The SMS message loop threat

If you plan to create an autoresponding SMS service, you should give a thought to the scenario depicted in Figure 1 and described below. The scenario shows that an endless message loop can occur in case of two autoresponding messaging applications start to talk to each other. This message loop can cost a lot of money, because it is often unnoticed by the operators of the autoresponding services. The good news is that Ozeki NG SMS Gateway has built in message loop prevention to make sure you don't run into this situation. On this page you can read about the message loop threat an the message loop prevention feature of Ozeki NG SMS Gateway.

The message loop threat can occur in case two autoresponding messaging applications start to talk with each other. An automatic responses sent from one system can trigger a response on the other causing an endless loop of messages, and a huge cost on the mobile phone bill (Figure 1).

the working of an endless loop — Figure 1 - Two SMS applications in an endless loop

A loop is often started by an unaware human user, who may send an SMS message using an SMS service, that can also reply to incoming messages. It is called "Other autoresponding SMS application in the figure above. The message will be delivered to the autoresponding service (possibly hosted by Ozeki NG).

This autoresponding service will generate a response and send it to the other autoresponding service, which - not interpreting the reply message - will send an error message to the reply, to which Ozeki NG - SMS Gateway may send an error message, and so on. This will create an endless loop, which may continue until one of the services is stopped and the phone number or a range of phone numbers of the recipient is barred.

The endless loop between two services may cause huge costs because of the enormous number of SMS messages that may be sent.

Ozeki NG SMS Gateway solution

To prevent such message loops, Ozeki NG SMS Gateway has a built in message loop prevention. This works the following way: Ozeki NG SMS Gateway registers outgoing messages. If the same text is sent to the same recipient phone number more then ten times in one hour, Ozeki NG SMS Gateway prevents message delivery to stop a possible message loop.

How to disable message loop prevention

In some cases the user might want to disable message loop prevention. This is possible by opening the "Server preferences" form in the "Edit menu" in Ozeki NG SMS Gateway (Figure 2).

On the server preferences form, click on the "Advanced" tab. In the advanced tab you need to uncheck the "Prevent message loops caused by autoresponding services" checkbox (Figure 3).

how to disable message loop protection — Figure 3 - Disable message loop protection

Please disable this feature with care. If you disable it, you must handle this possible threat some other way.

More information

Tutorials | Application Port Numbers in SMS