The HSS/HLR stores and manages the SIM database for mobile networks. It also manages multiple subscriber identities (from different technologies) in one server, providing seamless services over different networks. It is designed for use in GSM, UMTS, LTE, IMS, WiFi networks or any other type of network that uses MAP or Diameter for authentication.

The HSS/HLR includes a Home Location Register (HLR), an Authentication Center (Auc) (2G/3G) and a Home Subscriber Server (HSS) (4G LTE). The HSS/HLR exports a JSON API for integration with any SIM management and CRM systems. It is capable of interconnecting with all the VLRs implemented in a GSM mobile network, with any MME from a conventional LTE network, or with the UCN core network server.

As it is also an AuC, the HSS/HLR authenticates subscribers as they try to connect to the GSM, UMTS, or the LTE networks, to make phone calls, send SMSs and access mobile data.

HSS/HLR is easy to operate and manage remotely using the Mobile Management Interface (MMI) online. The interface makes it accessible to add a new HSS/HLR unit, to setup a cluster of HSS/HLRs, to add subscribers, to modify and configure subscribers┬┤ profiles and more. MMI’s main benefit is the fact that operators care remotely manage all their entire network equipment using a single web interface.

Features and benefits
  • The HSS/HLR is fully implemented in software and uses commodity hardware.
  • Can serve as a proxy between an existing 2G/3G HLR and an LTE network.
  • Uses the SS7 MAP interfaces when serving as an HLR with other 2G/3G network equipment.
  • Provides Diameter support.
  • Supports groups for mobile data and CAMEL profiles.
  • Scalable by adding more HSS/HLR components, either distributed or load balanced.
  • Exports a JSON API for custom features.
  • Managed via a web-based management interface.
Software specifications
RoamingSS7 MAP (2G/3G) | Diameter (4G)
InterfacesS6a/S6d (MME/SGSN to and from HSS/HLR) | Cx/Dx (I-CSCF/S-CSCF to and from HSS/HLR)
Call forwarding servicesCFU, CFB, CFNRC, CFNRY
Standard services and bearerstelephony, emergency calls, SMS
Supplementary servicesBAOC, BAIC, CW, HOLD, CLIP, CLIR, COLP, COLR, MPTY
SS/HLR Cluster Configuration

The HSS/HLR cluster is a mechanism that allows operators to increase the number of SS7 and Diameter transactions and the number of subscribers. A single cluster can contain up to 10 nodes and each node supports approximately 100,000 subscribers. Each node is identical to the others and contains:

  • a MySQL database for subscriber information
  • a cluster module that implements a custom protocol
  • a JSON API fo subscriber management and configuration

as well as other modules for SS7/MAP and Diameter.

How does the HSS/HLR cluster work?

The HSS/HLR cluster uses replication, so that each node contains the same subscriber information of the entire cluster. Replication allows for different equipment in the network to easily interrogate the HSS/HLR cluster, irrespective of subscribers’ possible identities.

Adding a new node

To add a new node, the operator needs to:

  • configure the new equipment
  • set the PC, GT, connections to the STP (M2PA link or M3UA), and the Diameter connection to the DRA
  • configure the cluster module by associating an unique ID (node_id) to this node
  • reconfigure the STPs and the DRAs
  • notify the roaming partners about the new Global Titles (GT) and the HSS identity of the HSS/HLR node

Operators can use the MMI management interface to easily perform the first two configuration steps. After configuring the new node identity, the cluster connection to the other nodes is done automatically.

The first node is usually the one though which all the subscriber data is added/modified and is used as a reference point. If the first node is unavailable, the MMI will use a different HSS/HLR server.

The cluster module

The cluster module synchronizes subscriber information within all the nodes in the cluster. The new node will automatically synchronize to the rest of the nodes in the cluster in less than an hour.

If a node in the cluster is down and during that time subscriber information is updated or changed, the old information will only be marked as deleted. The cluster module will update the new subscriber information to the reconnected node and will finally delete the old information from the entire cluster.

HSS/HLR cluster for SS7/MAP use

Identifying subscribers and their location can be done through both IMSI and MSISDN unique to each subscriber.

Identifying the subscriber by the MSISDN

In the case of a mobile terminated (MT) call, the Gateway Mobile Switching Center (GMSC) receives the call for the subscriber. It must send a sendRoutingInfo to the HSS/HLR asking for the location where the subscriber is registered. In this case the subscriber is identified by the MSISDN.

The GMSC connects to any of the STPs in the network, as they are equivalent and any of them can route the cluster to perform Location Update. The STPs have a common identity, while the HSS/HLR nodes have different identities.

Identifying the subscriber by the IMSI

When the mobile device first registers to the network or when it moves to another area, it contacts the Visitor Location Register (VLR). The VLR notifies the HSS/HLR of the subscriber’s new location by sending an updateLocation request for the IMSI associated to the subscriber’s SIM card.

HSS/HLR cluster for Diameter use

In the case of Diameter, a subscriber can be identified though multiple possible identities (IMSI, MSISDN or different IMS and SIP identities).

Identifying the subscriber by the IMS public/private identity

The subscriber registers a public identity, but the authentication is done using a private identity. The private identity can be provisioned in the SIM card or it can be derived from the IMSI. After the registration procedure, the HSS/HLR cluster knows which S-CSCF will provide services for this subscriber.

When the subscriber receives an MT call or an SMS, these are sent to one of his public identities. The I-CSCF interrogates any HSS/HLR cluster to find the S-CSCF that handles that service for the specific public identity.

Identifying the subscriber by the IMSI

When a subscriber connects to the MME in the Visited Network, its location needs to be updated through by the IMSI. The MME starts a location update procedure, and connects to a DRA. The DRA knows which HSS/HLR can perform the location update and interrogates the correct one.

The HSS/HLR replies with a single, longer message that contains all the requested information. The procedure is different in LTE network because Diameter is an IP based protocol that can route longer messages.

What happens when a node is down?

Ideally, all the nodes in the HSS/HLR clusters work without issues. However, some problems may still arise:

  • A server goes down (is completely unreachable). It can’t be accessed neither on the cluster side nor on the SS7/Diameter side.
    • In this case, a very small number of subscribers might be affected: just those whose location information changed recently and wasn’t propagated to the other servers.
    • The other nodes will handle all the requests until this node is back up and resynchronized.
    • If the users notice a problem and reboot their phones, the location information will be updated, and their service will be restored.
  • The node can’t be accessed on the clustering side, but the MAP and Diameter connections are still up.
    • In this case, the location could be updated in one node but the other node is interrogated.
    • It is advisable to disconnect the server completely. Still, if there are only two nodes, then resynchronizing them is trickier and is done on a case by case basis.

In conclusion, when problems appear with one of the nodes, some of the subscribers could experience some missed SMSs/calls, but the network continues to function and the other nodes take the load of the affected node.


We have noticed that most small operators and MVNOs need traffic capacity more than increasing their network’s subscriber capacity. By choosing our solution, operators can easily add a new node to increase the number of transactions and to balance traffic between the HSS/HLR nodes in the cluster. The HSS/HLR cluster allows operators to scale as they go, so there is no need to invest in an expensive solution from the start.

Through the cluster protocol that connects all nodes in the cluster, the new element rapidly synchronizes to the rest of the nodes and is ready for use. A cluster with nodes that use the replication technology reduces equipment investment because it does not require the deployment of custom STPs and DRAs, which can choose from the subscribers divided between the nodes.

Even if one of the entities is down and some subscribers could be affected if changes were updated in that node and weren’t replicated, the majority of the subscribers won’t be affected so service continuity is assured.

The HSS/HLR is an affordable subscriber management solution suited for MVNOs and smaller MNOs. It suits any network needs and its low licensing costs allow the operator to scale up with minimum effort. The combined HSS/HLR is a clustered solution offering high reliability and redundancy.

  • Scalable
    Each HSS/HLR server has a capacity of up to 100,000 subscribers. Because it uses software and commodity hardware, any number of new servers can be added to the network and automatically synchronized with the other servers.
  • Multi-technology
    The HSS/HLR is a unified solution for GSM, UMTS, LTE, IMS, and WiFi networks. It includes a Home Location Register (HLR) and Authentication Center (AuC) for 2G, 3G and 4G networks, and a Home Subscriber Server (HSS) for data and voice (IMS) in LTE.
  • Secure and reliable
    The HSS/HLR performs authentication over both Diameter and SS7 MAP for GSM, UMTS, LTE and WiFi. Unlike other solutions in its range, it supports configuration in a cluster of HSS/HLR nodes, which makes it redundant against failure.
  • Easy management
    The HSS/HLR uses a Linux-based operating system, allowing the operator to handle its management and operation. A JSON API and a web-based interface make the HSS/HLR easy to configure and manage.

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