Tabular Data Streams or TDS is the name given to the protocol that is used to connect Sybase clients with Sybase servers. A specification for the protocol can be obtained from Sybase, I had a copy but cannot seem to find it now.

The is a project that is reverse engineering the protocol and building a set of libraries independent of either Sybase or Microsoft, but able to connect to either of their servers. FreeTDS is a considerable way down the line, although I do not believe that it is production ready yet!