Quick technical background: What is a network identity? The network identity is a 5- or 6-digit code that identifies a cellular network uniquely in the world. The first three digits are a “mobile country code” (MCC). The next two or three digits are a “mobile network code” (MNC) within that country. MCCs are assigned to countries by the ITU. Within each country, the MNCs are assigned by the national regulator.
In territorial waters, you must use operating frequencies and network identities assigned by the national regulator for the territory. That is impractical for most on-vessel networks, so you will shut down your on-vessel network when you approach territorial waters of any country. As you approach a populated area, you will enter the coverage of land-based public networks. The solution to global coverage is to have roaming agreements with the land-based operators. In-port coverage for each device depends on its SIM and what roaming agreements are available to it.
In international waters, you are largely free to do what you want, but there are best practices and practical considerations for both choice of frequency and choice of network identity.
For frequency, your best options are the “850” and “900” MHz bands. These go by several names. The “850” band is called GSM850, but also called “Band 5”. This is band is commonly used for cellular service in ITU Region 2, the Americas. The “900” band is EGSM900, also called “Band 8”. This band is commonly used for cellular service in ITU Regions 1 and 3, the rest of the world outside the Americas. There are two reasons to use these bands:
- Widespread device support. Any cellular device intended for international use will support both of these bands.
- Penetration. On-vessel networks are cluttered radio environments, full of metal barriers. Lower frequencies are more likely to refract around metal objects, making fewer shadows. The 850 and 900 bands are the lowest bands standardized for GSM, which still plays a role in on-vessel IoT.
There are also bands in the 700 MHz range that are being standardized for international LTE and 5G operation, but running a non-GSM network sticks you with other limitations, addressed in other articles.
For network identity, the ITU recommends that you get an identity in mobile country code 901, a special MCC that is reserved for “non-geographic networks”. Because MCC 901 is not associated with any particular country, the MNCs here are allocated directly by the ITU. The ITU strongly warns against using the PLMN of any normal operator outside of the territory of that operator without special permission (from the ITU). If you are operating in cooperation with a satellite provider, the satellite provider may already have an identity in MCC 901 that you can also use for the on-vessel network.
At this point, many people also ask what this means for SIMs and what SIMs will work. The SIM gives the device a list of “preferred operators”, which starts with the home operator (the issuer of the SIM) followed by a list of operators with whom the home operator has roaming agreements. In an automatic network search, the device will prefer these operators in the given priority order. However, if no other service is available, which will be the case on the high seas, the device will try anything it can find, and come to your on-vessel network for service. What you do next depends on your roaming agreements and your choice of radio technology, topics for other articles.