IEEE MEDIA INDEPENDENT HANDOVER DCN: 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 proper actions for handover preparation.

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Background In , 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.

Amendment for Link_Going_Down.indication NameTypeValid RangeValue EventSourceLINK_EVENT _SOURCE The origination point from where the event is generated. MacMobileTerminalMAC AddressN/AMAC Address of Mobile Terminal MacNewPoAMAC AddressN/AMAC Address of New PoA (AP) MacOldAccessRouterMAC AddressN/AMAC Address of old Access Router MacNewAccessRouterMAC AddressN/AMAC Address of new Access Router TimeIntervalTime 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 ConfidenceLevelPercentage (0- 100) 0-100The confidence level for link to go down within the specified time interval Expressed in percentage (0~100) ReasonCodeEnumerated0-255The 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 UniqueEventIdentiferINTEGER0 – 65535To be used in case of event rollback

Amendment for MIH_Link_Going_Down.indication NameType Valid Range Value MacMobileTerminalMAC Address N/A MAC Address of Mobile Terminal MacNewPoAMAC Address N/A MAC Address of New PoA (AP) MacOldAccessRouterMAC Address N/A MAC Address of old Access Router MacNewAccessRouterMAC Address N/A MAC Address of new Access Router TimeIntervalTime 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 ConfidenceLevelPercentage (0-100)0-100The confidence level for link to go down within the specified time interval Expressed in percentage (0~100) ReasonCodeEnumerated 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 UniqueEventIdentiferINTEGER0 – 65535To 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.

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.

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.

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 re- transmission 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.

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. More Explanation to ReasonCode

More Explanation to ReasonCode Reserved: Reservation for extension in in the furture. RC_VENDOR_SPECIFIC: Vendor Specific reason codes.

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. More Explanation for Amendment