The latest GSM technology from manufacturers such as Telit ensures reliable data transmission, whereby the choice of provider is not predetermined.

© Wireless Netcontrol

The GSM modems mentioned are available in different versions: GPRS/GSM quadband modems, for example, are ideal for remote dial-in to establish point-to-point connections. Ideally, the devices are offered with different interfaces such as RS232, USB or LAN. The RS232 interface provides the usual service, USB is powered via the bus line and LAN allows access from the entire network without the need for a specific PC to be connected. These modems are available in DIN rail and standard housings.

Those who find the initial setup of such a modem too time-consuming can also fall back on more convenient plug-and-play solutions - such as the EasyConnect GSM modem from Wireless Netcontrol. The device supports dial-up via the data number, has an RS232 interface and takes care of most settings independently. This means that the analog modem can be replaced by a GSM modem in just a few simple steps and dial-in to other devices is possible again.

However, the data connection service via CSD (Circuit Switched Data) is not always the method of choice because:

• The data transmission speed with a baud rate of 9600 bits/second is relatively low.
• CSD / HSCSD is not billed according to data volume, but in time intervals.
• CSD / HSCSD data tariffs are relatively expensive compared to data package-oriented tariffs, as they are billed per minute.
• CSD / HSCSD is only offered by network providers for a limited time.
• CSD / HSCSD is not even available in some non-European countries.

As an alternative, GPRS, EDGE and UMTS are available to transport data; but here too, investment in new hardware and software would first be necessary because this IP-based technology works completely differently and requires different data transmitters.

In view of this situation, many users assume that they will have to convert all their hardware to IP-based technology (GPRS, EDGE, UMTS). But this is not really necessary! A modem adapted to the requirements of the dial-up connection can offer the user and the existing hardware the familiar working environment, while using data transmission via GPRS, EDGE or UMTS.

CSD simulation: At the interface, the speed modem simulates a point-to-point connection, but transmits the data in the mobile network via TCP/IP.

© Wireless Netcontrol

One example of such a modem is the GSM speed modem from Wireless Netcontrol. It simulates a point-to-point connection at the interface, but data is exchanged in the mobile network using data packets via TCP/IP. The speed modem addresses the connection partner via the IP address and the called remote station confirms the incoming call with a 'ring'. The request is then accepted either automatically or with the 'ata' command. A 'Connect' on both sides concludes the connection setup. Now the actual data can be transmitted.

The special feature of the GSM speed modem is that it simulates the dial-up procedure for the connected hardware systems, but actually realizes the data exchange via a GPRS data connection. The user therefore combines the use of the previous technology with IP-based data exchange, uses the high data rates of GPRS, UMTS and LTE (up to 100 Mbit/s) and saves money due to the well-known low costs. The user has two options to choose from:

1. With standard SIM cards with a temporary IP address assigned by the provider, each modem reports to a switching server and informs it of its current IP address. The switching server then establishes the connection to the partner modem sought by the caller.
2. It is easier with SIM cards that have a fixed IP address (fixed IP SIM). No switching server is required here, as an exclusively protected IP address space is used for each modem.

The software used by the user, which is often adapted to very specific requirements and is intended to carry out remote access via a modem connection, can carry out the dial-up procedure via the GSM speed modem in exactly the same way as with a normal modem and dial up to the device remotely.

A special feature of the speed modem is the 'serial tunnel' connection method, in which two modems are paired and thus work exclusively with this one partner.

Connection via the 'Serial Tunnel'

Under these conditions, there is no need for a dial-up procedure at all, because if the remote station is known and unchangeable, there is no need to dial at all. In this operating mode, the two modems are directly available as a serial, bidirectional connection, which can basically be used as a 'virtual serial cable' - i.e. as a serial tunnel. This solution makes it possible to provide serial cable connections over long distances - in principle worldwide in unlimited length. Especially with regard to global remote maintenance solutions, this is a very interesting approach that makes it possible to minimize the travel time of support staff.

Author:
Dr. Ulrich Pilz is Managing Director and Head of Development at Wireless Netcontrol.