 IEEE 802.21 MEDIA INDEPENDENT HANDOVER
 DCN: 21-06-xxxx-00-0000
 Title: Network-Initiated Handover Procedure Update
 Date Submitted: October 28, 2006
 Presented at IEEE 802.21 session in Dallas
 Authors or Source(s):
Yan Peng, Jing Liu
 Abstract: This document amends the procedure of networkinitiated handover, and offers a mechanism to handle handover
failure which may happen in the procedure by adding
corresponding primitives/messages.
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Background (I)
• Current Network-initiated Handover Procedure (A1.2)
MN
Serving PoS
Candidate PoSs ...
Target PoS
MIH_Get_Information Request
MIH_Get_Information Response
Network Selection Phase
MIH_Handover_Initiate Request
MIH_Handover_Initiate Response
MIH_Handover_Prepare Request ...
MIH_Handover_Prepare Response ...
MIH_Handover_Prepare Request ...
MIH_Handover_Prepare Response ...
Target Decision
MIH_Handover_Commit Request
MIH_Handover_Commit Response
MIH_Handover_Commit Request
MIH_Handover_Commit Response
Higher Layer Handover Exectuion
MIH_Handover_Complete Request
MIH_Handover_Complete Request
MIH_Handover_Complete Response
MIH_Handover_Complete Response
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Candidate
PoSs...
Information
Server
Background (II)
• In the case of network-initiated handover procedure (in A1.2), after
the Serving PoS makes handover target decision, it requests
handover commitment to the specified PoA by sending the
MIH_Handover_Commit Request message to MN. The MN replies
the result of the handover commitment by sending the
MIH_Handover_Commit Response message to the Serving PoS.
Then the Serving PoS notifies the target PoS of the fact that MN is
about to move to the network through the MIH_Handover_Commit
Request message.
• In figure 31, the message sequence of sending
MIH_Handover_Commit Request to MN is prior to the
MIH_Handover_Commit message exchange between the Serving
PoS and the target PoS.
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Problems Description
• The problem is that the target PoS may reject the request of
handover via MIH_Handover_Commit Response (with
HandoverStatus option set to 0), due to some reasons such as the
resources are unavailable now, how the MN could be notified this
failure and stop its handover procedure to the target PoS.
• In the current draft, the Serving PoS has no way to inform the MN
the information of rejection, because there is no message exchange
between the Serving PoS and MN, after MN sends the
MIH_Handover_Commit Response.
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Solution to this problem
• Adjust the message sequence of sending MIH_Handover_Commit
Request in figure 31.
MN
Candidate PoSs…
Target PoS
Serving PoS
Candidate
PoSs...
MIH_Get_Information Request
MIH_Get_Information Response
Network Selection Phase
MIH_Handover_Initiate Request
MIH_Handover_Initiate Response
MIH_Handover_Prepare Request
MIH_Handover_Prepare Response
MIH_Handover_Prepare Request
MIH_Handover_Prepare Response
Target Decision
MIH_Handover_Commit Request
MIH_Handover_Commit Request
MIH_Handover_Commit Response
MIH_Handover_Commit Response
Higher Layer Handover Execution
MIH_Handover Complete Request
MIH_Handover Complete Request
MIH_Handover Complete Response
MIH_Handover Complete Response
Figure 31 — Network-initiated Handover Procedure
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Information
Server
Further Problem
• In the modified procedure of network-initiated handover, it still exists
another problem:
after MN receives the handover commitment
– MN may also reject the request of handover for the sake of movement or
user intervention.
– In this case, the target PoS has no way to be notified the fact that the MN
won’t handover anymore and does not know whether it needs to release
the related context because there is no message exchange between the
Serving PoS and target PoS.
• There is no handover failure mechanism in 802.21 yet.
– Both the mobile node and the network may make decisions about
connectivity.
– The probability of refusing handover in the procedure may be very low.
However it cannot be ignored.
– 802.21 should offer a mechanism and corresponding primitives to handle
handover failure.
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Suggested Remedy (I)
• Solution:
– Introduce a pair of messages and corresponding primitives to handle
handover failure: MIH_Handover_Cancel Request and
MIH_Handover_Cancel Response.
– The messages may be used between MIHF of networks, or between
MIHF of network and terminal, to indication the cease of subsequent
handover procedure.
– The disposal status about the release of reserved context and the reason
for canceling handover may be included in the messages.
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Suggested Remedy (II)
• Network-initiated unsuccessful handover procedure
MN
Candidate PoSs…
Target PoS
Serving PoS
Candidate
PoSs...
MIH_Get_Information Request
MIH_Get_Information Response
Network Selection Phase
MIH_Handover_Initiate Request
MIH_Handover_Initiate Response
MIH_Handover_Prepare Request
MIH_Handover_Prepare Response
MIH_Handover_Prepare Request
MIH_Handover_Prepare Response
Target Decision
MIH_Handover_Commit Request
MIH_Handover_Commit Response
MIH_Handover_Commit Request
MIH_Handover_Commit Response
[HandoverStatus=0]
MIH_Handover_Cancel Request
MIH_Handover_Cancel Response
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Information
Server
Suggested Remedy (III)
• Modify step4 of A1.2:
A1.2 Network-initiated Handover Procedure
…………
The Network-initiated Handover Procedure operates as follows,
…………
4) The Serving PoS decides the handover target based on the resource
availability information of candidate networks through the received
MIH_Handover_Prepare Response message. The Serving PoS requests
handover commitment to the specified network type and PoA by sending the
MIH_Handover_Commit Request message to the MN. The Serving PoS
also notifies the target PoS of the fact that MN is about to move to the
network through the MIH_Handover_Commit Request messages. The MN
replies the result of the handover commitment by sending the
MIH_Handover_Commit Response message to the Serving PoS. If the MN
rejects the request of handover by sending MIH_Handover_Commit
Response (with HandoverStatus option set to 0), the Serving PoS may
notify the target PoS of the fact that the MN cancels handover and may
suggest the target PoS to release the corresponding context by sending
MIH_Handover_Cancel Request message. The target PoS replies the result
of cancellation by sending the MIH_Handover_Cancel Response message
to the Serving PoS.
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