1. IEEE 802.21 MEDIA INDEPENDENT HANDOVER DCN: 21-06-0631-00-0000
Title: The amendment for the Link Going Down primitive
Date Submitted: April, 20, 2006
Presented at IEEE session #14 in Jacksonville
Authors or Source(s):
 Zhou Yi, Liu Yuan, Guo Junxiang
Abstract: This contribution suggests an amendment to the Link Going Down event. By using the amended event, higher layers can take appropriate actions for handover preparation.

2. IEEE 802.21 presentation release statements
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3. Background
In , a Link_Going_Down (MIH_Link_Going_Down) trigger is usually used to indicate a link going down in advance and notify the upper layers for making a preparation to handover. It is necessary for the upper layers to know the reasons for why the link is going to be down. For example, when the battery level of the terminal is low and the currently used link will disconnect soon, a Link_Going_Down trigger may be generated in order to prepare for a handover to the module that has lower power consumption (As an example, a GSM module usually has lower battery consumption than a WiFi module) to lengthen the usable time of terminal. However, the current definition of the Link_Going_Down (MIH_Link_Going_Down) primitive has no parameters for why it has generated, so the upper layers can not take appropriate actions according to the received indications.
We propose to give an amendment to the primitive Link_Going_Down (MIH_Link_Going_Down) by adding a reason code in order to facilitate making appropriate handover decisions for upper layers.

4. Amendment for Link_Going_Down.indication
Name
Type
Valid Range
Value
EventSource
LINK_EVENT_SOURCE
The origination point from where the event is generated.
MacMobileTerminal
MAC Address
N/A
MAC Address of Mobile Terminal
MacNewPoA
MAC Address of New PoA (AP)
MacOldAccessRouter
MAC Address of old Access Router
MacNewAccessRouter
MAC Address of new Access Router
TimeInterval
Time in msecs
Time Interval in which the link is expected to go down. The link connectivity is expected to be available at least for time specified by TimeInterval . Unit: 1ms
ConfidenceLevel
Percentage (0-100)
0-100
The confidence level for link to go down within the specified time interval
Expressed in percentage (0~100)
ReasonCode
Enumerated
0-255
The reason for why the link is going to be down
0: RC_EXPLICIT_DISCONNECT
1: RC_PACKET_TIMEOUT
2: RC_NOBROADCAST
3: RC_LOW_POWER
4: RC_NORESOURCE
5: 127: Reserved
128~255: RC_VENDOR_SPECIFIC
UniqueEventIdentifer
INTEGER
0 – 65535
To be used in case of event rollback

5. More Explanation for Amendment
Meaning of Reason code presented above is as following
RC_EXPLICIT_DISCONNECT:
The link is going to be down because that explicit disconnect procedures will be initiated either by client or network. For example, when a BS has decided to shutdown for administrative reasons or an operator of the terminal has decided to execute a handover manually, a Link_Going_Down trigger may be sent to the MIH Function.
RC_PACKET_TIMEOUT:
The link is going to be down because no acknowledgements were received for transmitted packets within the specified time limit. The link layer may maintain a timer for waiting acknowledgements and when it is estimated that no acknowledgements will be received before time out, Link_Going_Down triggers may be sent to notify the MIH Function.
RC_NOBROADCAST:
The link is going to be down because broadcast messages (control frames such as beacons) could not be received by client device.

6. More Explanation for Amendment
RC_LOW_POWER:
The link is going to be down because power level of the terminal is low and the current link will not be maintained in such a low power level. Mobile terminals usually have limited battery supply, and when the battery level of the terminal is low, a terminal may choose a link that has lower power consumption for handover according to the received Link_Going_Down triggers with the reason code RC_LOW_POWER. This will lengthen the useable time of terminal.
RC_NORESOURCE:
The link is going to be down because there will be no resources to maintain the current connection. For example, a BS may have too many ursers and send Link_Going_Down indications to terminals when the links with them can not be kept because of insufficient resources. An another example is that the users with higher priority may preempt the ones with lower priority when no more resources can be allocated in 3GPP, and this also may cause a Link_Going_Down indication with RC_NORESOURCE reason code.
Reserved :
Reservation for extension in in the furture.
RC_VENDOR_SPECIFIC:
Vendor Specific reason codes.

7. Amendment for MIH_Link_Going_Down.indication
Name
Type
Valid Range
Value
MacMobileTerminal
MAC Address
N/A
MAC Address of Mobile Terminal
MacNewPoA
MAC Address of New PoA (AP)
MacOldAccessRouter
MAC Address of old Access Router
MacNewAccessRouter
MAC Address of new Access Router
TimeInterval
Time in msecs
Time Interval in which the link is expected to go
down. The link connectivity is expected to be available at least for time specified by TimeInterval . Unit: 1ms
ConfidenceLevel
Percentage (0-100)
0-100
The confidence level for link to go down within the
specified time interval
Expressed in percentage (0~100)
ReasonCode
Enumerated
0-255
The reason for why the link is going to be down
0: RC_EXPLICIT_DISCONNECT
1: RC_PACKET_TIMEOUT
2: RC_NOBROADCAST
3: RC_LOW_POWER
4: RC_NORESOURCE
5: 127: Reserved
128~255: RC_VENDOR_SPECIFIC
UniqueEventIdentifer
INTEGER
0 – 65535
To be used in case of event rollback

8. More Explanation for Amendment
Effect on receipt
Higher layers may take different actions on this notification. Upper layers may prepare to initiate handovers based on the reason code and confidence level reported as part of the event.