!!! Overview
[{$pagename}] is the [ITU-T] address format of the [X.25] [Protocol Suite] used as part of call setup to establish a switched virtual circuit between [Public Data Network]s ([PDN]s), connecting two network user addresses (NUAs). 

[{$pagename}] address format consists of a maximum of fourteen [binary]-coded [decimal] digits and is sent over the [Packet Layer Protocol] ([PLP]) after the [Packet Type Identifier] ([PTI]).

[{$pagename}] address is made up of the [International Data Number] ([IDN]), which consists of two fields: the 4 digit data network identification code (DNIC) and the (up to) 10 digit [National Terminal Number] ([NTN]).The DNIC has three digits to identify the country (one to identify a zone and two to identify the country within the zone) and one to identify the [PDN] (allowing only ten in each country). The [NTN] identifies the exact [network device] ([DTE], [Data Terminal Equipment]) in the [Packet-Switch Network] ([PSN]) and is often provided as an [NUA]. There are no rules to the structure of the [NTN].

[IPv4] addresses can be mapped to [{$pagename}] as described in [RFC 1236]. The 14.0.0.0/8 block used to be reserved for [X.121] use but was returned to [IANA] in [2008|Year 2008] to stave off [IPv4] address exhaustion.

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