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Content for TR 23.812 Word version: 11.0.0

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4 Analysis of IMS architecture p. 9

4.1 Session setup efficiency p. 9

4.1.1 Problems description p. 9

4.1.2 Summary p. 9

4.2 Load Balancing p. 9

4.2.1 Problems description p. 9

4.2.1.1 General p. 9

4.2.1.2 Analysis of P-CSCF Load Balancing p. 9

4.2.1.3 Analysis of S-CSCF Load Balancing p. 10

4.2.1.4 Analysis of SLF Load Balancing p. 10

4.2.1.5 Analysis of HSS Load Balancing p. 10

4.2.1.6 Analysis of I-CSCF Load Balancing p. 10

4.3 Recovery and Load Balancing p. 10

4.3.1 Problems description p. 10

4.3.1.1 General p. 10

4.3.1.2 Analysis of current entity-level redundancy/restoration mechanism p. 10

4.3.1.3 Analysis of current system-level reselection/restoration mechanism p. 10

4.3.2 Summary p. 11

4.4 Scalability p. 11

4.4.1 Problems description p. 11

4.4.2 Summary p. 11

5 Applicability of Overload Control and Load Balancing p. 11

5.1 Overload Control p. 11

5.1.1 Overload Control at the UNI p. 11

5.1.1.1 P-CSCF overload control p. 11

5.1.2 Overload Control at the NNI p. 12

5.1.3 Overload Control of Application Servers p. 12

5.1.4 S-CSCF overload control p. 12

5.2 Load Balancing p. 12

5.2.0 General p. 12

5.2.1 P-CSCF Load Balancing p. 12

5.2.2 S-CSCF Load Balancing p. 12

5.2.3 Applicability of P/S-CSCF Load Balancing based on periodic monitoring to massive restart of UEs p. 12

5.2.4 AS Load Balancing p. 14

6 Architecture alternatives p. 14

6.1 Architecture alternatives for Load Balancing p. 14

6.1.1 Load Balancing based on Load Detection Function p. 14

6.1.1.1 Load Detection Function (LDF) p. 14

6.1.1.1.1 General p. 14

6.1.1.1.2 Alternative 1 for LDF architecture p. 15

6.1.1.1.3 Alternative 2 for LDF architecture p. 15

6.1.1.1.4 Alternative 3 for LDF architecture p. 16

6.1.1.1.5 Alternative 4 for LDF architecture p. 17

6.1.1.2 P-CSCF Load Balancing with LDF p. 17

6.1.1.2.1 General p. 17

6.1.1.2.2 Information flow p. 18

6.1.1.3 S-CSCF Load Balancing during initial registration p. 18

6.1.1.3.1 General p. 18

6.1.1.3.2 Information flow p. 19

6.1.1.4 S-CSCF Load Balancing during re-registration p. 20

6.1.1.5 Load Balancing during S-CSCF restoration p. 21

6.1.1.5.1 General p. 21

6.1.1.5.2 Load Balancing during S-CSCF restoration (originating procedure) p. 21

6.1.1.5.3 Load Balancing during S-CSCF restoration (terminating procedure) p. 23

6.1.2 S-CSCF Load Balancing at Initial Registration based on HSS p. 24

6.1.3 Load balancing using IETF SOC Overload Control p. 24

6.1.4 Load Balancing based on dynamic DNS p. 25

6.1.4.1 Introduction p. 25

6.1.4.2 Method 1 Dynamic DNS p. 25

6.1.4.3 Method 2: Zone transfer p. 26

6.1.4.4 Method 3: SRV DNS resolution requests p. 27

6.1.5 Registration independent Serving Node Load Balancing based on HSS p. 28

6.1.5.1 General p. 28

6.1.5.2 Information flow for registration independent Serving Node Load Balancing by I-CSCF p. 29

6.2 Architecture alternatives for Overload Control p. 30

6.2.1 P-CSCF Overload Control p. 30

6.2.1.1 P-CSCF redirects to another P-CSCF p. 30

6.2.1.1.1 Description p. 30

6.2.1.1.2 Information flow p. 30

6.2.1.1.3 Co-existence with earlier releases p. 31

6.2.1.2 Using DNS to select another P-CSCF p. 31

6.2.1.2.1 Description p. 31

6.2.1.2.2 Information flow p. 31

6.2.1.3 P-CSCF Overload Control based on LDF p. 32

6.2.1.3.1 General p. 32

6.2.1.3.2 Information flow p. 32

6.2.1.4 UE selects another P-CSCF upon negative response from P-CSCF p. 33

6.2.1.4.1 General p. 33

6.2.1.4.2 During Initial Registration Procedure p. 33

6.2.1.4.3 During Re-Registration Procedure p. 33

6.2.2 S-CSCF Overload Control p. 34

6.2.2.1 S-CSCF Overload Control based on LDF p. 34

6.2.2.1.1 General p. 34

6.2.2.1.2 Information flow p. 35

6.2.3 Overload Control based on GOCAP p. 35

6.2.3.1 Overview p. 35

6.2.3.2 Applicability to the IMS p. 36

6.2.4 Overload Control based on IETF SOC WG solution as described in draft-ietf-soc-overload-control-01 p. 36

6.2.4.1 General p. 36

6.2.4.2 Applicability to the IMS p. 37

6.2.4.3 Example Information flow p. 38

6.2.5 Overload Control based on IETF SOC WG solution as described in draft-ietf-soc-load-control-event-package p. 38

6.2.5.1 General p. 38

6.2.5.2 Applicability to the IMS p. 39

6.2.5.3 Example Information flow p. 40

6.2.6 High Level Summary p. 40

6.3 S-CSCF re-selection p. 41

6.3.1 Architectural alternatives to detect whether S-CSCF re-selection may be desired p. 41

6.3.1.1 General p. 41

6.3.1.2 Detection mechanism 1 p. 41

6.3.1.2.1 Architectural details p. 41

6.3.1.2.2 Information flow p. 42

6.3.1.3 Detection mechanism 2 p. 42

6.3.1.3.1 Architectural details p. 42

6.3.1.3.2 Information flow p. 43

6.3.1.4 Detection mechanism 3 p. 43

6.3.1.4.1 Architectural details p. 43

6.3.1.4.2 Information flow (preparation step) p. 44

6.3.1.4.3 Information flow (actual detection step) p. 45

6.3.1.5 Detection Mechanism 4 p. 45

6.3.2 Alternatives to re-select the S-CSCF p. 45

6.3.2.1 General p. 45

6.3.2.2 Re-Selection mechanism 1 p. 46

6.3.2.3 Re-Selection mechanism 2 p. 47

6.3.2.4 Re-Selection mechanism 3 p. 49

7 Assessment p. 49

7.1 Assessment of alternatives for Overload Control p. 49

7.1.1 P-CSCF Overload Control p. 49

7.1.2 S-CSCF Overload Control during initial registration p. 50

7.1.3 S-CSCF reselection during re-registration p. 51

7.1.4 Exchange of Overload Control Information between IMS entities p. 53

7.2 Assessment of alternatives for Load Balancing p. 53

7.2.1 P-CSCF Load Balancing p. 53

7.2.2 S-CSCF Load Balancing p. 54

7.2.2.1 S-CSCF selection during initial registration p. 54

7.2.2.2 S-CSCF re-selection during re-registration p. 55

7.2.2.3 S-CSCF Load Balancing during restoration p. 57

7.2.2.4 Registration independent Serving Node Load Balancing p. 57

7.2.3 General consideration on Load Balancing p. 57

7.2.4 LDF architecture assessment p. 57

7.2.4.1 Assessment on the utilization of EMS/NMS for the LDF architecture p. 57

7.2.4.2 Solution comparison between centralized LDF and distributed LDF p. 58

8 Conclusion p. 59

8.1 Load Balancing p. 59

8.2 Overload Control p. 59

A DNS UPDATE Mechanism p. 60

B IMS Deployment Scenarios p. 61

C Example Load Information Required collected by LDF p. 63

$ Change history p. 64