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Showing posts from October, 2009

Radio Interface (UMTS)

Simplified radio interface (Uu) architecture.

MAC, RLC and RRC communicate with each other using some signals/messages called primitives.



Based on 3GPP 25.321.

Question and Answers

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
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.

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