Peer Tracker w. ALTO cli. ALTO Server --------+-------- --------+-------- --------+-------- | F1 Tracker query | | |======================>| | | | F2 ALTO query | | |---------------------->| | | F3 ALTO reply | | |<----------------------| | F4 Tracker reply | | |<======================| | | | | ==== Application protocol (i.e., tracker-based P2P app protocol) ---- ALTO protocol