What is the importance of sending ReestablishmentInfo in Handover Preparation message ?

Question

I just found an IE AS Context which contains ReestablishmentInfo in Handover Preparation message ?

Can any one signify the importance of this IE ?

HandoverPreparationInformation-r8-IEs ::= SEQUENCE {
ue-RadioAccessCapabilityInfo UE-CapabilityRAT-ContainerList,
as-Config AS-Config OPTIONAL, -- Cond HO
rrm-Config RRM-Config OPTIONAL,
as-Context AS-Context OPTIONAL, -- Cond HO
nonCriticalExtension HandoverPreparationInformation-v920-IEs OPTIONAL
}

AS-Context ::= SEQUENCE {
reestablishmentInfo ReestablishmentInfo OPTIONAL -- Cond HO
}

ReestablishmentInfo ::= SEQUENCE {
sourcePhysCellId PhysCellId,
targetCellShortMAC-I ShortMAC-I,
additionalReestabInfoList AdditionalReestabInfoList OPTIONAL,
...
}

AdditionalReestabInfoList ::= SEQUENCE ( SIZE (1..maxReestabInfo) ) OF AdditionalReestabInfo

AdditionalReestabInfo ::= SEQUENCE{
cellIdentity CellIdentity,
key-eNodeB-Star Key-eNodeB-Star,
shortMAC-I ShortMAC-I
}

Answer 1

As per my knowledge, while doing handover procedure, target eNodeB receives "RRC connection reconfiguration complete" message as part of successful handover fromUE or it may receive "RRC connection re-establishment request" message from UE when handover fails.

Assume, UE is not able to latch on target cell. In this case, UE does cell-reselection and it may initiate re-establishment towards target cell. To entertain this UE at target cell, cell should prepare to handle re-establishment request from this UE.

The information contains within the AS-Context is used to authenticate the UE which sent re-establishment request at target cell.

Content of re-establishment request message as following:

RRCConnectionReestablishmentRequest ::= SEQUENCE {
    criticalExtensions                  CHOICE {
        rrcConnectionReestablishmentRequest-r8
                                            RRCConnectionReestablishmentRequest-r8-IEs,
        criticalExtensionsFuture            SEQUENCE {}
    }
}
RRCConnectionReestablishmentRequest-r8-IEs ::= SEQUENCE {
    ue-Identity                         ReestabUE-Identity,
    reestablishmentCause                ReestablishmentCause,
    spare                               BIT STRING (SIZE (2))
}
ReestabUE-Identity ::=              SEQUENCE {
    c-RNTI                              C-RNTI,
    physCellId                          PhysCellId,
    shortMAC-I                          ShortMAC-I
}
ReestablishmentCause ::=            ENUMERATED {
                                        reconfigurationFailure, handoverFailure,
                                        otherFailure, spare1}

AS-context contains re-establishment info. which in turn contains so many other important information which is used by target eNodeB while handling re-establishment request message for an UE. If wee see re-establishment info of AS-context , it may contain "additionalReestabInfoList" which contains the information of list of all possible cells in which UE can send re-establishment request message.

Comments

Thanks for the explanation, even with out using this and using son pronciple we used to bring context from source after Target Receives reestablishment .... But additionalReestabInfoList contains all the cells o source enb ....so can u add some points on this statement "list of all possible cells in which UE can send re-establishment request message." ?

Answer 2

Reestablishment info used in case of handover preparation failure time to reinitiate handover request with the same contents from SeNB

Comments

can u add some more info in explaining the scenario ?

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for example i am doing handover from SeNB to TeNB due to limited resources tenb not able to admit requested resources, In this time handover failure occurs. To handle this scenario we are adding handover preparation information so that senb can reinitiate handover request to same tenb after some time if resources available .for more details plz go through rrc connection reestablishment request message in 36331