HLR
The home location register records where a subscriber attaches and whether the line can receive. An SMS route can query it before delivery.
Definitions only — a term explained here is not a service we sell.
The home location register is the database that holds where a subscriber currently attaches and whether the line can receive. A lookup answers reachability questions at that moment, which static number data cannot.
What the register holds
It stores the subscription profile: IMSI, MSISDN, subscribed services, barring state and the address of the VLR or MME serving the subscriber. It holds no message content, and it does not know whether the handset is switched on or off.
Where the lookup goes
- Application
- SMPP gateway
- SMSC
- HLR / HSS
- MSC / MME
- Handset
- Delivery receipt
Text description
The lookup returns the serving element and the subscription status, not proof of delivery.
How a route uses it
In LTE the HSS combines HLR and authentication functions; in 5G the UDM holds subscriber data. A route queries the register with send routing information for short messages before delivery. A number-portability lookup answers a different question: which network owns the number now. Live checks are regulated in many markets because they reveal whether a number exists and is active, so a query needs a lawful basis and a purpose. Use SMS route testing to confirm what a route asks.