Page 482 - 5G Basics - Core Network Aspects

1 Core network aspects

PD-FE MLM-FE (P)

TRC-FE
Handover decision and control
functional entity (HDC-FE)
RACF

Handover decision
UE function (HDF)

NID-FE Layer 2 Layer 3
Handover control Handover control
function (L2HCF) function (L3HCF)

Control plane
Forwarding plane
Layer 3
L2HE-FE Handover execution
function (L3HEF)
Y.2018(09)_F02

Figure 2 – Relations of HDC-FE sub-functions
6.4.2.1 Handover decision function (HDF)

The handover decision function (HDF) has the following responsibilities:
• receiving a list of candidate access links for handover from the UE and invoking RACF to verify session
QoS availability for each candidate access link for handover. In the case where the UE makes the
handover decision, the HDF provides the acceptable subset of links to the UE;

• requesting RACF to re-provision the resource and QoS for the sessions of the moved UE by
submitting binding information to the PD-FE in RACF with the following options:
– requesting to release resource and QoS configuration for the previous data path while
configuring resource and QoS for the new data path;
– requesting to leave the previous data path as it is while configuring resource and QoS for the
new data path, which makes make-before-break handover possible;
• requesting RACF to release resource and QoS for the data path which is verified not to be used
anymore;
• triggering handover upon request from the UE, in the case of network-triggered handover;
• invoking handover action at the L2HCF in the case of intra-subnetwork handover, and at the L3HCF
in the case of handover between subnetworks.
6.4.2.2 Layer 2 handover control function (L2HCF)

The layer 2 handover control function (L2HCF) communicates with the layer 2 handover execution functional
entity (L2HE-FE) to perform the following:
• relay link layer reports to the handover decision function;
• upon request from the HDF, invoke handover action at the appropriate instance of the L2HE-FE.

For movement within the same subnetwork, handover is at layer 2. In this case, the L2HCF may communicate
with L2HE-FE instances to create media paths between them during the handover process.

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