Conceptually, a PACS network is a cellular access network for voice transmission based on microcells. The cell diameter is about 300 meters. PACS has roaming and uses the TDMA method with eight time slots per frequency. PACS used in the U.S. has its transmission frequencies between 1.92 GHz and 1.93 GHz. Designed as a wireless access network, PACS provides circuit-switched and packet-switched interfaces to the user. Services supported include analog and digital voice, fax and X.25.