WWWombat could you try and simplify your posts as sometime it comes across as a technical rant which then leaves me understanding less of what you posted.
sincere apologies if my post is to harsh I like it simple
Oooph. I felt that
You're quite right, of course. I'm very technical, and can write about that stuff at a very high level. I can also simplify stuff for the audience if needed, but it is indeed hard to do both at the same time. Perhaps I need to do a "TT;DR" (a "too technical" equivalent to the more famous
TL;DR) section, or take some lessons from
Wikipedia's adviceIf anyone wants me to re-state something into a more understandable form, they just need to let me know.
You might well find that the small "local exchanges" aren't really local exchanges after all ... and are just remote concentrators, with a voice circuit back to a parent local exchange anyway. And where that is the case, what is the likelihood that the parent for voice services is the same exchange as the fibre head-end?
Let me revisit this statement, then...
I'm starting from the discussion on the BT architecture for NGA, where some exchanges become a "parent" for NGA fibre services (by having a fibre head-end, containing the optical OLT equipment), leaving many exchanges as "children" without such equipment - the fibre just passes on by.
What I wanted to point out was that there is nothing new in this architecture: that the history of telecoms is full of cases where "child exchanges" are, in reality, a very cut-down model that cannot provide much of a service alone, and are dependent on the existence of a more-complete "parent" exchange.
We recently discussed a model from the Strowger days - the
200-line UAX-13 meant for rural areas. The intention was that this was fully automatic "child" - and that any service requiring an operator (by dialling '0') was passed up to the parent exchange, as would services requiring longer-distance access (by dialling '9'). At full size, this "child" exchange could service 200 subscriber lines, with perhaps 40 lines connecting it to the parent (known as junctions), and perhaps a maximum of 40 parallel calls.
This same "parent-child" arrangement continues into the days of digital telecoms, with the architecture featuring in both the System X and System Y (AXE-10) systems used by BT.
The smaller "child" exchanges are again simplified installations, dependent on the full parent exchange for access to the complete set of services - and, in particular, access to the trunk network. The "child" exchanges are known as "remote concentrators", while the parent exchanges are known as "digital local exchanges".
I know the internals of the AXE-10 better than I do the System X, so I can decipher some of the statistics for their "RSS" (remote subscriber switch), which is used as the System Y "remote concentrator". One "child" RSS can support up to 2,000 subscriber lines, with perhaps 500 lines being used to connect it back to the "parent" 'digital local exchange'. Hence the name "concentrator" - because the unit concentrates 2,000 subscribers down into just 500 connections back to the parent.
A "TT;DR" aside: For those who want
serious details on the AXE-10 for "small" applications, there is a
lot of detail in a
1990 Ericsson publication. If you take a look and think of that as heavy going, please be assured that it is a reasonable non-technical summary! The real technical details are excruciatingly worse
For an idea of scale ...
- We, as members of the public, think of BT as having something like 5,000-6,000 exchanges dotted around the country.
- BT actually only has something like 800 "digital local exchanges" that are proper, complete, "parent" exchanges.
- BT also has 7,000 remote concentrators.
- BT has another 150-200 exchanges, whose job is on the trunk network side, without any subscribers at all
(All details from
this site, describing the BT telephone network - marked as "current" in 2000, so prior to any 21CN changes)
My post to @NewtronStar ended by pondering whether the new "parent-child" relationships between exchanges for NGA fibre would happen to mirror the existing "parent-child" relationships for voice within the System X/System Y design.
Hope this lays it out a little better...