5.13.2.1. Format-dependent INS/STNO Modification in Incoming Direction 
The conversion of the calling number information from an explicit
format into an implicit one is carried out in two steps:
Step 1:
The incoming ISDN number (NPI=ISDN), which may be any type of number
(TON), is set to the lowest possible format (TON=UNKNOWN) with the aid
of the ISDN codes stored in the system (ISDNAC, ISDNCC and ISDNLC parameters
of TDCSU AMO). Since this conversion also takes place in transit nodes,
these codes must also be assigned to tie-lines with the TDCSU AMO, if
these are used to transport numbers of the ISDN numbering plan. If you
do not want user displays to show the converted numbers in the lowest
possible format, you can set an alternative format with the KNFOR AMO.
Step 2:
Depending on the type of number (TON), the modified (shortened) ISDN
call number (see step 1) is then supplemented with the national prefix
(TON=NATIONAL) and international prefix (TON=INTERNAT) as well as the
breakout code (only if TON is not equal to UNKNOWN). The following AMO
settings are necessary for this:
- Define the breakout codes in all network nodes, and prefix codes specific
to the home node, with the KNPRE AMO, as follows:
ADD-KNPRE:DPLN=0,NPI=ISDN,TON=INTERNAT,EXIT=0,PREFIX=00; ADD-KNPRE:DPLN=0,NPI=ISDN,TON=NATIONAL,EXIT=0,PREFIX=0; ADD-KNPRE:DPLN=0,NPI=ISDN,TON=SUBSCR,EXIT=0;
Since EURO-ISDN exchanges always transport the calling number information in the explicit format defined by ETSI-E.164, the prefix settings in the TDCSU AMO are not required (ISDNIP and ISDNNP).