When the public network receives a specific private network Progress description value from the subsequent PINX, it shall transfer it to the physical PINX at the originating interface, without acting upon it.
Outgoing Gateway PINX functionality shall provide Progress indicator information elements as specified below and this information shall be transferred to the physical PINX. A Progress indicator information element shall be transmitted in a PROGRESS message, an ALERTING message or a CONNECT message as soon as the information becomes available, subject to a SETUP ACKNOWLEDGE or CALL PROCEEDING message having already been sent. A PROGRESS message shall be used unless an ALERTING or CONNECT message is to be sent at the time. All appropriate interworking indications shall be transmitted by the Outgoing Gateway PINX.
If one of the following progress descriptions has been received on a call exiting the CN, that information shall be passed on:
– No. 1 – Call is not end-to-end ISDN; further call progress information may be available inband.
– No. 2 – Destination address is non-ISDN.
– No. 4 – Call has returned to the ISDN.
– No. 8 – In-band information or appropriate pattern is now available.
If the call is to enter another network (public or private) which is not ISDN, a Progress indicator information element may be sent containing progress description No. 1, Call is not end-to-end ISDN; further call progress information may be available in-band.
The physical PINX at the originating interface may, optionally, include any of the specific private network Progress description values in the SETUP message, to enable indication of particular situations at the originating side to the subsequent PINX. The public network shall transfer it to the subsequent PINX.
Up to three Progress indicator information elements may be included in a SETUP, ALERTING, PROGRESS and CONNECT message.