PSTN Number

PSTN is short for public switched telephony network. To call a subscriber within the PSTN, the caller needs to dial the PSTN number of the callee. If the called number type mapping a call prefix is set to PSTN on the
MSOFTX3000 , all calls to the numbers with the prefix are routed out of the office through trunks. 
PSTNs are encoded in E.164 format.

Figure 1 PSTN structure

• A country code (CC) specifies the code of the country where an MSC is located according to the international PSTN numbering plan. CCs are allocated uniformly worldwide by the International Telecommunication Union - Telecommunication Standardization Sector (ITU-T). Its maximum length is three digits. For example, the CC of China is 86, and the CC of the Great Britain is 44.
• A national destination code (NDC), is a PLMN number. Its maximum length is three digits. NDCs are allocated uniformly within a country by the telecom management department.
• A subscriber number (SN) is a number of a user in a PLMN. SNs are allocated uniformly by a carrier in a PLMN. The coding format of an SN is H₀H₁H₂ABCD or H₀H₁H₂H₃ABCD.