Data Communications Networking Devices - 4th Ed.pdf

5.3 GATEWAYS __________________________________________________________________ 591Figure 5.31Using the 3172 Interconnect ControllerRing and Ethernet networks shown connected to the 3172. This in turn enables therouter- based connections to the Internet to reach the mainframe via the 3172.Software considerationsAlthough the 3172 and other gateway products provide users with the ability toroute data between devices that communicate using different protocols, you mustalso consider the software on the end station accessing the host to obtain a fullgateway capability. IBM's 3270 Information Display system uses special codes toenable and disable a variety of terminal features associated with that vendor'soriginal series of ®xed logic terminal devices. As PCs began to replace dumbterminals, emulation programs were required to enable PC-based LAN workstationsto obtain keyboard and screen operation compatibility with IBM hosts.One of the most popular IBM 3270 display station emulation programs is thePCOM/3270, an acronym for IBM's Personal Communications/3270 series ofemulation programs.If the 3172 can be considered as the Swiss Army knife of gateways, the PCOM/3270 can be considered to represent the Swiss Army knife of emulation programs.PCOM/3270 supports a variety of mainframe attachment methods, ranging fromLAN adapters and coaxial cable to asynchronous and synchronous serial communications.Figure 5.32 illustrates the PCOM/3270 Customize Communicationdisplay screen which shows four options for communicating from a coaxial-basedPC to a S/390 host. Note that the entry `COAX' in the column labeled `Adapter:' isshown selected, which results in the display of four attachment methods shown inthe middle of the illustration. In comparison, the use of a LAN adapter cardprovides a terminal emulation capability for a larger number of attachment options.Figure 5.33 illustrates the PCOM/3270 con®guration display after the LAN optionwas selected for the adapter card. In this example, the highlighted bar is shown