Section: 13.3.2.1 Direct communication
Content: In direct communication, authentication between network functions within one PLMN shall use one of the following methods: - If the PLMN uses protection at the transport layer as described in clause 13.1, authentication provided by the transport layer protection solution shall be used for authentication between NFs. - If the PLMN does not use protection at the transport layer, authentication between NFs within one PLMN may be implicit by NDS/IP or physical security (see clause 13.1). If the PLMN uses token-based authorization, the network shall use protection at the transport layer as described in clause 13.1.