Page 479 - 5G Basics - Core Network Aspects

Core network aspects 1

• If the UE indicates support of both network-based and host-based mobility, the operator's
policy decides which one will be used.
One possible way to indicate IP mobility mechanisms to be supported in the UE and network is
through the AAA process, but the detailed mechanism for indicating the mobility mechanism is out
of scope of this Recommendation.

b) UE and network do not support a common mobility mechanism, or UE support is not indicated:
In this case, there are two choices for the network, depending on the operator's policy: reject
network access for the UE or enforce network-based mobility.

6.3 High level functions
6.3.1 Network attachment control functions (NACF)

6.3.1.1 Network access authentication

When a UE establishes a connection to an NGN access network, the user authentication and authorization
procedure will be performed for the network access. In order to identify each UE, a user identifier associated
with the UE will be offered in signalling. Various types of user identifier may be used as defined in [ITU-T
Q.1707], and support of the network access identifier (NAI) based on [IETF RFC 4282] is required if 3GPP
Evolved Packet Core compliance is needed. Authentication defines the process that is used for access control,
i.e., to permit or deny a UE to attach to and use the resources of an NGN. Two authentication types are
defined: implicit authentication and explicit authentication (see [ITU-T Y.2014]). In explicit authentication,
the authentication signalling is executed between the UE and TAA-FE in NACF. Examples of authentication
signalling and its procedures are described in [b-IETF RFC 3748] and [b-3GPP TS 33.234].

6.3.1.2 Mobility service authentication and authorization
Mobility service is separate from transport service, and is controlled by additional parameters in the user
profile. In general, the user has separate identifiers for transport service and mobility service.
Mobility service authentication may be integrated into or separated from network access authentication. In
the integrated scenario, mobility service and network access are authenticated by the same operator. The
transport user identifier will be the same as the mobility service subscriber identifier.
In case of the split scenario, authentication for the mobility service and network access authentication are
performed separately. In this scenario, after network access authentication is finished, mobility service
authentication will be performed by the mobile service authorizer.

6.3.1.3 IP address allocation
IP address may be configured in two different approaches. In order to support mobility in the NGN, two kinds
of IP addresses need to be allocated, a persistent IP address and, in the host-based case, a temporary IP
address. The persistent IP address is allocated in the anchoring network while the temporary IP address is
allocated when a UE attaches to an access network which has a different subnet prefix from the persistent
IP address allocated to the UE. The persistent IP address is persistently maintained for a UE regardless of its
movement within a given scope, which may be global or local to a given network, whereas the temporary IP
address may be changed whenever the UE attaches to a new subnet.

The persistent IP address is a persistent logical location identifier and the temporary IP address is a temporary
logical location identifier in terms of the definition in clause 6.3.2 of [ITU-T Q.1707].
Details of the address allocation process are provided in the sub-clauses of clause 7.2.

The NAC-FE in NACF may be responsible for retrieving both IP addresses in NGN. NAC-FE assignment of the
persistent address is required only if none is present amongst the mobility service parameters retrieved by
the TAA-FE. The NAC-FE may bind the information between the mobility service subscriber ID and both IP
addresses and send the binding information to the MLM-FE(P) via the TLM-FE to trigger handover.

In network-based mobility, a UE always needs to be allocated and configured with a persistent IP address,
but a temporary IP address is not required.

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