VC may be established using X.121 addresses. The X.121 address consists of a three-digit data country code (DCC) plus a network digit, together forming the four-digit data network identification code (DNIC), followed by the national terminal number (NTN) of at most ten digits. Note the use of a single network digit, seemingly allowing for only 10 network carriers per country, but some countries are assigned more than one DCC to avoid this limitation. Networks often used fewer than the full NTN digits for routing, and made the spare digits available to the subscriber (sometimes called the sub-address) where they could be used to identify applications or for further routing on the subscribers networks.