VDSL filters and ADSL filters - does it matter?

Modified on Sat, 11 Jan 2020 at 04:25 PM

When upgrading an existing socket to VDSL (FTTC | GEA), it's possible that a previous ADSL faceplate will need to be removed and either replaced with a VDSL faceplate (recommended) or used with a suitable VDSL filter (not an ADSL filter). Here you'll find diagrams and links to the BT source documents.

There are a number of different face-plates that BT have supplied over the years, many do not display a version number. Here's a selection that do:

As you can see, the first one is only ADSL v1.0 compliant, the 2nd is ADSL 2+ and the 3rd is VDSL 2 compliant. The VDSL2 is backward-compatible.

If you are unsure of the type of face-plate, assume it's ADSL v1.0 - that means removing it if you plan to connect VDSL equipment.

Universal xDSL filter specifications are detailed in document ETSI Specification TS 101 952-1, available here: https://www.etsi.org/deliver/etsi_ts/101900_101999/10195201/01.01.01_60/ts_10195201v010101p.pdf

(Note sections A.2 and A.3 which detail the specific requirements for xDSL filters)

DSL version	Filter frequencies
[ Human voice \| Fax ]	300 Hz - 3.4 kHz
ADSL v.1.0 [ 8 Mbps ]	138 kHz - 1.104 MHz
ADSL 2+ [24 Mbps ]	138 kHz - 2.208 MHz
VDSL [ 40 Mbps ]	138 kHz - 12 MHz
VDSL2 [80 Mbps+ ]	138 kHz - 30 MHz

Here's a graphical diagram:

BT document SIN 498 outlines VDSL - you can download it here: https://www.btplc.com/SINet/SINs/pdf/498v7p5.pdf

(Pertinent section: "3.2.6 CPE VDSL2 Filter Requirements")

The equivalent ADSL document is BT SIN 346: https://www.btplc.com/SINet/SINs/pdf/346v2p11.pdf

Note sections "7.3 Additional notes about CPE filters" & "8. Out of band signals applied to the PSTN CPE", which explain the ADSL filter frequencies.

Best practice: fit the latest incarnation of VDSL2 filter for optimal xDSL performance, preferably a built-in face-plate.