Friday, October 16, 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.

Tuesday, October 13, 2009

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
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.

Monday, October 12, 2009

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 Management
  • MM - Mobility Management
  • SM - Session Management
  • CC - 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