scope:

The present document specifies the subscriber line protocol for the support of PSTN display services at  Local Exchange (LE) in "on-hook" state. The subscriber line protocol is accomplished by using asynchronous voice-band Frequency-Shift Keying (FSK) signalling. In addition, annex B is provided in order to allow the continuation of use in those networks that already implemented a Dual Tone Multi-Frequency (DTMF) based subscriber line protocol.

The requirements imposed on the FSK signalling-based subscriber line protocol deal with data encoading, dta transmission requirements and the three layers of the protocol at the network side of the interface: presentation layer, data link layer and physical layer.

The requiremetns imposed on the DTMF-based subsriber line protocol deal with the transfer of the DTMF coded display information. The procedures and the encoding arrangements are specified in Annex B of the present document.

Terminal Equipment (TE) can be conneted by analogue access directly to the LE or through an Access Network (AN). In the latter case, data transmission an be applied from the LE or from elsewhere in the network hence a transmission path needs to exist from the LE to the before transmission. It is the network operator's responsbibility to ensure transmission path establishment. Transmission path establishment procedures are outside the scope of the present document.