V. Mancuso, I. Tinnirello

Transcription

1 UMTS Core Network

2 GSM/GPRS Network Architecture Radio access network BSS GSM/GPRS core network MS BTS BSC MSC VLR GMSC HLR PSTN, ISDN BTS PCU SGSN AuC EIR IP Backbone GGSN database Internet

3 3GPP Rel. 99 Network Architecture Radio access network UTRAN Core network (GSM/GPRS-based) UE Uu BS BS Iub Iub RNC Iur RNC Iu CS Iu PS MSC VLR SGSN Gn GMSC HLR AuC EIR PSTN IP Backbone GGSN database Internet

4 3GPP Rel. 99 Network Architecture UE Radio access network UTRAN Uu BS BS Iub Iub Iur RNC RNC 2G => 3G MS => UE (User Equipment), often also called (user) terminal New air (radio) interface based on WCDMA access technology New RAN architecture (Iur interface is available for soft handover, BSC => RNC)

5 3GPP Rel. 99 Network Architecture Changes in the core network: MSC is upgraded to 3G MSC SGSN is upgraded to 3G SGSN GMSC and GGSN remain the same AuC is upgraded (more security features in 3G) Core network (GSM/GPRS-based) Iu CS MSC GMSC VLR HLR AuC SGSN Iu PS EIR Gn IP Backbone GGSN PSTN Internet

6 3GPP Rel.4 Network Architecture UTRAN (UMTS Terrestrial Radio Access Network) Circuit Switched (CS) core network MSC Server GMSC Server New option in Rel.4: SGW MGW MGW SGW PSTN GERAN (GSM and EDGE Radio Access Network) PS core as in Rel. 99

7 3GPP Rel.4 Network Architecture MSC Server takes care of call control signalling Circuit Switched (CS) core network The user connections are set up via MGW (Media GateWay) Lower layer protocol conversion in SGW (Signalling GateWay) SGW MSC Server MGW GMSC Server MGW SGW PSTN SS7 MTP RANAP / ISUP IP Sigtran PS core as in Rel. 99

8 3GPP Rel.5 Network Architecture UTRAN (UMTS Terrestrial Radio Access Network) GERAN (GSM and EDGE Radio Access Network) New core network part: IMS (IP Multimedia System) SGSN CS core MGW GGSN HSS PSTN Internet PS core

9 3GPP Rel.5 Network Architecture The IMS can establish multimedia sessions (using IP transport) via PS core between UE and Internet (or another IMS) Call/session control using SIP (Session Initiating Protocol) Interworking with the PSTN may be required for some time... IMS (IP Multimedia System) SGSN CS core PS core MGW HSS GGSN PSTN In nternet / other IMS

10 New Service Concept Content provider Content provider Service provider Service provider Carrier provider End user End user all want to make profit

11 OSA (Open Services Architecture/Access) OSA is being standardised, so that services provided by different service/content providers can be created and seamlessly integrated into the 3G network (this is the meaning of open architecture) OSA means in practice: Service Creation Environment (SCE) API API API 3G network API = Application Programming Interface (Standardised)

12 CAMEL (2G & 3G) CAMEL (Customised Applications for Mobile network Enhanced Logic) is a set of IN (intelligent network) type functions and procedures that make operator-specific IN services available to subscribers who roam outside their home network. CAMEL = IN technology + global mobility CAMEL Service Environment (CSE) is a logical entity in the subscriber s home network which processes IN related procedures CSE SCP in home network

13 The IMS The IP Multimedia Subsystem Vincenzo Mancuso, PhD

14 The IMS The Third generation networks aim to merge two most valuable resources in communication technology, along with local PSTN networks Cellular Networks The Internet Use packet switching, IP The IP Multimedia Subsystem or IMS is the solution to integrate all the services that the internet provides with the cellular and other networks Triple Play: coordination of voice, video and data

15 IMS Value-added added services IMS also can provide integrated service to the user Third party developed services can be provided by operators, thus developing value-added services Appropriate charging for multimedia sessions, according to the content and the service offered

16 IMS Service Integration Problem Statement: various networks providing services have a vertical infrastructure no horizontal links between networks The challenge: to integrate these networks and to create new applications that would provide service to next generation networks

17 Component #1: the media transport IP packets Codec RTP UDP IP After many other services, introduction of real time voice/video 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

18 Component #2: session initiation Registration of John s phone and address Registration of Betty s phone and address The 2 nd problem is more difficult: how to initiate the call? how to know the IPaddress 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

19 Why IMS? Solutions to make the address resolutions MSN, Yahoo, AOL have designed a calling architecture hypercentralized: 1 table worldwide, only 1 operator Skype promotes a hyper- decentralized architecture: 1 table per terminal with peer-to-peer update between terminals The introduction and development of solution like Skype is highly significant as it alters the notion of telecommunications operators by making the process fully electronic IDATE - ART, 2004 Operators dislike such approaches, so they push a way very similar to centralization per domain. This approach is named Internet Protocol Multimedia Subsystem, IMS.

20 IMS User Identities m tel: IMS Subscriber Private User Identity Sip:zehan.zeb@example.com tel: Public User Identities

21 User Identity Private identity Issued by home provider Used for AAA Saved on ISIM (not modifiable) Public identity Normal SIP address (URI or TEL) Identifies the user publicly IMS Subscription User has one or more identities Used for routing Can be grouped into implicit registration sets If one of the set is registered then the others are as well At least one is stored on ISIM In case no ISIM is provided Private User Identity 1 Private User Identity 2 Public User Identity 1 Public User Identity 2 Public User Identity 3 Public User Identity 4 Public User Identity 5 Public User Identity 6» Use a temporary identity derived from USIM during initial registration (derived from IMSI)» PIDs are then provided by the S-CSCF in its reply to the registration Implicitly Registered ID Set 1 Implicitly Registered ID Set 2 Implicitly Registered ID Set 3 Service Profile 1 Service Profile 2 Service Profile 3 Service Profile 4

22 UICC Universal Integrated Circuit Card Used to store data, including authentication information Contains one or more applications SMS Phonebook SIM GSM Subscriber Identity Module USIM UMTS SIM ISIM IMS SIM Applications are independent SIM, USIM and ISIM can coexist on the same UICC but SIM cannot be used for IMS access (for security reasons)

23 IP Multimedia Subsystem A standard Next-gen network architecture An enabler of new applications Service-layer Control-layer layer Transport-layer IMS SIP IP Network SIP SIP At Home On the Move SIP SIP SIP In the Office IMS is access agnostic, cost reducing, and service enhancing IMS gives the customer & carrier choice Converged Services Rich Communications Push-2-Talk Video Clips Push-2-View Sports, News Push-2-X Presence, Location- Voice based Services Picture Messaging, MM Messaging IM Streaming Games, Audio, Video Music Downloads Interactive Services, Interactive Gaming

24 IMS Goals & Tools

25 IMS goals Combine latest trends in tech Run fast, no time for standardization of services Mobile/Nomadic internet Create a platform for multimedia services and their development Exploit/allow mobile packetswitching networks Not a mere circuit-switching replacement

26 IMS requirements Support for establishing IP Multimedia Sessions Audio, video, messaging Support for mechanisms to negotiate QoS distinguish users operators want to control QoS Support for interworking with Internet with packet-switching networks Support for roaming Home and visited network Inter-operators roaming

27 IMS requirements (cont d) Support for user activity control policies imposed by the operator (general policies and per-user policies) accomplish to service agreements Support for fast service creation don t require service standardization Standardize service capabilities instead Support for multiple access Not only GPRS, UMTS IP is independent on lower protocol layers

28 Protocols in IMS 3GPP reuses protocol developed by other standards development organizations ETSI (European Telecommunications Standard Institute) IETF (Internet Engineering Task Force) ITU-T (International Telecommunications Union - Telecommunications) 3GPP interacts with standards development organizations as for the development of existing and new protocols Protocols RTP for media transport Session control protocols AAA protocols Other

29 Session Control Protocol SIP (Session Initiation Protocol, by IETF- RFC2821) Protocol to establish and manage multimedia session over IP SIP borrows some design principles from SMTP and HTTP Does not differentiate the user-to-network interface from the network-to-network interface (unlike BICC and H.323) It follows the client-server model Text-based protocol Easy to debug, extend and reuse for service building

30 AAA protocol: DIAMETER one protocol for many interfaces Authorization What service can be used? Authentication Are you really who you say you are? Accounting $ Diameter Client Application Session Management Routing Management Diameter Server Application Session Management Routing Management DIAMETER by IETF RFC3588 Evolution of RADIUS Base protocol Diameter applications Connection Management Base Protocol Connection Management Base Protocol Diameter applications used to customize/extend the base protocol for different interfaces, environments, and applications E.g.: interact with SIP session setup (Authorization and Authentication) E.g.: interact with the billing subsystem to control accounting E.g.: interact with routing entities

31 IMS Architecture

32 New services for mobile and fixed networks Open, standardised, operator friendly, NGN multimedia architecture for mobile and fixed services Based on SIP, DIAMETER and COPS controls Supports legal interception, localisation, PSTN interworking, etc. Access Independent 3G mobile Applications Internet WLAN WiMAX IMS Platform DSL Fibre Ethernet IP transport MGW PSTN

33 Functions and nodes IMS standardizes functions IMS does NOT standardize nodes The IMS Architecture is a collection of functions linked by standardized interfaces A function can be implemented through one or more nodes Multiple functions can share a node Commonly a function per node

34 A standard architecture for service delivery Application Layer AS AS SIP Session Control Layer HSS DIAMETER SIP SIP MR F MGCF Connectivity Layer IP Network SIP GGS N MGW PSTN/PLMN H.248 CPE

35 Access to IMS The user can connect to an IMS network in variety of ways, all of which use the standard Internet Protocol (IP) for packet switching e.g., IMS terminals can register directly on an IMS network e.g., mobile phones, personal digital assistants (PDAs) and computers even when they are roaming in another network or country (the visited network) The only requirement is that they can use IPv6 (also IPv4 in early IMS) and run SIP user agents

36 Other access examples Fixed access - e.g., Digital Subscriber Line (DSL), cable modems, Ethernet Mobile access e.g., W-CDMA, CDMA2000, GSM, GPRS Wireless access e.g., WLAN, WiMAX Other phone systems like plain old telephone service (POTS -- the old analogue telephones) or PSTN, H.323 and non IMS-compatible VoIP systems, are supported through gateways

37 IMS functional elements

38 Infrastructure of SIP Proxies (media do not traverse the IMS..)

39 IMS Functional Elements Session Management (SIP) Routing Databases Network Interoperability Elements Services and Support Components Charging Components

40 Nodes/Functions in the IMS User databases HSS (Home Subscriber Server) SLF (Subscriber Location Function) SIP servers CSCF (Call/Session Control Function) AS (Application Server) MRF (Media Resource Function) MRFC (MRF Controller) MRFP (MRF Processor) BGCF (Breakout Gateway Control Function) PSTN/CS gateways, decomposed into: SGW (Signaling Gateway) MGCF (Media Gateway Controller Function) MGW (Media Gateway) Charging collection functions

41 Databases (HSS,SLF) HSS is an evolution of the HLR (Home Location Register) of GSM Contains the user-related subscription data (e.g., location, authorization and authentication information) More than one HSS is possible If #HSS > 1 SLF required SLF maps users address to HSSs HSS and SLF use DIAMETER with an IMSspecific diameter application

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

43 More on HSS HSS is a master user database that supports all the IMS network functions that actually handle communications contains the subscription-related information (user profiles) performs authentication and authorization of the user can provide information about the user's physical location is similar to the GSM Home Location Register (HLR) and Authentication Centre (AUC) together

44 CSCF SIP servers or proxies, collectively called Call Session Control Function (CSCF), are used to process SIP signaling packets/messages in the IMS P-CSCF (Proxy) I-CSCF (Interrogating) S-CSCF (Server)

45 Call/Session Control Func. (CSCF) Diameter SIP P- CSCF I- CSCF SIP S- CSCF SIP SIP SIP CSCF Processes SIP Signaling P-CSCF First Point of User Contact (located in the visited domain) Authenticates user May Include Policy Functions S-CSCF Central Node of Control Plane Acts as Registrar for User (located in the home domain) Invokes Application Servers Performs Primary Routing Function I-CSCF Located at Edge of Administrative Domain (contact point for inter-domain messages) Is the Ingress Network Point Defined in DNS Shields Network Topology from External Networks

46 IMS Signaling Path (1 domain, no roaming)

47 IMS Signaling Path (4 domain roaming, media goes directly) Sweden User Irish User Sweden User In roaming Irish User In roaming

48 CSCF P-CSCF (Proxy) Outbound/Inbound proxy server First server contacted by the user Fixed while registered Security functions (integrity protection, IPSec, ) Authenticates the user and extend the authentication to other nodes within IMS Compress/decompress SIP messages Generates charging info

49 P-CSFC details SIP proxy that is the first point of contact for the IMS terminal It can be located either in the visited network (in full IMS networks) or in the home network (when the visited network isn't IMS compliant yet) The terminal discovers its P-CSCF with either DHCP or it is assigned in the PDP Context (GPRS) It is assigned to an IMS terminal during registration, and does not change for the duration of the registration It sits on the path of all signaling messages, and can inspect every message It authenticates the user and establishes an IPsec security association with the IMS terminal Other nodes trust the P-CSCF, and do not have to authenticate the user again It can also compress and decompress SIP messages it may include a Policy Decision Function (PDF), which authorizes media plane resources it also generates charging records

50 PDF for QoS in IMS (intermediary between the application-level level QOS and the 3G network-level QoS)

51 CSCF I-CSCF (Interrogating) SIP proxy at the edge of a domain Advertised by DNS Interface to HSS and SLF for routing purposes Optional: encryption of sensitive information about the domain (THIG: topology hiding inter-network gateway)

52 I-CSCF details It is another SIP function located at the edge of an administrative domain Its IP address is published in the DNS of the domain remote servers can find it, and use it as a forwarding point (e.g. registering) for SIP packets to this domain The I-CSCF queries the HSS using DIAMETER to retrieve the user location then it routes the SIP request to its assigned S-CSCF Up to Release 6 it can also be used to hide the internal network from the outside world (encrypting part of the SIP message) in which case it's called a THIG (Topology Hiding Inter-network Gateway) From Release 7 onwards this "entry point" function is removed from the I- CSCF and is now part of the IBCF (Interconnection Border Control Function) which is also a firewall and a nat.

53 CSCF S-CSCF (Server) SIP server with session control functions SIP registrar (maintains a mapping between user location and public user identity) SIP routing PEP Always located in the home network Interfaced with the HSS (e.g., to download the user s profile)

54 S-CSCF details It is the central node of the signaling plane SIP server + session control It is always located in the home network It uses DIAMETER to the HSS to download and upload user profiles All necessary information is loaded from the HSS. It handles SIP registrations bind the user location and the SIP address It sits on the path of all signaling messages, and can inspect every message It decides to which application server(s) the SIP message will be forwarded, in order to provide their services It provides routing services, typically using Electronic Numbering (ENUM) lookups There can be multiple S-CSCFs in the network for load distribution and high availability reasons It's the HSS that assigns the S-CSCF to a user, when it's queried by the I-CSCF.

55 Application Server (AS) AS ASAS AS Diameter SIP Contains Call Related Application Logic Facilitates a Service Creation Environment Queried by S-CSCF in Real Time to Execute Logic Filters can be applied at S-CSCF in order to inspect the SIP messages and decide whether involve or not the AS Generally Specialized for Each Service May Provide Gateway to Legacy Applications (e.g. AIN) Can Behave as a SIP Proxy or Terminal (and in this case receive the media!)

56 AS Three different AS types SIP AS native IMS application server OSA-SCS (Open Service Access Service Capability Server) Interface to Open Service Application (AS) framework application server (developed by 3GPP for UMTS) IM-SSF (IP Multimedia Service Switching Function) Reuse/interface with CAMEL (GSM) Gateway for GSM Service Control Function An AS can be located in the home network or in an external third-party network If located in the home network, it can query the HSS with the DIAMETER Sh interface (for a SIP-AS) or the Mobile Application Part (MAP) interface (for IM-SSF).

57 AS as a SIP Proxy (e.g. find a taxi)

58 AS as a SIP Terminal (e.g. web server: receive media data!)

59 Example of Filter Rule (at S-CSCF) User A wants to divert all calls from boss to an answering machine (i.e. the AS) (method=invite) AND (P-Asserted-Identity = boss@vodafone.com) AND (Session Case = Terminating) ->message is addressed to AS

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

61 MRF The MRF (Media Resource Function) provides a source of media in the home network It provides media related functions such as media manipulation (e.g. voice stream mixing, media trans-coding) and playing of tones and announcements. Each MRF is further divided into Media Resource Function Controller (MRFC) signaling plane Media Resource Function Processor (MRFP) media plane The MRFC acts as a SIP User Agent to the S-CSCF, and controls the MRFP with a H.248 interface The MRFP is a media plane node that implements all media-related functions

62 Multiparty Calls (MRF as a special AS) REFER: Ask other to join

63 Multiparty Call

64 Multiparty Call

65 BGCF The Breakout Gateway Control Function is a SIP server that includes routing functionality based on telephone numbers used when calling from the IMS to a phone in a circuit switched network e.g., IMS to Public Switched Telephone Network (PSTN) or to Public Land Mobile Network (PLMN) BGCF routes to the appropriate (remote) circuit switching domain BGCF selects the (local) PSTN/CS gateway

66 PSTN Gateway SIP BGCF SIP SGW SIP MGCF ISUP H.248 MGW TDM 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

67 Home Network - Functional Elements Domain Name Server Home Subscriber Server Centralized DB HLR successor User profile Filter criteria (sent to S-CSCF) Which applications Which conditions Application Servers Push-to-talk Instant messaging Telephony AS 3 rd party or IMS Vendor Media Resource Function Controller Pooling of Media servers (e.g. conference) Call Session Control Function SIP registration SIP session setup UA/UE SIP DNS ENUM P-CSCF SIP Home Network HSS I-CSCF SIP RTP Diameter SIP SIP AS ASAS AS S-CSCF SIP SIP BGCF SIP P-CSCF SIP MRFC MS MS MGCF MGW H.248 SIP UA/UE Media Gateway Control Function Interfaces to PSTN/PLMN by Converting SIP <-> ISUP Interworking RTP to circuit H.248 control of MGW TDM ISUP SS7 PSTN Proxy CSCF 1 st contact point for UA QoS Routes to S-CSCF Visited Network Interrogating CSCF Entry point for incoming calls Determines S-CSCF for Subscribers Hides network topology Serving CSCF Registrar Session control Application Interface Breakout Gateway Control Function Selects network (MGCF or other BGCF) in which PSTN/ PLMN breakout is to occur

68 Network-to-Network Connectivity SIP RTP RTP Access SIP DNS ENUM HSS Diameter AS ASAS AS SIP SIP P-CSCF SIP UA/UE Visited Network Backbone Packet Network Proxy/Serving CSCF Manages call origination Selects destination network Routes to I-CSCF SIP P/S-CSCF RTP SIP I-CSCF SIP Home Network SIP S-CSCF SIP BGCF SIP SIP MRFC MS MS MGCF MGW H.248 TDM ISUP SS7 PSTN Interrogating CSCF Entry point for incoming calls Determines S-CSCF for Subscribers Hides network topology

69 Home and Visited Networks Inherited from 2G, 3G Most of IMS nodes and functions are located in the Home network P-SCFC can be either in the home or visited network If GPRS access P-CSCF in the same network of the GGSN simplifies the operator s management allows roaming to non-ims GPRS CANs (Connectivity Access networks) Drawback: trombone effect when GGSN is in the home network (GGSN is in the media plane) In a long term perspective the P-CSCF will be located in the visited network Media servers can be out of both

70 IMS architecture Examples

71 John is calling Betty Introducing the HSS and the S-CSCF HSS When the phones get connected they register their name/ip to the HSS 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 S-CSCF SIP Changes the SIP message replacing Betty by its IP address found in the HSS

72 John is calling a taxi to meet Betty Introducing the Application Server (AS) 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 nearest Taxi application (location, fleet ) AS S-CSCF Changes the SIP message replacing taxi by the IP address of the nearest available taxi

73 John s and Betty s phones do not support a common voice encoding Introducing the MRFC and MRFP 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 trans-coding S-CSCF MRFC SIP MGCP, H248 Megaco RTP (codec: G729) MRFP RTP (codec: AMR)

74 During its travel John is calling Betty The operator has made a segmentation of its services offer Introducing the P-CSCF, I-CSCF 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 Visited Network HSS S-CSCF (consumers) P-CSCF I-CSCF Home Network S-CSCF (enterprises)

75 John is calling Betty who has a legacy phone Introducing the MGCF and the MGW 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 SIP RTP H248 MGCP, Megaco Legacy Call control (SS7) Phone transmission Internet MGW PSTN/PLMN network

76 IMS Communication Focus Roaming IMS Mobile Users Serving Network A Serving Network B Access Network A Service Platform A (AS A ) Service Platform B (AS B ) Access Network B P-CSCF C SIP / SDP SIP / SDP SIP / SDP P-CSCF D PDF S-CSCF A S-CSCF B PDF Gm SIP/SDP inviting uey@homeb.com Go Go Gm SIP/SDP UE A Data- Path SGSN GGSN GGSN SGSN IP Backbone Network UE B PDP Context PDP Context Sessionlevel(SIP/SDP signalling) Bearer level(pdp context activation / modification / Release) Interaction betweensession andbearer level(cops) I-CSCF (between P-CSCF and S-CSCF) not shown for simplicity

77 A Typical Example of an IMS Call Network X Network Y AS S-CSCF S-CSCF AS HSS I-CSCF I-CSCF HSS P-CSCF P-CSCF SGSN GRX DSL/Cable Modem Network Z (UMTS/GPRS) DSLAM/CMTS GGSN RNC User A User B

78 The Signaling Plane

79 SIP functionality SIP s main goal is to deliver a session descriptor to a user at his/her/its location A session descriptor contains the information needed for a remote user to join the session IP address and port Codecs SDP (Session Description Protocol) A (possible) text-based way to describe the media session

80 SDP version user subject Start time user IP Session-level Stream directio n G711µ-law H.261 codec Media-level

81 SIP entities Registrar User Agent SIP endpoints handled by users (also automatically, based on userdefined rules) Proxy server SIP routers Usually is co-located with the registrar, and always uses the information on the registrar (through a location server) to route the calls Forking proxy Parallel or serial forking in the message routing Redirect server For routing, but no message delivery

82 SIP transactions Transaction structure A request from the client Zero or more provisional responses from the server A final response from the server Each message begins with a start line Request line (in a request) Method Request URI Protocol version e.g.: INVITE sip:alice@domain.com SIP/2.0 Status line (in an answer) e.g.: SIP/ Ringing Protocol version Status code Human code Start line One or more headers (name:value) EMPTY LINE Message body (OPTIONAL) SIP message format

83 SIP methods ACK ack the final response for INVITE BYE terminate a session CANCEL cancel a pending request INFO transport PSTN telephony signaling INVITE establish a session NOTIFY notify a UA about a particular event OPTIONS queries a server about capabilities PRACK ack for provisional response PUBLISH upload UA s info to a server REGISTER map the current URI and location with the public URI SUBSCRIBE request to be notified about an event UPDATE update session characteristics MESSAGE instant message in the message body REFER instruct a server to send a request

84 SIP in the IMS In principle, no difference with the public Internet In practice, IMS imposes some constraints Wireless access Security QoS Roaming 3GPP/IETF defines a profile of utilization of SIP in the IMS environment E.g., RFC 3261 (redefinition of SIP) RFC 3665 and 3666 (Best Current Practice)

85 Prerequisites Two-phase registration Offline subscription Login to the IP access net Inbound/Outbound Fixed Proxy DHCP or Lower level mechanism Online registration

86 Entering the IP Connectivity Access Network The access to GPRS includes the assignment of servers and IP address

87 PDF Context Activation/De-Activation A PDP context is pre-setup for the SIP signaling Different PDP contexts are then activated for the media flows (e.g. according to the agreed codec) When the session ends, all PDP contexts are deactivated

88 P-CSCF discovery The IMS terminal has to discover the IP address of the P-CSCF The procedure can be stand alone (DHCP+DNS) integrated with the access to the IP (e.g., with the PDP context)

89 IMS-level registration The user requests authorization to use the IMS The IMS authenticate and eventually authorize the user SIP REGISTER is mandatory DIAMETER is used by the CSCF to contact the HSS For security reasons, the user is challenged to show its identity this require two SIP REGISTER messages

90 IMS-level registration The HSS tells the I-CSCF whether a S-CSCF was already allocated to the user. If not, I-CSCF will choose based on capabilities notified by HSS in the UAA Without authentication DL User Auth vector Challenge the User UAA: User Auth. Ans. MAA: Multiledia Auth.Ans SAA:Server Assignment Ans. authentication vector included DL User Profile UAR: User Auth. Req MAR:Multimedia Auth.Req SAR:Server Assignment Req.

91 Basic Session Setup

92 Session setup Many nodes and many messages involved in the setup Different planes/layers media signaling CAN core

93 Session setup (cont ed)