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