National Chung Cheng University Dept. Computer Science & Information Engineering 3GPP IP Multimedia Subsystem Chiang, Wei-Kuo (江為國) Assistant Professor Department of CSIE National Chung Cheng University Office : EA 311 Phone : 05-2720411~33126 Email : [email protected]URL : http://www.cs.ccu.edu.tw/~wkchiang/ National Chung Cheng University
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National Chung Cheng UniversityDept. Computer Science & Information Engineering
3GPP IP Multimedia Subsystem
Chiang, Wei-Kuo (江為國)
Assistant Professor Department of CSIE National Chung Cheng University Office : EA 311 Phone : 05-2720411~33126 Email : [email protected]
URL : http://www.cs.ccu.edu.tw/~wkchiang/
National Chung Cheng University
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem2
Next Generation Network
Internet Telecom & Wireless Communication
IP
MGCF
CSCF
T-SGW MGWMGW
WLAN
GPRS
CSCFSIP
Server
PSTN
InternetWireless App.Server
3rd Parties App.
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem3
Outline
Softswitch
Softswitch Architecture
Softswitch Operations
3GPP All IP Network
Network Architecture
Network Entities
3GPP IMS CSCF
Entities Behavior
Message Flows
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem4
Softswitch Overview (1/2)
Softswitch: Emulating Circuit Switching in Software
IN/SCP
PSTN
Local Switch
PSTN
Local SwitchSTP SS7 Network
IP Network
RTP Streams
MGC MGC
Trunk
GatewayTrunk
Gateway
SIP-T
SGSG
SIGTRAN
MEGACO
IP Phone
9000 Personalized VoIP
Service System
Application Server
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem5
Softswitch Overview (2/2)
Softswitch Provides Open Layered Architecture
• Solutions in a proprietary box
• Expensive
• Little room for innovation
Circuit-Switched
Transport
Hardware
Call Control &
Switching
Services &
Applications
P
R
O
P
R
I
E
T
A
R
Y
• Solutions are open standards-based
• Customers choose best-in-class products
• Open standards enable lower cost for innovation
Soft-Switched
Transport Hardware
Softswitch Call Control
Services, Applications & Features
(Management, Provisioning and
Back Office)
Open Protocols APIs
Open Protocols APIs
Open APIs for 3rd Party App develop.
Best-in-class Access Devices.
Scalable, Open Interfaces for Comm.
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem6
Softswitch Architecture (1/2)
CO
Switch
STP
SCP
CO
Switch
STP
SCP
Signaling Layer
Transport Layer
IP
SIP-T
Media
Server
RTP
SIP-?/
MGCP
SIP-TSI
Media
Gateway
Controller
MGCP/
MEGACO
Phones
App.
Server
Media
Gateway
Controller
SIGTRAN
SSA/SCTP
MGCP/MEGACOTrunking
Gateway
Signaling
(SS7)
Gateway
SS7 TCAP
ISUP/TCAP
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem7
至於 CSCF (Call Session Control Function) 主要是負責 Call Control 通話控制。MRF (Multimedia Resource Function)是作 Media Mixing, PlayAnnouncement,支援Multi-party Conferencing,類似 H.323裡面的MCU,Soft-switch 架構中的 Media Server 。
依此3GPP制定的架構來看 - 未來將是一個 All IP Core Network。
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem18
Circuit-Switched Services
RNC
Node B
Node B
MS
MS
T-SGW
PSTN
MSC Server
Legacy mobile
signaling network
HSS
MGWMGW
GMSC Server
R-SGW
MAP
MAP Mc
Nc
Nb
Iu_CS
(control part)
Mh
Gr
Iu_CS
(user traffic)
Mc
Signaling (SS7 or IP based)
Circuit
Packet (user traffic / signaling)
Call control function
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem19
備忘稿
All IP 架構中的 MSC Server 與舊有的 MSC 功能不盡相同。承襲了 MGCP/MEGACO 的概念,All IP 架構中將 MSC 的功能中的信令(signaling)以及媒體資料(media)分開成兩個元件:MSC Server 以及 MGW
(Media Gateway)。MSC Server 只處理信令的部份,利用 MGCP 或 MEGACO 來控制 MGW 來處理媒體資料的轉送。
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem20
Packet-Switched Services
RNC
Node B
Node B
MS
MS
SGSN InternetGGSN
HSS
Gi
Gr Gc
GnIu_PS
Gi
Signaling (SS7 or IP based)
Circuit
Packet (user traffic / signaling)
Call control function
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem21
Real-Time PS Services
RNC
Node B
Node B
MS
MS
SGSN InternetGGSN
Legacy mobile
signaling network
CSCFHSS
R-SGW
Gi
Mh
Gr Gc
Cx
Mm
Ms
GnIu_PS
GiMg
Gi
MrMRF
Signaling (SS7 or IP based)
Circuit
Packet (user traffic / signaling)
Call control function
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem22
Interworking with PSTN
RNC
Node B
Node B
MS
MS
SGSN
T-SGW
Internet
PSTN
GGSN
Legacy mobile
signaling network
CSCFHSS
MGW
R-SGW
McGi
Gi
Mh
Gr Gc
Cx
Mm
Ms
GnIu_PS
Gi
MGCF
Mg
Gi
MrMRF
Signaling (SS7 or IP based)
Circuit
Packet (user traffic / signaling)
Call control function
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem23
Home Subscriber Server
RNC
Node B
Node B
MS
MS
SGSN
T-SGW
Internet
PSTN
MSC Server
GGSN
Legacy mobile
signaling network
CSCFHSS
MGWMGW
GMSC Server
R-SGW
MAP
MAP Mc
McGi
Gi
Nc
Nb
Iu_CS
(control part)
Mh
Gr Gc
Cx
Mm
Ms
GnIu_PS
Iu_CS
(user traffic)
Gi
Mc
MGCF
Mg
Gi
MrMRF
Signaling (SS7 or IP based)
Circuit
Packet (user traffic / signaling)
Call control function
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem24
HSS (1/2)
HSS (Home Subscriber Server) is the master
database for a given user.
Functionalities
The HLR functionality required by the PS-Domain
The circuit switched part of the HLR
User control functions required by the IP
multimedia (IM) subsystem
HSS
MSC Server GMSC Server SGSN GGSN R-SGW CSCF
D C Gr Gc Mh Cx
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem25
Mobile Communication Networks 3GPP IP Multimedia Subsystem39
Outline
Softswitch
Softswitch Architecture
Softswitch Operations
3GPP All IP Network
Network Architecture
Network Entities
3GPP IMS CSCF
Entities Behavior
Message Flows
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem40
IP Multimedia Subsystem (1/2)
IP Multimedia (IM) CN subsystem
Comprising all CN elements for provision of
multimedia services.
The IM subsystem (IMS) utilizes the PS domain
to transport multimedia signaling and bearer
traffic.
The IMS attempts to be conformant to IETF
“Internet standards”.
SIP (Session Initiation Protocol) has been
selected as the interfaces between the IM CN
elements.
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem41
IP Multimedia Subsystem (2/2)
Internet3G/UMTS
App.Server
HSS
S-CSCF
GPRS
• Presence Server• OSA Gateway• ...
MRF
P-CSCF
I-CSCF
Visited Network External Network
Home Network
Signaling
Media
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem42
UE presence in IMS
Home Network
IM Subsystem
Visited Network
IM Subsystem
Inter-Network
IM Backbone
Internet
Intranets
UE
GGSN
BG
BG
SGSN
PDP Context
Visited Network
Gi
Virtual presence of UE
in visited network IM subsystem
(UE’s IP-address is here)
UE shall acquire the necessary IP address(es) as
part of the PDP context activation procedure(s)
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem43
Identification of IM Users
Private user identities
Assigned by the home network operator
Stored on USIM (UMTS Subscriber Identity Module)
Stored within the HSS (use for registration)
Contained in all registration requests passed from UE
to home network (for authentication)
Not used for routing of SIP messages
Public user identities
Every IM subscriber shall have one or more public
user identities.
The public user identity shall take the form of SIP
URL or E.164 number. (SIP URL for routing of SIP)
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem44
Call Session Control Function
The main function entity in 3G IM Subsystem
Behaves as SIP Proxy server
CSCFs may have different capabilities
Terminal and node behaviours should be
consistent, regardless of whether the user is
roaming
Three kinds of CSCFs defined
Proxy CSCF (P-CSCF)
Interrogating CSCF (I-CSCF)
Serving CSCF (S-CSCF)
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem45
Proxy CSCF
P-CSCF is the first contact point for the handset Its address is discovered by UEs following PDP
context activation procedure.
Behaving like a Proxy server
Also behaving as a User Agent in abnormal conditions
Functions
Forward SIP register request from the UE to I-CSCF
determined using the home domain name.
Forward SIP messages from the UE to the SIP server
(e.g. S-CSCF) whose name the P-CSCF has received as
a result of registration procedure.
Detect an emergency session and select a S-CSCF to
handle emergency sessions.
Authorization of bearer resources & QoS management.
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem46
Interrogating CSCF
I-CSCF is the contact point within an operator’s network for all connections destined to a subscriber of that network operator.
That is,I-CSCF is the first contact point within an
operator’s network for incoming call signaling.
Registration Assigning a Serving CSCF to a user performing SIP
registration
Session Flow Routing a SIP request received from the S-CSCF(Serving
Originating UE) towards the S-CSCF(Serving Terminating
UE)
Obtaining the S-CSCF address from HSS
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem47
I-CSCF(THIG)
Topology Hiding Inter-network Gateway
In the I-CSCF, the operator may use a Topology
Hiding Inter-network Gateway (THIG) function to
hide the configuration, capacity, and topology
of the network from the outside.
When an I-CSCF(THIG) is chosen to meet the
hiding requirement then for sessions traversing
across different operators domains, the I-
CSCF(THIG) may forward the SIP request or
response to another I-CSCF(THIG) allowing the
operators to maintain configuration
independence.
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem48
Serving CSCF
S-CSCF performs session control services for the UE
Maintaining a session state as needed by the
network operator for support of the services
Registration
As a Registrar, it accepts registration requests
and makes its information available through the
location server (e.g., HSS).
Session-related/-unrelated Flows
As a Proxy Server, it accepts requests & services
them internally or forwards them on.
As a User Agent, it may terminate & independently
generate SIP transactions.
Interaction with Service Platforms for support of
services
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem49
ENUM DNS Translation
The S-CSCF shall support the ability to
translate the E.164 address contained in a
request-URI in the non-SIP URL to SIP URL
Using ENUM DNS translation mechanism
RFC 2916
If the translation fails, then the session may
be routed to the PSTN or appropriate
notification shall be sent to the mobile.
Database aspects of ENUM are outside the
scope of 3GPP.
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Mobile Communication Networks 3GPP IP Multimedia Subsystem50
Registration Diagram
P-SCSF
S-CSCF
P-CSCF
GGSN
SGSN
Radio Access Network
GGSN
SGSN
Radio Access Network
I-CSCF
HSS
1. P-CSCF & GPRS within the same network.
2. Forward to I-CSCF by “home domain name.
3. User can register in the P-CSCF network ?
5. Request info about required S-CSCF cap. ?
4,6. Responses & Information.
7. Select S-CSCF.
8,9. Send S-CSCF to HSS for the subscriber.
10,11. Download user profile to access service.
12. Send Register info to Service Platform.
3,5 4,6
7
10,118,9 12
11
22
Home Network
Visited Network
App.
Server
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Mobile Communication Networks 3GPP IP Multimedia Subsystem51
Application Level Registration
I-CSCFP-CSCFUE HSS1. Register
S-CSCF
Visited/Home Network Home Network
2. Register3. Cx-Query
4. Cx-Query Resp.
5. Cx-Select-Pull
6. Cx-Select-Pull Resp.
7. Register
8. Cx-Put
9. Cx-Put-Resp.
10. Cx-Pull
11. Cx-Pull-Resp.
13. 200 OK
14. 200 OK15. 200 OK
12. Service Control
User can register in
the P-CSCF network ?
Request info about
required S-CSCF cap. ?
Send S-CSCF name to
HSS for the subscriber
Download user profile
to access service.
Store P-CSCF addressIf I-CSCF(THIG),
Encrypt S-CSCF
Send Register info
to Service Platform
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem52
Proxy-CSCF Discovery
1. PDP Context Activation
3. DNS - Query/Response
2. DHCP - Query/Response 2. DHCP -Relay
1. Activate PDP Context Request
3. Activate PDP Context Accept
1. Create PDP Context Request
3. Create PDP Context Response
DHCP server DNS serverUE GGSN
UE SGSN GGSN
2. Get IP address(es)
of P-CSCF(s)
Use of DHCP (Dynamic Host Configuration Protocol)
Transfer the P-CSCF address with the PDP
Context Activation signaling to the UE
GGSN acts as a DHCP Relay Agent
1.Create PDP context bearer ( TS 23.060)
2.UE requests a DHCP server
2a. P-CSCF domain name
2b. IP addresses of DNS servers
3. UE performs a DNS query
to retrieve P-CSCF(s) IP addresses
During PDP Context Activation signalling
1. UE indicates the request of P-CSCF
IP address(es) in PDP context request
1a. the indication forwarded to GGSN
2. GGSN gets IP-CSCF IP addresses
(internal configure, implement choice)
3. P-CSCF IP forwarded to UE
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem53
Call Setup Diagram
S-CSCF
P-CSCF
GGSN
SGSN
Radio Access Network
I-CSCF
HSS App.
Server
1
2
Originating Home Network
Visited/Home
Network
S-CSCFI-CSCF
HSS
4 5
6
Terminating Home Network
3
P-CSCF
GGSN
SGSN
Radio Access Network
8
7
App.
Server
Originating Terminating
Visited/Home
Network
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Mobile Communication Networks 3GPP IP Multimedia Subsystem54
Session Flow Procedures(1/2)
UE#1 S-CSCF#1 S-CSCF#2 UE#2
One of the S-CSCF to S-CSCF Invite
sequence information flows inserted
here
One of the MO Invite
Sequence information
flows inserted here
One of the MT Invite
Sequence information
flows inserted here
MO: Mobile Origination
MT: Mobile Termination
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Mobile Communication Networks 3GPP IP Multimedia Subsystem55
UE#1 S-CSCF#1 S-CSCF#2 UE#2
INVITE
Ringing
200 OK
ACK
SDP
Final SDP
Reserv Success
Session Flow Procedures(2/2)
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem56
CSCF Roles & Features
CSCF
P-CSCF(Proxy)
I-CSCF(Interrogating)
S-CSCF(Serving)
Behaving like Features/FunctionsRegister
Forward SIP register to I-CSCF by home domain name.
Session Flow
Forward SIP messages from UE to SIP server (S-CSCF)
as a result of registration procedure.
Detect an emergency session and select a S-CSCF to
handle emergency sessions.
Authorization of bearer resources & QoS management.
Proxy server
User Agent
(abnormal cases)
Proxy server
User Agent
(register reject)
Register
Assigning a Serving CSCF to the subscriber.
Session Flow
Routing a SIP request from another network towards
the S-CSCF(Serving Terminating UE)
Obtaining the S-CSCF address from HSS
Registrar
Proxy Server
User Agent
Register
As a Registrar, store registration info to HSS.
Session-related/unrelated Flow
S-CSCF performs session control services for the UE.
Interaction with Service Platforms.
Maintaining a session state as needed by the network
operator for support of the services.
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem57
IP Version Interworking
DNS
P-CSCF
IP-CAN
UEIPv6
S-CSCF I-CSCF
IMS-ALG
TrGW
IMS network
Mx
HSS
Ix
Mx
Other networkthat uses a different IP version
Signaling
Bearer
Note that the standardisation and functional requirements of Mx & Ix reference points are FFS.
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem58
IMS ALG & TrGW
IMS Application Level Gateway (ALG)
The IMS ALG needs to modify the SIP message bodies and
headers that have IP address association indicated.
The IMS ALG will request NA(P)T-PT to provide the bindings
data between the different IP addresses (IPv6 to IPv4 and
vice versa) upon session initiation, and will release the
bindings at session release.
The TrGW is a NA(P)T-PT
NAT-PT binds addresses in IPv6 network with addresses in
IPv4 network and vice versa
to provide transparent routing between the two IP domain
without requiring any changes to end points, like the UE.
IP-Connectivity Access Network:
that provides the underlying IP transport connectivity
between the UE and the IMS entities.
An example of an "IP-Connectivity Access Network" is GPRS.
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem59
Originating towards IPv4
UE(A) IP-CAN P-CSCF(A) S-CSCF(A) IMS-ALG TrGW User side(B)
2. S- CSCF
determines via DNS
query that the domain
of the terminating end
supports IPv4 only
1. Session Initiation
3. Link in the IMS-ALG and get
TrGW IPv4 addr/port information
for user (A)
.4.Session Initiation continues
5.5.5.Session signalling path
established
6. Media path established 6
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem60
Terminating from IPv4
UE(A) IP-CAN P-CSCF(A) S-CSCF(A)I-CSCF/IMS-ALG
TrGW User side(B)
2. IMS-ALG determines (viaDNS or preconfigured) theterminating I-CSCF and getsthe IPv6 addr/port for user(A) from TrGW & forwardsrequest to ICSCF so I-CSCF sees User (B) as IPv6
5.5.5.Session signalling path
established
6. Media path established 6
1. Session Initiation
3. Session
Initiation4. Session Initiation
National Chung Cheng University
Mobile Communication Networks 3GPP IP Multimedia Subsystem61
Useful Web Sites
International Packet Comm. Consortium
(IPCC) http://www.packetcomm.org/
International Softswitch Consortium(ISC)
IETF SIP & SIPPING Working Groups http://www.cs.columbia.edu/~hgs/sip/