British Telephone Sockets - Broadband

Broadband

In order to use Broadband internet services simultaneously with voice telephony, it is necessary to use a DSL filter. This is basically two filters, which divide the single line into two discrete channels. Enough bandwidth is retained for voice telephony and the majority is used for high speed data. All phones must be connected via a filter (either a separate filter for each phone or one filter covering multiple phones) to avoid interference between the phones and the DSL signal. Where the data transmission is still unduly audible, using two DSL filters, daisychained in tandem, will eliminate the problem. The DSL modem connects directly to the phone line (most DSL filters have a socket marked DSL that just connects directly through to the incoming phone line). The ringer wire is unnecessary in unfiltered parts of the wiring and its removal can often improve performance and reliability of the broadband service.

When ADSL was first introduced in the UK it was installed by an engineer who replaced the front part of the NTE5 (if the property still had an old style master socket it would be replaced with an NTE5) with one containing a filter. Any hardwired phone extensions were disconnected from the original front part and connected to filtered terminals on the back of the filter. The DSL modem (which at the time was also BT supplied) and, if present, a phone or plug-in extension, could then be plugged into the front. If it was desired to locate the DSL modem away from the master socket a plug-in ADSL extension kit could be purchased.

BT also offered "wires only" ADSL service and promoted the technique of using a separate plug-in filter on every socket. While both technically inferior and far less tidy than the solution BT engineers had used, it was usually adequate and was simple enough for a non technical householder to understand. The more discerning customer can purchase a variety of hardwired filtering products, including replacement front plates for the NTE5, some of which have unfiltered as well as filtered terminals on the back to avoid the need to plug in the extension wiring that leads to the DSL modem.

In 2008 BT trialed and launched their 'IPlate'; the "I" is for interstitial, as it is fitted between the socket and the front panel. This plate is fitted by the consumer inside the NTE 5 and reduces interference carried by the 3rd (bell) wire. The reduced interference allows faster broadband speeds - BT claim a speed improvement of up to 1.5 Mbit/s with a theoretical 4 Mbit/s. By November 2009 BT were calling the I-plate a "BT Broadband Accelerator".