IP Multimedia Subsystem
Interfaces description
Table:
Interface name

IMS entities

Description

Protocol

Technical specification

Cr

MRFC, AS

Used by MRFC to fetch documents (e.g. scripts, announcement files, and other resources) from an AS. Also used for media control related commands.

TCP/SCTP channels

Cx

(I-CSCF, S-CSCF), HSS

Used to send subscriber data to the S-CSCF; including filter criteria and their priority. Also used to furnish CDF and/or OCF addresses.

Diameter

TS29.229, TS29.212

Dh

AS (SIP AS, OSA, IM-SSF) <-> SLF

Used by AS to find the HSS holding the user profile information in a multi-HSS environment. DH_SLF_QUERY indicates an IMPU and DX_SLF_RESP return the HSS name.

Diameter

Dx

(I-CSCF or S-CSCF) <-> SLF

Used by I-CSCF or S-CSCF to find a correct HSS in a multi-HSS environment. DX_SLF_QUERY indicates an IMPU and DX_SLF_RESP return the HSS name.

Diameter

TS29.229, TS29.212

Gm

UE, P-CSCF

Used to exchange messages between SIP user equipment (UE) or Voip gateway and P-CSCF

SIP

Go

PDF, GGSN

Allows operators to control QoS in a user plane and exchange charging correlation information between IMS and GPRS network

COPS (Rel5), diameter (Rel6+)

Gq

P-CSCF, PDF

Used to exchange policy decisions-related information between P-CSCF and PDF

Diameter

Gx

PCEF, PCRF

Used to exchange policy decisions-related information between PCEF and PCRF

Diameter

TS29.211, TS29.212

Gy

PCEF, OCS

Used for online flow-based bearer charging. Functionally equivalent to Ro interface

Diameter

TS23.203, TS32.299

ISC

S-CSCF <-> AS

Reference point between S-CSCF and AS. Main functions are to :

Notify the AS of the registered IMPU, registration state and UE capabilities

Supply the AS with information to allow it to execute multiple services

Convey charging function addresses

SIP

Ici

IBCFs

Used to exchange messages between an IBCF and another IBCF belonging to a different IMS network.

SIP

Izi

TrGWs

Used to forward media streams from a TrGW to another TrGW belonging to a different IMS network.

RTP

Ma

I-CSCF <-> AS

Main functions are to:

Forward SIP requests which are destined to a public service identity hosted by the AS

Originate a session on behalf of a user or public service identity, if the AS has no knowledge of a S-CSCF assigned to that user or public service identity

Convey charging function addresses

SIP

Mg

MGCF -> I,S-CSCF

ISUP signalling to SIP signalling and forwards SIP signalling to I-CSCF

SIP

Mi

S-CSCF -> BGCF

Used to exchange messages between S-CSCF and BGCF

SIP

Mj

BGCF -> MGCF

Used for the interworking with the PSTN/CS domain, when the BGCF has determined that a breakout should occur in the same IMS network to send SIP message from BGCF to MGCF

SIP

Mk

BGCF -> BGCF

Used for the interworking with the PSTN/CS domain, when the BGCF has determined that a breakout should occur in another IMS network to send SIP message from BGCF to the BGCF in the other network

SIP

Mm

I-CSCF, S-CSCF, external IP network

Used for exchanging messages between IMS and external IP networks

SIP

Mn

MGCF, IM-MGW

Allows control of user-plane resources

H.248

Mp

MRFC, MRFP

Allows an MRFC to control media stream resources provided by an MRFP.

H.248

Mr
Mr'

S-CSCF, MRFC
AS, MRFC

Used to exchange information between S-CSCF and MRFC
Used to exchange session controls between AS and MRFC

Application server sends SIP message to MRFC to play tone and announcement. This SIP message contains sufficient information to play tone and announcement or provide information to MRFC, so that it can ask more information from application server through Cr Interface.

SIP

Mw

P-CSCF, I-CSCF, S-CSCF, AGCF

Used to exchange messages between CSCFs. AGCF appears as a P-CSCF to the other CSCFs

SIP

Mx

BGCF/CSCF, IBCF

Used for the interworking with another IMS network, when the BGCF has determined that a breakout should occur in the other IMS network to send SIP message from BGCF to the IBCF in the other network

SIP

P1

AGCF, A-MGW

Used for call control services by AGCF to control H.248 A-MGW and residential gateways

H.248

P2

AGCF, CSCF

Reference point between AGCF and CSCF.

SIP

Rc

MRB, AS

Used by the AS to request that media resources be assigned to a call when using MRB in-line mode or in query mode

SIP, in query mode (not specified)

Rf

P-CSCF, I-CSCF, S-CSCF, BGCF, MRFC, MGCF, AS

Used to exchange offline charging information with CDF

Diameter

TS32.299

Ro

AS, MRFC, S-CSCF

Used to exchange online charging information with OCF

Diameter

TS32.299

Rx

P-CSCF, PCRF

Used to exchange policy and charging related information between P-CSCF and PCRF

Replacement for the Gq reference point.

Diameter

TS29.214

Sh

AS (SIP AS, OSA SCS), HSS

Used to exchange User Profile information (e.g., user-related data, group lists, user-service-related information or user location information or charging function addresses (used when the AS has not received the third-party REGISTER for a user)) between an AS (SIP AS or OSA SCS) and HSS. Also allow AS to activate/deactivate filter criteria stored in the HSS on a per-subscriber basis

Diameter

Si

IM-SSF, HSS

Transports CAMEL subscription information, including triggers for use by CAMEL-based application services information.

MAP

Sr

MRFC, AS

Used by MRFC to fetch documents (scripts and other resources) from an AS

HTTP

Ut

UE and SIP AS (SIP AS, OSA SCS, IM-SSF) PES AS and AGCF

Facilitates the management of subscriber information related to services and settings

HTTP(s), XCAP

z

POTS, Analog phones and VoIP gateways

Conversion of POTS services to SIP messages

From the following table concerning 'IP Multimedia Subsystem' in the 'Interfaces description' section, summarise the highlighted cells in a single sentence and format it within the following JSON object {"answer": "YOUR ANSWER"}.