Why Does An Incoming Phone Call Affect Upstream?

I've always noticed that when we having an incoming phone call, there are several upstream CRC's. Why does this happen? Is it because the upstream spectrum is closer to the phone signal's?

Edited by deleted (Tue 04-Apr-17 19:14:36)

That is correct.

Always remember my Telecoms lecturer at college saying voice occupies 300-3400hz on the telephone line. Upstream isn't that far off.

For ADSL, on VDSL2 things are different a quick version of the bands https://en.wikipedia.org/wiki/VDSL

http://www.niccstandards.org.uk/files/current/ND1436... and note the chat about band plans

I wonder if this also occurs on out-going phone calls, particularly to the same numbers if the CRCs are confined to certain numbers on the incoming calls?

Thanks for explaining. I don't notice any upstream CRC's with outgoing phone calls. Maybe this is because Upstream data is sent from the EU instead of receive.

In reply to a post by WilliamGrimsley:

Thanks for explaining. I don't notice any upstream crcs with outgoing phone calls. Maybe this is because Upstream data is sent from the EU instead of receive.

It's a minor line fault, As there should be no interaction going on between data And PSTN services My VDSL line started doing this but i see around 20 error seconds whilst the phone is ringing , it is in part to do with the increase in voltage that occurs only whilst ringing,

Edited by tommy45 (Wed 05-Apr-17 14:38:43)

I hope not, just had a telephony fault fixed and the broadband boost engineer told me my line pair was "perfect".

In reply to a post by tommy45:

In reply to a post by WilliamGrimsley:

Thanks for explaining. I don't notice any upstream crcs with outgoing phone calls. Maybe this is because Upstream data is sent from the EU instead of receive.

It's a minor line fault, As there should be interaction going on between data And PSTN services My VDSL line started doing this but i see around 20 error seconds whilst the phone is ringing , it is in part to do with the increase in voltage that occurs only whilst ringing,

And not much you can do about it! Hitting the filter with a burst of 75v cadenced to provide the ringing will always have an effect.

Oh yes! It still fascinates me about how it all works!

Edited by deleted (Wed 05-Apr-17 13:40:46)

A perfect line pair can still be subject to burst radio frequency interference

Understood. The downstream SNR margin can drop by about 0.4 dB when there's a phone call.

Edited by deleted (Wed 05-Apr-17 17:09:16)