Up to 20 simultaneous calls Up to 10 DECT cordless handsets Up to 10 SIP accounts Support Opus audio codec Noise Reduction System TLS and SRTP security encryption No Perception Upgrade Supported the new endpoints W73H and can be perfectly compatible with W53H, W56H, W59R, CP930W and color screen DDPhone (T54W+DD10K). Due to the performance of the handset, only W73H and W59R support no perception upgrade.