Page 483 - 5G Basics - Core Network Aspects

Core network aspects 1

6.4.2.3 Layer 3 handover control function (L3HCF)

The layer 3 handover control function (L3HCF) communicates with the Layer 3 handover execution function
(L3HEF) to perform the following:
• upon request from the HDF, invoke and coordinate handover action at the appropriate instances of
the L3HEF.

6.4.3 Network information distribution functional entity (NID-FE)
The network information distribution functional entity (NID-FE) communicates with the entity making the
handover decision during the network discovery phase described in clause 7.1. The handover decision may
be made either by the UE or by the HDC-FE. The NID-FE has the following responsibilities:
• distributing handover policy, which is a set of operator-defined rules and preferences that affect the
handover decisions taken by the UE or HDC-FE.
For example, a handover policy can indicate that vertical handover from E-UTRAN access to WLAN
access is not allowed. It can also indicate e.g., that WiMAX access is preferable to WLAN access;
• distributing other information provided by the NIR-FE.
6.4.3.1 Network information repository functional entity (NIR-FE)

The network information repository functional entity (NIR-FE) provides static information on neighbouring
networks to the NID-FE to assist the access network discovery and selection decision. The information
provided by the NIR-FE may include:
• information on neighbouring access networks in the vicinity of the UE. These access networks are
possible target networks for the potential handover from the current UE location. The information
may include access network identifier, access type, operator who runs the network, security and
network QoS capabilities, etc.;

• information on attachment points (base stations, NodeB, access points, etc.) such as attachment
point identifiers, L1/L2 address, bit rates supported, and network address configuration policy;
• operator policies such as charging mode and rates (cost for the usage of the network), roaming
agreements, mobility mechanism selection policies, etc.

The means by which the NIR-FE acquires its information is out of the scope of this Recommendation.
6.4.4 Additional functions required in the forwarding plane

6.4.4.1 Layer 2 handover execution functional entity (L2HE-FE)
The layer 2 handover execution functional entity (L2HE-FE) resides in the access transport functional block.
It acts on commands from the HDC-FE to:
• take access-technology-specific action as required to preserve flow continuity during handover;
• complete handover execution in the direction toward the UE when it has determined that the UE
has executed handover.
In support of media independent handover (see [b-IEEE 802.21]), it also reports link layer events to the HDC-
FE.

6.4.4.2 Layer 3 handover execution function (L3HEF)
The layer 3 handover execution function (L3HEF) resides in the access transport and core transport functional
blocks. It acts on commands from the HDC-FE to:
• execute tunnel set-up, modification, or take-down during handover;
• buffer user packets as required to preserve flow continuity during handover;

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