The Swiss telephone numbering plan implements the ITU-T recommendation E.164 and is designated E.164/2002, based on its last major revision in 2002. It is a closed numbering plan, which means that all telephone numbers, including the area code, have a fixed number of digits. Swiss area codes are officially termed "national destination codes" (NDC). A complete telephone number consists of ten digits: . Two formats are distinguished: three digits for the NDC and seven digits for the subscriber number, and four digits for the NDC and six digits for the subscriber number. However, a few exceptions exist.