As well as understanding the benefits of Robustel, you must also understand the different types of Sims that are utilised within M2M/ IoT applications:
Single Network Sims
These SIMs provide coverage on a single network typically in a single country. This means that if there is no coverage on the network at the installation location (especially if it is in a building) then the communications will not work. Additionally, if the deployment is multinational then lots of different SIM agreements for different territories need to be agreed which is logistically difficult and virtually impossible to manage at scale. The traditional solution proposed to these problems has been to offer a roaming or ‘multi-network’ SIM typically offered by aggregators. What most people don’t realise is that not all roaming SIM cards are equal!
Steered Roaming Sims
Steered Roaming Sims ‘can’ access multiple networks per country but will favour a specific network or subset of networks for the mobile operator’s commercial benefit. The majority of the time, steering it is not implemented for the benefit of reliable communications but to make the scheme less expensive by using ‘preferred’ networks. This is generally the opposite of what is wanted by IoT service/system providers who need as close to 100% network uptime as possible. Steering of roaming is a complex subject matter not covered in this document. The primary and simplest solution is to select a good quality un-steered roaming SIM although clever marshalling of steered roaming schemes can help to achieve desirable commercial outcomes.
Un-steered Roaming Sims
As the downsides of Steered roaming have become more visible in the market, certain mobile service providers have started to provide and champion un-steered roaming sims. This has meant that the sim has no preferred network lists onboard and does not suffer operator-side steering at the network level. Essentially, an un-steered roaming sim is a blank canvas that simply provides access to networks as and when required with no ‘loading of the dice’. This is arguably the most preferable starting point for any M2M/IoT application where uptime / reliability is key.
As mentioned earlier, Sims do not play an active role in network selection; choosing an appropriate network is a function of the hardware and/or how the hardware is told to behave by associate firmware such as AT Commands. There are 2 different types of network selection;
Automatic Network Selection
With automatic network selection, the device selects and attempts registration on other PLMN/ Access technology combinations. These network selection rules were originally defined many years ago and do not use the ability for TCP/IP communications to work as an indicator of a usable network. This means the cellular device could be on a network with good signal strength but due to other reasons there is no ability to transmit data. This is extremely undesirable for any IoT/M2M service provider. Another critical point is that prior to this selection process, the hardware will always try to use the “last known good network” or RPLMN (Registered PLMN) which means that even a reboot will not necessarily push an unconnected system into a working state. The RPLMN concept could mean that a router keeps attaching to a network without working Data Comms due to the failings of the automatic network selection process. Net effect of this is quite simply loss of Data comms. This very obscure point is commonly not understood and has big implications for those expecting everything to ‘just work’ when a roaming SIM is used with automatic network selection. The automatic network selection process has no empathy for packet-switched Comms so an application that sees good signal strength but cannot communicate with a server on the internet will continue in a state with no connectivity and will not automatically recover. To avoid this problem, some supplementary logic is required in the device firmware. It is this fundamental issue that Robustel’s ‘SMART Roaming’ Application aims to solve using the simplicity of Automatic network selection but supplementing it with Health-checks and the use of Manual network selection to make sure reliability is as high as it possibly can be.
Manual Network Selection
In comparison, manual network selection is relatively very simple as compared to automatic network selection. A device can request connectivity on a specific network and so long as registration for the appropriate services is allowed by the SIM/provider, then a connection is made. At this stage, it would be reasonable to ask, “Why don’t all M2M applications use manual network selection?” A lack of understanding by hardware manufacturers combined with a relatively high level of risk / complexity in the development process for such subroutines means many shy away from adding such ‘polish’ to their connected products. Robustel’s ‘SMART Roaming’ overcomes the limitations of Automatic Network selection to allow Cellular IoT Devices that require high uptime to connect with confidence.