3GPP and IMS
1
GPRS Operation and PDP Contexts




MS (mobile station)는 GPRS attach 절차로 SGSN에 알림.
Attach되면, Packet Data Protocol (PDP) context를 활성화시킴.
GPRS에서는 PDP Context Activate message에 있는 QoS profile과
자원의 가용도(availability)에 근거해서 admission control 을 수행함
PDP context:




PDP: Network layer protocol, is a virtual connection between the MS and
GGSN
Includes an identifier (e.g., IP), QoS parameters etc.
Establish a GPRS “tunnel” between GGSN and SGSN using GPRS
Tunneling Protocol (GTP)
QoS profile (to each PDP context) consists of:





QoS Profile은 QoS attribute (속성)의 집합임
Delay: acceptable transfer time from one edge of GPRS system to the other
edge
Service precedence: drop preference during network abnormalities
Reliability: tolerance for error rates and need for re-transmission
Mean throughput, peak throughput: specify average rate and maximum rate
2
PDP Contexts

PDP Context는 Parameter들의 집합으로, 단대단 접속을 설립하는데
필요한 모든 정보로 구성됨







PDP Type
PDP address type (IPv4 or IPv6)
QoS profile request (이용자가 요청하는 QoS parameters)
QoS profile negotiated (망과 협약된 QoS parameters )
Authentication type
DNS type
PDP Context Activate가 성공한 경우:


SGSN maps QoS profile into appropriate Radio Link Control (RLC)/Medium
Access Control (MAC) priority level to indicate the use in uplink access
SGSN also maps accepted QoS profile into an appropriate IP QoS
procedure (e.g., marking in Differentiated Services for QoS provisioning
over core networks
3
GPRS Attach Procedure
1
BTS
SCP
GMSC
BSC with PCU
PSTN
ISDN
BSS
3
4
HLR
AUC
2
3
Public ISP
1.
MS send a requests to the SGSN to be attached to the
network. Capabilities are stated multislot, ciphering
algorithms, CS and/or PS required
Corporate
RADIUS
2.
Authentication between terminal and HLR
3.
Subscriber data downloaded to MSC/VLR and SGSN
4.
SGSN notifies terminal that it is attached, enters
READY state
4
PDP Context Activation
aka “how is the connection set up?”
1
MT
BTS
SCP
GMSC
BSC with PCU
PSTN
ISDN
juniper.net
BSS
HLR
AUC
2
Juniper.net
1.
MS requests PDP context activation type, APN, QoS
2.
3.
SGSN validates request against subscription information
downloaded from HLR during GPRS Attach
APN sent to DNS, IP address(s) of suitable GGSNs returned
4.
Logical connection using GTP created between SGSN and GGSN.
5.
IP address allocated to Mobile via local pools, RADIUS or DHCP
- from operators own address range, or other
- fixed addresses held in HLR
- Proxy to RADIUS server in ISP or corporate domain
4
5
RADIUS
3
DNS
Public ISP
5
PDP Context Procedures

MS initiated
MS
BSS
Activate PDP Context Request
Activate PDP Context Accept

SGSN
GGSN
Create PDP Context
Request
Create PDP Context
Response
Packets from ext. nw.
GGSN initiated
PDU notification req.
PDU notification resp.
Request PDP Context activation
Activate PDP Context Request
Activate PDP Context Accept
Create PDP Context
Request
Create PDP Context
Response
6
PDP Context Activation
…
…
7
Transport of IP packets
IP tackets are tunnelled through the UMTS/GPRS network
(GTP – GPRS tunneling protocol)
User IP (v4 or v6)
UTRAN
Terminal
Radio Bearer
SGSN
GTP-U
Application
Server
GGSN
GTP-U
응용
IP
v4 or v6
IP
IP
v4 or v6v4 or v6
Relay
Relay
PDCP
PDCP GTP-U
GTP-U GTP-U
GTP-U
RLC
RLC
UDP/IP
v4 or v6
UDP/IP
v4 or v6
UDP/IP
v4 or v6
UDP/IP
v4 or v6
MAC
MAC
AAL5
AAL5
L2
L2
L2
L1
L1
ATM
ATM
L1
L1
L1
Uu
Iu-PS
Gn
[Source:
3GPP]
Gi
8
IP Transport: Concepts

PDP contexts activation






Access Point Names (APN)




APN은 외부망의 식별자 (logical Gi interface of GGSN)
PDP context activation 과정에서, SGSN은 DNS에 문의하여, 단말이 요청한 APN을
지원하는 GGSN을 찾아냄.
DNS 응답은 GGSN 주소 목록을 갖고 있으며, SGSN은 이들 중에서 라운드 로빈 방식에
의해 하나의 주소를 선택함.
Traffic Flow Templates (TFTs)



데이터 전송전에 UE에 의해서 수행됨
APN 사양과 traffic parameters
GGSN은 IP 주소를 UE에 전달
set-up of bearers in SGSN and GGSN
activation of multiple PDP contexts possible
A set of packet filters (source address, subnet mask, destination port range, source
port range, TOS (IPv4), Traffic Class (v6), Flow Label (v6)
GGSN이 사용하는 것으로서, 외부 망에서 입력되는 IP 패킷에 적절한 PDP context를
할당하는데 사용됨.
GPRS Tunnelling protocol (GTP)

모든 UE에 대해서, 신호를 위해서 한 개의 GTP-C tunnel이, 이용자 데이터 전송을
위해서 복수개의 GTP-U tunnels이 설립되는데, GTP-U는 PDP context (i.e.,
session)마다 하나임.
9
IP Transport: PDP Context & APNs
Same PDP (IP) address and APN
APN X
PDP Context X1 (APN X, IP address X, QoS1)
PDP Context X2 (APN X, IP address X, QoS2)
ISP Y
GGSN
PDP Context Y (APN Y, IP address Y, QoS)
APN Y
PDP Context selection
based on TFT (downstream)
PDP Context Z (APN Z, IP address Z, QoS)
APN Z
Terminal
SGSN
ISP X
GGSN
ISP Z
[Source:
3GPP]
10
QoS Framework in UMTS R5/R6
외부 IP QoS Domain
UMTS IP QoS Domain
Service Request
Authorization Token
Policy-based Framework
Service Provision with QoS
AF
Gq
PDF
Go
IP BS Manager
PDP QoS로 변환
UMTS BS
Iu BS
RAB
UTRAN
GERAN
RNC
GTP
Tunneling
Over IP
DiffServ or
ATM AAL5
Backbone BS
GTP
Tunneling
Over IP
DiffServ
IP QoS
Parameters
IP BS
Manager
QoS
Enforcement
Gate
Function
IP
Backbone
DiffServ망
11
3GPP Releases

Release '99



Release 4



1999년 12월에 제정완료
UTRA 정의 및 많은 초기 기능들이 정의됨.( 초기 3G의 기본이 됨)
2001년 3월에 제정. R99의 개선과 핵심망에서 제어평면과 이용자 평면이
분리됨.
low chip rate TDD mode (TD-SCDMA) 정의됨.
Release 5


2002.년 3월 제정
R4의 개선과 함께,
• IMS - IP-based Multimedia Services
• HSDPA - High Speed Downlink Packet Access

Release 6


2004년 제정
IMS의 2단계로서, 멀티미디어 통신을 위한 다양한 기능을 포함함.
12
3GPP 패킷도메인 진화 과정 요약
Release 4
Release 5
UAProf
UAProf
As
in Release 4
As
& WB (M)
AAC LC, LTP (O)
As
in Release 4
File Format (.3gp)
As
Capability
Exchange
NONE
Video
Codecs
H.263
Audio & Speech
Codecs
AMR-NB
Media
File Format
3GPP
Session
Establishment
RTSP
Data
Transport
RTP/RTCP
QoS
NONE
(only if network provied
QoS)
As
Rate
Control
NONE
Annex.G
P0L10 (M), P3L10
(O)
MPEG-4 VSP L0 (O)
MPEG-4
.amr
Release 6
(M)
SDP (M)
HTTP (O)
(M)
in Release 4
P0 L45 (O)
MPEG-4 VSP L 0b (0)
H.264 Full Baseline (O)
As in Release 4
AMR-WB+ or AACPlus (O)
H.263
in Release 4
ISO Base Format
Conformance (M)
Timed-text (O)
As
As
As
in Release 4
As
in Release 4
Progressive Download
(O)
in Release 4
(video only)
in Release 5
3GP file profiles (server, MMS, progr.
downloadable, generic)(O)
DRM (O)
Different
in Release 4
Alternatives in SDP
Metadata signalling in SDP (O)
MBMS - FLUTE (M)
Media
As
in Release 5
Download (M)
DRM (O)
SRTP(O)
Additional RTSP & SDP level signalling (O)
QoE Protocol (O)
RTCP extentions (O)
MBMS
As
in Release 5
Rate Adaptation (O)
3GPP
13
IMS에 의한 음성통신서비스 사례

비교 :R99인 경우 회선교환방식으로 음성제공
Uu
12.2kbps AMR speech

3.4kbps Signalling
IMS:
SF-128
Uu
UE
UTRAN
PS
PS
UTRAN
IMS
Domain
Domain
Session control Signaling (SIP / SDP)
UE
SF-??
Media ( RTP)
Real Time Media Control (RTCP)
RRC+NAS
Source: R2-032164
14
IMS의 음성통신 프로토콜 스택
AMR
SIP/SDP
RTP
RTCP1
UDP
UDP
UDP
IP
IP
IP
RAB/RB #1
PDCP-SAP
RAB/RB #2
RAB/RB #3
SRB#1
SRB#2
SRB#3
SRB#4
PDCP-SAP
PDCP Entity#1
ROHC
Comp
ROHC
Decomp
RLC UM
DTCH#1
MAC -D
DCH#1
PDCP Entity#2
ROHC
Comp
ROHC
Decomp
RLC UM
DTCH#2
MAC -D
DCH#2
PDCP
RLC AM
DTCH#3
MAC -D
DCH#3
RLC UM RLC AM RLC AM RLC AM
DCCH
MAC -D
DCH#4
Physical Layer
Source: R2-032166
15
R5 참조구조
R-SGW
?
Sh
HSS
SIP
IM-SSF
SIP
Dx
Sc
Gr
COPS
MAP
Sr
?
Gm
Gc
Go
SIP
SIP Mj
MGCF
Mg
Mc
Mp
MRF-C
T-SGW
H248
Mr
SIP
?
MRF-P
R-SGW
MGW
H248
GERAN
Uu
UTRAN
TCP
UDP
CS Domain
-orPSTN
-orLegacy
-orExternal
TCP/IP/UDP/RTP/…
Gn
TE
R
SIP
„Gi-Cloud“
GGSN
MT
Mi
Mw
CSCF
PCF
AS
UE
Mm
BGCF
?
SIP
CAP
SLF
Cx
OSA-SCS
SCP
SIP Mk
SIP
OSA
CAP
ISC
Others
Multimedia
IP
Networks
BGCF
CSCF
Diameter
?
HTTP
IM Subsystem
?
SIP
Applications
and
Services
SGSN
Iu
PS Domain
Alternative
Access Networks
16
3G Release 6
TS 23.221
BICC
RTP
or
AAL2
UDP/IP or AAL2
NodeB
Iu cs
Iu b
H.248
TDM
ATM
IP
Iu ps
USIM
Circuit switched
call control server
PSTN
IP/AAL5
IMS enhancements for conversational
Internet
Corporate
Multimedia Broadcast/Multicast Service
(MBMS) – conferencing etc
UMTS/GPRS - WLAN Interworking
Definition in R6, implementation sooner
Service charging
enhancements
SIP IP Multimedia
CSCF
17
Establishing IP-CAN for IMS Signalling
GPRS Attach
PDP Context Activation
Local P-CSCF Discovery
Application Level Registration
Ready for Internet Access
and SIP signalling
- UE GGSN link setup
- UE’s IP address allocation
Find a local SIP server
User-network authentication
and location registration
Ready for IMS Session
18
Local CSCF (P-CSCF) Discovery
DHCP/DNS Procedure
visit1.net
5555::aaa:bbb:ccc:ddd
DNS
Server
DHCP
Server
PDP Context Activation Procedure
DHCP query
pcscf.visit1.net, IP addr of DNS
???
P-CSCF
pcscf1.visited1.net
UDP port 5060
5555::aba:dab:aaa:daa
pcscf.visit1.net NAPTR ?
_sip._udp.pcscf.visit1.net
_sip._udp.pcscf.visit1.net SRV ?
pcscf1.visited1.net , port 5060, 5555::aba:dab:aaa:daa
19
Local CSCF (P-CSCF) Discovery
DHCP Procedure with DHCPv6 options for SIP servers
visit1.net
5555::aaa:bbb:ccc:ddd
DHCPv6 options
for SIP Servers
DHCP
Server
PDP Context Activation Procedure
DHCP query
P-CSCFs IP address list
20
Local CSCF (P-CSCF) Discovery
GPRS Procedure
5555::aaa:bbb:ccc:ddd
Activate PDP Context Request
visit1.net
Create PDP Context Request
Obtain IP addresses
of P-CSCF
Create PDP Context Response
Activate PDP Context Reponse
21
AKA: Authentication and Key Agreement
SN
UE
HE
VLR/SGSN
HLR/AuC
Authentication data request
MAP Request
Parameter{IMSI or TMSI/P-TMSI}
Generate
Authentciation
vectors on the
AuC side
Distribution of
authentication vectors
from HE to SN
Authentication data response
MAP Response
Parameter AV[1..n] = {RAND, AUTN, XRES, CK, IK}
Store Authentication
vectors AV[1..n]
Select one Authentication
vector AV[i]
User Authentication request
Authentication Request
Parameter {RAND, AUTN}
Verify AUTN (MAC = XMAC)
and generate RES, CK & IK
Authentication and
Key establishment
User Authentication response
Authentication Response
Parameter {RES}
Compare RES (from UE) with XRES
(from AV vector) and select CK & IK
22
Application Level (SIP) Registration Procedure
Initial Registration
Home Network
S-CSCF scscf1.home1.net
HSS
Query:
Public User Identity
Private User Identity
Visited Network Identifier
Response:
S-CSCF list
icscf1_p.home1.net
I-CSCF
pcscf1.visit1.net
P-CSCF discovery
(pcscf1.visited1.net
UDP port 5060
5555::aba:dab:aaa:daa )
UE#1
DNS
Server
DNS:
P-CSCF
PDP Context
user1_public1@home1.net visit1.net
user1_private1@home1.net
Visited Network
5555::aaa:bbb:ccc:ddd
REGISTER sip:scscf1.home1.net SIP/2.0
Via: SIP/2.0/UDP icscf1_p.home1.net;
SIP/2.0/UDP pcscf1.visit1.net;
SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]
Path: <sip:term@pcscf1.visit1.net;lr>
REGISTER sip:registrar.home1.net SIP/2.0
home1.net
Via: SIP/2.0/UDP pcscf1.visited1.net;
SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd
Path: <sip:term@pcscf1.visit1.net;lr>
REGISTER sip:registrar.home1.net SIP/2.0
Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd];
From: <sip:user1_public1@home1.net>;tag=4fa3
To: <sip:user1_public1@home1.net>
Contact: <sip:[5555::aaa:bbb:ccc:ddd];comp=sigcomp>;expires=6000
00
Authorization: Digest username="user1_private@home1.net", realm=
"registrar.home1.net", nonce="", uri="sip:registrar.home1.net", respon
se=""
Security-Client: ipsec-3gpp; alg=hmac-sha-1-96; spi-c=23456789; spi
-s=12345678; port-c=2468; port-s=1357
Require: sec-agree
Proxy-Require: sec-agree
23
Application Level (SIP) Registration Procedure
Challenge
Home Network
AV selection
SIP/2.0 401 Unauthorized
Cx:
HSS
From: <sip:user1_public1@home1.net>;tag=4fa3
authentication S-CSCF scscf1.home1.net
To: <sip:user1_public1@home1.net>; tag=5ef4
Querry:
Public User Identity
Private User Identity
S-CSCF name
Response:
AV list
AV=RAND | AUTN | XRES | CK | IK icscf1_p.home1.net
I-CSCF
Call-ID: apb03a0s09dkjdfglkj49111
WWW-Authenticate: Digest realm="registrar.home1.net", non
ce=base64(RAND + AUTN + server specific data), algorithm=
AKAv1-MD5, ik="00112233445566778899aabbccddeeff", ck=
"ffeeddccbbaa11223344556677889900"
home1.net
pcscf1.visit1.net
DNS
Server
UE#1
P-CSCF
PDP Context
SIP/2.0 401 Unauthorized
WWW-Authenticate: Digest realm="registrar.home1.net", non
ce=base64(RAND + AUTN + server specific data), algorithm=
AKAv1-MD5
Security-Server: ipsec-3gpp; q=0.1; alg=hmac-sha-1-96; spi-c
=98765432; spi-s=87654321; port-c=8642; port-s=7531
user1_public1@home1.net visit1.net
user1_private1@home1.net
Visited Network
5555::aaa:bbb:ccc:ddd
24
Application Level (SIP) Registration Procedure
Registration with Response (Integrity Protected)
Home Network
Querry:
Public User Identity
Private User Identity
S-CSCF name
Response:
User Profile
Query:
Public User Identity
Private User Identity
Visited Network Identifier
Response:
S-CSCF list
Authentication
Authorization: Digest username="user1_private@home1.net",
Cx:
realm="registrar.home1.net", nonce=base64(RAND + AUTN +
HSS
scscf1.home1.net
server specific data), algorithm=AKAv1-MD5,
S-CSCF
Reg. notification
uri="sip:registrar.home1.net",
response="6629fae49393a05397450978507c4ef1", integrityprotected="yes"
icscf1_p.home1.net
I-CSCF
pcscf1.visit1.net
DNS
Server
DNS:
P-CSCF
Generation of Response
and Session Key
UE#1
REGISTER sip:scscf1.home1.net SIP/2.0
PDP Context
user1_public1@home1.net visit1.net
user1_private1@home1.net
Visited Network
5555::aaa:bbb:ccc:ddd
home1.net
REGISTER sip:registrar.home1.net SIP/2.0
REGISTER sip:registrar.home1.net SIP/2.0
Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd];
From: <sip:user1_public1@home1.net>;tag=4fa3
To: <sip:user1_public1@home1.net>
Contact: <sip:[5555::aaa:bbb:ccc:ddd];comp=sigcomp>;expires=600000
Authorization: Digest username="user1_private@home1.net", realm="regi
strar.home1.net", nonce=base64(RAND + AUTN + server specific data), a
lgorithm=AKAv1-MD5, uri="sip:registrar.home1.net", response="6629fae4
9393a05397450978507c4ef1"
Security-Client: ipsec-3gpp; alg=hmac-sha-1-96; spi-c=23456789; spi-s=1
2345678; port-c=2468; port-s=1357
Security-Verify: ipsec-3gpp; q=0.1; alg=hmac-sha-1-96; spi-c=98765432;
spi-s=87654321; port-c=8642; port-s=7531
Require: sec-agree
Proxy-Require: sec-agree
25
Application Level (SIP) Registration Procedure
200 OK response
Home Network
SIP/2.0 200 OK
Via: SIP/2.0/UDP icscf1_p.home1.net;
S-CSCF scscf1.home1.net
SIP/2.0/UDP pcscf1.visited1.net;
HSS
icscf1_p.home1.net
I-CSCF
SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]:1357
Path: <sip:icscf1_p.home1.net;lr>, <sip:term@pcscf1.visited1.
net;lr>
Service-Route: <sip:icscf1_p.home1.net;lr>, <sip:orig@scscf1.
home1.net;lr>
P-Associated-URI: <sip:user1_public2@home1.net>, <sip:user
home1.net
1_public3@home1.net>, <sip:+1-212-555-1111@home1.net;u
ser=phone>
pcscf1.visit1.net
DNS
Server
UE#1
P-CSCF
PDP Context
SIP/2.0 200 OK
Via: SIP/2.0/UDP pcscf1.visited1.net;
SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]:1357
Service-Route: <sip:icscf1_p.home1.net;lr>, <sip:token(orig@scs
cf1.home1.net;lr)@home1.net;tokenized-by=home1.net>
user1_public1@home1.net visit1.net
user1_private1@home1.net
Visited Network
5555::aaa:bbb:ccc:ddd
26
Assigning CSCF for a User

Criteria for assigning a S-CSCF for a User







Required capabilities for user services (provided by the HSS)
Operator preference on a per-user basis (provided by the HSS)
Capabilities of individual S-CSCFs in the home network (internal information)
Topological (i.e. P-CSCF) information of where the user is located (internal
information)
Topological information of where the S-CSCF is located
(internal information)
Availability of S-CSCFs (internal information)
Assignment of I-CSCF

DNS-based mechanism
27
IMS Session Setup: 1. Initial SDP Offer
Originating Home Network
AS
Terminating Home Network
HSS
Location
Query/Response
Service control
S-CSCF
I-CSCF
I-CSCF
home1.net
Service control
I-CSCF
S-CSCF
home2.net
I-CSCF
INVITE
sip:[5555::eee:fff:aaa:bbb]:8805
INVITE sip:user2_public1@home2.net
Require: precondition, sec-agree
Video codec H.263 or MPEG-4
Audio codec AMR
AS
P-CSCF
P-CSCF
(pcscf1.visited1.net
UDP port 5060
5555::aba:dab:aaa:daa )
UE#1
visit1.net
user1_public1@home1.net
Originating Visited Network
user1_private1@home1.net
5555::aaa:bbb:ccc:ddd
visit2.net
user2_public1
@home2.net
5555::eee:fff:aaa:bbb
UE#2
Terminating Visited Network
28
IMS Session Setup: 2. Offer Response
Originating Home Network
AS
S-CSCF
I-CSCF
I-CSCF
home1.net
visit1.net
P-CSCF
Authorize
QoS Resources
Terminating Home Network
HSS
AS
I-CSCF
S-CSCF
home2.net
I-CSCF
Authorizevisit2.net
P-CSCF QoS Resources
183 Session Progress
Video codec H.263 or MPEG-4
Audio codec AMR
UE#1
UE#2
Originating Visited Network
Terminating Visited Network
29
IMS Session Setup: 3. Response Conf (Opt SDP)
Originating Home Network
Terminating Home Network
AS
S-CSCF
I-CSCF
I-CSCF
home1.net
HSS
AS
I-CSCF
S-CSCF
home2.net
I-CSCF
PRACK sip:user2_public1@home2.net
Video codec H.263
Audio codec AMR
visit1.net
GPRS: Activate
PDP Context accept
UE#1
GPRS: Activate
PDP Context
P-CSCF
COPS:RPT
GPRS: Create
PDP response
P-CSCF
visit2.net
COPS: REQ
COPS:DEC
Resource
Reservation
Originating Visited Network
GPRS: Create
PDP Context
UE#2
Terminating Visited Network
30
IMS Session Setup: 4. Conf ACK (Opt SDP)
Originating Visited Network
Terminating Home Network
AS
S-CSCF
I-CSCF
visit1.net
I-CSCF
home1.net
P-CSCF
HSS
AS
I-CSCF
S-CSCF
home2.net
I-CSCF
P-CSCF
COPS:RPT
Secondary PDP Context
UE#1
Originating Visited Network
COPS: REQ
COPS:DEC
GPRS: Create
PDP response
visit2.net
200 OK (PRACK)
GPRS: Activate
PDP Context accept
Resource GPRS: Create GPRS: Activate
PDP Context
PDP Context
Reservation
Terminating Visited Network
UE#2
31
IMS Session Setup: 5. Reservation Conf
Originating Home Network
AS
S-CSCF
I-CSCF
I-CSCF
home1.net
visit1.net
P-CSCF
Terminating Home Network
HSS
AS
I-CSCF
S-CSCF
home2.net
I-CSCF
P-CSCF
visit2.net
Alert
User
UPDATE
Secondary PDP Context
Secondary PDP Context
UE#1
UE#2
Originating Visited Network
Terminating Visited Network
32
IMS Session Setup: 6. Reservation Conf
Originating Home Network
AS
S-CSCF
I-CSCF
I-CSCF
home1.net
visit1.net
P-CSCF
Terminating Home Network
HSS
AS
I-CSCF
S-CSCF
home2.net
I-CSCF
P-CSCF
visit2.net
200 OK (UPDATE)
Secondary PDP Context
Secondary PDP Context
UE#1
UE#2
Originating Visited Network
Terminating Visited Network
33
IMS Session Setup: 7. Ringing
Originating Home Network
AS
S-CSCF
I-CSCF
I-CSCF
home1.net
visit1.net
P-CSCF
Alert
User
Terminating Home Network
HSS
AS
I-CSCF
S-CSCF
home2.net
I-CSCF
P-CSCF
visit2.net
180 Ringing
Secondary PDP Context
Secondary PDP Context
UE#1
UE#2
Originating Visited Network
Terminating Visited Network
34
IMS Session Setup: 8. 200 OK (INVITE)
Originating Home Network
Terminating Home Network
AS
S-CSCF
I-CSCF
I-CSCF
home1.net
visit1.net
Start
Media
P-CSCF
COPS:RPT
Secondary PDP Context
UE#1
HSS
AS
I-CSCF
S-CSCF
home2.net
I-CSCF
P-CSCF
COPS: DEC
(Open gate)
Approval of
QoS Commit
Originating Visited Network
COPS:RPT
COPS: DEC
(Open gate)
visit2.net
200 OK
Secondary PDP Context
Approval of
QoS Commit
Terminating Visited Network
Start
Media
UE#2
35
IMS Session Setup: 9. ACK
Originating Home Network
AS
S-CSCF
I-CSCF
I-CSCF
home1.net
visit1.net
P-CSCF
Terminating Home Network
HSS
AS
I-CSCF
S-CSCF
home2.net
I-CSCF
P-CSCF
visit2.net
ACK
UE#1
UE#2
Originating Visited Network
Terminating Visited Network
36