HLR Or Home Location Register: 

When a person buys the new sim card. Mobile operator configures new sim in a database. The database is the HLR. Along with storing subscriber profile, hlr have full stack for GSM protocols for supporting voice, sms , data and other services.  HLR is located in the home network of the mobile subscriber. Its a SS7 node, and have a global title (gt) for address.  The gt address is called HLR number.

A mobile moves from one place to other. By doing this mobile changes its location. Roaming network keep updated the HLR for current location of a subscriber. Roaming information is the dynamic information stored in hlr. Dynamic information is VLR and MSC or SGSN number.

A sim card configuration on hlr have IMSI and MSISDN as primary key. On a location update , hlr assigns mobile number or MSISDN Number  , to the SIM card.

HLR for voice and SMS:

Voice and sms service for a sim card is not configured by default.  HLR stores a teleservice list  for Voice and SMS. Upon location update the list of services are transferred to vlr/msc, then roaming network uses the information to allow or disallow the call. Following are key parameters stored in HLR.

VLR Number :

This is the dynamic information stored in database. Upon registration of phone , hlr gets location update from the network. The location update have the VLR number.  The VLR number is a MSISDN. If location updates gets successful,  VLR number is stored in database.  Requests initiated from HLR , will have VLR number , to reach the roaming network of a phone.

MSC Number:

This is similar to the VLR number. Most of the time MSC and VLR are co-located.  This is the dynamic information stored in database.


This is the mobile number of the subscriber. Upon location update HLR assigns the mobile number to the sim card. It is a static information.

Call Forwarding:

This is the service, a mobile operator provides to its subscribers. This allow a subscriber to receive calls on another number.  Mobile user can activate call forwarding from phone.  On hlr , a call forwarding data have. Call forwarding type and the mobile number to forward the call. Call forwarding type can be , Call Forwarding Unconditionally, Call forwarding when busy and call forwarding when not reachable.

Camel Subscription Info:

This is static data. MSC or GMSC uses this data for real time prepaid charging. It list of camel subscription for or CSI. A CSI can be for mobile originated calls or MO-CSI.

GPRS data subscription in hlr:

Mobile operator provides different data services to the mobile subscribers.  The service may be for 2G, 3G and 3G+.  Each service have Quality of Service associated with it. For accessing data service, roaming network should know the GGSN for a gateway from mobile device to the internet or PDN.

HLR stores the GPRS subscription profile for a subscriber. This includes APN , identifies a GGSN to get data. Quality of Service, this includes maximum and minimum bandwidth. On location update for gprs, sgsn downloads the gprs subscription data. Based on data , sgsn creates a bearer towards the mobile device.  The APN received from HLR, identifies the GGSN. GGSN allocates the ip address to the device. The HLR may have a static ip configuration also for an APN.


Prepaid Online Charging:

When in roaming, mobile subscriber is charged in real time for a call. This is possible because of intelligent network. Mobile operator deploys charging platform which is Camel Protocol based. Charging node is in home network. On location update HLR sends the charging gateway address for online prepaid charging to the VLR/MSC.  Gateway address is the global title of charging node.






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