use “Bidir LR, 10 km, TX1310, RX1490-1550 nm”, as 1G, 10G, or 25G, depending on which you order.

      To distringuish such a setup from a PON setup I have seen it being called point-to-point (P2P).

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