An apparatus comprising: at least one processor; and at least one memory including computer program code; the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to: receive, by a first function, a request for establishing a data connection supporting interworking between a first radio access technology system and a second radio access technology system; allocate, by a first function, at least one identifier identifying traffic within the data connection in the second radio access technology system; and cause, by the first function, the at least one identifier to be sent to a second function; wherein the first radio access technology system is a 5G system; the second radio access technology is an Evolved packet system; the at least one identifier is an Evolved packet system bearer identifier; the first function is an access management function; the second function is a session management function; characterized in that the at least one identifier is sent to the second function in a Nsmf_PDUSession_CreateSMContext Request; and/or the at least one identifier is sent to the second function in a Nsmf_PDUSession_Create Request. at least one processor; and at least one memory including computer program code; the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to: receive, by a first function, a request for establishing a data connection supporting interworking between a first radio access technology system and a second radio access technology system; allocate, by a first function, at least one identifier identifying traffic within the data connection in the second radio access technology system; and cause, by the first function, the at least one identifier to be sent to a second function; wherein the first radio access technology system is a 5G system; the second radio access technology is an Evolved packet system; the at least one identifier is an Evolved packet system bearer identifier; the first function is an access management function; the second function is a session management function; characterized in that the at least one identifier is sent to the second function in a Nsmf_PDUSession_CreateSMContext Request; and/or the at least one identifier is sent to the second function in a Nsmf_PDUSession_Create Request. receive, by a first function, a request for establishing a data connection supporting interworking between a first radio access technology system and a second radio access technology system; allocate, by a first function, at least one identifier identifying traffic within the data connection in the second radio access technology system; and cause, by the first function, the at least one identifier to be sent to a second function; wherein the first radio access technology system is a 5G system; the second radio access technology is an Evolved packet system; the at least one identifier is an Evolved packet system bearer identifier; the first function is an access management function; the second function is a session management function; characterized in that the at least one identifier is sent to the second function in a Nsmf_PDUSession_CreateSMContext Request; and/or the at least one identifier is sent to the second function in a Nsmf_PDUSession_Create Request.