The two-tier environment allows LAN clients to directly log in to the Server Option, which eliminates the need for a DirectConnect for z/OS Option gateway. However, server-to-server communication is not possible in a two-tier (gateway-less) environment. Other drawbacks of the two-tier environment include the client being limited to accessing a single CICS region, loss of the ability to group transactions, and loss of gateway security features.
If you have standardized on TCP for connectivity between LAN clients and z/OS, you can use the two-tier environment.
