Cite

    Institution,, B. S. (1996). Essential requirements for connection of terminal equipment to 2-wire analogue interfaces, without capacitive termination, of public switched telecommunication networks using either the earth calling, the loop calling-disconnect clearing, the loop calling-guarded clearing or the loop calling-unguarded clearing signalling method.. London : British Standards Institution. http://access.bl.uk/ark:/81055/vdc_100104599692.0x000001