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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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NAS is a layer for communication between Ue and Core Network (CN). This communication is transparent for underlaying Access Stratum.
NAS protocols:
GMM - GPRS Mobility ManagementMM - Mobility Management SM - Session ManagementCC - Call Control SS - Supplementary Services SMS - Short Message Services SM, SMS, SS and CC form a group of protocols called Connection Management.


Figure - Inter protocols communication MS side [3GPP 24.007]



SM - its functions is to activate, deactivate or modify PDP contexts which are sessions for PS traffic in UMTS/GPRS networks

Figure 1 - Simplified PDP context activation procedure



Figure 2 - Inter protocol communication for PDP context activation - MS side



CC - its functions is to establish, maintain and finally release CS calls in UMTS/GPRS/GSM networks

Figure 3- Simplified CS call proceeding


Figure 4 - Inter protocol communication for CS call setup



Abbreviations

ABCDEFGHIJKLMNPRSTUWV
3GPPThird Generation Partnership Project
AALATM Adaptation Layer
ADCHAssociated DCH
ADSLAsymetric Digital Subscriber Line
ALCAPAccess Link Control Application Part
ARFCNAbsolute Radio Frequency Channel Number
ARQAutomatic Repeat reQuest
ATMAsynchronous Transfer Mode
BCCHBroadcast Control Channel
BCHBroadcast ChannelBERBit Error RateBICCBearer Independent Call ControlBLERBlock Error RateBPSKBinary Phase Shift KeyingBSCBase Station ControllerBSSBase Station SubsystemBTSBase Transceiver StationCAMELCustomised Applications for Mobile network Enhanced Logic
CCCall Control
CCCHCommon Control Channel
CDMCode Division Multiplexing
CDMACode Division Multiple Access
CNCore Network
CMConnection Management
CPICHCommon Pilot Channel
CQIChannel Quality Indicator
CRCCyclic Redundancy Check
C-RNTICell Radio Network Temporary Identifier
CSCirciut Switch
CRNCControlling Radio Network Controller
DCHDedicated Channel
DNSDomain Name Server
DL-SCHDownlink Shared Channel
DRNCDrift Radio Network Controller
DS-CDM…

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Now, our two devices know “how to talk” to each other, but they need to be connected somehow. For this purpose an Interface would be defined. Interface would be generally another device, with or without dedicated software, that would allow connecting, inter-working and changing messages(signals) between our devices – connected using this interface.
Sometimes when connecting two devices using interface there is a need for two protocols. First protocol would allow first device to control how works the second one. This kind of protocol is part of control plane. Second protocol wo…