Page 504 - 5G Basics - Core Network Aspects

1 Core network aspects

7.3.3 New path establishment and resource reservation

This clause applies only to handover at layer 3.
New path creation and resource reservation along that path are triggered by a bind indication from the MLM-
FE(P) to the HDC-FE. This indication must contain the information required for both path creation and for
retrieval by RACF of the session QoS descriptor for the old path.
With this information, the HDC-FE sends a request to RACF to allocate QoS resources on the new path
matching the session QoS allocated to the old path. When this operation is complete, the HDC-FE locates the
appropriate instance(s) of the L3HEF and issues a request to them to establish a tunnel between the new
endpoints. When the tunnel is complete, the L3HEF instance at the anchor point begins to monitor for data
flows from the UE through the new tunnel, and decapsulates and forwards them as well as packets received
from the old tunnel. In the case of network-based mobility it is possible that a temporary tunnel is established
between the old and new tunnel lower end points, in support of seamless handover.
Figure 9 illustrates this procedure.

L3HEF
(upper)
New New L3HEF
MLM-FE HDC-FE (lower) RACF

From UE
or TAA-FE
Handover indication
(Table 22)
Resource re-provisioning request (Table 16)

Retrieve
session
descriptor

Grant
QoS
Resource re-provisioning response (Table 17)

Locate L3HEF
instances
Establish end point (...)
Establish end point (...)
Y.2018(09)_F09

Figure 9 – Procedure for establishing a new layer 3 path
7.3.4 Handover execution

This clause applies only to handover at layer 3.
Handover execution may be initiated in three ways:

a) if the UE has the required capabilities or the tunnel lower end lies in the network (network-based
mobility), handover execution is carried out under the explicit control of the HDC-FE; or
b) the L2HE-FE instance monitoring the old access link detects and reports a 'link down' event; or

c) the MLM-FE(P) on the old path receives an unbind indication from the UE and notifies the HDC-FE.
In case a), the HDC-FE receives direct confirmation from the tunnel lower end that it has executed handover.
In case b) or c), UE readiness is inferred from its actions.

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