ISIM stores IMS subscription data on the UICC. These parameters give the UE the identities and home-network information needed for IMS registration, emergency registration, P-CSCF discovery, and related authentication features.

This page summarizes the ISIM parameters used by IMS procedures and the elementary files defined in 3GPP TS 31.103.

Contents

• Parameters for Registration
• Parameters for Emergency Registration
• ISIM Parameters Specified in 31.103
  • EF_DOMAIN
  • EF_IMPU
  • EF_IMPI
  • EF_P-CSCF
  • EF_GBABP
  • EF_IST

Parameters for Registration

IMS registration uses the ISIM identities to construct the SIP REGISTER request and to identify the subscriber toward the IMS home network. Based on 3GPP TS 24.229 section 5.1.1.1A, the UE uses the following ISIM-contained parameters.

• The private user identity, specified in IMPI.
• One or more public user identities, specified in IMPU. This field can have multiple items.
• The home network domain name used to address the SIP REGISTER request.

Parameters for Emergency Registration

Emergency registration uses a reduced identity selection rule so the UE can initiate emergency IMS service even when normal registration handling is limited. Based on 3GPP TS 24.229 section 5.1.1.1A, the first IMPU item is used.

• The first item in IMPU.

ISIM Parameters Specified in 31.103

3GPP TS 31.103 defines the ISIM elementary files that store IMS identities, domain information, P-CSCF addresses, bootstrapping data, and service availability information.

EF_DOMAIN

EF_DOMAIN contains the home operator network domain. The home network domain name, or FQDN, is encoded as an octet string using UTF-8 encoding rules as specified in IETF RFC 3629. The tag value of the Home Network Domain Name TLV data object is '80'.

EF_IMPU

EF_IMPU contains the IMS public user identity. This field can have one or more records. According to 3GPP TS 31.103, the first or only record in the EF is used when performing emergency registration or as the default SIP identity when no record is explicitly selected in the current session or carried over from a prior session.

EF_IMPI

EF_IMPI contains the IMS private user identity. See 3GPP TS 31.103 section 4.2.2.

EF_P-CSCF

EF_P-CSCF contains one or more Proxy Call Session Control Function addresses. The first record in the EF has the highest priority, and the last record has the lowest priority.

Note: if service no. 1 and/or service no. 5 is available, this file shall be present.

EF_GBABP

EF_GBABP stands for GBA Bootstrapping Parameters. This field contains the AKA random challenge RAND and Bootstrapping Transaction Identifier B-TID associated with a GBA bootstrapping procedure. See 3GPP TS 31.103 section 4.2.9.

Note: if service no. 2 is available, this file shall be present.

EF_IST

EF_IST contains the ISIM Service Table. It indicates which ISIM services are available to the UE. See 3GPP TS 31.103 section 4.2.7.

Contents:

• Service no. 1: P-CSCF address
• Service no. 2: Generic Bootstrapping Architecture (GBA)
• Service no. 3: HTTP Digest
• Service no. 4: GBA-based Local Key Establishment Mechanism
• Service no. 5: Support of P-CSCF discovery for IMS Local Break Out
• Service no. 6: Short Message Storage (SMS)
• Service no. 7: Short Message Status Reports (SMSR)
• Service no. 8: Support for SM-over-IP including data download via SMS-PP as defined in TS 31.111
• Service no. 9: Communication Control for IMS by ISIM
• Service no. 10: Support of UICC access to IMS