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Q & A

Questions and Answers concerning particular and often very detailed issues given without introduction.

Comments, questions are of course welcome!!!

Q: Why AAL2 on Iu interface needs ALCAP and AAL5 does not need this signaling protocol ?
A: AAL5 is using PVC configured by O&M, hence there is no need to establish, release or maintain this connections. AAL2 is not using PVC but VC/VP which need to be established, released and maintained by separate signaling protocol i.e. ALCAP.

Q: What is the meaning of PDU and SDU and what is the difference between them ?
A: PDU is Protocol Data Unit and SDU is Service Data Unit. Difference between them and their role should describe following figure
PDU and SDU illustration

Q: What means NNI and UNI ? This two terms can be seen together with SAAL layer.
A: NNI means Network-to-Network Interface also known as Network-Node Interface. UNI means User-to-Network Interface.

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NAS: Non-Access Stratum

This post is to give short description of NAS protocols, procedures and functions.
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…

Protocols, interfaces, User Plane and Control Plane

When two devices would like to communicate with each other they would use a defined protocol. Protocol is set of rules describing how those two devices can communicate in way that receiver would understand what sender “had in mind” while sending message. Protocol description is usually description of messages (signals) that can be sent and received, it is also description for particular procedures and functions.
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…