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 802.21 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 proper actions for handover preparation.
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Background
• In 802.21, a Link_Going_Down/MIH_Link_Going_Down event is often used
to indicate that current link is going to be disconnected and handover should be
prepared. 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 current link will be disconnected soon, a MIH_Link_Going_Down
event 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 has no parameter for why it has generated, so the
upper layers can not take proper 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
proper handover decisions for upper layers.
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Amendment for Link_Going_Down.indication
Name
Type
Valid Range
Value
EventSource
LINK_EVENT
_SOURCE
MacMobileTerminal
MAC Address
N/A
MAC Address of Mobile Terminal
MacNewPoA
MAC Address
N/A
MAC Address of New PoA (AP)
MacOldAccessRouter
MAC Address
N/A
MAC Address of old Access Router
MacNewAccessRouter
MAC Address
N/A
MAC Address of new Access Router
TimeInterval
Time in msecs
0-65535
ConfidenceLevel
Percentage (0100)
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_UNSPECIFIC
1: RC_EXPLICIT_DISCONNECT
2: RC_PACKET_TIMEOUT
3: RC_NOBROADCAST
4: RC_NORESOURCE
5: 127: Reserved
128~255: RC_VENDOR_SPECIFIC
UniqueEventIdentifer
INTEGER
0 – 65535
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The origination point from where the event is generated.
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
To be used in case of event rollback
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
N/A
MAC Address of New PoA (AP)
MacOldAccessRouter
MAC Address
N/A
MAC Address of old Access Router
MacNewAccessRouter
MAC Address
N/A
MAC Address of new Access Router
TimeInterval
Time in msecs
0-65535
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_UNSPECIFIC
1: RC_EXPLICIT_DISCONNECT
2: RC_PACKET_TIMEOUT
3: RC_NOBROADCAST
4: RC_LOW_POWER
5: RC_NORESOURCE
6: 127: Reserved
128~255: RC_VENDOR_SPECIFIC
UniqueEventIdentifer
INTEGER
0 – 65535
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To be used in case of event rollback
More Explanation to ReasonCode
• RC_UNSPECIFIC:
The link is going to be down because of undefined reasons.
Use Case:
The reasons that cause current link to be disconnected may be unknown, so upper
layers are notified by the Link_Going_Down event with RC_UNSPECIFIC.
• RC_EXPLICIT_DISCONNECT:
The link is going to be down because that explicit disconnect procedures will be
initiated either by client or network.
Use Case:
As the description in the current draft, when a BS has decided to shutdown for
administrative reasons, the BS may send Link_Going_Down event with
RC_EXPLICIT_DISCONNECT to the MIHF in the terminal before disconnecting
the current link.
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More Explanation to ReasonCode
• RC_NORESOURCE:
The link is going to be down because there will be no resources to maintain the
current connection.
Use Case:
In 3GPP, users with higher priority may preempt the ones with lower priority when
resources are insufficient. The BS may send Link_Going_Down events with
RC_NORESOURCE to the terminals having lower priority to indicate that no
resources can be allocated to them and the current links will be disconnected.
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More Explanation to ReasonCode
• RC_LOW_POWER (only for MIH_Link_Going_Down):
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.
Use Case:
Mobile terminals usually have limited battery supply, and when the battery level
is low and the current link can not be maintained, a terminal may choose a link
that has lower power consumption for handover according to the
MIH_Link_Going_Down event with RC_LOW_POWER. This will lengthen
the useable time of terminal.
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More Explanation to ReasonCode
• RC_PACKET_TIMEOUT:
The link is going to be down because no ACKs are received for transmitted
packets within the specified time limit.
Use Case:
The MAC layer may maintain a timer for waiting the ACK of a transmitted
packet, and re-transmit this packet when no ACK is received until the times of retransmission has reached a limit. A threshold may be configured and when the
times of re-transmission has reached the threshold, a Link_Going_Down
with RC_PACKET_TIMEOUT will be sent to indicate the current link is going
to be disconnected.
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More Explanation to ReasonCode
• RC_NOBROADCAST:
The link is going to be down because broadcast messages (control frames such as
beacons) could not be received by client device.
Use Case:
The MAC layer may use a timer to detect broadcast messages periodically, and
link may disconnect because that the MAC layer can not listen to broadcast
messages within the time limit. A Link_Going_Down event with
RC_NOBROADCAST may be sent just before time out of the timer.
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More Explanation to ReasonCode
• Reserved:
Reservation for extension in 802.21 in the furture.
• RC_VENDOR_SPECIFIC:
Vendor Specific reason codes.
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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.
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