Pre-Spirits Implementations of PSTN-initiated Services. - Hui-Lan Lu; Igor Faynberg; John Voelker; Mark Weissman; Weizhong Zhang; Sung-Yurn Rhim; Jinkyung Hwang; Shinji Ago; S. Moeenuddin; S. Hadvani; Soren Nyckelgard; John Yoakum; et al. (RFC, 2000)