4 ms·

> ISPs tend to oversubscribe these services as well (where you and your 10 neighbors might all be able to sign up for 1Gbps symmetric service, but not everyone

> ISPs tend to oversubscribe these services as well (where you and your 10 neighbors might all be able to sign up for 1Gbps symmetric service, but not everyone can leverage that full 1Gbps at the same time). How does this work for FTTH? I know nothing about fibre optic networks. I had the impression that each subscriber has their own wavelength, or rather a range of wavelengths that captures their bandwidth, and that does not overlap with other subscribers. Otherwise I have no idea how passive optical networks could even work.

cesarb 2y ago
> How does this work for FTTH? I know nothing about fibre optic networks. I had the impression that each subscriber has their own wavelength, or rather a range of wavelengths that captures their bandwidth, and that does not overlap with other subscribers. The keyword to search for is GPON. It's multiplexed, each subscriber receives a few time slots in a shared wavelength. The transmissions from the subscribers don't collide because their time slots don't overlap.
chaz6 2y ago
In a typical passive optical network, one PON port is connected to 128 clients through the use of PLC splitters - unlike a WDM splitter which will insert or remove a specific wavelength, these simply split the whole signal. Where I work, that is a 4-4-8 configuration using 3 layers of splitters. The OLT (optical line terminal, head-end) will tell each ONU/ONT (optical network unit/terminal) how much airtime they can use to transmit - each ONT will take their turn in transmitting so as not to interrupt others. Part of this calculation is the distance the ONT is from the OLT - each ONT will be a different distance depending on the geographic location, which means each ONT will have a different latency. The ONU can request additional airtime if it has a large amound of data to transmit. The amount of airtime the OLT will allocate depends upon the CIR (committed information rate i.e. what will the ISP guarantee at a minimum) and the PIR (peak information rate - the maximum rate based on the subscribers service).
- rssoconnor 2y ago
  TDMA. Now that is a name I haven't heard in a long time.

cesarb 2y ago

> How does this work for FTTH? I know nothing about fibre optic networks. I had the impression that each subscriber has their own wavelength, or rather a range of wavelengths that captures their bandwidth, and that does not overlap with other subscribers. The keyword to search for is GPON. It's multiplexed, each subscriber receives a few time slots in a shared wavelength. The transmissions from the subscribers don't collide because their time slots don't overlap.

chaz6 2y ago

In a typical passive optical network, one PON port is connected to 128 clients through the use of PLC splitters - unlike a WDM splitter which will insert or remove a specific wavelength, these simply split the whole signal. Where I work, that is a 4-4-8 configuration using 3 layers of splitters. The OLT (optical line terminal, head-end) will tell each ONU/ONT (optical network unit/terminal) how much airtime they can use to transmit - each ONT will take their turn in transmitting so as not to interrupt others. Part of this calculation is the distance the ONT is from the OLT - each ONT will be a different distance depending on the geographic location, which means each ONT will have a different latency. The ONU can request additional airtime if it has a large amound of data to transmit. The amount of airtime the OLT will allocate depends upon the CIR (committed information rate i.e. what will the ISP guarantee at a minimum) and the PIR (peak information rate - the maximum rate based on the subscribers service).

rssoconnor 2y ago
TDMA. Now that is a name I haven't heard in a long time.