The Best of Both Worlds
Ensuring continuous connectivity through automatic failover, secure private fixed IP, and multi-network redundancy.
Why Consider Dual SIM Solutions?
For certain high usage data applications, a pay per MB SIM card is simply not economic when you can purchase hundreds of gigabytes per month or even unlimited SIM cards for a low fixed monthly fee. This is especially relevant for fixed locations where you can be confident that a single network will have consistent bandwidth.
Downside #1: Limited Coverage
Cheaper SIM cards only connect to a single network, resulting in less coverage area. See our OFCOM report for more information on network coverage differences.
Downside #2: Contractual Restrictions
In many cases, unlimited consumer SIM cards are contractually prohibited for business use, IoT applications, or reselling. Always check your terms and conditions.
The Dual SIM Solution
Let's assume you have checked your contractual terms and conditions. Now imagine you could benefit from all the savings on your contractually allowed IoT unlimited SIM cards whilst maintaining the security and resilience of a multi network SIM. That is precisely what you can do using dual SIM or dual modem devices such as the ones featured in our Teltonika article. Using a dual SIM device allows you to get the best of both worlds, using the cheap data of your unlimited SIM paired with the security and resilience of a KeySIM.
Understanding the Difference
Not all dual SIM solutions are created equal. Understanding the difference between dual SIM and dual modem devices is crucial for selecting the right solution for your application.
Dual SIM & Dual Modem
This is what we would call utopia! You have 2 separate modems and 2 SIM card slots which means you are running 2 separate connections to the internet at all times.
Zero interruption: If one SIM card fails or loses coverage, the other seamlessly takes over with no connection disruption.
Example: Teltonika RUTX12 at £299 when purchased with an active KeySIM connection—great value for money.
Dual SIM & Single Modem
Not quite the same as a dual modem but incredibly useful nonetheless. The additional cost of an additional modem is avoided but there are still 2 SIM slots available.
Note: There will be a brief period of outage as the SIM card switches from one slot to another.
This is often not a major problem unless your IoT application is extremely time critical, such as live streaming.
Configuring SIM Switching
So you have decided that a dual SIM solution is the way forward. Let's take a look at the conditions in which a Teltonika modem can be programmed to switch from SIM1 to SIM2 and back again.
Check Interval
How many seconds between connection checks on the primary SIM card.
Attempts Before SIM Switch
How many connection fails on the primary SIM card before switching to the backup.
Weak Signal
Enter the dBm limit on the primary SIM before switching to the backup.
Data Limit
If you have a monthly data limit on your primary SIM, switch to backup when this limit has been consumed.
SMS Limit
If your IoT application uses many SMS messages, switch to backup after a certain quantity have been sent.
On Roaming
Useful if you don't want to consume data on your primary SIM overseas.
No Network
When service is completely lost on the primary SIM, switch to backup SIM.
On Network Denied
If authentication on the primary SIM card fails, switch to the backup SIM.
On Data Connection Fail
Set up an echo test to ping Google at predetermined periods from the primary SIM card and switch to the backup SIM card if the ping fails.
Automatic Failback
On the backup SIM card you can set a timeout period in minutes which sets how long it will wait before attempting to revert back to the primary SIM. If the primary SIM card is experiencing the same conditions which made it switch over in the first instance, the router will revert back to the backup SIM and the cycle repeats itself.
Manual SIM Switching via SMS
There may be occasions when despite all the best forward planning your automated routines do not quite work as you anticipated during setup. For those unforeseen situations when you want to perform a SIM switch manually, the SIM switch SMS command is perfect.
SMS Command: switch_SIM
With a simple text message you can switch between the SIM cards manually, just like having the router's interface in front of you. Just remember to ensure that your authentication rules are met and that your SIM card is SMS enabled.