The difference between HLR and VLR: the HLR (Home Location Register) is the mobile operator's central, permanent database of its subscribers, while the VLR (Visitor Location Register) is a temporary database attached to a switching centre that holds data for the subscribers currently in its area. The HLR knows who you are and which VLR serves you now; the VLR knows you are here.
What is HLR and VLR?
Both are databases in GSM and UMTS (2G and 3G) core networks.
- HLR (Home Location Register): one logical database per operator. It stores each subscriber's permanent profile: IMSI (the SIM identity), MSISDN (the phone number), allowed services, call forwarding and barring settings, and a pointer to the VLR and switching centre currently serving the subscriber. It works with the AuC (Authentication Centre), which holds the secret keys used to authenticate SIMs.
- VLR (Visitor Location Register): usually built into each MSC (Mobile Switching Centre). When a phone enters that MSC's area, the VLR copies the subscriber's profile from the HLR and records the location area. It serves calls and SMS locally without asking the HLR each time. Data is removed when the phone moves away.
Difference between HLR and VLR
| HLR | VLR | |
|---|---|---|
| Type of data | Permanent subscriber profile | Temporary copy plus current location area |
| How many | One logical HLR per operator (often several physical nodes) | One per MSC area |
| Covers | All of the operator's own subscribers, wherever they are | Everyone currently in the area, including roaming visitors |
| Location detail | Which VLR/MSC serves the subscriber | Which location area the phone is in |
| Updated when | Subscription changes, or the subscriber moves to a new VLR | The phone registers, moves or switches off |
| Used by | Network routing of incoming calls and SMS, roaming partners, HLR lookups | Local call and SMS handling, paging |
How do HLR and VLR work together?
- Registration: a phone switches on in an area. The VLR there asks the HLR for the subscriber's profile; the HLR authenticates via the AuC, sends the profile and records which VLR now serves the subscriber.
- Roaming: abroad, the visited network's VLR contacts the home HLR over international signalling. The HLR updates the location and the old VLR deletes its copy.
- Incoming SMS: the sending SMS centre asks the HLR where to deliver. The HLR answers with the serving MSC, which uses its VLR data to page the phone and deliver the message.
- Incoming call: the gateway switch asks the HLR, which asks the serving VLR for a temporary roaming number, and the call is routed there.
What does an HLR VLR lookup show?
A commercial HLR lookup uses the same signalling query an SMS centre makes before delivery. It can return whether the number exists and is active, the home network (as MCC and MNC), whether it has been ported, and sometimes whether it is roaming or which network is serving it. It does not reveal the subscriber's identity or precise location. Senders use it to clean lists and route correctly; see phone number validation API. Because the HLR also tells the network where to send SMS, it plays a part in number portability routing and in operator SMS firewalls, which block suspicious signalling queries.
Do HLR and VLR exist in 4G and 5G?
Their roles continue under new names. In 4G (LTE), the HSS (Home Subscriber Server) takes over the HLR's role, and the MME tracks the phone's location, a role close to the VLR's. In 5G core networks, the UDM (Unified Data Management) holds subscriber data and the AMF handles registration and mobility. Many networks still run HLR functions for 2G and 3G and for SMS delivery, and HLR lookups remain widely available.
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Frequently asked questions
What is the full form of HLR and VLR?
HLR stands for Home Location Register and VLR stands for Visitor Location Register. Both are databases in GSM and UMTS mobile core networks: the HLR holds permanent subscriber data for the operator, and the VLR holds temporary data for subscribers currently in a switching centre's area.
What is the role of AuC with HLR?
The AuC (Authentication Centre) stores the secret key shared with each SIM and generates the authentication data the network uses to check that a SIM is genuine. It usually works alongside the HLR, which passes this data to the VLR when a subscriber registers.
Where is the VLR located?
The VLR is usually integrated into the Mobile Switching Centre (MSC) it serves, so each MSC area has its own VLR. When a phone moves into a new MSC area, the new VLR registers it and the HLR tells the old VLR to delete its copy.
What is EIR in GSM?
The EIR (Equipment Identity Register) is a database of device IMEI numbers. Operators can use it to block stolen or unapproved handsets. It identifies the device, while the HLR and VLR deal with the subscriber and the SIM. Not every operator uses it in the same way.
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