The public switched telephone network more commonly known as the PSTN is the network of the world's public circuit-switched telephone networks. In the UK, the PSTN is currently a network of fixed-line analogue telephones but BT plan to have upgraded their network to digital by 2011 with their 21CN roll-out.
TalkTalk's use of MSANs comes into play here, as all phone calls are converted to digital, and sent across the network. This saves costs as each call is essentially a VOIP call.
PSTN
