IMS (Internet Protocol Multimedia Subsystem)

IMS (Internet Protocol Multimedia Subsystem) is a reference architecture defined by 3GPP that comprises all 3GPP/3GPP2 core network elements providing IP multimedia services that support audio, video, text, pictures alone or in combination, delivered over a packet switched domain.

3GPP (3rd Generation Partnership Project)

A collaboration agreement that was established in December 1998. The collaboration agreement brings together a number of telecommunications standards bodies which are known as “Organizational Partners”.

3GPP2 (3rd Generation Partnership Project 2)

A collaborative third generation (3G) telecommunications specifications-setting project comprising North American and Asian interests developing global specifications for ANSI/TIA/EIA-41 Cellular Radio telecommunication Intersystem Operations network evolution to 3G and global specifications for the radio transmission technologies (RTTs) supported by ANSI/TIA/EIA-41. A sister project to 3GPP.

CSCF (Call Session Control Function)

General term for a functional entity within a IMS core network that can act as Proxy CSCF (P-CSCF), Serving CSCF (S-CSCF), or Emergency CSCF (E-CSCF).

E-CSCF (Emergency Call Session Control Function)

The entity in the IMS core network that handles certain aspects of emergency sessions, e.g., routing of emergency requests to the correct emergency center or PSAP.

P-CSCF (Proxy Call Session Control Function)

The first contact point for the user equipment (UE) within the IMS core network. For an IMS-based emergency call, the P-CSCF detects the emergency call and forwards it to an E-CSCF.

S-CSCF (Serving-CSCF)

The entity in the IMS core network that handles the session states.

E-SMLC (Evolved Serving Mobile Location Center)

Manages the overall co-ordination and scheduling of resources required for the location of user equipment that is attached to E-UTRAN (Evolved UMTS Terrestrial Radio Access Network). It also calculates the final location and velocity estimate and estimates the achieved accuracy. The E-SMLC interacts with the user equipment in order to exchange location information applicable to user equipment assisted and user equipment based position methods and interacts with the E-UTRAN in order to exchange location information applicable to network assisted and network based position methods.

HSS (Home Subscriber Server)

A common functional entity to both the circuit switched and packet switched mobile domains in 3GPP/3GPP2. The HSS is the master database that supports the IMS network entities. It is the entity containing the subscription-related information to support the network entities and performs authentication and authorization of the user and can provide information about the subscriber's location and IP information.

IP-CAN (Internet Protocol-Connectivity Access Network)

The collection of network entities and interfaces that provides the underlying IP transport connectivity between the user endpoint and the IMS entities.

LRF (Location Retrieval Function)

The IMS associated functional entity that handles the retrieval of location information for the emergency caller including, where required, interim location information, initial location information and updated location information. The LRF may interact with a separate RDF or contain an integrated RDF in order to obtain routing information for an emergency call.

LS (Location Server)

General term for the entity responsible for obtaining the location of the User Equipment (UE). See 3GPP TS 23.167.

RDF (Routing Determination Function)

The IMS-associated functional entity, which may be integrated in a Location Server (e.g., GMLC) or in an LRF and provides the proper outgoing address to the E‑CSCF for routing the emergency request towards a PSAP. It can interact with a location functional entity (e.g., GMLC) to manage ESQK allocation and management and deliver location information to the PSAP.

SMLC (Serving Mobile Location Center)

The node responsible for managing the overall co-ordination and scheduling of resources required to perform positioning of a mobile, and calculating the final location estimate and accuracy.


 * NENA-STA-010, Detailed Functional and Interface Standards for the NENA i3 Solution
 * NENA 08-504, VoIP Standards Development Organizations – NENA Technical Information Document (TID)


 * 3GPP website
 * 3GPP Specification #: 48.031
 * 3GPP Specification #: 23.167