6.9 Connectivity models

22.2613GPPRelease 18Service requirements for the 5G systemTS

6.9.1 Description

The UE (remote UE) can connect to the network directly (direct network connection), connect using another UE as a relay UE (indirect network connection), or connect using both direct and indirect connections. Relay UEs can be used in many different scenarios and verticals (inHome, SmartFarming, SmartFactories, Public Safety and others). In these cases, the use of relays UEs can be used to improve the energy efficiency and coverage of the system.

Remote UEs can be anything from simple wearables, such as sensors embedded in clothing, to a more sophisticated wearable UE monitoring biometrics. They can also be non-wearable UEs that communicate in a Personal Area Network such as a set of home appliances (e.g. smart thermostat and entry key), or the electronic UEs in an office setting (e.g. smart printers), or a smart flower pot that can be remotely activated to water the plant.

When a remote UE is attempting to establish an indirect network connection, there might be several relay UEs that are available in proximity and supporting selection procedures of an appropriate relay UE among the available relay UEs is needed.

Indirect network connection covers the use of relay UEs for connecting a remote UE to the 3GPP network. There can be one or more relay UE(s) (more than one hop) between the network and the remote UE.

6.9.2 Requirements

The following set of requirements complement the requirements listed in 3GPP TS 22.278 [5], clauses 7B and 7C.

6.9.2.1 General

The 5G system shall support the relaying of traffic between a remote UE and a gNB using one or more relay UEs.

The 5G system shall support different traffic flows of a remote UE to be relayed via different indirect network connection paths.

The connection between a remote UE and a relay UE shall be able to use 3GPP RAT or non-3GPP RAT and use licensed or unlicensed band.

The connection between a remote UE and a relay UE shall be able to use fixed broadband technology.

The 5G system shall support indirect network connection mode in a VPLMN when a remote UE and a relay UE subscribe to different PLMNs and both PLMNs have a roaming agreement with the VPLMN.

The 5G system shall be able to support a UE using simultaneous indirect and direct network connection mode.

The network operator shall be able to define the maximum number of hops supported in their networks when using relay UEs.

6.9.2.2 Services and Service Continuity

A 5G system shall be able to support all types of traffic e.g. voice, data, IoT small data, multimedia, MCX for indirect network connection mode.

The 5G system shall be able to support QoS for a user traffic session between the remote UE and the network using 3GPP access technology.

The 5G system shall be able to provide indication to a remote UE (alternatively, an authorized user) on the quality of currently available indirect network connection paths.

The 5G system shall be able to maintain service continuity of indirect network connection for a remote UE when the communication path to the network changes (i.e. change of one or more of the relay UEs, change of the gNB).

6.9.2.3 Permission and Authorization

The 5G system shall enable the network operator to authorize a UE to use indirect network connection. The authorization shall be able to be restricted to using only relay UEs belonging to the same network operator. The authorization shall be able to be restricted to only relay UEs belonging to the same application layer group.

The 5G system shall enable the network operator to authorize a UE to relay traffic as relay UE. The authorization shall be able to allow relaying only for remote UEs belonging to the same network operator. The authorization shall be able to allow relaying only for remote UEs belonging to the same application layer group.

The 5G system shall support a mechanism for an end user to provide/revoke permission to an authorized UE to act as a relay UE.

The 5G system shall support a mechanism for an authorized third-party to provide/revoke permission to an authorized UE to act as a relay UE.

The 5G system shall provide a suitable API by which an authorized third-party shall be able to authorize (multiple) UEs under control of the third-party to act as a relay UE or remote UE.

The 5G system shall provide a suitable API by which an authorized third-party shall be able to enable/disable (multiple) UEs under control of the third-party to act as a relay UE or remote UE.

6.9.2.4 Relay UE Selection

The 3GPP system shall support selection and reselection of relay UEs based on a combination of different criteria e.g.

– the characteristics of the traffic that is intended to be relayed (e.g. expected message frequency and required QoS),

– the subscriptions of relay UEs and remote UE,

– the capabilities/capacity/coverage when using the relay UE,

– the QoS that is achievable by selecting the relay UE,

– the power consumption required by relay UE and remote UE,

– the pre-paired relay UE,

– the 3GPP or non-3GPP access the relay UE uses to connect to the network,

– the 3GPP network the relay UE connects to (either directly or indirectly),

– the overall optimization of the power consumption/performance of the 3GPP system, or

– battery capabilities and battery lifetime of the relay UE and the remote UE.

NOTE: Reselection may be triggered by any dynamic change in the selection criteria, e.g. by the battery of a relay UE getting depleted, a new relay capable UE getting in range, a remote UEs requesting additional resources or higher QoS, etc.

6.9.2.5 Satellite and Relay UEs

For a 5G system with satellite access, the following requirements apply:

– A 5G system with satellite access shall be able to support relay UE’s with satellite access.

NOTE: The connection between a relay UE and a remote UE is the same regardless of whether the relay UE is using satellite access or not.

– A 5G system with satellite access shall support mobility management of relay UEs and the remote UEs connected to the relay UE between a 5G satellite access network and a5G terrestrial network, and between 5G satellite access networks.

– A 5G system with satellite access shall support joint roaming between different 5G networks of a relay UE and the remote UEs connected to that relay UE.