With more and more service providers / MVNOs interested in pursuing IMSI-based connectivity over SIM-resale in the US, it’s important to understand what numbering assets are required for enabling voice, SMS / text messaging and data connectivity.
Đang xem: What is a msisdn?
The International Mobile Subscriber Identity (IMSI) is a requirement for all subscriptions accessing a public wireless / mobile network – whether human end-users or devices (e.g. in M2M / IoT use cases).
The IMSI is a unique non-public identity by which the behaviour of a particular subscription can be controlled from the Home Location Register (HLR) or Home Subscriber Server (HSS), including which Radio Access Networks (RAN) the IMSI can attach to and in what priority order, what services it can support (e.g. whether roaming is enabled or not) and how data traffic is routed (e.g. APN).
The IMSI is usually presented as a 15-digit number with the first three digits representing the Mobile Country Code (MCC), followed by the Mobile Network Code (MNC) and finally the Mobile Subscription Identification Number (MSIN), which is usually 9-10 digits long.
The combination of MCC and MNC is referred to as the Home Network Identity (HNI) or Public Land Mobile Network (PLMN) identity. The HNI / PLMN identifies the wireless carrier / MNO whose HLR and HSS a particular subscriber is served from.
In the US, ownership of PLMN’s is tied to spectrum ownership i.e. only companies holding spectrum can request and be assigned IMSI’s.
The Mobile Station International Subscriber Director Number (MSISDN) is basically your mobile phone number – used as a unique identity used to enable routing of voice and SMS traffic to and from a specific subscription / device on a wireless / mobile network.
To enable a particular service (e.g. a voice call or Short Message Service (SMS) also known as text messaging) to be delivered, the MSISDN is not enough on its own but it needs to be paired with the IMSI with both registered and mapped together on the HLR and HSS.
This pairing of MSISDN and IMSI enables a voice call or an SMS to be sent using an MSISDN, which is visible to the subscriber (i.e. the subscribers phone number) to be routed to a specific IMSI based on the Subscriber Identity Module (SIM).
A SIM, whether in physical card form factor or e.g. in eSIM format, has one primary IMSI, but can have multiple MSISDN’s associated with it. The MSISDN associated with a SIM can also be changed, while the primary IMSI typically remains the same.
In summary, if a particular subscription requires support for two-way voice, SMS and data i.e. with the subscription being able to connect to and from other public wireless / mobile networks, it requires both an IMSI and an MSISDN.
However, if the device is in a closed network, such as a M2M / IoT use, with the device needing to be reached by a server within the closed network rather than any subscriber around the world, then MSISDN may not be needed and virtual numbering used instead to enable the routing of messaging.
Solution for IMSI-Based Connectivity Needs
Limitless Mobile is an FCC-regulated regional wireless carrier with spectrum, RAN and serving retail customers in central Pennsylvania. We also serve wholesale customers nationwide as well as internationally, with access to e.g. Limitless Mobile’s neutral IMSI and MSISDN assets and supporting multiple integration models, from hosting and managing the IMSI’s and MSISDN’s on Limitless Mobile’s Tier 1 Ericsson mobile core network, to supporting wholesale customers wanting to host and manage the IMSI’s and MSISDN’s on their own mobile core network.
If you’re in the market for IMSI based connectivity in the US or want to learn more about numbering, please feel to get in touch with us at sales
Group CEO at Limitless Mobile
Here’s second in my series or short articles addressing various topics in wholesale wireless / mobile connectivity, focusing on topics that we regularly get asked about.