Airbus Industrie Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude
Flight Crew FLC complied w / Automation / Advisory
Human Factors
We were descending to 6;000 feet on a vector of 170 about 30 miles north of MSY. Passing 10;000 feet at 1;000 fpm we got an RA for traffic 900 feet below us. I immediately followed the commands of the RA which called for a climb; passing about 10200 feet; we received a clear of conflict call out.  We informed ATC of the RA and that we were climbing.  ATC acknowledged and said we were cleared to continue our descent. We continued to MSY for an uneventful landing.Failure of ATC to call out traffic and giving us a clearance through an altitude which was occupied by another aircraft. Also failure of the TCAS  to give a traffic call out for which we may have been able to level off and prevent the RA.
As a footnote if you reference a report I submitted [about a year ago] the EXACT scenario happened. I mean EXACT.  That is too much of a coincidence. There is something systemic.
Airbus widebody flight crew reported receiving an RA during descent into MSY; noting that ATC failed to advise them of traffic.