This counter tracks the number of ADD PARTY messages, used to bring an additional participant into an existing multipoint SVC that this port has transmitted, per the description. This counter is specific to multiparty/point-to-multipoint call usage on this port, so on a trunk carrying only point-to-point traffic it should sit at or near zero, while on a conferencing or broadcast-style ATM application it tracks how often new legs are being added to live calls. For example, a conferencing gateway adding participants throughout a call might show this counter incrementing 5-10 times per active multipoint session.