Modem Library

TOPKAPI enables communication with Remote Terminal Units (RTUs) connected through the Telephone Network (switched or cellular). Connection is established through manufacturer front-ends or basic off-the-shelf modems.

The MODEM32.DLL library is the software tool enabling management of the modem(s) when there is no intermediate front end.

It enables saving on the acquisition of a front end, its configuration and testing, as well as subsequent maintenance. TOPKAPI includes a wizard called SOFTLINK generating the connection interface for each station..



In its basic version, the MODEM32.DLL library enables associating each RTU with a single modem within TOPKAPI. For example, RTU Nbr3 dials the telephone number for the modem connected to serial port Nbr6 on the TOPKAPIPC , and that one only. Reciprocally, TOPKAPI uses the modem connected to serial port Nbr6 on the PC to connect to station Nbr3.

Therefore, when a connection is open with another station, you must wait for the call to complete before RTU Nbr3 can log on:

  • either upon an incoming call to the PC (alarm or periodical connection on station initiative).
  • or upon an outgoing call made by the PC to the station (upon operator request or periodical or event-based connection upon the PC's initiative).

Connection to a station can last from about 45 seconds to several minutes, according to the volume of data time-stamped at the source which must be transmitted to the SCADA system.

We usually consider that a modem can handle about thirty RTUs with a good availability rate, and about sixty with a lesser comfort of use.

Using a single modem library, you can:

  • use several protocols on different modems.
  • use several modems with the same protocol, by distributing the stations concerned among these modems.

For example, using a modem with the single modem library is similar to using a vendor front end managing a single PSTN modem, such as Monet by Wit.



This optional version of the MODEM32.DLL library enables dynamic allocation of a modem to the link with a station.

  • upon an outgoing call from the PC to a station: TOPKAPI selects the first modem available.
  • upon an incoming call from the station to the PC: TOPKAPI establishes the dialogue with the station regardless of the modem used. This requires either several call numbers in the RTU, or using trunks (selection is then made by the PBX according to line use).

At this moment, a modem can be allocated to one protocol only; therefore, one must group the modems per protocol, and a group of modems should be created for each communication protocol used on a same machine.

The benefits from dynamic allocation of a modem is a higher rate of availability. Usually, cyclic night calls are programmed, spreaded over time. A modem then remains available at all times for receiving alarms. During the day, alarms reception and viewing/command by the operator can occur concurrently.

TOPKAPI frequently manages about thirty modems (up to 256 possible) and several hundreds RTUs.



The MODEM library provides all the connection management information:

  • Manual and automatic connection functions..
  • Current status of the link, time before hang up.
  • Date and time of the last connection and exchange status.
  • Periodical connection functions, date and time, periodicity.
  • Periodical connection monitoring, with call test fault signaling.
  • Logs, call time counting and monitoring, online setting of call times.

All these functions are implemented virtually automatically through the SOFTLINK configuration wizard.