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Author Topic: Carrier A43 and A43C  (Read 4429 times)


  • Reg Member
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Carrier A43 and A43C
« on: July 02, 2015, 11:18:55 AM »

A few days ago I had a daytime resync and my Fritzbox is now reporting it's on 'Carrier Record A43c' rather than 'A43' which as always been the case since purchase. I've had a quick Google and can find only minuscule references to it being an alternate tone set. Observations are that on A43c my line is super stable with no errors at all over a 4 day period.

Anyone else come across this?
Fritzbox 7490 l Plusnet FTTC


  • Kitizen
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Re: Carrier A43 and A43C
« Reply #1 on: July 02, 2015, 01:01:32 PM »

My SNRM has just shot up. I wonder if it's related?


  • Kitizen
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Re: Carrier A43 and A43C
« Reply #2 on: July 02, 2015, 02:49:03 PM »

The BT SIN 498, governing GEA over FTTC modems, requires a modem to support these 2 tonesets, and requires it to support no other ones (B43, V43, etc)

When I've looked in the past about what these tonesets actually are, the English description makes it sound like the complete set of tones for use in VDSL2 - but that's the job of the bandplan, to my mind. However, the ITU documents also have a table which (to my understanding) shows just 3 tones for upstream and 3 tones for downstream - and the A43 and A43C tonesets differ only in the 3 downstream tones.

That table suggests a very small set of tones, rather than a complete set.

However, the table comes under a heading of "Handshake", which suggests they might be definitions of the initial set of tones used by the modem to begin the handshake process ... during which the complete tones (defined by the bandplan) get agreed on.