The present document investigates solutions for a simple, optional transport format for the Nb interface and IP transport that allows transporting several RTP/NbFP/codec payload PDUs of different user plane connections within one packet. The solution shall minimise impacts to existing network characteristics, in particular jitter and packet delay. The transport format shall be suitable for any type of payload transported within NbFP. Though primarily intended and possibly optimised for NbFP transport within 3GPP circuit-switched core networks, the multiplexing design shall be generic and future proof by not precluding support of non-NbFP payload types, e.g. standard VoIP bearers or other interfaces such as Iu. Furthermore, backward compatible signalling extensions required to negotiate the use of this transport option, to set up multiplexing connections, and to assign bearers to these connections are investigated. The benefits and drawbacks of multiplexing at the Nb interface are investigated.