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CELLULAR COMMUNICATIONS 12. IMS. 2 Existing Telecommunications  Benefits:  Worked well for stand-alone systems  Challenges:  Many Networks = High.

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Presentation on theme: "CELLULAR COMMUNICATIONS 12. IMS. 2 Existing Telecommunications  Benefits:  Worked well for stand-alone systems  Challenges:  Many Networks = High."— Presentation transcript:

1 CELLULAR COMMUNICATIONS 12. IMS

2 2 Existing Telecommunications  Benefits:  Worked well for stand-alone systems  Challenges:  Many Networks = High Operational and Interworking Costs  Slow to introduce new services  Users require different devices for different services Difficult to integrate new services or technologies Services Transport & Access

3 3 Emerging Telecommunications Services and access technologies only need to interface to the common transport layer (IP) Access Transport Services Internet Protocol  Benefits:  Rapid Service Deployment = New Service Revenues  Allow continued growth of the network  Flexible architecture for future growth and new technologies  Allows for competition at individual layers  Challenges:  Legacy policy frameworks are challenged by the emerging telecommunications model throughout the world Source: ASTAP05/WS-IP&NGN/13

4 4 Access and Service Independence  Each service must be integrated to a specific access technology.  With many services converging it becomes complex to integrate single access.  IP provides a common interface for access and services  One point of interface simplifies the introduction of new devices and services. videodatavoice dslwi-ficable Internet Protocol videodatavoice dslwi-ficable Source: ASTAP05/WS-IP&NGN/13

5 What is IMS? 5 | IMS in I&R | January 2007  The “Internet Protocol Multimedia Subsystem” (IMS) has been created for the 3G networks and is now considered to be the standard for fix and mobile Internet- based telephony by Operators.  Developed in 3GPP (R5,R6,R7) since2001 but now adopted by 3GPP2(MMD in 2003) ETSI/TISPAN R1(2005) & R2 (on going)  The protocols come from the IETF:  RTP for media  SIP for signaling/address resolution

6 6 RNC MSC(Server) SGSN GGSN CN MGW BSC UMTS/GPRS WLAN Corporate P-CSCF I-CSCF MRF MGW MGCF IMS S-CSCF SIP Application Servers SIP Application Servers HSS CDMA 2000 DSL/Cable Modem DSLAM/CMTS IMS Access Network Independence

7 Why IMS? The Voice over IP: the impulse 7 | IMS in I&R | January 2007  After many other services, introduction of voice/video calls on Internet  The 1 st problem is easy: How to transmit voice/video?  RTP (Real-Time Protocol) is a protocol which transports an encoded multimedia stream as pieces, with a timestamp on each piece, and sends them using UDP/IP Any encoding is permitted for voice/video with a Codec: MP3, ACC, MPEG4, AMR… Several streams (voice+video) can be sent in parallel with the same timestamp The timestamp is used by the receiver to play the voice/video in a regular way for quality  RTP is the media transport IP packets Codec RTP UDP IP

8 Why IMS? Transmission of voice/video is ok, … but transmission to which IP-address? 8 | IMS in I&R | January 2007  The 2 nd problem is more difficult: how to initiate the call? how to know the IP-address of the called phone?  It is necessary to have a table which translates a symbolic name “Betty” into an IP address  Each time a terminal service is put on, it must notify its presence to update the table  So, thanks to an access to this table, it is possible to make the address resolution : name -> IP address  The control of the address table creates a tough competition… Registration of Betty’s phone and address Registration of John’s phone and address

9 Why IMS? Solutions to make the address resolutions 9 | IMS in I&R | January 2007  MSN, Yahoo, AOL have designed a calling architecture hyper-centralized: 1 table worldwide, only 1 operator  Skype promotes a hyper- decentralized architecture: 1 table per terminal with peer- to-peer update between terminals Operators dislike such approaches, so they push a way very similar to centralization per domain. This approach is named “Internet Protocol Multimedia Subsystem”, IMS.

10 Why IMS? SIP (IETF) is replacing H323 signaling (ITU)  The Session Initiation Protocol (SIP) performs 1 function: signaling.  SIP covers the registration for address resolution of users/terminals as well as the call handling  In fact, Internet Telephony call processing is working on the text of SIP messages to prepare the RTP voice/video flows.  SIP is naturally integrated in Internet as an increment to existing services  DNS “url” naming, like  Any transmission protocol. e.g., RTP  Any codec, voice/video  SIP messages are small texts 10 | IMS in I&R | January 2007

11 Introduction  SIP is the core protocol for initiating, managing and terminating sessions in the Internet  These sessions may be text, voice, video or a combination of these  SIP sessions involve one or more participants and can use unicast or multicast communication.

12 SIP Message Types Requests – sent from client to server  INVITE  ACK  BYE  CANCEL  OPTIONS  REGISTER  INFO

13 SIP Message Types (Contd.) Responses – sent from server to the client  Success  Redirection  Forwarding  Request failure  Server failure  Global failure

14 Courtesy – The RADVISION SIP Whitepaper

15 SIP Session Establishment and Call Termination From the RADVISION whitepaper on SIP

16 John is calling Betty – introducing the HSS and the S-CSCF 16 | IMS in I&R | January 2007  The HSS is the table user/address  The S-CSCF is a SIP proxy which works on messages to provide users (consumers, enterprises) with calling services including registration being a mediation SIP2DIAMETER SIP HSS S-CSCF When the phones get connected they register their name/IP to the HSS Changes the SIP message replacing “Betty” by its IP address found in the HSS SIP

17 John is calling a taxi to meet Betty – introducing the Application Server (AS) 17 | IMS in I&R | January 2007  In addition to the basic name/address translation, the S-CSCF routes SIP messages to:  The network of Betty, if different  The applications such as: Push-To-Talk, Instant Messaging, Advance Call Control, Voice/video mailbox, nearest Taxi… running on AS, a SIP proxy application server S-CSCF AS … nearest Taxi application (location, fleet…) Changes the SIP message replacing “taxi” by the IP address of the nearest available taxi

18 John’s and Betty’s phones do not support a common voice encoding – introducing the MRFC and MRFP 18 | IMS in I&R | January 2007  Intercepting the SIP “invite” message, the S-CSCF/AS detects a non compatibility between the codecs of the phones : it forwards it to the MRFC (a SIP proxy).  The MRFC adjusts the SIP messages in order to orient the RTP flow to the MRFP (a RTP proxy), for transcoding MRFC MRFP MGCP, H248 Megaco RTP (codec: AMR) SIP S-CSCF RTP (codec: G729)

19 During its travel John is calling Betty – introducing the P-CSCF The operator has made a segmentation of its services offer – introducing the I-CSCF 19 | IMS in I&R | January 2007  The P-CSCF is the 1 st SIP proxy seen by the terminal  It controls the bearer plan via COPS protocol  It adjusts the SIP message (e.g., compression) and forwards it to the I-CSCF of the home network  The operator may have several S-CSCFs (e.g., offer segmentation)  So it introduces, the I-CSCF SIP proxy as the entry point of its network also used as the entry point for calls from other operators Home NetworkVisited Network P-CSCF … S-CSCF (consumers) S-CSCF (enterprises) I-CSCF HSS

20 John is calling Betty who has a legacy phone – introducing the MGCF and the MGW 20 | IMS in I&R | January 2007  At the border of the IMS network with the phone network, an adaptation is necessary.  The MGCF handles the control for the 2 worlds and drives the MGW (Media gateway)  … controls circuits and MGW much like a VoIP softswitch MGCF MGW H248 MGCP, Megaco SIP Legacy Call control (SS7) Phone transmission … InternetPSTN/PLMN network RTP

21 21 Visited Network UE Home Network AS SLF HSS GGSN S-CSCFP-CSCF I-CSCF Session control services Registration AS interaction Charging etc. Access Point to Network Hides Topology & Configuration First Point of Contact Privacy Control & QoS Authorisation Local Services: Emergency & Local Numbering Diameter Protocol SIP Protocol IMS basic components CSCF – Call State Control Functions P – Proxy I – Interrogating S – Serving UE – User Equipment SLF- Subscriber Location Function HSS- Home Subscriber Server AS – Application Server Gateway GPRS Support Node Source: ASTAP05-WP.IP&NGN-08_ETSI

22 Simplified IMS architecture 22 | IMS in I&R | January 2007

23 Standardisation Overview 3GPP / TISPAN IMS Architectural Overview 23 | IMS in I&R | January 2007 This is only a logical (functional) architecture, not a physical one. IMS-MGW UE IPv6 PDN (IPv6 Network) MGCF PDF I-CSCFS-CSCF BGCF Application (SIP AS, OSA AS, CAMEL SE) MRFC MRFP MRF BB (IP v4/ IPv6) P-CSCF SGW OSA SCS IM SSF SIP AS AS RAN BG IMS Session Signalling IMS User Plane Data HSS ‘IMS Data’ SLF ALG TrGW IMS GW IPv4 PDN (IPv4 Network) IPv4 based Signalling IPv4 User Plane Data PEF CSCF HLR/AuC (‘CS/PS’) 3gpp R5 WLAN PDG UE WLAN WAG 3gpp R6 GGSN SGSN CS Networks (PSTN, CS PLMN) BAS UE DSLAM 3gpp R7 / TISPAN R1… SPDF/ A-RACF NASS

24 24 FUNCTIONAL ELEMENTS DESCRIPTIONS  Home Subscriber Server (HSS)  Application Server (AS)  Call Session Control Function (CSCF)  Breakout Gateway Control Function (BGCF)  Media Gateway Function (MGW)  Media Gateway Control Function (MGCF)  Multimedia Resource Function Controller (MRFC)  Multimedia Resource Function Processor (MRFP)

25 25 Home Subscriber Server (HSS)  Presence, Location and Profile  End-User Identity  Private and Public End-User Information  Registration Information  Service Initiation Information  Subscriber Service Profile (SSP)  Downloaded to CSCF at Registration HSS Diameter

26 26 Application Server (AS)  Contains Call Related Application Logic  Facilitates a Service Creation Environment  Queried by S-CSCF in Real Time to Execute Logic  Generally Specialized for Each Service  May Provide Gateway to Legacy Applications (e.g. AIN) AS AS AS SIP Diameter

27 27 Call/Session Control Function (CSCF)  CSCF – Processes SIP Signaling  P-CSCF  First Point of User Contact  Authenticates user  May Include Policy Functions  C-CSCF  Central Node of Control Plane  Acts as Registar for User (Downloads SSP from HSS)  Invokes Application Servers  Performs Primary Routing Function  I-CSCF  Located at Edge of Administrative Domain  Is the Ingress Network Point Defined in DNS  Shields Network Topology from External Networks I-CSCFS-CSCFP-CSCF SIP Diameter

28 28 PSTN (Circuit Switched) Gateway  BGCF – Routes to Gateway Based Upon Telephone Number  MGCF – Controlling Function for SGW and MGW  SGW – Provides Signaling Conversion Between SIP and ISUP  MGW – Provides Conversion between RTP and TDM MGCF MGW H.248 ISUP BGCF SIP TDM SGW SIP

29 29 Multimedia Resource Function (MRF)  Offers Services Such as Conferencing  MRFC – SIP User Interface toward S-CSCF  MRFP – Controls the Media Server (MS) SIP MSMS MRFC


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