UMTS Core Network
V. Mancuso, I. Tinnirello GSM/GPRS Network Architecture
Radio access network GSM/GPRS core network BSS PSTN, PSTN, ISDN
MSC GMSC
BTS VLR MS BSC HLR PCU AuC SGSN EIR BTS
IP Backbone GGSN
database Internet
V. Mancuso, I. Tinnirello 3GPP Rel.’99 Network Architecture
Radio access network Core network (GSM/GPRS-based) UTRAN PSTN
Iub RNC MSC GMSC Iu CS BS VLR UE HLR Uu Iur AuC Iub RNC SGSN Iu PS EIR BS Gn
IP Backbone GGSN
database Internet
V. Mancuso, I. Tinnirello 3GPP RelRel.’99.’99 Network Architecture
Radio access network 2G => 3G MS => UE UTRAN (User Equipment), often also called (user) terminal Iub RNC New air (radio) interface BS based on WCDMA access UE technology Uu Iur New RAN architecture Iub RNC (Iur interface is available for BS soft handover, BSC => RNC)
V. Mancuso, I. Tinnirello 3GPP Rel.’99 Network Architecture
Changes in the core Core network (GSM/GPRS-based) network: PSTN MSC is upgraded to 3G MSC GMSC Iu CS MSC VLR SGSN is upgraded to 3G HLR SGSN AuC SGSN GMSC and GGSN remain Iu PS EIR the same Gn GGSN AuC is upgraded (more IP Backbone security features in 3G)
Internet
V. Mancuso, I. Tinnirello 3GPP Rel.4 Network Architecture
UTRAN Circuit Switched (CS) core network (UMTS Terrestrial Radio Access Network) MSC GMSC Server Server
SGW SGW PSTN MGW MGW New option in Rel.4: GERAN (GSM and EDGE Radio Access Network) PS core as in Rel.’99
V. Mancuso, I. Tinnirello 3GPP Rel.4 Network Architecture
MSC Server takes care Circuit Switched (CS) core of call control signalling network
The user connections MSC GMSC are set up via MGW Server Server (Media GateWay) SGW SGW PSTN “Lower layer” protocol conversion in SGW MGW MGW (Signalling GateWay)
RANAP / ISUP PS core as in Rel.’99 SS7 MTP IP Sigtran
V. Mancuso, I. Tinnirello 3GPP Rel.5 Network Architecture
UTRAN CS core
(UMTS Terrestrial Radio PSTN Access Network) MGW New core network part: IMS (IP Multimedia HSS System) GERAN Internet (GSM and EDGE Radio Access Network) SGSN GGSN
PS core
V. Mancuso, I. Tinnirello 3GPP Rel.5 Network Architecture
The IMS can establish CS core multimedia sessions PSTN (using IP transport) MGW via PS core between UE and Internet (or
IMS (IP Internet /other IMS another IMS) Multimedia HSS Call/session control System) using SIP (Session Initiating Protocol) SGSN GGSN Interworking with the PSTN may be required for some time ... PS core
V. Mancuso, I. Tinnirello New Service Concept
Content provider Content provider
Service provider Service provider
Carrier provider
all want to make profit End user End user
V. Mancuso, I. Tinnirello 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 = Application API API API Programming Interface 3G network (Standardised)
V. Mancuso, I. Tinnirello 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
V. Mancuso, I. Tinnirello The IMS
The IP Multimedia Subsystem
Vincenzo Mancuso, PhD
V. Mancuso, I. Tinnirello 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
V. Mancuso, I. Tinnirello IMS ValueValue--addedadded 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
V. Mancuso, I. Tinnirello 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
V. Mancuso, I. Tinnirello Component #1: the media transport
After many other services, introduction of real time voice/video on Internet The 1 st problem is easy: how to transmit voice/video? IP packets RTP (Real-Time Protocol) is a protocol which transports an encoded multimedia stream as pieces, with a timestamp on each piece, and sends Codec them using UDP/IP RTP Any encoding is permitted for voice/video with UDP a Codec: MP3, ACC, MPEG4, AMR… IP 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 V. Mancuso, I. Tinnirello Component #2: session initiation
The 2 nd problem is more difficult: how to initiate the call? how to know the IP- Registration of Betty’s phone and address 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 Registration of John’s phone and address address
The control of the address table creates a tough competition…
V. Mancuso, I. Tinnirello Why IMS? Solutions to make the address resolutions
MSN, Yahoo, AOL have designed a calling architecture hyper- centralized: 1 table worldwide, only 1 operator
Skype promotes a hyper- “The introduction and development of decentralized architecture: solution like Skype is highly significant as it alters the notion of 1 table per terminal with telecommunications operators by peer-to-peer update making the process fully electronic“ between terminals IDATE - ART, 2004
Operators dislike such approaches, so they push a way very similar to e-mail: centralization per domain. This approach is named “Internet Protocol Multimedia Subsystem”, IMS.
V. Mancuso, I. Tinnirello IMS User Identities
tel:+17324567888 [email protected] m
Private User Identity IMS Subscriber Sip:[email protected]
tel:+88028112347
Public User Identities V. Mancuso, I. Tinnirello User Identity
Private identity Public Service User Identity 1 Profile 1 Issued by home provider Implicitly Registered ID Used for AAA Private Public Set 1 Service Saved on ISIM (not modifiable) User Identity 1 User Identity 2 Profile 2 Public identity Public User Identity 3 Normal SIP address (URI or TEL) IMS Implicitly Subscription Registered ID Set 2 Identifies the user publicly Public Service User Identity 4 Profile 3 User has one or more identities
Used for routing Private Public User Identity 2 User Identity 5 Can be grouped into implicit registration sets Implicitly Registered ID Set 3 If one of the set is registered then the others are as well Public Service User Identity 6 Profile 4 At least one is stored on ISIM In case no ISIM is provided » 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
V. Mancuso, I. Tinnirello 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) V. Mancuso, I. Tinnirello IP Multimedia Subsystem
Next-gen An enabler A standard network of new architecture applications
Converged Services SIP Rich Communications IMS Push ---222---Talk SIP Video Clips PushPush----2222----ViewView Sports, News PushPush----2222----XXXX IP Network Presence, LocationLocation---- SIP Voice based Services SIP SIP ServiceService----layerlayer SIP Picture Messaging, EEE-E---mailmail MM Messaging IMIMIM ControlControl----layerlayer At Home On the Move In the Office Streaming Games, Audio, Video Music IMS is access agnostic, cost reducing, and service Downloads TransportTransport----layerlayer enhancing Interactive Services, Interactive Gaming IMS gives the customer & carrier choice
V. Mancuso, I. Tinnirello IMS
Goals & Tools
V. Mancuso, I. Tinnirello 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 packet- switching networks Not a mere circuit-switching replacement
V. Mancuso, I. Tinnirello 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 …
V. Mancuso, I. Tinnirello 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
V. Mancuso, I. Tinnirello 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
V. Mancuso, I. Tinnirello 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
V. Mancuso, I. Tinnirello AAA protocol: DIAMETER one protocol for many interfaces
Authorization Diameter Diameter Client Application Server Application What service can be used? Authentication Are you really who you say you are? Session Management Session Management Accounting € $ £ Routing Management Routing Management
• DIAMETER – by IETF RFC3588 Connection Connection Management Management – Evolution of RADIUS – Base protocol Base Protocol Base Protocol – Diameter applications • 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 V. Mancuso, I. Tinnirello IMS Architecture
V. Mancuso, I. Tinnirello 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 Applications Internet 3G mobile
WLAN IMS Platform WiMAX DSL Fibre PSTN Ethernet IP transport MGW
V. Mancuso, I. Tinnirello 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
V. Mancuso, I. Tinnirello A standard architecture for service delivery
Application Layer AS AS
SIP DIAMETER SIP Session MR SIP Control HSS F Layer MGCF
MGW H.248 Connectivity SIP Layer PSTN/PLMN IP Network GGS N
CPE
V. Mancuso, I. Tinnirello 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
V. Mancuso, I. Tinnirello 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
V. Mancuso, I. Tinnirello IMS functional elements
V. Mancuso, I. Tinnirello Infrastructure of SIP Proxies (media do not traverse the IMS..)
V. Mancuso, I. Tinnirello IMS Functional Elements
Session Management (SIP) Routing Databases Network Interoperability Elements Services and Support Components Charging Components
V. Mancuso, I. Tinnirello 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 V. Mancuso, I. Tinnirello 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 IMS- specific diameter application
V. Mancuso, I. Tinnirello Home Subscriber Server (HSS)
HSS
Diameter 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
V. Mancuso, I. Tinnirello 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
V. Mancuso, I. Tinnirello 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)
V. Mancuso, I. Tinnirello Call/Session Control Func.Func (. (CSCF)CSCF)
Diameter
PP-- II-- SIP SS-- CSCF CSCF CSCF SIP 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
V. Mancuso, I. Tinnirello IMS Signaling Path (1 domain, no roaming)
V. Mancuso, I. Tinnirello IMS Signaling Path (4 domain roaming, media goes directly)
Sweden User
Irish User
Sweden User In roaming
Irish User In roaming
V. Mancuso, I. Tinnirello 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
V. Mancuso, I. Tinnirello PP--CSFCCSFC 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
V. Mancuso, I. Tinnirello PDF for QoS in IMS (intermediary between the applicationapplication--levellevel QOS and the 3G networknetwork--levellevel QoS))QoS
V. Mancuso, I. Tinnirello 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)
V. Mancuso, I. Tinnirello II--CSCFCSCF 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.
V. Mancuso, I. Tinnirello 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)
V. Mancuso, I. Tinnirello SS--CSCFCSCF 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. V. Mancuso, I. Tinnirello Application Server (AS)
ASAS ASASASAS
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!) V. Mancuso, I. Tinnirello ASAS
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).
V. Mancuso, I. Tinnirello AS asas a SIP Proxy (e.g. find a taxi)
V. Mancuso, I. Tinnirello AS asas a SIP Terminal (e.g. web server: receive media data!)
V. Mancuso, I. Tinnirello Example of Filter Rule (at SS--CSCF)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
V. Mancuso, I. Tinnirello Multimedia Resource Function (MRF)
SIP MRFC
MSMS MSMS
Offers Services Such as Conferencing MRFC – SIP User Interface toward S-CSCF MRFP – Controls the Media Server (MS)
V. Mancuso, I. Tinnirello 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
V. Mancuso, I. Tinnirello Multiparty Calls (MRF as a special AS)
REFER: Ask other to join
V. Mancuso, I. Tinnirello Multiparty Call
V. Mancuso, I. Tinnirello Multiparty Call
V. Mancuso, I. Tinnirello 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
V. Mancuso, I. Tinnirello PSTN Gateway
SGW ISUP SIP SIP SIP BGCF MGCF
H.248
TDM MGW
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
V. Mancuso, I. Tinnirello Home Network --FunctionalFunctional Elements
Home Subscriber Server • Centralized DB • HLR successor Application Servers • User profile • Push-to-talk • Filter criteria (sent to S-CSCF) • Instant messaging Media Resource Function Controller • Which applications • Telephony AS • Pooling of Media servers (e.g. conference) Domain Name Server • Which conditions • 3rd party or IMS Vendor
Home Network UA/UE SIP DNS ASAS HSS ASASASAS PP--CSCFCSCF ENUM Media Gateway Diameter Control Function SIP • Interfaces to PSTN/PLMN by • Converting SIP <-> ISUP SIP SIP PP--CSCFCSCF II--CSCFCSCF SS--CSCFCSCF MRFC • Interworking RTP to circuit UA/UE SIP • H.248 control of MGW MSMS MSMS SIP SIP SIP SIP BGCF MGCF ISUP Call Session SIP H.248 SS7 Control Function • SIP registration RTP TDM PSTN • SIP session setup MGW
Proxy CSCF Serving CSCF • Registrar • 1st contact point for UA Visited • Session control • QoS Network • Application Interface • Routes to S-CSCF Interrogating CSCF • Entry point for incoming calls Breakout Gateway Control Function • Determines S-CSCF for Subscribers • Selects network (MGCF or other BGCF) V. Mancuso,• Hides network I. topology Tinnirello in which PSTN/ PLMN breakout is to occur NetworkNetwork--toto--NetworkNetwork Connectivity
UA/UE SIP Access DNS ASAS HSS ASASASAS PP--CSCFCSCF SIP RTP ENUM Diameter RTP SIP SIP SIP
Backbone SIP SIP SIP MRFC Packet P/SP/S--CSCFCSCF II--CSCFCSCF SS--CSCFCSCF Visited Network SIP MSMS MSMS SIP Network SIP SIP BGCF MGCF ISUP
Home H.248 SS7 Network RTP TDM PSTN MGW Proxy/Serving CSCF •Manages call origination •Selects destination network • Routes to I-CSCF
Interrogating CSCF • Entry point for incoming calls • Determines S-CSCF for Subscribers V. Mancuso,• Hides network I. topology Tinnirello 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
V. Mancuso, I. Tinnirello IMS architecture
Examples
V. Mancuso, I. Tinnirello John is calling Betty IIntroducingntroducing the HSS and the SS--CSCFCSCF
The HSS is the table user/address The S-CSCF is a SIP proxy which works on messages to provide users HSS (consumers, enterprises) with calling services including registration being a When the phones mediation SIP2DIAMETER get connected they register their name/IP to the HSS
SIP S-CSCF SIP Changes the SIP message replacing “Betty” by its IP address found in the HSS
V. Mancuso, I. Tinnirello 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 V. Mancuso, I. Tinnirello 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 SIP MRFC
MGCP, H248 Megaco
RTP (codec: G729) RTP (codec: AMR) MRFP V. Mancuso, I. Tinnirello During its travel John is calling Betty The operator has made a segmentation of its services offeofferr IIntroducingntroducing the PP--CSCF,CSCF, I--CSCFI 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 S-CSCF (enterprises) Home Network V. Mancuso, I. Tinnirello 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 Legacy Call control (SS7) SIP H248 MGCP, … Megaco RTP Phone transmission Internet MGW PSTN/PLMN network
V. Mancuso, I. Tinnirello IMS Communication Focus Roaming IMS Mobile Users
Serving Network A Serving Network B
Access Network A Service Platform A Service Platform B Access Network B (AS A) (AS B)
SIP / SDP SIP / SDP SIP / SDP P-CSCF C P-CSCF D PDF S-CSCF A S-CSCF B PDF
Gm Gm SIP/SDP SIP/SDP inviting Go Go [email protected]
SGSN GGSN Data- Path GGSN SGSN IP Backbone Network UE A 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
V. Mancuso, I. Tinnirello A Typical Example of an IMS Call Network Y Network X
AS AS S-CSCF S-CSCF
HSS HSS I-CSCF I-CSCF
P-CSCF
P-CSCF SGSN GRX
DSL/Cable Modem Network Z (UMTS/GPRS)
GGSN DSLAM/CMTS
RNC
User A User B
V. Mancuso, I. Tinnirello The Signaling Plane
V. Mancuso, I. Tinnirello 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
V. Mancuso, I. Tinnirello SDP
version
user subject user IP Session-level Start time G711 µ-law Stream directio H.261 codec Media-level n
V. Mancuso, I. Tinnirello SIP entities
Registrar User Agent SIP endpoints handled by users (also automatically, based on user- defined 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
V. Mancuso, I. Tinnirello 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:[email protected] SIP/2.0
Status line (in an answer) Start line One or more headers ( name:value ) e.g.: SIP/2.0 180 Ringing ------EMPTY LINE ------Message body (OPTIONAL) Status Human Protocol version code code SIP message format V. Mancuso, I. Tinnirello 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
V. Mancuso, I. Tinnirello 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)
V. Mancuso, I. Tinnirello Prerequisites TwoTwo--phasephase registration
Offline subscription
Login to the Inbound/Outbound IP access net Fixed Proxy
DHCP or Lower level mechanism Online registration
V. Mancuso, I. Tinnirello Entering the IP Connectivity Access Network The access to GPRS includes the assignment of servers and IP address
V. Mancuso, I. Tinnirello PDF Context Activation/DeActivation/De--ActivationActivation
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
V. Mancuso, I. Tinnirello PP--CSCFCSCF 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)
V. Mancuso, I. Tinnirello IMSIMS--levellevel 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
V. Mancuso, I. Tinnirello •The HSS tells the I-CSCF whether a S-CSCF was already allocated to the user. IMSIMS--levellevel registration •If not, I-CSCF will choose based on capabilities notified by HSS in the UAA
Without authentication
DL User Auth :Multiledia Auth.Ans : User Auth. Ans. Auth. :User
vector :ServerAns. Assignment UAA MAA SAA Challenge the User
authentication vector included
DL User :Multimedia Auth.Req : User Auth. Req Auth. :User
Profile :ServerReq. Assignment UAR MAR SAR V. Mancuso, I. Tinnirello Basic Session Setup
V. Mancuso, I. Tinnirello Session setup
Many nodes and many messages involved in the setup
Different planes/layers •media •signaling •CAN •core V. Mancuso, I. Tinnirello Session setup ((cont’edcont’ed))
V. Mancuso, I. Tinnirello