1. IEEE 802.21 MEDIA INDEPENDENT HANDOVER DCN: 21-07-0019-02-0000
Title: Handover flow diagram for abnormal handover case
Date Submitted: March 6, 2007
Presented at IEEE session in Orlando, FL
Authors or Source(s): Junxiang Guo, Yan Peng, Bin Xia
Abstract: This contribution proposes handover flow diagram for abnormal handover case.

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3. Background
In current draft, MN can discover and obtain information of a list of neighbor PoAs, so when handover decision is made MN can have multiple choices of target PoAs, but the current draft does not allow the user to initiate a second handover after an initial handover failed, e.g. when MIH_ MN_HO _Candidate_Query Reponse, or MIH_MN_HO_Candidate _Commit Response is received by MN or serving PoS and they include parameters indicating handover failure, then the handover process will be ceased finally, this does not allow the MN or serving PoS to perform handover to another suitable candidate neighbor PoA. So it does not fully make use of the result of PoA discovery and scanning. Current handover procedure is inefficient and will cause higher handover failure ratio.

4. Proposal
Here we suggest two flow diagrams for two types of handover failure case:
MIH_ MN_HO_Candidate_Query Reponse:
HandoverAck=0: Abort Handover
MIH_MN_HO_Candidate_Commit Response: HandoverStatus=0: Abort Handover
We suggest to adopt the following two flow diagrams into Annex A (add a subclause A.6).

5. Annex A.6.1 A.6 Handover flow diagram for abnormal case
A.6.1 Example handover flow diagram for abnormal case at handover query stage
When MIH_ MN_HO_Candidate_Query Reponse indicate the handover initiator to abort handover (HandoverAck=0), the MN will initiate handover process to another suitable target PoA. The following is the handover flow diagram for this case:

6. Annex A.6.1
Figure A-8

7. Annex A.6.2
A.6.2 Example handover flow diagram for abnormal case at handover commit stage
When MIH_MN_HO_Candidate_Commit Response indicate the handover initiator to abort handover (HandoverStatus=0) the MN will issue MIH_MN_HO_Candidate_Commit Request to another suitable target PoA, i.e. MN reuses the previous Query result and needs not repeat Query process again. The following is the handover flow diagram for this case:

8. Annex A.6.2
Figure A-9

9. Annex A.6.2
Figure A-9

10. Thank you!