This is a text description of Figure 1-1. This illustration of the gateway architecture is adequately described in the "Architecture" section of the chapter, which is presented before the figure.  The Client connects to an Oracle integrating server via Oracle Net or via a local connection.  The Oracle integrating server connects via Oracle Net and/or via local connections to either of two gateway (TG4DRDA) instances, one of which is linked via SNA to a DRDA server, the other of which is linked via TCP/IP to a DRDA server.