Quote:
Originally Posted by Graham M
Most street cabinets have a thicker Coax cable running between them and the fiber terminates at the larger cabinets which you can normally tell apart as theyre about 6ft tall and hum (like me  ) |
Those aren't actually the nodes those are telco muxes and not related to the CATV side of the network. CATV fibre nodes are silent unless they need extra cooling and no bigger than your average cabinet.
---------- Post added at 23:03 ---------- Previous post was at 22:43 ----------
Quote:
Originally Posted by Sephiroth
I'm grateful for this link.
It is a good primer, but written in the 512Kbps days - 8 or 9 years ago, I guess. Now we're at 20 & 50 Mbps, it would be interesting to see an update; they haven't moved the UBR to the node so we're begining to unravel the postcode lottery issues, I'd have thought.
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I'll write up some more but basically where previously there was 1 downstream port feeding 10 nodes of 500 homes passed for example there are now 1 or 2 downstream ports feeding each node of 500 homes passed.
Downstream ports feed multiple nodes via optical splitting in the hubsite on the downstream side, and optical combining on the upstream side as it runs the other way.
Where nodes are larger, such as say 5000 homes passed, these nodes have had fibre deployed deeper into them, replacing some of the coax with fibre and reducing the size of the node. Nodes usually feed up to 4 coaxial trunks, so simply have 4 bits of string to the node instead of 1 and you have split it into 4 nodal areas (areas able to be logically and physically separated from the rest of the network by virtue of their own fibre feed from hubsite) of 1250 homes passed.
Once each coaxial trunk has its' own fibre the only solution then is to go further down the chain to where that trunk has 'branches' and replace that run of copper with fibre by building a new node. Feed 4 bits of string down to the next 4-way junction on the coaxial network and you've just split a 1250 home node down into 4 nodal areas of just over 300 homes each.
That's pretty much it. The CATV network is like a tree, push the fibre deeper into the network and closer towards the end of the branches as the less customers or leaves to continue the analogy share the fibre.
Rather than using additional fibre to produce new nodal areas one can also use WDM / wave division multiplexing and digitise the analogue signals at for transport down the WDM'd fibre and decode back to analogue when they reach their destination for delivery to CPE or CMTS depending if downstream or upstream.
On the VM network downstreams are largely 38Mbps apart from most of the new DOCSIS 3 downstreams which deliver around 50Mbps. A few legacy network downstreams are 27Mbps.