Thursday, November 26, 2009

UMTS Layers, Interfaces, Protocols - Iub interface.

Just to remind - Iub interface connects Node B (RBS) and RNC.
As for general view (general info) in this interface one can describe layers (i.e. Radio and Transport Network Layer), planes (i.e. user and control plane) and some protocols within those planes.

Figure 1. Iub Control Plane - ATM transport.

NBAP - Node Application Part
SSCF-UNI - Service Specific Coordination Function for support of signaling at the User Network Interface [ITU-T 2130]
SSCOP - Service Specific Connection Oriented Protocol
AAL5 - ATM Adaptation Layer 5

In some papers reader can a bit different protocol stack than presented in Figure1. In fact stack is not different but SSCF-UNI, SSCOP and AAL5 forms a layer called SAAL-UNI (Signaling ATM Adaptation Layer). Figure 2 shows this protocol stack.
Figure 2. Iub control plane (SAAL-UNI)

In the Figure 1 control plane for Iub interface is shown.  It consists of NBAP (NodeB Application Part) protocol and protocol stack for Transport Layer. NBAP is described in 3GPP TS 25.433.
Iub Control Plane IP transport

Figure 3. Iub Control Plane - IP transport.

SCTP - Stream Control Transmission Protocol

From 3GPP Release 5 of specification it is possible to use ATM or IP for transport of NBAP messages. Figure 1 shows ATM version while Figure 3 shows the second one - IP protocol used for transport

Figure 4 shows user plane for the Iub interface (with ATM used for transport). In Radio Network Layer there is Frame Protocol used. In fact it is not one but whole set of protocols. Separate protocols are defined for dedicated channels and described in 3GPP TS 25.427 and ones for common channels described in 3GPP TS 25.435.
Figure 5shows the same User Plane but IP is used for transport.

Iub User Plane ATM transport
Figure 4. Iub User Plane - ATM transport
Iub User Plane IP transport
Figure 5. Iub User Plane - IP transport.
To establish transport connection special dedicated protocol has been defined. Whole protocol stack used in Transport Network Layer in Control Plane is shown in Figure 6. On the top of the protocol stack ALCAP is located.

Figure 6. Iub Transport Network Layer Control Plane

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