Session establishment method and apparatus

An apparatus comprising:

• a processor;
• and
• a memory coupled to the processor and having program instructions stored thereon which, when executed by the processor, cause the apparatus to perform operations comprising:
• receiving, from a control plane function entity during establishment of a packet data network (PDN) connection in a fourth generation (4G) network, single network slice selection assistance information (S-NSSAI) corresponding to the PDN connection and a public land mobile operator network (PLMN) Identifier (ID), wherein the PLMN ID indicates that the S-NSSAI corresponding to the PDN connection received from the control plane function is a home PLMN S-NSSAI;
• mapping, based on a correspondence between home PLMN S-NSSAI and visited PLMN S-NSSAI, the home PLMN S-NSSAI corresponding to the PDN connection to a visited PLMN S-NSSAI corresponding to the PDN connection;
• and
• sending a session establishment request when transferring the PDN connection to a fifth generation (5G) network, wherein the session establishment request comprises the visited PLMN S-NSSAI corresponding to the PDN connection.

A control plane function entity, comprising:

• a processor;
• and
• a memory coupled to the processor and having program instructions stored thereon which, when executed by the processor, cause the apparatus to perform operations comprising:
• sending, during establishment of a packet data network (PDN) connection in a fourth generation (4G) network, single network slice selection assistance information (S-NSSAI) corresponding to the PDN connection and a public land mobile operator network (PLMN) identifier (ID) to a terminal, wherein the PLMN ID indicates that the S-NSSAI corresponding to the PDN connection sent to the terminal is a home PLMN S-NSSAI;
• and
• receiving a session establishment request when transferring the PDN connection to a fifth generation (5G) network, wherein the session establishment request comprises the S-NSSAI corresponding to the PDN connection.