H

half-duplex transmission

Two-way electronic communication that takes place in only one direction at a time. Contrast with full-duplex transmission.

HLLAPI

High-Level Language Application Programming Interface. An API that allows you to develop and run programmer-operator applications on IBM PCs (or compatibles) that communicate with IBM mainframes using 3270 emulation.

hot backup

(1) The ability to take systems online and offline without disrupting service. (2) A configuration in which one resource (such as a server running SNA Server software) can automatically handle sessions if another cannot. Such servers can provide hot backup for 3270, LUA, or downstream sessions through pools containing LUs from multiple servers. Servers running SNA Server software can provide hot backup for 5250 terminal emulation through the use of LU names that are the same on multiple servers.