Hi @zoe ,
I am not entirely sure I understand what differences you are after?
SSL and RSSL are transport protocols - where SSL delivers legacy MarketFeed format data and RSSL delivers binary encoded RWF/OMM data. If you connect to a given feed and request a given instrument SSL and RSSL should deliver the same set of FIDs - albeit string-based MF format for SSL and Binary encoded for RSSL. e.g. a price field such as TRDPRC_1 would be delivered as
RSSL/OMM is much more efficient - allowing greater throughput/lower latency compared to the legacy SSL/MF formats. OMM also allows for richer content sets such as Full Depth Order Book, Yield curves etc.
In terms of comparing IDN with RDFD (I assume you mean Direct Feeds) - IDN which is a consolidated feed is now referred to as Refinitiv Real-Time. To discover the differences between RRT and one of the Direct feeds you would need to consult a venue guide/specialist for the specific direct feeds to identify the difference.
This forum is aimed at answering "how to" types of questions about using Refinitiv APIs and the moderators are not Content/Data specialists. The Refinitiv Real-time feeds carry over 80million RICs from 10,000+ sources - and we have Content specialists covering specific content sets.
Therefore, for Content type questions like yours, please raise a Content Ticket with My.Refinitiv so that the right specialist can help you. I would recommend specifying which direct feed venues you are interested in - so the query gets routed to the correct team.