User's Manual

Table Of Contents
Ver.
CHAPTER 4. Message Flow
1.0
Step Description
1) The source Indoor Pico Cell determines whether to perform S1-based handover to the
target Ind
oor Pico Cell. The source Indoor Pico Cell can make this decision if there is no
X2 connection to the target Indoor Pico Cell or if an error is notified by the target Indoor
Pico Cell after an X2-based handover has failed, or if the source Indoor Pico Cell
dynamically receives the related information.
2) The target Indoor Pico Cell transmits the HANDOVER REQUIRED message to the
MME.
The source Indoor Pico Cell notifies the target Indoor Pico Cell which bearer is used for
data forwarding and whether direct forwarding from the source Indoor Pico Cell to the
target Indoor Pico Cell is possible.
3)~4)
The MME transmits the HANDOVER REQUEST message to the target Indoor Pico Cell.
This message makes the target Indoor Pico Cell create a UE context containing the
bearer-related information and the security context.
The target Indoor Pico Cell transmits the HANDOVER REQUEST ACKNOWLEDGE
message to the MME.
5)~6) If indirect forwarding is used, the MME transmits the Create Indirect Data Forwarding
Tunnel Request message to the S-GW. The S-GW responds to the MME with the
Delete Indirect Data Forwarding Tunnel Response message.
7)~8) The MME transmits the HANDOVER COMMAND message to the source Indoor Pico
Cell.
The source Indoor Pico Cell creates the RRCConnectionReconfiguration message
using the Target to Source Transparent Container IE encapsulated in the HANDOVER
COMMAND message and then transmits it to the UE.
9)~10)
To transmit the PDCP and HFN status of the E-RABs of which the PDCP status must be
preserved, the source Indoor Pico Cell transmits the eNB/MME STATUS TRANSFER
message to the target Indoor Pico Cell via the MME. The source Indoor Pico Cell must
start forwarding the downlink data to the target Indoor Pico Cell through the bearer
which was determined to be used for data forwarding. This can be either direct or
indirect forwarding.
11)
The UE performs synchronization with the target Indoor Pico Cell and connects to the
target cell via the RACH.
The target Indoor Pico Cell responds with UL allocation and a timing advance value.
12)
After successfully synchronizing with the target cell, the UE uses the
RRCConnectionReconfigurationComplete message to notify the target Indoor Pico Cell
that the handover procedure is complete. The downlink packets retransmitted by the
source Indoor Pico Cell can be forwarded to the UE. The uplink packets can also be
transmitted from the UE to the S-GW via the target Indoor Pico Cell.
13) The target Indoor Pico Cell transmits the HANDOVER NOTIFY message to the MME.
The MME starts the timer which tells when the source Indoor Pico Cell resources and
the temporary resources used for indirect forwarding at S-GW will be released.
14) The MME transmits the Modify Bearer Request message for each PDN connection to
the S-GW. Downlink packets are transmitted immediately from the S-GW to the target
Indoor Pico Cell.
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