2. Registration to the network
UE IMS
GSN
1. Bearer Level Registration: GPRS
2. PDP Context Activation
HLR
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2. PDP Context Activation
3. CSCF Discovery
4. Application Level Registration
3. The I-CSCF finds the
S-CSCF allocated to
this user or selects a
new S-CSCF for this
user.
I-CSCF
The I-CSCF contacts
the HSS to find the S-
CSCF serving this
subscriber.
I-CSCF
The S-CSCF
challenges the
subscriber
S-CSCF
The P-CSCF finds the
I-CSCF with the help
of DNS
P-CSCF
The S-CSCF
downloads the
authentication vector
for this subscriber
from the HSS
S-CSCF
A UE initiates a SIP
Registration including
his public user ID and
his private user ID
Subscriber
S-CSCF
Home A
I-CSCF
5. REGISTER
8. Unauthorized
SIP-AS
Application level Registration (I)
HSS
3 4
6
7
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2. REGISTER 9. Unauthorized
P-CSCF
Visited A
10. Unauthorized
1. REGISTER
8. Unauthorized
A
GGSN
SGSN
Radio Access Network
4. The I-CSCF contacts
the HSS to find the S-
CSCF serving this
subscriber.
I-CSCF
The S-CSCF
authorizes the
registration and
informs the subscriber
S-CSCF
The S-CSCF informs
the HSS that this S-
CSCF is serving the
subscriber. The HSS
sends the S-CSCF the
service profile
S-CSCF
The S-CSCF informs
the other Application
Servers about the
user's registration
S-CSCF
The I-CSCF finds the
S-CSCF allocated to
this user
I-CSCF
The P-CSCF finds the
I-CSCF with the help
of DNS
P-CSCF
The UE calculates the
credentials and
re- initiates the SIP
Registration
Subscriber
S-CSCF
Home A
I-CSCF
15. REGISTER
20. OK
SIP-AS
Application level Registration (II)
HSS
13 14
16
17
18. REGISTER
19. OK
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12. REGISTER 21. OK
P-CSCF
Visited A
22. OK
11. REGISTER
20. OK
A
GGSN
SGSN
Radio Access Network
5. The I-CSCF fetches
from the HSS the
address of the S-CSCF
that is serving
subscriber B
I-CSCF
The I-CSCF routes the
message to the
originating S-CSCF
I-CSCF
The P-CSCF is the first
point of contact in the
IMS for the subscriber.
It forwards the INVITE
request to the I-CSCF
P-CSCF
The S-CSCF in Home
B performs service
invocation for
subscriber B. It
forwards the INVITE
to the P-CSCF and UE
S-CSCF
The S-CSCF in Home
A performs service
invocation for
subscriber A. The S-
CSCF finds the entry
point in Home B
S-CSCF
The HSS returns the
address of the S-CSCF
serving subscriber B
HSS
Subscriber A initiates
a SIP invitation
including the SIP URI
of subscriber B.
Subscriber
S-CSCF
Home A
13. OK
S-CSCF
Home B
I-CSCF
7. INVITE
12. OK
4. INVITE
I-CSCF
3. INVITE
14. OK
5 6
HSS SIP-AS
Session Establishment
SIP-AS
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P-CSSF
Visited B
1. INVITE
2. INVITE 8. INVITE
11. OK
13. OK
15. OK
P-CSCF
Visited A
16. OK
12. OK
14. OK
A Calls B
B
A
9. INVITE
10. OK
GGSN
SGSN
Radio Access Network
GGSN
SGSN
Radio Access Network
6. The MG performs the
bearer interworking
between RTP/IP and
the bearer used in
the PSTN network
MG
Subscriber A initiates
a SIP invitation
including the E.164
number of
subscriber B.
Subscriber
The S-CSCF detects:
No SIP URL assigned
to the E.164 number.
The call is routed to
a home BGCF.
S-CSCF.
The S-CSCF queries
the DNS for the tel
URL. DNS returns a
negative match.
S-CSCF/DNS
11. IAM
The BGCF selects
the MGCF in the
breakout network
BGCF
S-CSCF
Home A
14. OK
MGCF
BGCF
8. INVITE
6. INVITE
I-CSCF
3. INVITE
12. ANM
IMS Gateway
IMS-CS interworking
DNS
4
5
BGCF
7. INVITE
15. OK
The home BGCF
selects another
BGCF, perhaps in
another network
BGCF
The MGCF performs
the signalling
interworking between
SIP and the
BICC/ISUP in PSTN
MGCF
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1. INVITE
2. INVITE 9. ADD 10. RESP
17. OK
P-CSCF
Visited A
18. OK
13. OK
16. OK
A Calls B (CS Subscriber)
A
GGSN
SGSN
Radio Access Network
MG
12. ANM
7. Call flows:
Mobile
origination
1. INVITE
3. INVITE
UE#1 P-CSCF S-CSCF
8. 183 Session
Progress
11. 183 Session
Progress
12. PRACK
6. INVITE
9.183 Session
Progress
5. Evaluation of Initial
Filter Criterias
2. 100 Trying
4. 100 Trying
7. 100 Trying
Visited Network Home Network
10. Authorize QoS resources
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27. 180 Ringing
12. PRACK
16. 200 OK
25. 180 Ringing
28. PRACK
31. 200 OK
35. 200 OK
37. 200 OK
19. UPDATE
22. 200 OK
38. ACK
26. 180 Ringing
34. 200 OK
13. Resource
Reservation 14. PRACK 15. PRACK
17. 200 OK
18. 200 OK
20. UPDATE
21. UPDATE
23. 200 OK
24. 200 OK
29. PRACK 30. PRACK
32. 200 OK
33. 200 OK
39. ACK
40. ACK
36. Approval of QoS commit
8. Call flows:
Network-to-
Network 4. INVITE
S-CSCF#1 S-CSCF#2
13. 183 Session
I-CSCF HSS
7 INVITE
1. INVITE
10. INVITE
12. 183 Session
Home Network#2
Originating Network Terminating Network
2. 100 Trying
8. 100 Trying
11. 100 Trying
5. 100 Trying
3. Evaluation of
initial filte criterias
9. Evaluation of
nitial filtr criterias
Home Network#1
6. Cx: User location query
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29. 180 Ringing
13. 183 Session
Progress
16. PRACK
19. 200 OK
32 PRACK
35. 200 OK
39. 200 OK
22. UPDATE
25. 200 OK
42. ACK
14. 183 Session
Progress
15. 183 Session
Progress
12. 183 Session
Progress
28. 180 Ringing
31. 180 Ringing
38. 200 OK
41. 200 OK
30. 180 Ringing
40. 200 OK
17. PRACK 18. PRACK
20. 200 OK
21. 200 OK
23. UPDATE
24. UPDATE
26. 200 OK
27. 200 OK
33. PRACK 34. PRACK
36. 200 OK
37. 200 OK
43. ACK
44. ACK
9. Call Flows:
Mobile
terminating 4. INVITE
S-CSCF P-CSCF
7. 100 Trying
10. 183 Session
Progress
12. PRACK
UE#2
6. INVITE
1. INVITE
11. 183 Session
Progress
3. Evaluation of initial
filter criterias
2. 100 Trying
5. 100 Trying
8. 183 Session
Progress
13. PRACK 14. PRACK
Home Network Visited Network
9. Authorize QoS Resources
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25. 180 Ringing
26. 180 Ringing
17. 200 OK
28. PRACK
31. 200 OK
34. 200 OK
36. 200 OK
19. UPDATE
38. ACK
27. 180 Ringing
37. 200 OK
18. Resource
Reservation
15. 200 OK
16. 200 OK
21. UPDATE
22. 200 OK
24. 200 OK
29. PRACK
30. PRACK
32. 200 OK
33. 200 OK
39. ACK
40. ACK
20. UPDATE
23. 200 OK
35. Approval of QoS commit
10. The Filter Criteria
• Collection of triggers for a particular public user identity
• It defines the application servers to contact on a per session basis
– Only applicable to SIP request that create a dialog (e.g., INVITE,
SUBSCRIBE) or standalone requests (e.g., REGISTER, OPTIONS)
• Downloaded at user's registration time.
• Example of Filter Criteria semantics:
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• Example of Filter Criteria semantics:
– For terminating INVITE attempts
– To public user ID sip:user1@home1.net
– When the From or P-Asserted-Identity header is set to
sip:user1s_mother@home1.net
– Action: send the signalling to application server sip:users_mother@as33.home1.net
• When as33.home1.net receives the INVITE addressed to
sip:user1@home1.net, if the current time is between 9 and 17, it invokes the
answering machine with a personalized service to the user's mother.
Otherwise, it progresses the session to the final user
11. The Filter Criteria (2)
IMS Subscriber Profile
Subscriber Service Profile
Filter Criteria 1
-SIP Application server Address (SIP URI)
-Filter rule
-Priority
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-Priority
-Default Handling
-Service Information
Filter Criteria 2
Filter Criteria n
…
12. The S-CSCF evaluates the
Filter Criteria for
sip:user1@home1.net
S-CSCF
The Filter Criteria
indicates:
- INVITE requests
- Coming from mom
- Forward to AS 33
Filter Criteria
The S-CSCF forwards the
INVITE request to AS33
S-CSCF
As the time is 11:00, the
AS terminates the INVITE
and answers with a 200
OK response
AS
The S-CSCF forwards the
200 OK response
S-CSCF
AS plays the personalized
message for the user's
mom. The session is
established
AS
Involvement of Application Servers
The S-CSCF receives an
INVITE addressed to
sip:user1@home1.net
S-CSCF
AS 33
2. INVITE
INVITE sip:user1@home1.net SIP/2.0
3. OK
AS 38
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S-CSCF
1. INVITE
INVITE sip:user1@home1.net SIP/2.0
From: sip:users_mom@home1.net
To: sip:user1@home1.net
From: sip:users_mom@home1.net
To: sip:user1@home1.net
Route: sip:users_mom@as33.home1.net,
sip:scsf1.home1.net
13. The S-CSCF evaluates the
Filter Criteria for
sip:user1@home1.net
S-CSCF
The Filter Criteria
indicates:
- INVITE requests
- Coming from mom
- Forward to AS 33
Filter Criteria
The S-CSCF forwards the
INVITE request to AS33
S-CSCF
AS, acting as a SIP proxy,
forwards the SIP INVITE
again to the S-CSCF
AS 33
The S-CSCF receives an
INVITE addressed to
sip:user1@home1.net
S-CSCF
The evaluates again the
filter criteria, search for
other possible application
servers interested in
receiving the signalling
S-CSCF
The S-CSCF forwards the
INVITE to AS 38
S-CSCF
AS 38 applies a Call
Forwarding Service. It re-
writes the Request-URI in
the INVITE request and
forwards it to the S-CSCF
AS 38
As the time is 19:00, the
AS is not interesting in
executing the service
AS 33
The S-CSCF forwards the
INVITE to the destination
S-CSCF
INVITE sip:user1@home1.net SIP/2.0
Involvement of Application Servers (2)
AS 33
2. INVITE
INVITE sip:user1@home1.net SIP/2.0
3. INVITE
AS 38
4. INVITE 5. INVITE
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From: sip:users_mom@home1.net
To: sip:user1@home1.net
Route: sip:scscf1.home1.net
S-CSCF
1. INVITE
INVITE sip:user1@home1.net SIP/2.0
From: sip:users_mom@home1.net
To: sip:user1@home1.net
From: sip:users_mom@home1.net
To: sip:user1@home1.net
Route: sip:users_mom@as33.home1.net,
sip:scscf1.home1.net
4. INVITE 5. INVITE
6. INVITE
INVITE sip:user44@home33.net SIP/2.0
From: sip:users_mom@home1.net
To: sip:user1@home1.net
Route: sip:scscf1.home1.net
