Post on 03-Jun-2018
8/12/2019 Bai Giang Umts_giangdl
1/73
User IdentityUser 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
User has one or more identities
PrivateUser Identity 1
PublicUser Identity 1
PublicUser Identity 2
PublicUser Identity 3
ImplicitlyRegistered ID
Set 1
PublicUser Identity 4
ImplicitlyRegistered ID
Set 2
ServiceProfile 1ServiceProfile 2
ServiceProfile 3
IMSSubscription
V. Mancuso, I. Tinnirello
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
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
ImplicitlyRegistered ID
Set 3PrivateUser Identity 2 PublicUser Identity 5
PublicUser Identity 6 ServiceProfile 4
8/12/2019 Bai Giang Umts_giangdl
2/73
UICCUICC
Universal Integrated Circuit Card
Used to store data, including authenticationinformation
Contains one or more applications SMS
Phonebook
SIM
V. Mancuso, I. Tinnirello
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)
8/12/2019 Bai Giang Umts_giangdl
3/73
IP Multimedia SubsystemIP Multimedia Subsystem
A standard
An enabler
of new
applications
Next-gen
network
architecture
SIPIMSIMSIMSIMSConverged ServicesConverged ServicesConverged ServicesConverged Services
Rich CommunicationsRich CommunicationsRich CommunicationsRich Communications
V. Mancuso, I. Tinnirello
ServiceServiceServiceService----layerlayerlayerlayer
ControlControlControlControl----layerlayerlayerlayer
TransportTransportTransportTransport----layerlayerlayerlayer
IMS is access agnostic, cost reducing, and serviceIMS is access agnostic, cost reducing, and serviceIMS is access agnostic, cost reducing, and serviceIMS is access agnostic, cost reducing, and service
enhancingenhancingenhancingenhancing
IMS gives the customer & carrier choiceIMS gives the customer & carrier choiceIMS gives the customer & carrier choiceIMS gives the customer & carrier choice
SIP
SIP SIPSIP
At HomeAt HomeAt HomeAt Home In the OfficeIn the OfficeIn the OfficeIn the OfficeOn the MoveOn the MoveOn the MoveOn the Move
IP NetworkIP NetworkIP NetworkIP Network
SIP
usususus ---- ---- aaaaPushPushPushPush----2222----ViewViewViewView
PushPushPushPush----2222----XXXX
Presence, LocationPresence, LocationPresence, LocationPresence, Location----based Servicesbased Servicesbased Servicesbased Services
Interactive Services,Interactive Services,Interactive Services,Interactive Services,Interactive GamingInteractive GamingInteractive GamingInteractive Gaming
Games,Games,Games,Games,MusicMusicMusicMusic
DownloadsDownloadsDownloadsDownloads
PicturePicturePicturePictureMessaging,Messaging,Messaging,Messaging,
MM MessagingMM MessagingMM MessagingMM Messaging
VoiceVoiceVoiceVoice
Video ClipsVideo ClipsVideo ClipsVideo ClipsSports, NewsSports, NewsSports, NewsSports, News
EEEE----mailmailmailmailIMIMIMIM
StreamingStreamingStreamingStreamingAudio, VideoAudio, VideoAudio, VideoAudio, Video
8/12/2019 Bai Giang Umts_giangdl
4/73
IMSIMS
V. Mancuso, I. Tinnirello
Goals & Tools
8/12/2019 Bai Giang Umts_giangdl
5/73
IMS goalsIMS goals
Combine latest trends in tech
Run fast, no time for standardization of services
Mobile/Nomadic internet
Create a platform for multimedia
V. Mancuso, I. Tinnirello
services and their development
Exploit/allow mobile packet-
switching networks
Not a mere circuit-switching replacement
8/12/2019 Bai Giang Umts_giangdl
6/73
IMS requirementsIMS requirements
Support for establishing IP MultimediaSessions Audio, video, messaging
Support for mechanisms to negotiate QoS distinguish users
V. Mancuso, I. Tinnirello
Support for interworking with Internet with packet-switching networks
Support for roaming Home and visited network Inter-operators roaming
8/12/2019 Bai Giang Umts_giangdl
7/73
IMS requirementsIMS requirements (contd)(contd)
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
V. Mancuso, I. Tinnirello
Standardize service capabilities instead
Support for multiple access Not only GPRS, UMTS IP is independent on lower protocol layers
8/12/2019 Bai Giang Umts_giangdl
8/73
Protocols in IMSProtocols in IMS
3GPP reuses protocol developed by otherstandards development organizations ETSI (European Telecommunications Standard Institute) IETF (Internet Engineering Task Force) ITU-T (International Telecommunications Union - Telecommunications)
3GPP interacts with standards
V. Mancuso, I. Tinnirello
development of existing and newprotocols
Protocols RTP for media transport
Session control protocols AAA protocols Other
8/12/2019 Bai Giang Umts_giangdl
9/73
Session Control ProtocolSession Control Protocol
SIP (Session Initiation Protocol, byIETF- RFC2821)
Protocol to establish and manage multimedia sessionover IPSIP borrows some design principles from SMTP and
V. Mancuso, I. Tinnirello
Does not differentiate the user-to-network interface fromthe network-to-network interface (unlike BICC andH.323)
It follows the client-server modelText-based protocolEasy to debug, extend and reuse for service building
8/12/2019 Bai Giang Umts_giangdl
10/73
AAA protocol: DIAMETERAAA protocol: DIAMETERone protocol for many interfacesone protocol for many interfaces
Authorization What service can be used?
Authentication
Are you really who you say youare?
Accounting $
Diameter
Client Application
Diameter
Server Application
Session Management Session Management
V. Mancuso, I. Tinnirello
Routing Management
Connection
Management
Connection
Management
Base Protocol Base Protocol
Routing Management
DIAMETER
by IETF RFC3588
Evolution of RADIUS
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
8/12/2019 Bai Giang Umts_giangdl
11/73
IMS ArchitectureIMS Architecture
V. Mancuso, I. Tinnirello
8/12/2019 Bai Giang Umts_giangdl
12/73
New services for mobileNew services for mobile
and fixed networksand 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.
V. Mancuso, I. Tinnirello
Access Independent
MGW
3G mobile
PSTNPSTN
IP transport
IMS PlatformWLANWiMAX
DSLFibre
Ethernet
ApplicationsInternetInternet
8/12/2019 Bai Giang Umts_giangdl
13/73
Functions and nodesFunctions and nodes
IMS standardizes functions
IMS does NOT standardize nodes
The IMS Architecture is a collection offunctions linked by standardizedinterfaces
V. Mancuso, I. Tinnirello
A function can be implemented through one or more nodesMultiple functions can share a node
Commonly a function per node
8/12/2019 Bai Giang Umts_giangdl
14/73
A standard architecture forA standard architecture for
service deliveryservice delivery
ASApplication
Layer
SessionSIP
SIP
DIAMETER
AS
SIPMR
V. Mancuso, I. Tinnirello
MGCFLayer
ConnectivityLayer PSTN/PLMNPSTN/PLMNPSTN/PLMNPSTN/PLMN
IP Network
H.248SIP
CPE
MGW
GGS
N
8/12/2019 Bai Giang Umts_giangdl
15/73
Access to IMSAccess to IMS
The user can connect to an IMS network invariety of ways, all of which use thestandard Internet Protocol (IP) for packetswitchinge.g., IMS terminals can register directly
on an IMS network
V. Mancuso, I. Tinnirello
. ., ,
even when they are roaming in another network or country (the visitednetwork)
The only requirement is that they can use IPv6 (also IPv4 in early IMS)and run SIP user agents
8/12/2019 Bai Giang Umts_giangdl
16/73
Other access examplesOther access examples
Fixed access
- e.g., Digital Subscriber Line (DSL), cable modems, Ethernet
Mobile access e.g., W-CDMA, CDMA2000, GSM, GPRS
Wireless access
V. Mancuso, I. Tinnirello
e.g., WLAN, WiMAXOther phone systems like plain old
telephone service (POTS -- the oldanalogue telephones) or PSTN, H.323
and non IMS-compatible VoIP systems,are supported through gateways
8/12/2019 Bai Giang Umts_giangdl
17/73
IMS functional elementsIMS functional elements
V. Mancuso, I. Tinnirello
8/12/2019 Bai Giang Umts_giangdl
18/73
Infrastructure of SIP ProxiesInfrastructure of SIP Proxies
(media do not traverse the IMS..)(media do not traverse the IMS..)
V. Mancuso, I. Tinnirello
8/12/2019 Bai Giang Umts_giangdl
19/73
IMS Functional ElementsIMS Functional Elements
Session Management (SIP)
Routing
Databases
Network Interoperability Elements
V. Mancuso, I. Tinnirello
Services and Support ComponentsCharging Components
8/12/2019 Bai Giang Umts_giangdl
20/73
Nodes/Functions in the IMSNodes/Functions in the IMS
User databases HSS (Home Subscriber Server) SLF (Subscriber Location Function)
SIP servers CSCF (Call/Session Control Function)
AS (Application Server)
V. Mancuso, I. Tinnirello
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
8/12/2019 Bai Giang Umts_giangdl
21/73
Databases (HSS,SLF)Databases (HSS,SLF)
HSS is an evolution of the HLR (HomeLocation Register) of GSM
Contains the user-related subscription data (e.g., location,authorization and authentication information)
More than one HSS is possible
V. Mancuso, I. Tinnirello
If #HSS > 1 SLF requiredSLF maps users address to HSSs
HSS and SLF use DIAMETER with an IMS-
specific diameter application
8/12/2019 Bai Giang Umts_giangdl
22/73
Home Subscriber Server (HSS)Home Subscriber Server (HSS)
Presence, Location and Profile
End-User Identity
HSSHSS
Diameter
V. Mancuso, I. Tinnirello
Private and Public End-User InformationRegistration Information
Service Initiation Information
Subscriber Service Profile (SSP)Downloaded to CSCF at Registration
8/12/2019 Bai Giang Umts_giangdl
23/73
More on HSSMore on HSS
HSS is a masteruser database thatsupports all the IMS network functions
that actuallyhandle communicationscontains the subscription-related information (user profiles)
performs authentication and authorization of the user
V. Mancuso, I. Tinnirello
can provide information about the user's physical locationis similar to the GSM Home Location Register (HLR) and
Authentication Centre (AUC) together
8/12/2019 Bai Giang Umts_giangdl
24/73
CSCFCSCF
SIP servers or proxies, collectively called CallSession Control Function (CSCF), are used to
process SIP signaling packets/messages inthe IMS
P-CSCF (Proxy)
V. Mancuso, I. Tinnirello
I-CSCF (Interrogating)S-CSCF (Server)
8/12/2019 Bai Giang Umts_giangdl
25/73
Call/SessionCall/Session ControlControl FuncFunc. (. (CSCF)CSCF)
CSCF Processes SIP Signaling P-CSCF
First Point of User Contact (located in the visited domain)
II--CSCFCSCF
SS--CSCFCSCF
PP--CSCFCSCF
SIP
SIP
SIPSIP
SIP
Diameter
V. Mancuso, I. Tinnirello
May Include Policy Functions S-CSCF
Central Node of Control Plane Acts as Registrarfor 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
8/12/2019 Bai Giang Umts_giangdl
26/73
IMS Signaling PathIMS Signaling Path(1 domain, no roaming)(1 domain, no roaming)
V. Mancuso, I. Tinnirello
8/12/2019 Bai Giang Umts_giangdl
27/73
IMS Signaling PathIMS Signaling Path(4 domain roaming, media goes directly)(4 domain roaming, media goes directly)
IrishUser
SwedenUser
V. Mancuso, I. Tinnirello
Irish UserIn roaming
Sweden UserIn roaming
8/12/2019 Bai Giang Umts_giangdl
28/73
CSCFCSCF
P-CSCF (Proxy)
Outbound/Inbound proxy server
First server contacted by the user
Fixed while registered
V. Mancuso, I. Tinnirello
, ,
Authenticates the user and extend the authentication toother nodes within IMS
Compress/decompress SIP messages
Generates charging info
8/12/2019 Bai Giang Umts_giangdl
29/73
PP--CSFC detailsCSFC details
SIP proxy that is the first point of contact for the IMSterminal
It can be located either in the visited network (in full IMSnetworks) 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
V. Mancuso, I. Tinnirello
oes no c ange or e ura on o e reg s ra on
It sits on the path of all signaling messages, and caninspect every message
It authenticates the user and establishes an IPsec securityassociation 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
8/12/2019 Bai Giang Umts_giangdl
30/73
PDF forPDF for QoSQoS in IMSin IMS(intermediary between the application(intermediary between the application--level QOS andlevel QOS and
the 3G networkthe 3G network--levellevel QoSQoS))
V. Mancuso, I. Tinnirello
8/12/2019 Bai Giang Umts_giangdl
31/73
CSCFCSCF
I-CSCF (Interrogating)
SIP proxy at the edge of a domain
Advertised by DNS
Interface to HSS and SLF for routing purposes
V. Mancuso, I. Tinnirello
Optional: encryption of sensitive information aboutthe domain (THIG: topology hiding inter-networkgateway)
8/12/2019 Bai Giang Umts_giangdl
32/73
II--CSCF detailsCSCF details
It is another SIP function located at the edge of anadministrative 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 re uest to its assi ned S-CSCF
V. Mancuso, I. Tinnirello
Up to Release 6 it can also be used to hide theinternal network from the outside world (encryptingpart 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.
8/12/2019 Bai Giang Umts_giangdl
33/73
CSCFCSCF
S-CSCF (Server)
SIP server with session control functions
SIP registrar (maintains a mapping between userlocation and public user identity)
V. Mancuso, I. Tinnirello
SIP routingPEP
Always located in the home network
Interfaced with the HSS (e.g., to download theusers profile)
d ild il
8/12/2019 Bai Giang Umts_giangdl
34/73
SS--CSCF detailsCSCF 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 ath of all si nalin messa es and can
V. Mancuso, I. Tinnirello
inspect every message
It decides to which application server(s) the SIPmessage will be forwarded, in order to provide theirservices
It provides routing services, typically usingElectronic Numbering (ENUM) lookups
There can be multiple S-CSCFs in the network forload distribution and high availability reasons
It's the HSS that assigns the S-CSCF to a user, whenit's queried by the I-CSCF.
8/12/2019 Bai Giang Umts_giangdl
35/73
Application Server (AS)Application Server (AS)
Contains Call Related Application Logic
ASASASAS
ASAS
SIP
Diameter
V. Mancuso, I. Tinnirello
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 thiscase receive the media!)
8/12/2019 Bai Giang Umts_giangdl
36/73
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)
V. Mancuso, I. Tinnirello
Reuse/interface with CAMEL (GSM)
Gateway for GSM Service Control Function
An AS can be located in the homenetwork 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).
8/12/2019 Bai Giang Umts_giangdl
37/73
T i lT i l
8/12/2019 Bai Giang Umts_giangdl
38/73
ASAS asas a SIP Terminala SIP Terminal(e.g. web server: receive media data!)(e.g. web server: receive media data!)
V. Mancuso, I. Tinnirello
E l f Fil R lE l f Fil R l
8/12/2019 Bai Giang Umts_giangdl
39/73
Example of Filter RuleExample of Filter Rule(at S(at S--CSCF)CSCF)
User A wants to divert all calls from bossto an answering machine (i.e. the AS)
(method=INVITE) AND(P-Asserted-Identity = boss@vodafone.com) AND
(Session Case = Terminating) ->message is addressed to
V. Mancuso, I. Tinnirello
8/12/2019 Bai Giang Umts_giangdl
40/73
Multimedia Resource Function (MRF)Multimedia Resource Function (MRF)
SIP
MSMS MSMS
MRFCMRFC
V. Mancuso, I. Tinnirello
Offers Services Such as Conferencing
MRFC SIP User Interface toward S-CSCF
MRFP Controls the Media Server (MS)
8/12/2019 Bai Giang Umts_giangdl
41/73
MRFMRF
The MRF (Media Resource Function) provides asource of media in the home network
It provides media related functions such as media
manipulation (e.g. voice stream mixing, mediatrans-coding) and playing of tones andannouncements.
Each MRF is further divided into
V. Mancuso, I. Tinnirello
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
M lti t C llM lti t C ll
8/12/2019 Bai Giang Umts_giangdl
42/73
Multiparty CallsMultiparty Calls(MRF as a special AS)(MRF as a special AS)
V. Mancuso, I. Tinnirello
REFER:
Ask otherto join
8/12/2019 Bai Giang Umts_giangdl
43/73
Multiparty CallMultiparty Call
V. Mancuso, I. Tinnirello
8/12/2019 Bai Giang Umts_giangdl
44/73
Multiparty CallMultiparty Call
V. Mancuso, I. Tinnirello
8/12/2019 Bai Giang Umts_giangdl
45/73
BGCFBGCF
The Breakout Gateway Control Function is aSIP server that includes routingfunctionality based on telephone numbers
used when calling from the IMS to a phone in a circuit switchednetwork
V. Mancuso, I. Tinnirello
e.g., o u c w c e e ep one e wor or o
Public Land Mobile Network (PLMN)
BGCF routes to the appropriate (remote)circuit switching domain
BGCF selects the (local) PSTN/CS gateway
TT
8/12/2019 Bai Giang Umts_giangdl
46/73
PSTN GatewayPSTN Gateway
MGCFMGCF
H.248
ISUP
BGCFBGCF SIP
SIP
SGWSGW
SIP
V. Mancuso, I. Tinnirello
BGCF Routes to Gateway Based Upon TelephoneNumber
MGCF Controlling Function for SGW and MGW
SGW Provides Signaling Conversion Between SIPand ISUP
MGW Provides Conversion between RTP and TDM
MGWMGWTDM
Home NetworkHome Network -- Functional ElementsFunctional Elements
8/12/2019 Bai Giang Umts_giangdl
47/73
Home NetworkHome Network Functional ElementsFunctional Elements
HSSHSSDNSDNS
ENUMENUM
Home Network
ASASASASASAS
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 3rd party or IMS VendorDomain Name Server
SIPDiameter
Media GatewayControl Function Interfaces to PSTN/PLMN by
Converting SIP ISUP
Media Resource Function Controller Pooling of Media servers (e.g. conference)
PP--CSCFCSCFSIP
UA/UE
V. Mancuso, I. Tinnirello
VisitedVisitedNetworkNetwork
II--CSCFCSCF SS--CSCFCSCFPP--CSCFCSCF
MGCFMGCF
MGWMGWPSTNPSTN
H.248
ISUPBGCFBGCF
SIP
SS7SS7
SIP
SIPSIP
SIP
RTP TDM
Call SessionControl Function SIP registration SIP session setup
MSMS MSMS
Interworking RTP to circuit H.248 control of MGW
Breakout Gateway Control Function Selects network (MGCF or other BGCF)
in which PSTN/ PLMN breakout is to occur
Proxy CSCF 1st contact point for UA QoS Routes to S-CSCF
Interrogating CSCF Entry point for incoming calls Determines S-CSCF for Subscribers
Hides network topology
Serving CSCF Registrar Session control Application Interface
SIP
UA/UE
8/12/2019 Bai Giang Umts_giangdl
48/73
NetworkNetwork--toto--Network ConnectivityNetwork Connectivity
HSSHSSDNSDNS
ENUMENUM
SIP
ASASASASASASAccessAccess
SIP
SIPDiameter
RTP
RTPPP--CSCFCSCF SIP
SIP
UA/UE
V. Mancuso, I. Tinnirello
II--CSCFCSCF SS--CSCFCSCF
VisitedNetwork
HomeNetwork
P/SP/S--CSCFCSCFPacketPacketNetworkNetwork
MGCFMGCF
MGWMGWPSTNPSTN
H.248
ISUPBGCFBGCF
SIP
SS7SS7
SIP
SIPSIP
RTP TDM
MSMS MSMS
Proxy/Serving CSCFManages call originationSelects destination network Routes to I-CSCF
Interrogating CSCF Entry point for incoming calls Determines S-CSCF for Subscribers
Hides network topology
H d Vi it d N t kH d Vi it d N t k
8/12/2019 Bai Giang Umts_giangdl
49/73
Home and Visited NetworksHome and Visited Networks
Inherited from 2G, 3G
Most of IMS nodes and functions are locatedin the Home network
P-SCFC can be either in the home or visitednetwork
-
V. Mancuso, I. Tinnirello
simplifies the operators managementallows roaming to non-IMS GPRS CANs (Connectivity Access networks)
Drawback: trombone effect when GGSN is in the home network (GGSN isin 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
8/12/2019 Bai Giang Umts_giangdl
50/73
IMS architectureIMS architecture
V. Mancuso, I. Tinnirello
Examples
John is calling BettyJohn is calling Betty
8/12/2019 Bai Giang Umts_giangdl
51/73
John is calling BettyJohn is calling BettyIIntroducingntroducing the HSS and the Sthe HSS and the S--CSCFCSCF
The HSS is the table user/address
The S-CSCF is a SIP proxy which workson messages to provide users
(consumers, enterprises) with callingservices including registration being amediation SIP2DIAMETER
HSS
When the phones
get connected they
V. Mancuso, I. Tinnirello
SIP S-CSCF
register their
name/IP to the HSS
Changes the SIP message replacing Betty by its IP
address found in the HSS
SIP
John is calling a taxi to meet BettyJohn is calling a taxi to meet Betty
8/12/2019 Bai Giang Umts_giangdl
52/73
John is calling a taxi to meet BettyJohn is calling a taxi to meet BettyIntroducingIntroducing the Application Server (AS)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
V. Mancuso, I. Tinnirello
S-CSCF
AS
nearest Taxi application (location, fleet)
Changes the SIP message replacing taxi by
the IP address of the nearest available taxi
Johns and Bettys phones doJohns and Bettys phones do not supportnot support a commona common
8/12/2019 Bai Giang Umts_giangdl
53/73
y py p pppp
voice encodingvoice encoding
Introducing the MRFC and MRFPIntroducing the MRFC and MRFP
Intercepting the SIP invite message, the S-CSCF/AS
detects a non compatibility between the codecs of thephones : it forwards it to the MRFC (a SIP proxy).
The MRFC adjusts the SIP messages in order to orient theRTP flow to the MRFP a RTP rox for trans-codin
V. Mancuso, I. Tinnirello
MRFC
MRFP
MGCP, H248 Megaco
RTP (codec: AMR)
SIPS-CSCF
RTP (codec: G729)
During its travel John is calling BettyDuring its travel John is calling Betty
ThTh t h d t ti f it i fft h d t ti f it i ff
8/12/2019 Bai Giang Umts_giangdl
54/73
TheThe operator has made a segmentation of its services offeroperator has made a segmentation of its services offerIIntroducingntroducing thethe PP--CSCF, ICSCF, I--CSCFCSCF
The P-CSCF is the 1st 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
V. Mancuso, I. Tinnirello
network
also used as the entry point for calls from other operators
Home Network
Visited Network
P-CSCF
S-CSCF (consumers)
S-CSCF (enterprises)I-CSCF
HSS
John is calling Betty who hasJohn is calling Betty who has
8/12/2019 Bai Giang Umts_giangdl
55/73
g yg y
a legacy phonea legacy phoneIntroducing the MGCF and the MGWIntroducing 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 drivesthe MGW (Media gateway)
controls circuits and MGW much like a VoIP softswitch
V. Mancuso, I. Tinnirello
MGCF
MGW
H248 MGCP,Megaco
SIPLegacy Call control (SS7)
Phone transmission
Internet PSTN/PLMN network
RTP
8/12/2019 Bai Giang Umts_giangdl
56/73
A Typical Example of an IMS CallA Typical Example of an IMS Call
8/12/2019 Bai Giang Umts_giangdl
57/73
A Typical Example of an IMS CallA Typical Example of an IMS CallNetwork XNetwork X Network YNetwork Y
P-CSCF
I-CSCF
I-CSCF
S-CSCF
S-CSCF
HSSHSS
ASAS
V. Mancuso, I. Tinnirello
User B
DSL/Cable ModemDSL/Cable Modem
DSLAM/CMTS
RNC
GGSN
Network Z (UMTS/GPRS)Network Z (UMTS/GPRS)
User A
SGSN
GRXGRX
P-CSCF
8/12/2019 Bai Giang Umts_giangdl
58/73
The Signaling PlaneThe Signaling Plane
V. Mancuso, I. Tinnirello
SIP functionalitySIP functionality
8/12/2019 Bai Giang Umts_giangdl
59/73
SIPs main goal is to deliver asession descriptorto auser 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
8/12/2019 Bai Giang Umts_giangdl
60/73
SIP entitiesSIP entities
8/12/2019 Bai Giang Umts_giangdl
61/73
SIP entitiesSIP entities
Registrar
User Agent SIP endpoints handled by users (also automatically, based on user-
defined rules)
Proxy server
V. Mancuso, I. Tinnirello
Usually is co-located with the registrar, and always uses the informationon 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
SIP transactionsSIP transactions
8/12/2019 Bai Giang Umts_giangdl
62/73
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)
V. Mancuso, I. Tinnirello
e.g.: INVITE sip:alice@domain.com SIP/2.0
Status line (in an answer)
e.g.: SIP/2.0 180 Ringing
Start line
One or more headers (name:value)
---------EMPTY LINE ---------
Message body (OPTIONAL)
SIP message format
Method Request URI Protocol version
Protocol versionStatus
code
Human
code
8/12/2019 Bai Giang Umts_giangdl
63/73
8/12/2019 Bai Giang Umts_giangdl
64/73
PrerequisitesPrerequisitesTwoTwo--phase registrationphase registration
8/12/2019 Bai Giang Umts_giangdl
65/73
TwoTwo phase registrationphase registration
Inbound/Outbound
Offline subscription
Login to the
V. Mancuso, I. Tinnirello
Fixed Proxy
Online registration
IP access net
DHCP or
Lower level
mechanism
8/12/2019 Bai Giang Umts_giangdl
66/73
8/12/2019 Bai Giang Umts_giangdl
67/73
PP--CSCF discoveryCSCF discovery
8/12/2019 Bai Giang Umts_giangdl
68/73
The IMS terminal has to discover the IP address of theP-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--level registrationlevel registration
8/12/2019 Bai Giang Umts_giangdl
69/73
The user requests authorization to usethe IMS
The IMS authenticate and eventuallyauthorize the user
SIP REGISTER is mandatory
V. Mancuso, I. Tinnirello
DIAMETER is used by the CSCF to contact the HSS
For security reasons, the user is challenged to show itsidentity this require two SIP REGISTER messages
IMSIMS--level registrationlevel registrationThe 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
8/12/2019 Bai Giang Umts_giangdl
70/73
UAA:UserA
uth.Ans.
MAA:Multi
lediaAuth.Ans
SAA:ServerAssignmentAns.
p y
Without
authentication
DL User Auth
vector
V. Mancuso, I. Tinnirello
UAR:UserAuth.
Req
MAR:Multim
ediaAuth.Req
SAR:ServerA
ssignmentReq.
Challenge the User
DL User
Profile
authentication
vector included
8/12/2019 Bai Giang Umts_giangdl
71/73
Basic Session SetupBasic Session Setup
V. Mancuso, I. Tinnirello
SessionSession
8/12/2019 Bai Giang Umts_giangdl
72/73
setupsetup
V. Mancuso, I. Tinnirello
many messages
involved in the setup
Different
planes/layers
mediasignalingCANcore
Session setup (Session setup (contedconted))
8/12/2019 Bai Giang Umts_giangdl
73/73
V. Mancuso, I. Tinnirello