From the CPU's and systems programmer's point of view, it is more efficient to designate one PC as the gateway. The mainframe polls the gateway PC, and the gateway is responsible for polling each workstation. A fourth gateway type is a channel-attached gateway. This is the highest performance method, and is most often used when other mainframes, mini-computers, and engineering workstations need to communicate with the mainframe. Because a coax gateway and an SDLC gateway communicate through a cluster controller or front end processor, they are limited by the controller to a raw throughput of 56 Kbps.
Most gateways are PC-based.
The most basic function of a mainframe gateway is distributing the mainframe's sessions to the PC users. A PC or terminal explicitly defined in VTAM is said to have static or dedicated LUs. In dynamic pooling, sessions are grouped together. So one pool could be printer sessions, another, terminal sessions.