A "roaming" SIM is one that can use networks beyond its home operator. For an IoT fleet that travels across countries, or even across one country with patchy coverage, roaming is the difference between staying online and dropping off. This article explains what data roaming and national roaming actually do, and what you need to do on the device to make them work.
Data roaming
Data roaming is the ability for a SIM to attach to a network operated by a carrier other than its home operator. It typically applies when the device crosses an international border, the home operator has no presence in the new country, so the device attaches to a foreign carrier under a roaming agreement.
How it works:
The device powers on in a foreign country.
It searches for available networks.
It picks one that the home operator has a roaming agreement with.
The home operator authorises the connection. Traffic from the device flows through the foreign network, then back to the home operator's gateway, then to the internet.
For Simbase SIMs, data roaming is enabled by default on the SIM, but the device may need to be told to allow it. Many consumer phones and some IoT modules ship with data roaming disabled in software as a cost-protection default. If you're using a Simbase SIM and the device disables roaming, the SIM will register but won't pass traffic.
Roaming behaviour can also be restricted by the plan attached to the SIM in the Simbase dashboard. Some plans limit roaming to specific regions or block it entirely. Check the SIM's plan if data roaming is enabled on the device but the SIM still won't attach abroad.
National roaming
National roaming is the equivalent inside a single country. Instead of the SIM being locked to one home operator within its home country, it's allowed to use any operator that has a roaming agreement.
For consumer SIMs, national roaming is rare, most carriers want to keep their subscribers on their own network. For IoT, it's a critical feature. If your device is in a basement that gets no signal from operator A but five bars from operator B, national roaming lets the device use B and stay online.
For Simbase SIMs:
Multi-IMSI profiles (Black, Green) carry several operator identities, so the SIM is permitted on more networks in a country. The device chooses which network to attach to, and the SIM presents whichever identity is valid there.
eUICC profiles (Blue, Yellow) achieve it through pre-provisioned profiles or operator agreements built into the active profile.
The result is the same: your device picks the best available network in the country, automatically.
When roaming changes the SIM's behaviour
Roaming can affect a few things you might not expect:
Latency can rise when roaming, because traffic may route through the home operator's gateway before reaching the internet. Simbase's regional breakouts (
simbase.eu, simbase.us) reduce this for Black/Red/Green profiles in the EU and US. See Set up the Simbase APN and Quality of service (QCI).IP address assignment is normally unchanged, your SIM still gets an IP from Simbase's gateway, not the foreign operator's.
SMS behaviour can vary. Outbound SMS generally works on most networks; inbound SMS may not, depending on the foreign carrier's policies.
Voice is not supported. Simbase is an IoT data product; SIM cards don't carry voice service. National emergency calls are an exception.
Common questions
Data roaming lets a SIM use a network in another country. National roaming lets it use a different operator's network within the same country. Simbase SIMs do both, which is why a device can switch to whichever local operator has the best signal rather than being locked to one.
First check that data roaming is enabled on the device, it's the most common cause. If it is, check the plan attached to the SIM in the dashboard, as some plans restrict roaming to specific regions or block it entirely.
Rates vary by country, not by whether the SIM is roaming. With Simbase, your per-MB rate depends on the coverage plan attached to the SIM and where the device is operating. See Billable items.
Network selection is controlled by the device, not the SIM. Simbase SIMs aren't steered, the modem scans available networks and chooses which to attach to. The SIM determines which networks it's permitted to use; the device decides which of those it actually connects to. Most modems handle this automatically, though some let you set a preferred network or lock to a specific operator.
Related
SIM Profiles, coverage by profile
Multi-IMSI vs eUICC, how the underlying tech enables roaming
Set up the Simbase APN, regional breakouts for lower roaming latency
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