As described in Section , a phone number in ISDN networks has, in addition to the actual digits, additional information on NPI and TON. If this information is not included, for example, in the case of analog sets, or if the information has a value of UNKNOWN, only the digits must be meaningful; i.e., the address must be able to be reached solely by the dialing of the digits. This case is trivial since it appears during each dialing of a phone number by the user. Such a number that can be evaluated at any time by WABE has an implicit format according to the definition.

During the transport of the phone number, however, certain information contained in the digits can be extracted. Exit codes thus provide information on the selected numbering plan (NPI) and the prefix of the level of the number (TON). A dialed implicit phone number 0-0-89-722-4711 can thus also be transferred as 89-722-4711 with the additional information NPI=ISDN (since 0 is considered to be the exit in the CO numbering plan in this case) and TON=NATIONAL (since 0 is the prefix of a national number). These numbers, which contain no exit codes and no prefixes, but which are labeled by NPI and TON, are called explicit phone numbers. They cannot be analyzed by WABE and must thus be converted into an implicit format before evaluation.

According to definition, an explicit number must have an NPI not equal to UNKNOWN and a TON not equal to UNKNOWN. It may thus not contain exit codes or prefixes. The other way round an implicit number must always have TON = UNKNOWN and all required digits must possibly contain the exit code an prefixes. Table 1 shows the NPI/TON combinations defined in the ETSI standard. The designations on the AMO interface are marked with capital letters.

The advantage of an explicit number lies in its independence from exit codes or prefixes, which, as previously mentioned, often differ in different networks and countries and, on the other hand, in the possibility of performing a source-independent number modification at any time, for example, if a call that was originally a national call is routed via an international network. In the standard case for explicit numbers, a source/destination-dependent modification thus becomes completely unnecessary with AMO KNMAT.

AMO KNPRE regulates the relationship between the explicit and implicit numbers. This defines which exit code belongs to which prefix for a certain NPI/TON combination. In the example above, the exit "0" thus belongs to the combination NPI=ISDN and TON=NATIONAL. The actual codes (e.g. CC, AC, LC) are saved in AMO KNDEF in the case of explicit numbers.

Since external nodes that understand only implicit numbers possibly supply the NPI/TON information incorrectly (e.g. station with NPI=ISDN, TON=SUBSCR), which leads to errors in the number modification, the COT parameter LINO was introduced.

RULE:

The COT parameter LINO (line with implicit numbers) causes the format of all numbers to be overwritten with UNKNOWN by default whether incoming or outgoing. If an explicitly signaled, external node (e.g. central office) can be reached by means of a set with this number, an entry for this node must exist with AMO KNFOR.