A location server, such as a Serving Mobile Location Center (SMLC) or E-SMLC and mobile terminal selectively implement the reliable transport mechanism used in, e.g., LPP or LPPe protocols, thereby decreasing unnecessary delays. The reliable transport mechanism may be selectively implemented by not requiring an acknowledgement for specific messages, such as an unsolicited assistance data message. When assistance data is solicited, however, the responsive assistance data message includes an acknowledgement request as per the reliable transport mechanism.