Chris Cox Communications
Career profile
UMTS specifications
Website terms and conditions

25 series - Iu interface protocol stack

Up to the 25 series 25.410 - UTRAN Iu interface: General aspects and principles 25.411 - UTRAN Iu interface layer 1 25.419 - UTRAN Iu-BC interface: Service Area Broadcast Protocol (SABP) 25.415 - UTRAN Iu interface user plane protocols 25.414 - UTRAN Iu interface data transport and transport signalling 25.414 - UTRAN Iu interface data transport and transport signalling 25.412 - UTRAN Iu interface signalling transport 25.413 - UTRAN Iu interface Radio Access Network Application Part (RANAP) signalling


The Iu interface connects the radio access network to the core network.

Like the other UTRAN interfaces, its protocol stack is divided into two layers. All the UMTS-related issues are in the radio network layer, while the transport network layer contains standard technology used for the underlying transport. The stack is also divided into three planes. The user plane handles data streams that eventually reach the UE, the control plane handles Iu signalling messages and the transport network control plane manages the underlying transport.

So there are three important protocols here: the RANAP defines the signalling messages exchanged over the Iu interface, the SABP defines the data streams used by the cell broadcast service, and the frame protocols define the CS and PS data streams.


BCBroadcast centre
CSCircuit switched
PSPacket switched
SABPService area broadcast protocol
RANAPRadio access network application part
Copyright Chris Cox Communications © 2019. All rights reserved.