When it comes to SMS text messaging Enterprise Alert supports several options:
- Have a direct connection (or direct connections) to the SMSC (or SMSC’s) of the mobile operator
- Have a connection to an SMS service provider / SMS aggregator
- Use one or more GSM modems
A combination of the above methods is possible in order to support fail-over, e.g. you can use a direct SMSC link and if this one fails Enterprise Alert switches to a GSM modem.
You can also use multiple GSM modems and one possible approach for this is the following. Derdack recommends Multitech iSMS modems because they can be connected via the LAN which makes virtualization easier.
In the following scenario we have two Enterprise Alert servers and two iSMS modems. Both Enterprise Alert servers can use both iSMS modems for sending SMS messages but for receiving SMS messages each Enterprise Alert server receives messages from only one modem. How does this work?
The first Enterprise Alert server is connected to the first iSMS modem for sending and receiving SMS messages and uses the second iSMS modem as fail-over link for sending only.
The second Enterprise Alert server is connected to the second iSMS modem for sending and receiving messages and uses the first iSMS modem as fail-over link for sending only.
The reason for this approach is that Enterprise Alert supports fail-over links for sending SMS messages, i.e. Enterprise Alert is the client in this case. But for the receiving part Enterprise Alert acts as server and the iSMS modem sends the SMS packets to the IP address you have configured in the iSMS settings.