IP Multimedia Subsystem (IMS) 江培文
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Transcript of IP Multimedia Subsystem (IMS) 江培文
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IP Multimedia Subsystem(IMS)
江培文
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Agenda
Background IMS Definition IMS Architecture IMS Entities IMS-CS Interworking
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Background - AMPS
Advanced Mobile Phone System (AMPS)First generation (1G) cellular network Analog mobile phone system Standardized by ANSI Operate in the 800 MHz bandVoice call
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Background - GSM
Global System for Mobile communications (GSM)Second generation (2G) cellular network Digital mobile phone system Most GSM networks operate in 900 MHz
or 1800 MHz bandsEach radio channel bandwidth is 200
kHzStandardized by ETSIVoice call, short message service
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Background - GPRS
General Packet Radio Service (GPRS) 2.5G packet oriented mobile networkProvide data rates from 56 up to 114
kbpsStandardized by ETSI/3GPP Short Message Service (SMS), Wireless
Application Protocol (WAP), Multimedia Messaging Service (MMS), Internet Access
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Background - EDGE
Enhanced Data rates for GSM Evolution (EDGE)2.75G packet oriented mobile networkData rate up to 236.8 kbps Standardized by 3GPP Multimedia services, Internet access
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Background - WCDMA
Wideband Code Division Multiple Access (WCDMA)Third generation (3G) cellular network1885–2025 MHz for uplink band and 2110–2
200 MHz for downlink band Each radio channel bandwidth is 5 MHz Data rate up to 384 kbps Standardized by 3GPP The world's first commercial WCDMA netwo
rk, FOMA, was launched by NTT DoCoMo in Japan in 2001.
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Background - HSDPA
High Speed Downlink Packet Access (HSDPA) 3.5G packet oriented mobile networkAdaptive Modulation and Coding (AMC)
Depend on signal quality and cell usage QPSK in initial scheme, 16QAM in good radio
condition. Data rate up to 14.4 Mbps for downlink
and 384 kbps for uplinkStandardized by 3GPP (since release 5)
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Background - LTE
Long Term Evolution (LTE) Fourth generation (4G) cellular network? Orthogonal FDMA (OFDMA) for downlink and
Single Carrier FDMA (SC-FDMA) for uplink Support Multiple-Input and Multiple-Output
(MIMO) Improve communication performance Increase data throughput Without additional bandwidth or transmit power
Channel bandwidth between 1.5 and 20 MHz All IP Network (AIPN) Data rate up to 326.4 Mbps for downlink and
86.4 Mbps for uplink Standardized by 3GPP (since release 8)
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IMS Definition
3GPP Release 5 introduced the IMS as part of 3GPP specifications in March 2002
The IMS is supposed to be a standardized access-independent IP-based architecture that interworks with existing voice and data networks for both fixed (e.g., PSTN, Internet) and mobile (e.g., GSM, WCDMA) users
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IMS in Converged Networks
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IMS Architecture
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IMS Entities
Routing and Session Management Databases Services Interworking Functions Support Functions
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Routing and Session Management
Call Session Control Functions (CSCF)Proxy Call Session Control Function (P-
CSCF) Interrogating Call Session Control
Function (I-CSCF)Serving Call Session Control Function (S-
CSCF)
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P-CSCF
The first contact point for users within the IMS
SIP compression IPSec security association Interaction with Policy Decision
Function (PDF) Emergency session detection
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I-CSCF
Obtain the name of the S-CSCF or Application Server (AS) from the Home Subscriber Server (HSS)
Assign an S-CSCF based on received capabilities from the HSS
Route incoming requests to an assigned S-CSCF or AS
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S-CSCF
Handle registration process Store service profile Make routing decision Maintain session state
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IMS Entities
Routing and Session Management Databases Services Interworking Functions Support Functions
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Databases
Home Subscriber Server (HSS) Subscription Locator Function (SLF)
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HSS
The main data storage for all subscriber and service-related dataUser identities
Private and public user identitiesRegistration informationAccess parameters
Allocated S-CSCF namesService triggering information
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SLF
The resolution mechanism that enables the I-CSCF, the S-CSCF and the AS to find the address of the HSS that holds the subscriber data for a given user identity when multiple and separately addressable HSSs have been deployed by the network operator.
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IMS Entities
Routing and Session Management Databases Services Interworking Functions Support Functions
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Services
Multimedia Resource Function Controller (MRFC)
Multimedia Resource Function Processor (MRFP)
Application Server (AS)
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MRFC
A signalling plane node Provide the mechanism for bearer-relat
ed services such as announcement Handle SIP communication to/from the
S-CSCF Control the MRFP
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MRFP
A media plane node Mix the incoming media streams for
multiple parties Process the media stream source for
multimedia announcements
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AS
Provide value-added multimedia services
Process the incoming SIP sessions from the S-CSCF
Originate SIP requests Send accounting information to the
charging functions
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IMS Services
Presence Multimedia Chat Push to talk Over Cellular (POC) Conferencing
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IMS Entities
Routing and Session Management Databases Services Interworking Functions Support Functions
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Interworking Functions
For exchanging signalling and media between IMS and CS Core Network
Breakout Gateway Control Function (BGCF)
Media Gateway Control Function (MGCF) Signalling Gateway (SGW) IMS Media Gateway (IMS-MGW)
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BGCF
It chooses where a breakout to the CS domain occurs
If the breakout happens in the same network, then the BGCF selects a MGCF to handle the session.
If the breakout takes place in another network, then the BGCF forwards the session to another BGCF in a selected network.
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MGCF
Send a converted request via the Signalling Gateway (SGW) to the CS CN
Control the IMS Media Gateway (IMS-MGW)
Perform protocol conversion between SIP and ISDN User Part (ISUP)
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SGW
Perform signalling conversion at the transport level between the IP-based transport of signalling and the Signalling System No. 7 (SS7)
i.e., between SCTP and SS7
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IMS-MGW
Provide the user plane link between CS domain and IMS domain
Perform transcoding for the user plane traffic
i.e., between TDM and RTP
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IMS Entities
Routing and Session Management Databases Services Interworking Functions Support Functions
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Support Functions
Policy Decision Function (PDF) Security Gateway (SEG)
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Session establishment in the IMS involves the end-to-end messages exchange using SIP and SDP
The P-CSCF forwards the relevant SDP information to the PDF
The PDF authorizes the IP flows of the media components and transfers the authorized IP QoS parameters to the GGSN to establish an IMS session
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SEG
Protect control plane traffic between security domains
Enforce the security policy of a security domain
Coincide with operator borders
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IMS-CS Interworking
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CS-IMS Interworking
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Thank You