The acronym TDA refers to "Trilateral Document Access", which is a VPN like connection used by USPTO, CNIPA, EPO,KIPO,EUIPO and JPO to connect to WIPO DAS.
The main difference is that their documents are not hosted in DAS, whenever DAS receives a retrieval request for a document of these offices, the request is forwarded to the office.
The document is then prepared by the TDA Office and a response is sent to DAS.
The whole process has a delay (since the reception of the request from the OSF to DAS sending the document back to it), that varies between half an hour to two days (in average).