Subsystem
IMS IMS = IP Multimedia Subsystem What is it? IMS Components Session Initiated Protocol (SIP) Session Set-up Procedure Multimedia Resource Function Media Gateway Enabling IPv6
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IMS Copyright R. H. M. Hafez 1996-2005
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This section explain in some details this new domain called IP Multimedia Subsystem, and its associated signaling scheme known as Session Initiated Protocol SIP. IMS/SIP are defined in the 3GPP but they do apply to other IPbased networks and technologies.
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The All-IP Model
Applications & Services
Legacy Mobile Signaling Network
SGW
Mh Ms E-HLR Um Cx Mm
Multimedia IP Network
CSCF
Mg Gm Gc Gr Gi
E-RAN
Iu-cs
MRF
Gi
MS Uu
MGCF
Mc
E-SGSN
Iu-ps
Gn
PSTN
E-GGSN
Gf Gi EIR
UTRAN
Gp Gn UE
MGW
GGSN SGSN
Signaling
Other PLMN
Data + Signaling
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IMS Copyright R. H. M. Hafez 1996-2005
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This is the vision of All-IP access. GTRAN will continue to support voice and UTRAN will support multimedia. The BSC will play a more significant role. It will be the main interface point to an all-IP networking. Since there are a lot more BSC's than MSCG's or GGSG's the work will be more distributed and fiber optics will play a significant role in transporting the wireless traffic in urban areas.
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What is IMS
It is an International Standard defined by 3GPP/3GPP2 It defines a Generic Architecture for IP services. It takes care of:
Establishing the connection Controlling the session Charging Integrating IP services Mobility
CORE
SGW
CSCF MRF
MGCF
MGW
A subsystem of servers, databases, codecs, algorithms and procedures to facilitate a range of IP services
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IMS
Copyright R. H. M. Hafez 1996-2005
IMS is the key technology that will enable a large array of flexible IP applications It is a system defined at the application level and constitute simplified signaling structure that support a new array of attractive applications. IMS uses the Session Initiated Protocol (SIP) to affect the connectivity. IMS allows various concurrent communication scenarios including: Person-to-Person, Group Interaction using voice, video , presentations .. Etc ..
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Enabling IP Services Using IMS/SIP
IMS
SIP
UMTS
SIP
Terminal-to-Terminal IP connection
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IMS Copyright R. H. M. Hafez 1996-2005
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This slide illustrates the basic idea of the IMS/SIP system. A caller initiates the session by clicking on a link or pushing a bottom. The IMS system searches for and locate the called-in party and sends an invite command The two parties negotiates exactly how the call will proceed. Then the IP session is opened until terminated by another SIP command.
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Services Enables by IMS/SIP
IMS Services Person-to-Person Rich voice Video Packet Switched Services Circuit Switched Services Person-to-Person Voice Person-to-Server Browsing Streaming MMS Chat PoC Multi-Users Voice Conference Video Conference Document sharing
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IMS Copyright R. H. M. Hafez 1996-2005
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This slides lists the many services that are supported by the IMS system The list in not complete or all inclusive but it is clear that the new flexibility introduced by the IMS will enable a wide range of applications.
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IMS Components
Call State Control Function (CSCF):
P-CSCF S-CSCF I- CSCF Proxy CSCF Serving CSCF Interrogating CSCF
Gateways:
MGW Media Gateway SGW Signaling Gateway MGCF Media Gateway Control Function BGCF Breakout Gateway Control Function
Multimedia Resources:
MRFP MRFC Multimedia Resource Function Processor Multimedia Resource Function Controller
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IMS Copyright R. H. M. Hafez 1996-2005
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IMS is a large signaling systems with various components and resources. This slide just lists the components Some details about these components are given in the next few slides.
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IMS All-IP Network Model
External Networks IMS RAN All-IP CORE
EIR
Legacy Mobile Signaling Network
SGW
Applications & Services
CSCF E-RAN
HSS
MGCF
MRF
Multimedia IP Network
MS
E-SGSN UTRAN
E-GGSN MGW GGSN
UE
Other PLMN SGSN
PSTN
MGW
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IMS Copyright R. H. M. Hafez 1996-2005
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This is another presentation of the all-IP model There are five distinct sections: The UE, the access network, the CORE, the IMS and the external networks It is also important to observe that some components carry the user data while other are for signaling and control. Onlt the data-bearer connections are shown in this slides.
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What is SIP?
SIP = Session Initiated Protocol
Signaling QoS
Media
H.323
SIP
RTSP
RSVP
RTCP
RTP
TCP
UDP
IPv4 / IPv6
Link Layer Protocols
Physical
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IMS Copyright R. H. M. Hafez 1996-2005
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This slide just illustrates where the SIP protocol fits in the of stack IP protocols. It is a signaling protocol that exists at the application level
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Major Characteristics of SIP
SIP is a protocol that establishes sessions in an IP network Signaling language between the endpoints SIP allows to change parameters in the middle of a session SIP uses email-style addressing SIP proxy uses DNS to find addresses SIP is used by the IMS subsystem or the CSCF can be viewed as a SIP proxy
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IMS Copyright R. H. M. Hafez 1996-2005
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SIP addresses looks like normal emails and the user experience is expected to be similar to Internet chatting One of the biggest advantages of SIP is that it allows a total flexibility during the session. Parallel sessions and or new users could be added or removed from the session while in progress
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Home Subscriber Server [HSS]
HSS I an advanced Home Location Registry Its a large data base It holds the subscription details of a large number of users It also hold the service profiles profiles of these users It has access to authentication data bases
IMS Copyright R. H. M. Hafez 1996-2005
EIR HSS AuC
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HSS is an upgraded HLR with more detailed information about the users and its capabilities
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Call State Control Function [CSCF]
CSCF is a network of elements that set up the IP session across different networks The CSCF tracks the location of the called-in party The CSCF consists of three types: Proxy, Interrogating and Serving A fourth element would be the Home Subscriber Server (HSS)
P-CSCF
I-CSCF
S-CSCF
HSS
IMS
Copyright R. H. M. Hafez 1996-2005
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This is the normal sequence of connection and interrogation during a SIP procedure. Assuming that the caller does not know the location of the called in terminal the proxy CSCF will contact the Interrogating CSCF which will contact the home serving CSCF. The current location of an active terminal is stored in the HSS the same way the current location of a cell phone is stored in the HLR
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SIP Registration of a Terminal
Retrieve Subscriber Information 5 P-CSCF 2 S-CSCF 4 3 Update Subscriber Location HSS
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IMS
Copyright R. H. M. Hafez 1996-2005
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This is a simple procedure of a UE registering its location with its home S-CSCF The Proxy-CSCF is always the first point of contact (it plays a role similar to the VLR in the GSM network)
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IN-Home Network SIP Call
K O
P-CSCF 3
OK
2 S-CSCF
te vi In
1
PSTN
Inv ite
4
MGW IP call through The media gateway
IMS
Copyright R. H. M. Hafez 1996-2005
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This is a simple example of placing an IP call to a normal phone through the PSTN and MGW When the I-CSCF is absent, it means that there was no need to interrogate a different network. The S-CSCF sets up the call through the media gateway and responds positively to the invite command.
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Session Set-up
Visited Home
HSS
Home
HSS
Visited
S-CSCF
S-CSCF
P-CSCF
I-CSCF
I-CSCF
P-CSCF
IP Network Caller Called
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IMS
Copyright R. H. M. Hafez 1996-2005
A session is a connection between two endpoints The session is initiated from one endpoint using the SIP protocol. Session negotiation goes through two steps: Finding the second end-point Negotiating the details of the session facilities
The IMS infrastructure is used to locate the called-in endpoint. SIP is an IP standard defined by 3GPP
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Multimedia Resource Function [MRF]
MRF coordinates the media processing among the various participants in an IMS conference call It consists of two components:
MRFP MRFC Media Resource Function Processor Media Resource Function Controller
MRF coordinates the media processing among the various participants in an IMS conference call The MRF negotiates the set of codecs that will be used during the session and their parameters
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IMS
Copyright R. H. M. Hafez 1996-2005
The MRF provides support of the various codecs and plug ins needed to facilitate the audio/video/text communications in an IP conference call
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IMS Serves Several Networks
Applications
WLAN
MRF
HSS
CSCF
UMTS Internet
MGCF
MGW
2G GRRS
MGW
PSTN
IMS Sub-System
IMS Copyright R. H. M. Hafez 1996-2005
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It is important to realize that IMS is not only limited to cellular networks. It is a universal standard that can support IP applications within the UMTS, cdma2000, GSM network, WLAN and even wired networks such as Ethernet and ADSL.
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IMS Conference
IMS
SIP
UMTS
SIP
server
IMS
Copyright R. H. M. Hafez 1996-2005
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This mode shows the general capabilities of the IMP/SIP system Several users can negotiate a conference with compatible codecs. Users and or communication modes can change during the session
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