DSDS is short for "dual-SIM dual-standby". It allows phone calls to be placed or received on one SIM while the other remains on standby. Calls cannot be in progress on both SIMs at the same time.
DSDA is short for "dual-SIM dual-active". It will be the successor to DSDS. It will allow calls to be in progress on both SIMs at the same time. We don't expect that it will require much work for the dialer team since we believe that the front-end changes needed will be minimal.
Doug or Anthony are the best people to contact for issues here.