Architectural Overview of IP Multimedia Subsystem -IMS

Transcription

1 Architectural Overview of IP Multimedia Subsystem -IMS Presented by: Masood Khosroshahy June 2006 B E G I N N I N G 1 Project supervisor: Prof. Elie Najm

2 Simplified view of the layered architecture in IMS 2 From [4]

3 3GPP IMS Architectural Overview HSS IMS Data Handling SLF SIP AS IM SSF AS OSA SCS Application (Ext. SIP AS, OSA AS, CAMEL SE) HLR/AuC ( CS/PS ) S-CSCF CSCF I-CSCF BGCF P-CSCF MGCF MRF IMS IPGW SGW PDF MRFC MRFP ALG TrGW IMS-MGW CS Networks (PSTN, CS PLMN) IMS Terminal TE AN IP CAN PEF /TP F ABG IPv4/IPv6 BB BG IPv6 PDN (IPv6 Network) IPv4 PDN (IPv4 Network) 3 From [2]

4 3GPP IMS Architectural Overview: Serving CSCF (S-CSCF) HSS IMS Data Handling SLF SIP AS IM SSF AS OSA SCS Application (Ext. SIP AS, OSA AS, CAMEL SE) HLR/AuC ( CS/PS ) S-CSCF CSCF I-CSCF BGCF P-CSCF MGCF MRF IMS IPGW SGW PDF MRFC MRFP ALG TrGW IMS-MGW CS Networks (PSTN, CS PLMN) IMS Terminal TE AN IP CAN PEF /TP F ABG IPv4/IPv6 BB BG IPv6 PDN (IPv6 Network) IPv4 PDN (IPv4 Network) 4

5 Serving CSCF (S-CSCF) Functions Acts like a SIP Registrar, it binds the public user ID to a location. The S-CSCF retrieves the subscriber profile from the HSS. Provides session control for the endpoint's sessions (service logic is performed by an Application Server, not the S- CSCF). Handles SIP routing for originating and terminating endpoints. Ensures that the media for a session, as indicated by SDP, are within boundaries of subscriber's profile. Interacts with Application Server platforms for the support of services. 5

6 3GPP IMS Architectural Overview: Interrogating CSCF (I-CSCF) HSS IMS Data Handling SLF SIP AS IM SSF AS OSA SCS Application (Ext. SIP AS, OSA AS, CAMEL SE) HLR/AuC ( CS/PS ) S-CSCF CSCF I-CSCF BGCF P-CSCF MGCF MRF IMS IPGW SGW PDF MRFC MRFP ALG TrGW IMS-MGW CS Networks (PSTN, CS PLMN) IMS Terminal TE AN IP CAN PEF /TP F ABG IPv4/IPv6 BB BG IPv6 PDN (IPv6 Network) IPv4 PDN (IPv4 Network) 6

7 Interrogating CSCF (I-CSCF) Functions Serves as the initial point of contact from other networks. Performs a stateless SIP proxy function. Selects a S-CSCF for a user during SIP registration. Routes SIP requests received from another network to the S-CSCF. Queries the HSS for the address of the S-CSCF. If no S-CSCF is currently assigned (e.g., unregistered subscriber), then assigns an S-CSCF to handle the SIP request. Provide Topology Hiding Interworking Gateway (THIG) function. 7

8 3GPP IMS Architectural Overview: Proxy CSCF (P-CSCF) HSS IMS Data Handling SLF SIP AS IM SSF AS OSA SCS Application (Ext. SIP AS, OSA AS, CAMEL SE) HLR/AuC ( CS/PS ) S-CSCF CSCF I-CSCF BGCF P-CSCF MGCF MRF IMS IPGW SGW PDF MRFC MRFP ALG TrGW IMS-MGW CS Networks (PSTN, CS PLMN) IMS Terminal TE AN IP CAN PEF /TP F ABG IPv4/IPv6 BB BG IPv6 PDN (IPv6 Network) IPv4 PDN (IPv4 Network) 8

9 Proxy CSCF (P-CSCF) Functions Serves as the initial point of contact for the user terminal to network. Performs a stateful SIP proxy function. Sends the SIP REGISTER request received from the UE to an I-CSCF determined using the home domain name, as provided by the UE. Sends all subsequent SIP messages from the UE to the S- CSCF, whose name the P-CSCF has received as part of registration. Inserts a valid public user identity for UE initiated requests. Performs SIP message compression to reduce the amount of data sent over the radio interface. 9

10 3GPP IMS Architectural Overview: Policy Decision Function HSS IMS Data Handling SLF SIP AS IM SSF AS OSA SCS Application (Ext. SIP AS, OSA AS, CAMEL SE) HLR/AuC ( CS/PS ) S-CSCF CSCF I-CSCF BGCF P-CSCF MGCF MRF IMS IPGW SGW PDF MRFC MRFP ALG TrGW IMS-MGW CS Networks (PSTN, CS PLMN) IMS Terminal TE AN IP CAN PEF /TP F ABG IPv4/IPv6 BB BG IPv6 PDN (IPv6 Network) IPv4 PDN (IPv4 Network) 10

11 Policy Decision Function (PDF) Functions Responsible for making policy decisions based on session and media-related information obtained from the P-CSCF Acts as policy decision point for Service-based Local Policy (SBLP) control. Some of policy decision point functionalities: - To store session and media-related information - The capability to enable the usage of an authorized bearer (e.g. PDP context) - To inform P-CSCF when the bearer is lost or modified. - To pass an IMS-charging identifier to the GGSN and to Pass a GPRS-charging identifier to the P-CSCF 11

12 3GPP IMS Architectural Overview: Home Subscriber Server/ Subscription Locator Function HSS IMS Data Handling SLF SIP AS IM SSF AS OSA SCS Application (Ext. SIP AS, OSA AS, CAMEL SE) HLR/AuC ( CS/PS ) S-CSCF CSCF I-CSCF BGCF P-CSCF MGCF MRF IMS IPGW SGW PDF MRFC MRFP ALG TrGW IMS-MGW CS Networks (PSTN, CS PLMN) IMS Terminal TE AN IP CAN PEF /TP F ABG IPv4/IPv6 BB BG IPv6 PDN (IPv6 Network) IPv4 PDN (IPv4 Network) 12

13 Home Subscriber Server/ Subscription Locator Function SLF is used as resolution mechanism to find the address of the HSS that holds the subscriber data The HSS supports IMS level Authentication, and Authorization. Holds IMS subscriber profile. Keeps track of currently assigned S-CSCF. Supports interactions with CSCFs and ASs. 13

14 3GPP IMS Architectural Overview: Application Server (AS) HSS IMS Data Handling SLF SIP AS IM SSF AS OSA SCS Application (Ext. SIP AS, OSA AS, CAMEL SE) HLR/AuC ( CS/PS ) S-CSCF CSCF I-CSCF BGCF P-CSCF MGCF MRF IMS IPGW SGW PDF MRFC MRFP ALG TrGW IMS-MGW CS Networks (PSTN, CS PLMN) IMS Terminal TE AN IP CAN PEF /TP F ABG IPv4/IPv6 BB BG IPv6 PDN (IPv6 Network) IPv4 PDN (IPv4 Network) 14

15 Application Server (AS) The AS provides service control for IMS. May be directly connected to S-CSCF or via an OSA Gateway for 3rd party application support with security. Interacts with the HSS to obtain subscriber profile information. Supports applications such as telephony services, presence, conference control, PoC, etc. 15

16 Application Server Types Not pure IMS entities, rather, functions on top of IMS Application Servers: - SIP Application Server - Open Service Architecture (OSA) Service Capability Server (SCS) - CAMEL IP Multimedia Service Switching Function (IM-SSF) 16 From the perspective of the S-CSCF, all application servers exhibit the same reference point behavior

17 3GPP IMS Architectural Overview: Breakout Gateway Control Function (BGCF) HSS IMS Data Handling SLF SIP AS IM SSF AS OSA SCS Application (Ext. SIP AS, OSA AS, CAMEL SE) HLR/AuC ( CS/PS ) S-CSCF CSCF I-CSCF BGCF P-CSCF MGCF MRF IMS IPGW SGW PDF MRFC MRFP ALG TrGW IMS-MGW CS Networks (PSTN, CS PLMN) IMS Terminal TE AN IP CAN PEF /TP F ABG IPv4/IPv6 BB BG IPv6 PDN (IPv6 Network) IPv4 PDN (IPv4 Network) 17

18 Breakout Gateway Control Function (BGCF) Functions Selects the network in which PSTN breakout is to occur. Selects a local MGCF or a peer BGCF. 18

19 3GPP IMS Architectural Overview: Media Gateway Control Function (MGCF) HSS IMS Data Handling SLF SIP AS IM SSF AS OSA SCS Application (Ext. SIP AS, OSA AS, CAMEL SE) HLR/AuC ( CS/PS ) S-CSCF CSCF I-CSCF BGCF P-CSCF MGCF MRF IMS IPGW SGW PDF MRFC MRFP ALG TrGW IMS-MGW CS Networks (PSTN, CS PLMN) IMS Terminal TE AN IP CAN PEF /TP F ABG IPv4/IPv6 BB BG IPv6 PDN (IPv6 Network) IPv4 PDN (IPv4 Network) 19

20 Media Gateway Control Function (MGCF) Controls the MGW to provide IMS connections to PSTN trunks. Performs protocol conversion between ISUP and SIP. May process out of band information such as DTMF signaling received in MGCF which it may forward to the CSCF or MGW. 20

21 3GPP IMS Architectural Overview: Media Gateway (MGW) HSS IMS Data Handling SLF SIP AS IM SSF AS OSA SCS Application (Ext. SIP AS, OSA AS, CAMEL SE) HLR/AuC ( CS/PS ) S-CSCF CSCF I-CSCF BGCF P-CSCF MGCF MRF IMS IPGW SGW PDF MRFC MRFP ALG TrGW IMS-MGW CS Networks (PSTN, CS PLMN) IMS Terminal TE AN IP CAN PEF /TP F ABG IPv4/IPv6 BB BG IPv6 PDN (IPv6 Network) IPv4 PDN (IPv4 Network) 21

22 Media Gateway (MGW) Functions Interacts with the MGCF for resource control. Terminates trunks from the circuit switched network and media streams from the packet network (e.g. RTP streams). Supports media conversion, bearer control, and payload processing May detect events (i.e. bearer loss, DTMF digits, etc.) and notifies the MGCF. May perform DiffServ Code Point (DSCP) markings on the IP packets sent towards the UE. 22

23 3GPP IMS Architectural Overview: Media Resource Function Controller (MRFC) HSS IMS Data Handling SLF SIP AS IM SSF AS OSA SCS Application (Ext. SIP AS, OSA AS, CAMEL SE) HLR/AuC ( CS/PS ) S-CSCF CSCF I-CSCF BGCF P-CSCF MGCF MRF IMS IPGW SGW PDF MRFC MRFP ALG TrGW IMS-MGW CS Networks (PSTN, CS PLMN) IMS Terminal TE AN IP CAN PEF /TP F ABG IPv4/IPv6 BB BG IPv6 PDN (IPv6 Network) IPv4 PDN (IPv4 Network) 23

24 Media Resource Function Controller (MRFC) Functions Controls the media stream resources in the MRFP. Interprets information from an AS via the S-CSCF (using SIP) and controls the MRFP accordingly. May be co-located with an AS to provide capabilities such as conference services. 24

25 3GPP IMS Architectural Overview: Media Resource Function Processor (MRFP) HSS IMS Data Handling SLF SIP AS IM SSF AS OSA SCS Application (Ext. SIP AS, OSA AS, CAMEL SE) HLR/AuC ( CS/PS ) S-CSCF CSCF I-CSCF BGCF P-CSCF MGCF MRF IMS IPGW SGW PDF MRFC MRFP ALG TrGW IMS-MGW CS Networks (PSTN, CS PLMN) IMS Terminal TE AN IP CAN PEF /TP F ABG IPv4/IPv6 BB BG IPv6 PDN (IPv6 Network) IPv4 PDN (IPv4 Network) 25

26 Media Resource Function Processor (MRFP) Functions Under the control of MRFC Mixes incoming media streams (e.g. for multiple parties). Sources media streams (for multimedia announcements). Processes media streams (e.g. audio transcoding). Provide tones and supports DTMF within the bearer path. 26 Notifies the MRFC when an event has occurred such as DTMF digit collection.

27 3GPP IMS Architectural Overview: Signaling Gateway HSS IMS Data Handling SLF SIP AS IM SSF AS OSA SCS Application (Ext. SIP AS, OSA AS, CAMEL SE) HLR/AuC ( CS/PS ) S-CSCF CSCF I-CSCF BGCF P-CSCF MGCF MRF IMS IPGW SGW PDF MRFC MRFP ALG TrGW IMS-MGW CS Networks (PSTN, CS PLMN) IMS Terminal TE AN IP CAN PEF /TP F ABG IPv4/IPv6 BB BG IPv6 PDN (IPv6 Network) IPv4 PDN (IPv4 Network) 27

28 Signaling Gateway Used to interconnect different signaling networks, such as SCTP-IP-based signaling networks and SS7 signaling networks. Performs signaling conversion at the transport level. Does not interpret application layer messages. 28

29 Two Procedures Registration Simple Call 29

30 2-phase registration UE GPRS IMS 1. Bearer Level Registration: e.g.gprs Attach (2. Establishing signaling link e.g. PDP Context Activation) 3. CSCF Discovery 4. Application (IMS) Level Registration 30 From [2]

31 SIP Registration of a Mobile Node 31 From [3]

32 Simple SIP Call: Caller Side (1) 32 From [3]

33 Simple SIP Call: Caller Side (2) 33 From [3]

34 References [1] The IMS M Poikselka et al., 2004, John Wiley, ISBN X [2] Policy and Regulatory Requirements for Future Mobile Networks F. Courau & M. Olsson, June 22nd 2005, Alcatel-Ericsson Presentation [3] SIP and Mobility: IP Multimedia Subsystem in 3G Release 5 Jorg Ott, 11 November 2002, Presentation at Bremen [4] IMS IP Multimedia Subsystem Oct 2004, Ericsson Whitepaper [5] The IP Multimedia Subsystem 2006, Twister Consulting whitepaper 34

35 Thank you for your attention E N D 35