The HG 3500 line gateway is a OpenScape 4000 peripheral card that plugs into an AP 3300 and an AP 3700 access points. However, HG 3500 cards require more than average power due to components with high power demands (DSPs). This limits the total number of HG 3500 cards to a maximum of 6 cards per AP 3700 IP (9 slot) and 10 cards per AP 3700 (13 slot).