BT's PSTN switch off question (FTTC Users)

Hey all,

Now that BT will be switching off their PSTN system in the very near future does this mean a potential increase to bandwidth/sync speed?

What I mean by this is that there must've been a % of phone line allocated for the PSTN part of the phone line for voice calls (let's just say for arguments sake, this was 10%), and the remainder (90%) was used for digital internet traffic. When the PSTN switches off, this will mean a 100% data phone line. Will we see a slight increase in sync speed in lieu of that 10% PSTN switch off?

TIA

In reply to a post by Bobby_Valentino:

Hey all,

Now that BT will be switching off their PSTN system in the very near future does this mean a potential increase to bandwidth/sync speed?

What I mean by this is that there must've been a % of phone line allocated for the PSTN part of the phone line for voice calls (let's just say for arguments sake, this was 10%), and the remainder (90%) was used for digital internet traffic. When the PSTN switches off, this will mean a 100% data phone line. Will we see a slight increase in sync speed in lieu of that 10% PSTN switch off?

No, those who are migrated from FTTC (with a analogue telephone service) to SOGEA (with digital voice service) typically see not uplift in speed.

To put it simply VDSL2 broadband uses a defined range of frequency bands higher than the PSTN voice range. This will not change when PSTN is removed so there will be no change to actual sync speeds or bandwidth.

If there's no change in bandwidth/sync speed, what happens to the capacity of the PSTN voice traffic when it's removed? That vacant 10% just gets removed and sits there unused?

Can't that PSTN section not be used to increase speed/sync somehow? (I know we're talking very small amounts here ... but hey every little helps).

Edited by Bobby_Valentino (Wed 18-Sep-24 23:03:14)

Post

Edited by MHC (Thu 19-Sep-24 00:28:25)

The SOGEA frequency profile is the same as the FTTC frequency profile thats why you see no uplift. At this point this is not going to change as there are lots of other considerations including a 5 year trial.

I wonder why they kept the profile the same. They could've repurposed the dropped PSTN frequency spectrum and added it to the upload/download frequency spectrum, rather than letting it go unused.

They knew the switch off was happening, so trails/R & D etc... could've been done along ago, ready for repurposing the dropped PSTN frequency to increase the upload/download.

Edited by Bobby_Valentino (Wed 18-Sep-24 23:19:49)

It just isn't worth the effort.

The baseband PSTN audio plus guard bands before the first upstream VDSL block of bands is 0.025875 MHz of the 17.664 MHz utilised by the 17a profile, so it would add a fraction of a percent to the upstream bandwidth, even taking into account that there are usually more bits per tone for lower frequencies. There would be no change to the downstream bandwidth.

In reply to a post by tdw42:

It just isn't worth the effort.

The baseband PSTN audio plus guard bands before the first upstream VDSL block of bands is 0.025875 MHz of the 17.664 MHz utilised by the 17a profile, so it would add a fraction of a percent to the upstream bandwidth, even taking into account that there are usually more bits per tone for lower frequencies. There would be no change to the downstream bandwidth.

That's assuming using the Profile 17a right? What about a shift to the Profile 35b which is designed to make full use of the line without any presence of PSTN.

In reply to a post by Bobby_Valentino:

In reply to a post by tdw42:

It just isn't worth the effort.

The baseband PSTN audio plus guard bands before the first upstream VDSL block of bands is 0.025875 MHz of the 17.664 MHz utilised by the 17a profile, so it would add a fraction of a percent to the upstream bandwidth, even taking into account that there are usually more bits per tone for lower frequencies. There would be no change to the downstream bandwidth.

That's assuming using the Profile 17a right? What about a shift to the Profile 35b which is designed to make full use of the line without any presence of PSTN.

Why would a business want to spend the time and money to achieve a minimal benefit when they are trying to get rid of the technology anyway by migrating to fibre-optic?