This topic

PON infrastructure question

PlanetVisitor — Sat, 25 Oct 2025 14:46:04 GMT

I’m a little bit confused here. Doing some research on how FTTP works:

So, an OLT port provides a single fibre to an SASA. (The SASA is in a cabinet, I assume). The SASA then splits this into 30 separate fibres. Each fibre then goes to a CBT that provides the connection to the home. Fine so far, (I think).

However, I see CBTs come in 4, 8 and 12 port and pictures appear to show a single input and multiple output ports on these devices.

So, my question is, is it one fibre from the SASA that is then split again by the CBT or does a 4 port CBT (for example) require 4 fibres feeding it to provide the 4 outputs? (It maybe that the "single" input is actually one cable with multiple fibres, of course).

I'd be grateful if anyone could clarify this point for me please.

Re: PON infrastructure question

iniltous — Sat, 25 Oct 2025 15:08:38 GMT

SASA are in a enclosure (Node ) not a cabinet , they are passive, not requiring power so no need to put them in something like a cabinet….large and extra large Nodes are always mounted underground, small and medium nodes can be mounted on a telegraph pole as well as underground , UG Nodes are mounted in underground structures (jointboxes ).

Although a single cable enters a CBT , it’s a multi fibre cable (12 fibres ) only the required nunber of fibres are spliced through at the Node , so for example, if a CBT had a ‘demand’ of 7 addresses , an 8 port CBT is used , ( it has a 12 fibre tail ) , 7 of the 12 fibres in that tail are spliced through from splitter outputs to the CBT , making 7 ports on the CBT ‘live’ , fibres 8-12 usually put into storage in the Node , ports 7 & 8 on the CBT are ‘dark’ , no light present on them .

The size of CBT is determined by the number of addresses it’s designed to service ( ‘the demand’ )

Re: PON infrastructure question

PlanetVisitor — Sat, 25 Oct 2025 15:07:09 GMT

Excellent. Thanks for the prompt reply.

I'd give you a thumb up but it doesn't seem to be available.