Roaming SIMs and Automatic Network Selection
Open roaming SIMs are widely used today in IoT and telematics applications, for good reasons. Coverage is extended by allowing access to all (or at least several) network operators in any given country, with obvious benefits for real-time communications in almost any location. However, there can be problems with automatic network selection routines, which were defined back in the days of GSM, before packet-switched internet services were launched.
The launch of GPRS packet-switched services around 20 years ago revolutionised our industry and kick-started the huge growth of the telematics industry. Surprisingly though, nothing has changed with automatic network search and selection criteria, which are essentially based on only circuit-switched services (i.e. voice and SMS). ETSI TS 123 122 specifications state “If an entry indicates at least one access technology supported by the ME, the entry shall be used..”. Since GSM circuit-switched service is a precursor (prerequisite) to packet-switched services, and required for network registration, this means that its written into the ETSI standards that GPRS packet-switched services are superfluous in the operator selection process.
Usually this is of no consequence, as we can typically assume that all operators in all locations will have packet-switched services available in addition to circuit-switched. However, in the (admittedly) rare cases where that is not the case, there are problems for devices that rely on internet access for their primary functions. The scenario goes like this. A device registers with an operator, which (in this location at least), does not offer packet-switched (internet) services. This can be for reasons of capacity / availability, maintenance or faults. Now, the device stays with this operator until such time as the coverage is lost, when it resumes a new search for a new operator. During that time, the device will be offline for typical telematics / IoT purposes.
This issue is becoming more common, as we progress through the 2G sunset, and channels are gradually reallocated from 2G to other services, such as 4G and 5G. Its reasonable to expect that this issue will become more commonplace as we progress to the final years of the 2G sunset in many countries.
Sounds a bit grim, especially for devices which only support 2G communications! However, there are options to manage this from the IoT device. Some of you may have used manual network selection on your mobile phone handset, in which case you will be aware that it can be a little slow and inconvenient. The same option is available for IoT devices, although it’s rarely used in the industry, because automatic network selection has been our convenient and trusted ‘friend’ for decades.
Astra Telematics recognised this issue several years ago, and hence all our current devices, and even our previous generation of devices support a self-learning manual network selection option. This feature kicks in only when a device finds itself in the situation where it has circuit-switched services without packet-switched service available. That scenario triggers and manual network search and selection, and a self-learning process, where the device keeps track of problematic operators and tries to avoid them (at least when others are available). This mode is enabled by the command $COPS,1. Please refer to our Generic Command Reference Guide or contact our Technical Support team for more details.