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UMTS (Interfaces) - 5

Interfaces [Under UMTS]
» Radio interface layer - 25.301 «
» Phy layer services - 25.302 «
» NAS - 24.007/8 «
» UTRAN description - 25.401 «
» UTRAN Iu interface - 25.410 «

Separation of radio access details from non-access protocols (like CC, MM) has been one of the major goals of UMTS. This is evident in following overall diagram of interface from UE point of view. Unlike GPRS, UMTS do not have LLC layer.

Similarly, in Iu protocol, Radio network layer is designed to be independent from Transport network layer. To achieve it, both the planes of Radio network layer use services from Transport network layer with Transport layer having its own control and user planes as shown below in Iu interface model:

Depending on plane, bearers will be used in Transport layer - Signaling bearers will be used in Control plane and Data bearers will be used in User plane. ALCAP is in charge of setting up and tearing down transport bearers - signaling bearers for transport layer's own signaling (e.g. O&M) and Data bearers to carry user data. For example, in Iu-CS interface, ALCAP sets up data bearers that will be required to carry voice data as per signaling done by Application Protocol in control plane. ALCAP is a generic name and stands for Access Link Control Application Part; it differs for each Iu interface.

Application protocol specific to Iu interface are: RANAP for Iu-(CS/PS), RNSAP (Iur), NBAP (Iub), SABP (Iu-BC).

Depending on Iu interface, protocol stacks differs for planes shown in above Iu model.

Next step would be look at protocol stacks for above interfaces. But before we do that we need to look at UMTS Services.

References: UMTS by Sanchez and Thioune, and WCDMA for UMTS by Holma and Toskala.

Copyright © Samir Amberkar 2010§ §

R5 core network « UMTS Index » Services