IMS Interface Specification

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
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
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 utilizing 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 PCRFReplacement 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

 

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