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TR 29.807 (CT4) ★
Study on GPRS
Tunnelling Protocol for Control plane (GTP-C)
Overload Control Mechanisms

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V12.0.0 (Wzip) 2014/06 78 p.

Rapporteur: Mr. Salot, Nirav

The present document investigates various aspects related to the support of the GTP-C signalling based load / overload control solution as specified in TS 23.401 and TS 23.060, as also concluded in TR 23.843, with the main focus on:

Definition of "Load Control" and "Overload Control" related information with enough precision to guarantee a common multi-vendor interpretation of this information allowing inter-operability between various GTP-C nodes;
Mechanisms to address various "Notes", which are targeted to the stage 3, specified in clause 8.2.5, clause 8.2.6 and clause 10.2 of the TR 23.843.

This technical report addresses the following aspects related to the "GTP-C signalling based load and overload control" feature in detail:

Investigation and study of the following aspects related to the "Load Control Information" to fulfill the normative requirements or to produce recommendations.

Definition of the "Load Control Information" by evaluating various parameters which can be exchanged under this information.
Inclusion of "Load Control Information" in GTP-C messages.
Potential enhancements to the existing node selection algorithm to take information received from "Load Control Information" into account.

Investigation and study of the following aspects related to the "Overload Control Information" to fulfill the normative requirements or to produce recommendations.

Definition of the "Overload Control Information" by evaluating various parameters which can be exchanged under this information.
Inclusion of the "Overload Control Information" in GTP-C messages.
Message throttling algorithms and message prioritization when congestion mitigation is applied.
Propagation of the MME/SGSN identity to the PGW to ensure that the overload mitigation is always applied to the currently serving MME/SGSN.
Potential interactions with the existing overload control mechanisms when the overload factor is received within the "Overload Control Information".

Investigation and study of the following the other deployment related aspects to fulfill the normative requirements or to produce recommendations.

Applicability of this feature to 3GPP and non-3GPP based GTP-C interfaces.
Methods to discover the support of this feature by the peer node in the network.
Supporting the feature across the PLMN boundary.
Issues within the network with partial support of this feature.
Overload mitigation policies when this feature support is not enabled in the network.

full Table of Contents for TR 29.807 Word version: 12.0.0

1 Scope Word-p. 9

3 Definitions, symbols and abbreviations Word-p. 10

3.1 Definitions

3.3 Abbreviations

4 Introduction to GTP-C overload control

4.0 GTP-C overload problem

4.1 Scenarios leading to GTP-C overload Word-p. 11

4.2 GTP-C signalling based Load and Overload Control solution Word-p. 12

4.2.1 Description

4.2.2 Principles of Load Control

4.2.3 Principles of Overload Control Word-p. 13

4.2.4 Applicability to 3GPP and non-3GPP access based interfaces

4.2.4.1 Introduction

4.2.4.2 GTP-C load control Word-p. 14

4.2.4.2.1 Description

4.2.4.2.2 Conclusions

4.2.4.3 GTP-C overload control

4.2.4.3.1 General

4.2.4.3.2 Applicability to 3GPP access based interfaces Word-p. 15

4.2.4.3.2.1 Description

4.2.4.3.2.2 Conclusions Word-p. 16

4.2.4.3.3 Applicability to non-3GPP access based interfaces

4.2.4.3.3.1 General

4.2.4.3.3.2 Untrusted WLAN access Word-p. 17

4.2.4.3.3.3 Trusted WLAN access Word-p. 18

4.2.4.3.3.4 Conclusions Word-p. 21

5 Load Control Information

5.1A APN level load control

5.1A.1 Description

5.1A.2 Requirements

5.1A.3 Example use case Word-p. 22

5.1A.4 Issues when APN load control is not used Word-p. 23

5.1A.4.1 Node selection using DNS weight-factor only

5.1A.4.2 Node selection using node level load information and DNS weight-factor

5.1A.5 Information needed for APN load control Word-p. 24

5.1A.6 Impacts on node level load control

5.1A.7 Conclusion Word-p. 26

5.2.1 Requirements

5.2.2 Alternative 1 - New Load Control Information IE piggybacked in existing GTP-C signalling Word-p. 27

5.2.2.1 Description

5.2.2.1.1 General

5.2.2.1.2 Parameters Word-p. 28

5.2.2.1.2.1 Load Metric

5.2.2.1.2.2 Load Control sequence number

5.2.2.1.2.3 List-of-APN_&_ResourceLimit Word-p. 29

5.2.2.1.3 Parameter Evaluation Word-p. 30

5.2.3 Conclusion

5.3 Frequency of inclusion Word-p. 31

5.3.1 Requirements

5.3.2 Alternative 1 - Inclusion by piggybacking only when the new/changed value has not been provided to a peer

5.3.2.1 Description

5.3.2.2 Using a subset of the applicable messages

5.3.2.3 Advantages Word-p. 32

5.3.2.4 Drawbacks

5.3.3 Alternative 2 - Inclusion by piggybacking in every message towards a peer

5.3.3.1 Description

5.3.3.2 Using a subset of the applicable messages

5.3.3.3 Advantages

5.3.3.4 Drawbacks Word-p. 33

5.3.4 Alternative 3 - Hybrid of Alternative 1 and Alternative 2

5.3.4.1 Description

5.3.4.2 Advantages

5.3.4.3 Drawbacks

5.3.5 Alternative 4 - Inclusion by piggybacking the load control information periodically

5.3.5.1 Description

5.3.5.2 Advantages Word-p. 34

5.3.5.3 Drawbacks

5.3.6 Conclusion

5.4 Interaction with existing mechanisms Word-p. 36

5.4.2 Information received from DNS

5.4.2.1 With node level load information

5.4.2.2 With APN level load information Word-p. 37

5.4.2.3 Conclusion Word-p. 38

5.5 Limit on maximum number of instances Word-p. 39

5.5.1 Description

5.5.2 At message level

5.5.3 At node level

5.5.3.1 Alternative 1 - Same as at message level & providing full set of information

5.5.3.1.1 Description

5.5.3.1.2 Advantages

5.5.3.1.3 Drawbacks Word-p. 40

5.5.3.2 Alternative 2 - Higher than or same as at message level & providing partial set of information

5.5.3.2.1 Description

5.5.3.2.2 Advantages

5.5.3.2.3 Drawbacks

5.5.4 Conclusion

6 Overload Control Information Word-p. 41

6.2.1 Requirements

6.2.2 Alternative 1 - New Overload Control Information IE piggybacked in existing GTP-C signalling Word-p. 42

6.2.2.1 Description

6.2.2.1.1 General

6.2.2.1.2 Parameters Word-p. 43

6.2.2.1.2.1 Overload-Reduction-Metric

6.2.2.1.2.2 Period-Of-Validity Word-p. 44

6.2.2.1.2.3 Overload-Sequence-Number

6.2.2.1.2.4 APN-List Word-p. 45

6.2.2.1.3 Parameter Evaluation Word-p. 46

6.2.3 Conclusion

6.3 Frequency of inclusion

6.3.1 Requirements

6.3.2 Alternative 1 - Inclusion by piggybacking only when the new/changed value has not been provided to a peer Word-p. 47

6.3.2.1 Description

6.3.2.2 Using a subset of the applicable messages

6.3.2.3 Advantages

6.3.2.4 Drawbacks

6.3.3 Alternative 2 - Inclusion by piggybacking in every message towards a peer Word-p. 48

6.3.3.1 Description

6.3.3.2 Using a subset of the applicable messages

6.3.3.3 Advantages

6.3.3.4 Drawbacks

6.3.4 Alternative 3 - Hybrid of Alternative 1 and Alternative 2 Word-p. 49

6.3.4.1 Description

6.3.4.2 Advantages

6.3.4.3 Drawbacks

6.3.5 Alternative 4 - Inclusion by piggybacking the overload control information periodically

6.3.5.1 Description

6.3.5.2 Advantages

6.3.5.3 Drawbacks Word-p. 50

6.3.6 Conclusion

6.4 Message throttling Word-p. 52

6.4.1 Throttling algorithms Word-p. 53

6.4.1.1 General

6.4.1.2 Throttling by "Loss" algorithm

6.4.1.2.1 Description

6.4.1.2.2 Implementation

6.4.1.2.3 Advantages Word-p. 54

6.4.1.2.4 Drawbacks

6.4.1.3 Conclusion

6.4.2 Message prioritization Word-p. 55

6.4.2.1 Description

6.4.2.2 Based on procedures

6.4.2.3 Based on session parameters Word-p. 57

6.4.2.4 Conclusion

6.5 Propagation of MME/S4-SGSN identity to PGW

6.5.1 Description

6.5.2 Updating PGW with current serving MME/S4-SGSN identity

6.5.2.1 Introduction

6.5.2.2 Alternative 1: Always send MBReq over S5/S8 Word-p. 58

6.5.2.3 Alternative 2: Only send MBReq over S5/S8 normally

6.5.2.4 Alternative 3: Opt Alt 2 - send over S5/S8 if not provided previously

6.5.2.5 Alternative 4: Send MBReq over S5/S8 when source in overload

6.5.2.6 Conclusion Word-p. 59

6.5.3 Updating PGW with overload control information of target MME/S4-SGSN

6.5.3.1 Introduction

6.5.3.2 Alternative 1: Forward MBReq over S5/S8 if target sends OCI

6.5.3.3 Alternative 2: Opt Alt 1 - Forward only if target OCI not previously sent

6.5.3.4 Alternative 3: Only send MBReq over S5/S8 normally Word-p. 60

6.5.3.5 Conclusion

6.6 Interaction with existing mechanisms

6.6.1 DDN throttling

6.6.1.1 Description

6.6.1.2 Conclusion Word-p. 61

6.6.2 Congestion control using APN back-off timer

6.6.2.1 Description

6.6.2.2 Alternative 1 - To allow simultaneous usage Word-p. 62

6.6.2.2.1 Description

6.6.2.2.2 Advantages

6.6.2.2.3 Drawbacks

6.6.2.3 Alterative 2 - To only allow exclusive usage

6.6.2.3.1 Description

6.6.2.3.2 Advantages

6.6.2.3.3 Drawbacks

6.6.2.4 Conclusion Word-p. 63

6.7 Enforcement of overload control

6.7.2 Aspects related to enforcement of the overload control

6.7.2.1 Good throughput of the network

6.7.2.2 Message processing efficiency at the source node

6.7.2.3 Self-protection by the target node

6.7.3 Enforcement approaches Word-p. 64

6.7.3.1 Hop-by-hop only

6.7.3.1.1 Description

6.7.3.1.2 Example scenario

6.7.3.1.2.1 Overload condition

6.7.3.1.2.2 Outcome of the overload control enforcement

6.7.3.1.3 Advantages

6.7.3.1.4 Drawbacks Word-p. 65

6.7.3.2 End-to-end only

6.7.3.2.1 Description

6.7.3.2.2 Example scenario

6.7.3.2.2.1 Overload condition

6.7.3.2.2.2 Outcome of the overload control enforcement

6.7.3.2.3 Advantages

6.7.3.2.4 Drawbacks Word-p. 66

6.7.3.3 End-to-end and intermediate node

6.7.3.3.1 Description

6.7.3.3.2 Example scenario

6.7.3.3.2.1 Overload condition

6.7.3.3.2.2 Outcome of the overload control enforcement - Implementation 1 Word-p. 67

6.7.3.3.2.3 Outcome of the overload control enforcement - Implementation 2

6.7.3.3.3 Advantages Word-p. 68

6.7.3.3.4 Drawbacks

6.7.4 Conclusion

6.8 Behaviours of GTP-C entities Word-p. 69

6.8.1 Sender of overload information

6.8.2 Receiver of overload information

6.9 Limit on maximum number of instances

6.9.1 Description

6.9.2 At message level

6.9.3 At node level Word-p. 70

6.9.3.1 Alternative 1 - Same as at message level & providing full set of information

6.9.3.1.1 Description

6.9.3.1.2 Advantages

6.9.3.1.3 Drawbacks

6.9.3.2 Alternative 2 - Higher than or same as at message level & providing partial set of information

6.9.3.2.1 Description

6.9.3.2.2 Advantages Word-p. 71

6.9.3.2.3 Drawbacks

6.9.4 Conclusion

7 Deployment related considerations Word-p. 72

7.2 Discovery of the support of the feature by the peer node

7.2.1 Description

7.2.2 Across the PLMN boundary

7.2.3 Within the PLMN boundary

7.2.3.1 Alternative 1 - Using protocol based indicator

7.2.3.1.1 Advantages

7.2.3.1.2 Drawbacks

7.2.3.2 Alternative 2 - Using PLMN-wide local configuration Word-p. 73

7.2.3.2.1 Advantages

7.2.3.2.2 Drawbacks

7.2.4 Conclusion

8 Heterogeneous network related considerations

8.2 Implicit overload control mechanisms Word-p. 74

8.3 Issues in the network with partial support of the feature

8.3.1 Partial support of the load control

8.3.1.1 Among the nodes performing the node selection function

8.3.1.2 Among the nodes advertising the load control Word-p. 75

8.3.1.3 Conclusion

8.3.2 Partial support of the overload control

8.3.2.1 General

8.3.2.2 Conclusion

9 Conclusions and recommendations

A Change history Word-p. 78