| Derived Services Network (DSN) | ||
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Introduction April 1985 saw the launch of the 0800 and 0345 numbers in the UK. Prior to this, free calls could only be connected via the operator. Directly dialled freephone calls were a new concept in the UK, and as the majority of telephone exchanges still used analogue switching, then a separate network to handle these new type of calls was established. An overlay of eight fully interconnected switching points, on the existing trunk network was provided. Thus, the Derived Services Network (DSN) was set up with eight Derived Services Switching Centres (DSSCs). In November 1986, three sites were fitted with digital switches, the 5ESS PRX, made by APT- a consortium of AT & T from the States and Philips. Shortly after, all eight sites were upgraded as the Digital Derived Services Network (DDSN)become fully operational. The Codes Calls to 0345 XXXXXX numbers were charged at local rate to the caller regardless of the origin in the BT Network. Calls to 0800 XXXXXX numbers were free of charge to the caller. |
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