Home Subscriber Server (HSS)

Home Subscriber Server(HSS) By : M.Samie

Home Subscriber Server • What is HSS? • HSS in IMS • Main Data in HSS • HSS Subsets • HSS Logical Functions • Reference Points & Interfaces • Subscription Locator Function • Implementation Issues • Maintenance Issues

What is HSS? • Is the master database for a given user • Containing the subscription-related information to support the network entities • Is considered as Data Repository for IM CN Subsystem user related data Note : A Home Network may contain one or several HSSs

HSS in IMS

AS AS AS IMS Functional Entities • Home Subscriber Server • Centralized DB • HLR successor • User profile • Filter criteria (sent to S-CSCF) • Which applications • Which conditions • Application Servers • Push-to-talk • Instant messaging • Telephony AS • 3rd party or IMS Vendor • Media Resource Function Controller • Pooling of Media servers (e.g. conference) Home Network UA/UE P-CSCF SIP DNS ENUM HSS • Media GatewayControl Function • Interfaces to PSTN/PLMN by • Converting SIP <-> ISUP • Interworking RTP to circuit • H.248 control of MGW Diameter SIP MRFC P-CSCF I-CSCF S-CSCF SIP SIP UA/UE SIP MS MS SIP SIP SIP BGCF MGCF SIP ISUP SIP SS7 H.248 PSTN MGW RTP TDM • Serving CSCF • Registrar • Session control • Application Interface • Proxy CSCF • 1st contact point for UA • QoS • Routes to S-CSCF Visited Network • Interrogating CSCF • Entry point for incoming calls • Determines S-CSCF for Subscribers • Hides network topology • Breakout Gateway Control Function • Selects network (MGCF or other BGCF) in which PSTN/ PLMN breakout is to occur

Main Data in HSS • Presence, Location and Profile • End-User Identity • Private and Public End-User Information • Registration Information • Service Initiation Information • Subscriber Service Profile (SSP) • Downloaded to CSCF at Registration

HSS Subsets • Home Location Register (CS Domain) • Home Location Register (PS Domain) • Authentication Center (CS Domain) • Authentication Center (PS Domain) • IMS related subset CS Domain HLR AUC IM CN DR AUC HLR PS Domain

Home Location Register • It is needed to enable subscriber access to the PS Domain services. • It supports PS Domain entities such as the SGSN and GGSN, through the Gr and Gc interfaces and the 3GPP AAA Server for the I-WLAN through the D'/Gr' interface. • It is needed to enable subscriber access to the CS Domain services and to support roaming to legacy GSM/UMTS CS Domain networks. • It supports CS Domain entities such as the MSC and GMSC, through the C and D interfaces.

Authentication Center • The AuC is associated with an HLR and stores an identity key for each mobile subscriber registered with the associated HLR. • The AuC communicates only with its associated HLR over a non-standardised interface denoted the H-interface. • The HLR requests the data needed for authentication and ciphering from the AuC via the H-interface. • HLR delivers them to the VLR and SGSN which need them to perform the security functions for a mobile station.

SNMP Agent function Support 3GPP TS 23.002 HSS Identification Handling Mobility Management User Security Info Generation Service Authorization Access Authorization User Security Support Service Provisioning Support Application Services Support Call/Session Establishment Support CAMEL Services Support GUP Data Repository Cx Si Sh Sh C Gr Gc D Applications Rp IM-SSF OSA-SCS CSCF GUP Server GGSN SGSN GMSC MSC/VLR Rp SIP Application Server PS Domain CS Domain AAA Server IM CN Subsystem Wx, Gr’, Gc’

HSS Logical Functions • Mobility Management • HSS supports MM by location updating • Call Session Establishment Support • HSS provides information on which call/session control entity currently hosts the user • User Security Support • The HSS generates user authentication and ciphering data for the CS and PS Domains and for the IM CN subsystem.

HSS Logical Functions(Cont.) • User Identification Handling • The HSS provides the appropriate relations among all the identifiers uniquely determining the user in the system • CS Domain (IMSI and MSISDNs) • PS Domain (IMSI, MSISDNs and IP addresses) • IM CN subsystem (private identities and public identities) • Access Authorization • The HSS authorises the user for mobile access when requested by the MSC/VLR, SGSN, 3GPP AAA Server or CSCF, by checking that the user is allowed to roam to that visited network.

HSS Logical Functions(Cont.) • Service Authorization Support • The HSS provides basic authorisation for MT call/session establishment and service invocation. • The HSS updates the appropriate serving entities (i.e., MSC/VLR, SGSN, 3GPP AAA Server, CSCF) with the relevant information related to the services to be provided to the user. • Service Provisioning Support • The HSS provides access to the service profile data for use within the CS Domain, PS Domain and IM CN subsystem.

HSS Logical Functions(Cont.) • Application Service and CAMEL Service Support • The HSS communicates with the SIP Application Server and the OSA-SCS to support Application Services in the IM CN subsystem. • The HSS communicates with the IM-SSF to support the CAMEL Services related to the IM CN subsystem. • The HSS communicates with the gsmSCF to support CAMEL Services in the CS Domain and PS Domain.

HSS Logical Functions(Cont.) • GUP Data Repository • The HSS supports the storage of IM CN Subsystem user related data, and provides access to these data through the Rp reference point by GUP Server*. * GUP Server is a functional entity providing a single point of access to the Generic User Profile data of a particular subscriber. (TS 23.240)

HSS and Basic Interfaces HSS D Gc C Rp Cx Gr GGSN MSC GUP Server CSCF GMSC SGSN

Reference Points & Interfaces • Interfaces internal to the CS domain • Interfaces internal to the PS domain • Interfaces used by CS and PS domains • IM Subsystem Reference Points • Diameter Protocol

Interfaces to CS domain HLR - VLR (D-interface) (TS 29.002) • Is used to exchange the data related to the location of the mobile station and the management of the subscriber. • Signalling on this interface uses the Mobile Application Part (MAP), which in turn uses the services of Transaction Capabilities.

Interfaces to CS domain HLR - MSC (C-interface) (TS 29.002) • The Gateway MSC must interrogate the HLR of the required subscriber to obtain routing information for a call or a short message directed to that subscriber. • Signalling on this interface uses the Mobile Application Part (MAP), which in turn uses the services of Transaction Capabilities.

Interfaces to PS domain HLR – SGSN (Gr-interface) (TS 29.002) • This interface is used to exchange the data related to the location of the mobile station and to the management of the subscriber. • Signalling on this interface uses the Mobile Application Part (MAP), which in turn uses the services of Transaction Capabilities.

Interfaces to PS domain HLR – GGSN (Gc-interface) (TS 29.002) • Is used by the GGSN to retrieve information about the location and supported services for the mobile subscriber, to be able to activate a packet data network address. • Signalling on this interface uses the Mobile Application Part (MAP), which in turn uses the services of Transaction Capabilities.

Interfaces used by CS and PS domains HLR - AuC (H-interface) • When an HLR receives a request for authentication and ciphering data for a Mobile Subscriber and it does not hold the requested data, the HLR requests the data from the AuC. • The protocol used to transfer the data over this interface is not standardised.

IM Subsystem Reference Points • HSS – CSCF (Cx Reference Point) • HSS – SIP AS or OSA SCS (Sh Reference Point) • HSS – CAMEL IM-SSF (Si Reference Point) • AAA Server - HLR (D'/Gr' Reference Point) • AAA Server - HSS (Wx Reference Point) • GUP Server – HSS (Rp Reference Point) • Applications – HSS (Rp Reference Point) • CSCF- SLF (Dx Reference Point) • AS- SLF (Dh Reference Point) • AAA Server - SLF (Dw reference point)

IM Subsystem Reference Points HSS – CSCF (Cx Reference Point) (TS 23.228) • Procedures related to Serving CSCF assignment • Procedures related to routing information: retrieval from HSS to CSCF • Procedures related to authorisation (e.g., checking of roaming agreement) • Procedures related to authentication: transfer of security parameters of the subscriber between HSS and CSCF • Procedures related to filter control: transfer of filter parameters of the subscriber from HSS to CSCF

IM Subsystem Reference Points AAA Server - HSS (Wx Reference Point) AAA Server - HLR (D'/Gr' Reference Point) (TS 23.234) • Retrieval of authentication vectors • Retrieval of WLAN access-related subscriber information (profile) • Registration of the 3GPP AAA Server of an authorised WLAN user in the HSS • Indication of change of subscriber profile • Retrieval of online/offlinecharging

IM Subsystem Reference Points GUP Server – HSS Applications – HSS (Rp Reference Point) (TS 23.240) • Enables the GUP Server and the Applications to access GUP Data Repositories • The HSS is one of the GUP Data Repositories. It stores the IM CN Subsystem user related data.

Diameter Protocol • Is a signaling protocol that has been specified by IETF (RFC 3588 – 3589) • IS defined as a base protocol used in conjunction with a set of applications • It provides mechanisms for reliable transport, message delivery and error handling between Diameter clients and servers.

Diameter Functions • Delivery of AVPs (Attribute Value Pair) • Capabilities negotiation • Error notification • Basic Services necessary for applications, such as handling of user sessions or accounting Note : Diameter can be extended through addition of new commands and AVPs for set of new application requirements

Subscription Locator Function (SLF) Is used as a resolution mechanism that enables the I-CSCF, the S-CSCF and the AS to find the address of the HSS that holds the subscriber data for a given user identity when multiple and separately addressable HSSs have been deployed by the network operator.

IM Subsystem Reference Points CSCF- SLF (Dx Reference Point) AS- SLF (Dh Reference Point) AAA Server - SLF (Dw reference point) (TS 23.228) • Is used to retrieve the address of the HSS which holds the subscription for a given user. • Is not required in a single HSS environment.

Implementation Issues • In IMS arch. the HSS is a central database that contains all of the information needed to properly control sessions. • Functions in the network interact with the HSS using IETF Diameter Protocol. • The HSS is involved in every session and maybe queried multiple times during a call so it must have high performance. • The HSS must be exceptionally reliable, as without it sessions cannot be created.

Implementation Issues • Software Modules • Agents supports protocols and Interfaces • Information Storage & Retrieval Module • Agents supports authorization requested by components • Other functions inherited from PS & CS domains • Data Organization • Storage Media • Memory Hierarchy • Efficient/Reliable Transfer • Hardware Techniques ( RAID disks ) • Software Techniques ( Buffer Mgmt ) • Storage Strategies • Tuples on Disks • Tuples on Pages, Clusters, …

Maintenance Issues • The main issue is adding capacity while maintaining performance • Simply adding processing power on HSS • Adding additional mirror database nodes either at the same location or distributed geographically • Segregating different groups of subscribers in different databases • Result is a network that seamlessly support growth to millions call per “Busy Hour” without stressing any single point in the network

Any Question?

Data in HSS The main data stored in the HSS include [3GPP TS 23.002]: • User identities • private user identities • public user identities • registration information • access parameters • user authentication • allocated S-CSCF names • roaming authorization • service-triggering information

Subscriber Data • Subscriber data for CS and PS domains • Subscriber data for IP Multimedia domain

Subscriber data for CS and PS domains(TS 23.008) • Data related to subscription, identification and numbering • Data related to Mobile Station types • Data related to authentication and ciphering • Data related to roaming • Data related to basic services • Data related to supplementary services • Mobile station status data • Data related to Operator Determined Barring • Data related to handover • Data related to short message support • Data related to subscriber trace • Data related to the support of voice group and broadcast calls • Data related to GPRS NAM • Data related to CAMEL • Data related to charging

Subscriber data for IP Multimedia domain(TS 23.008) • Data related to subscription, identification and numbering • Data related to registration • Data related to authentication and ciphering • Data related S-CSCF selection information • Data related to Application and service triggers • Data related to Core Network Services Authorization • Data related to Charging • Data related to CAMEL Support of IMS Services

Home Subscriber Server (HSS)