Log Transfer Managers (LTMs) and RepAgents are the processes that transfer data between ASE and the Replication Server.

LTMs were delivered with the first releases of Replication Server. Each LTM is a separate process at the operating system level that runs along side ASE and Replication Server. As with ASE and Replication Server, a RUN_<ltm_server> and configuration file is required for each LTM. One LTM is required for each database being replicated.

Along with ASE 11.5 a new concept was introduced, that of RepAgent. I am not sure if you needed to use RepServer 11.5 as well, or whether the RepAgents could talk to earlier versions of Replication Server. Each RepAgent is, in effect, a slot-in replacement for an LTM. However, instead of running as separate operating system process, it runs as a thread within ASE. Pretty much all of the requirements for replication using an LTM apply to the RepAgents. One per database being replicated, etc. but now you do not need to have separate configuration files.