Lava Computer HQ-ST Link - Manual (Page 3)

Rev. A00 HQ-ST System Manual Page 1 of 32
Introduction
System Design
The LAVA HQ-ST Link consists of ST Plus devices installed at each store. The ST Plus devices communicate with an
assigned and dedicated HQ-Plus device at the head office. The ST Plus devices are attached to the cash register(s) in
each store, and to the store's Internet connection. Polling software running on a head office computer can poll each
cash register, via the HQ Plus.
The system is supported by the included ST Plus Configuration Console application, which makes configuring ST Plus
units simple, and at the head office by the HQ Basic application, which shows the connection status of ST Plus devices
in stores.
The system is also enhanced by the HQ Plus Remote Console and the HQ Plus Remote Poller, hardware interfaces that
enable an installer or owner to perform head office tasks from other locations.
Theory of Operation of the LAVA HQ-ST Link
A LAVA HQ-ST Link provides reliable "always on-line" communication path between remote/distributed ST Plus
devices and a centrally located HQ Plus device. The ST Plus establishes a TCP/IP connection to the IP address:TCP port
of a designated HQ Plus. This connection then provides the HQ Plus with the current IP address:TCP port of the ST Plus.
Whenever the ST Plus is reset or powered up, the ST Plus establishes this connection, and expects the HQ Plus to send
an "I (HQ Plus) still see You (ST Plus)" packet to the ST Plus once every three minutes at a minimum. If the ST Plus does
not receive this “keep-alive” message from the HQ Plus, the ST Plus will reset and try to re-connect to the HQ Plus.
Similarly, in the event of some change at the ST Plus's site, the ST Plus will re-connect to the HQ Plus. Typical incidents
could be: power cycling off and on, an IP address change of the ST Plus due to dynamic IP address re-assignments , re-
location of the ST Plus, initial installation of the ST Plus, interruption of Internet service, and so on.
The HQ-ST System provides a "telephone modem-like communications environment" to the equipment connected at
both ends. However, the data path between the ST Plus and HQ Plus is over Ethernet using TCP/IP communications.
The Ethernet TCP/IP communications are used only as the communications medium between the HQ Plus and the ST
Plus devices, and are "invisible" to the serial side data I/O activities at the HQ Plus and ST Plus devices.
Figure 1: HQ-ST Layout