IMS HSS OV – Cx and Sh Interface Procedure Study
1). HSS defines and maintains IMS service/user profile for CSCFs:
During a UE registration
§ HSS provides a) required capabilities for user services and b) operator preference on a per-user basis, to I-CSCF (Cx-Query, Cx-Select-Pull).
§ I-CSCF selects and informs a S-CSCF. Then HSS receives from S-CSCF its name and user identity, and sends other user information to this S-CSCF (Cx-Put and Cx-Pull).
Support Authorization and Authentication :
§ Cx-Query+Cx-Select-Pull (or Diameter UAR): authorization, from I-CSCF
§ Cx-AuthDataReq (or MAR): authentication, from S-CSCF
During call setup (Session Initiation)
§ Provides address of current serving-CSCF for the terminating user to I-CSCF (Cx-Location-Query)
During de-registration
§ HSS asks S-CSCF to deregister a user (Cx-Deregister), or, S-CSCF asks HSS to remove itself for this user (Cx-Put)
For subscription update
§ HSS asks S-CSCF to update the subscription data for a given user (Cx-Update_Subscr_Data)
2). Functional classification of Cx interface procedures
Operations on the Cx interface are classified in functional groups:
2-1. Location management procedures
§ Registration and De-registration: The operations regarding registration and de-registration.
§ Location retrieval operation: S-CSCF location retrieval operation
Typical scenarios for Location Management
§ Registration for non-registered user (UAR/UAA à MAR/MAA à UAR/UAA à SAR/SAA)
§ Registration for registered user: Re-registration (UAR/UAA à SAR/SAA)
§ Mobile initiated de-registration (UAR/UAA à SAR/SAA)
§ Network initiated administrative de-registration (RTR/RTA)
§ Initiation of a session to a non-registered user (LIR/LIA à SAR/SAA)
2-2. User data handling procedures
§ Download of user information during registration: The download of user information during registration and to support recovery mechanisms.
§ Support updating of user data to S-CSCF: Operations to support the updating of user data and recovery mechanisms.
Typical scenarios for user data handling and related messages
User data download scenario
§ Refer to “registration for registered user” scenario
User Data or Profile download
§ Refer to “registration for registered user” scenario
§ Server-Assignment-Request/Answer (SAR/SAA)
§ Request direction : S-CSCF>HSS
HSS initiated update of User Profile
§ Push-Profile-Request/Answer (PPR/PPA)
§ Request direction : HSS>S-CSCF
2-3. User authentication procedures: HSS provides the function of Authentication Center for IMS
§ IMS ‘Digest-AKAv1-MD 5’ authentication
§ UMTS/GSM AKA authentication
§ IETF HTTP Digest MD5 Password Authentication
Typical Scenario of User Authentication and Related Message
In authentication scenario, HSS can provide authentication data:
§ Password Authentication (IETF)
§ Stored in database after encrypted, got from database after decrypted.
§ MD5 data (IMS or IETF)
§ Calculate by provisioned security parameters, with MD5 algorithm
§ AKA data (UMTS/GSM)
Calculate by provisioned security parameters, with MINLINAGE algorithm
§ Triplets for GSM network
§ Quintets for UMTS network
User Authentication
§ Multimedia-Auth-Request/Answer (MAR/MAA)
§ Request direction : S-CSCF>HSS
3). Cx : Diameter command
User-Authorization-Request & Answer : UAR/UAA (I-CSCF -- HSS)
§ Registration and Re-registration, Mobile initiated de-registration
§ I-CSCF sends UAR to HSS to query subscriber registration status and to request the authorization of the registration of a multimedia user.
Multimedia-Auth-Request & Answer : MAR/MAA (S-CSCF -- HSS)
§ User Authentication and to request security information
Server-Assignment-Request & Answer : SAR/SAA (S-CSCF -- HSS)
§ User Profile download and to request it to store the name of the server that is currently serving the user.
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Location-Info-Request & Answer : LIR/LIA (I-CSCF -- HSS) Session initiation
§ Initiation of a session to a non-registered user: I-CSCF sends LIR to HSS to query subscriber location information and to request name of the server that is currently serving the user (e.g., S-CSCF name)
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Registration-Termination-Request & Answer : RTR/RTA (HSS -- S-CSCF) de-registration
§ Network initiated administrative de-registration and to request the de-registration of a user
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Push-Profile-Request & Answer : PPR/PPA (HSS -- S-CSCF)
§ HSS initiated update of user profile and to update the subscription data of a multimedia user in the Diameter Multimedia client whenever a modification has occurred in the subscription data that constitutes the data used by the client.
4). Cx message to Diameter command mapping
Not Applicable Here
5). Cx message parameters to Diameter AVP mapping
Not Applicable Here
6). The HSS supports the following user data handling functionalities via Sh interface:
§ User data read
§ User data update
§ Subscription
§ Notification
7). Operations on the Sh interface are classified in functional groups:
1. Data handling procedures
§ The download of data from the HSS to an AS.
§ The update of data in the HSS.
2. Subscription/notification procedures
§ An AS can subscribe to receive notifications from the HSS of changes in data.
§ The HSS can notify an AS of changes in data for which the AS previously had subscribed.
8). Sh : Diameter command
User data read (Data read (Sh-Pull))
§ User-Data-Request/Answer(UDR/UDA)
§ Request direction: AS>HSS
§ To read transparent and/or non-transparent data for a specified user from the HSS
User data update (Data Update (Sh-Update))
§ Profile-Update-Request/Answer(PUR/PUA)
§ Request direction: AS>HSS
§ To allow the AS to update the transparent (repository) data stored at the HSS for a specified each IMS Public User Identity or Public Service Identity.
Subscription (Subscription to notifications (Sh-Subs-Notif))
§ Subscribe-Notifications-Request/Answer(SNR/SNA)
§ Request direction: AS>HSS
§ To subscribe to Notifications for when particular transparent and/or non-transparent data for a specified IMS Public User Identity or Public Service Identity is updated, from the HSS.
Notification (Notifications (Sh-Notif))
§ Push-Notification-Request/Answer(PNR/PNA)
§ Request direction: HSS>AS
§ To inform the AS of changes in transparent and/or non-transparent data to which the AS has previously subscribed to receive Notifications for, using Sh-Subs-Notif
9). Sh message to Diameter command mapping
Not Applicable Here
10). Cx and Sh Message Flows
Not Applicable Here
